U.S. patent application number 17/015836 was filed with the patent office on 2020-12-31 for radar image processing device and radar image processing method.
This patent application is currently assigned to Mitsubishi Electric Corporation. The applicant listed for this patent is Mitsubishi Electric Corporation. Invention is credited to Yumiko KATAYAMA, Kei SUWA.
Application Number | 20200408901 17/015836 |
Document ID | / |
Family ID | 1000005093353 |
Filed Date | 2020-12-31 |
United States Patent
Application |
20200408901 |
Kind Code |
A1 |
KATAYAMA; Yumiko ; et
al. |
December 31, 2020 |
RADAR IMAGE PROCESSING DEVICE AND RADAR IMAGE PROCESSING METHOD
Abstract
A radar image processing device includes a phase difference
calculating unit for calculating a phase difference, which is the
difference between the phases, with respect to the radio wave
receiving points different from each other, of each of a plurality
of reflected signals present in one pixel, and the rotation amount
calculating unit that calculates each of the phase rotation amounts
in a plurality of pixels included in the second radar image from
the respective phase differences, in which the difference
calculating unit rotates the phases in the plurality of pixels
included in the second radar image on the basis of the respective
rotation amounts, and calculates a difference between pixel values
of pixels at corresponding pixel positions among the plurality of
pixels included in the first radar image and the plurality of
pixels obtained by the phase rotation included in the second radar
image.
Inventors: |
KATAYAMA; Yumiko; (Tokyo,
JP) ; SUWA; Kei; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Mitsubishi Electric Corporation |
Tokyo |
|
JP |
|
|
Assignee: |
Mitsubishi Electric
Corporation
Tokyo
JP
|
Family ID: |
1000005093353 |
Appl. No.: |
17/015836 |
Filed: |
September 9, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
PCT/JP2018/036184 |
Sep 28, 2018 |
|
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17015836 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G01S 13/9027 20190501;
G06T 2207/20212 20130101; G01S 13/9023 20130101; G06T 2207/10044
20130101; G06T 7/97 20170101; G06T 7/70 20170101 |
International
Class: |
G01S 13/90 20060101
G01S013/90; G06T 7/00 20060101 G06T007/00; G06T 7/70 20060101
G06T007/70 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 30, 2018 |
JP |
PCT/JP2018/013795 |
Claims
1. A radar image processing device, comprising: processing
circuitry performing a process of: calculating a phase shift
component in a first axis direction on a two-dimensional inclined
surface included in the first radar image and the second radar
image, the first axis being an axis of the inclined surface
inclined with respect to a ground-range direction; calculating a
phase on a surface parallel to the inclined surface with respect to
the inclined surface; and calculating a phase difference in each of
a plurality of reflected signals present in each of pixels included
in first and second radar images, the phase difference being a
difference between phases with respect to the respective radio wave
receiving points from a phase shift component calculated and a
phase calculated; calculating each of phase rotation amounts in a
plurality of pixels included in the second radar image from each
phase difference calculated; and rotating phases in a plurality of
pixels included in the second radar image on a basis of the
respective rotation amounts calculated, and calculating a
difference between pixel values of pixels being complex numbers at
corresponding pixel positions among a plurality of pixels included
in the first radar image and a plurality of pixels resulting from
phase rotation included in the second radar image.
2. The radar image processing device according to claim 1, wherein
a radar image group includes two or more radar images capturing one
observation area from radio wave receiving points different from
each other, the process calculates the phase shift component in the
first axis direction on the inclined surface for each combination
of two radar images included in the radar image group, one of the
radar images included in each combination being the first radar
image, the other of the radar images included in each combination
being the second radar image, the process calculates, for each
combination of two radar images, the phase difference in each of
the plurality of reflected signals from the phase shift components
calculated for each combination and the phases calculated, the
process calculates, for each combination of two radar images, each
of the phase rotation amounts of the plurality of pixels included
in the second radar image from the respective phase differences
calculated for each combination, the process rotates, for each
combination of two radar images, the phases of the plurality of
pixels included in the second radar image on a basis of the
respective rotation amounts calculated for each combination, and
calculates a difference between pixel values of pixels at
corresponding pixel positions among the plurality of pixels
included in the first radar image and the plurality of pixels
resulting from the phase rotation included in the second radar
image, and the radar image processing device includes combining
differences at corresponding pixels position among the respective
differences calculated for each combination.
3. The radar image processing device according to claim 2, further
comprising: calculating an image in which the plurality of
reflected signals are extracted, from pixel values of the plurality
of pixels included in the first radar image and the respective
differences obtained by the combining.
4. The radar image processing device according to claim 1, wherein
a first combination includes any two radar images among three or
more radar images capturing one observation area from radio wave
receiving points different from each other, and a second
combination includes two radar images among the three or more radar
images, at least one of the two radar images in the second
combination being different from the two radar images included in
the first combination, the process calculates, for each of the
first and second combination, the phase shift component in the
first axis direction on the inclined surface, one of radar images
included in each combination being the first radar image, the other
of the radar images included in each combination being the second
radar image, the process calculates, for each of the first and
second combinations, the phase difference in each of the plurality
of reflected signals from the phase shift components calculated for
each combination and the phases calculated, the process calculates,
for each of the first and second combinations, each of the phase
rotation amounts of the plurality of pixels included in the second
radar image from the respective phase differences calculated for
each combination, the processs rotates, for each of the first and
second combinations, the phases of the plurality of pixels included
in the second radar image on a basis of the respective rotation
amounts calculated for each combination, and calculates a
difference between pixel values of pixels at corresponding pixel
positions among the plurality of pixels included in the first radar
image and the plurality of pixels resulting from the phase rotation
included in the second radar image, and calculating, as
interference phases, phases at respective pixel positions from the
differences at the respective pixel positions calculated for the
first combination and the differences at the respective pixel
positions calculated for the second combination.
5. The radar image processing device according to claim 4, further
comprising: estimating a position of a scatterer present in the
observation area by using the interference phases calculated.
6. A radar image processing device comprising: processing circuitry
performing a process of: calculating a phase difference in each of
a plurality of reflected signals present in each of pixels included
in first and second radar images, the first radar images capturing
an observation area from a first radio wave receiving points and
the second radar images capturing an observation area same as the
observation area from a second radio wave receiving points, the
phase difference being a difference between a phase with respect to
the first radio wave receiving point and a phase with respect to
the second radio wave receiving point, with respect to a
two-dimensional surface inclined by an inclination angle .alpha.
against a ground-range direction; calculating each of phase
rotation amounts in a plurality of pixels included in the second
radar image from each phase difference calculated; and rotating
phases in a plurality of pixels included in the second radar image
on a basis of the respective rotation amounts calculated, and
calculating a difference between pixel values of pixels at
corresponding pixel positions among a plurality of pixels included
in the first radar image and a plurality of pixels resulting from
phase rotation included in the second radar image.
7. The radar image processing method, comprising: calculating a
phase shift component in a first axis direction on a
two-dimensional inclined surface included in the first radar image
and the second radar image, the first axis being an axis of the
inclined surface inclined with respect to a ground-range direction;
calculating a phase on a surface parallel to the inclined surface
with respect to the inclined surface; and calculating a phase
difference in each of a plurality of reflected signals present in
each of pixels included in first and second radar images, the phase
difference being a difference between phases with respect to the
respective radio wave receiving points from a phase shift component
calculated and a phase calculated; calculating each of phase
rotation amounts in a plurality of pixels included in the second
radar image from each phase difference calculated; and rotating
phases in a plurality of pixels included in the second radar image
on a basis of the respective rotation amounts calculated, and
calculating a difference between pixel values of pixels being
complex numbers at corresponding pixel positions among a plurality
of pixels included in the first radar image and a plurality of
pixels resulting from phase rotation included in the second radar
image.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a Continuation of PCT International
Application No. PCT/JP2018/036184 filed on Sep. 28, 2018, which
claims priority under 35 U.S.C. .sctn. 119(a) to Patent Application
No. PCT/JP2018/013795 filed in Japan on Mar. 30, 2018, all of which
are hereby expressly incorporated by reference into the present
application.
TECHNICAL FIELD
[0002] The present invention relates to a radar image processing
device and a radar image processing method for calculating
differences between pixels included in a first radar image and
pixels obtained by phase rotation included in a second radar
image.
BACKGROUND ART
[0003] A tall building or the like may appear as a scatterer in a
radar image acquired by a radar device.
[0004] The distance from a platform on which the radar device is
mounted to a high position of the scatterer is shorter than that
from the platform to a low position of the scatterer by the height
of the scatterer.
[0005] When the distance from a platform to a high position of a
scatterer is shorter than that to a low position of the scatterer,
layover, which is a phenomenon that a signal reflected at the high
position of the scatterer is displaced toward the platform,
occurs.
[0006] When layover occurs, a signal reflected at a high position
of a scatterer is displaced and thus overlaps with another
reflected signal present at the position to which the reflected
signal is displaced, which may result in presence of a plurality of
reflected signals in one pixel in a radar image.
[0007] Non-patent Literature 1 mentioned below teaches a radar
image processing device that calculate a difference between a pixel
included in a first radar image and a pixel included in a second
radar image.
[0008] By calculating the difference, the radar image processing
device can suppress a reflected signal with a phase difference
between the phase with respect to a first radio wave receiving
point and the phase with respect to a second radio wave receiving
point being zero among a plurality of reflected signals present in
one pixel.
[0009] The first radio wave receiving point refers to the position
of a platform when a first radar image is taken, and the second
radio wave receiving point refers to the position of the platform
when a second radar image is taken.
CITATION LIST
Non-Patent Literature
[0010] Non-patent Literature 1: D. L. Bickel, "A null-steering
viewpoint of interferometric SAR," IGARSS2000
SUMMARY OF INVENTION
Technical Problem
[0011] The radar image processing device of the related art can
suppress a reflected signal with a phase difference between the
phase with respect to a first radio wave receiving point and the
phase with respect to a second radio wave receiving point being
zero among a plurality of reflected signals present in one
pixel.
[0012] As for a reflected signal that is scattered at the same
height as the position where a reflected signal that can be
suppressed is scattered among a plurality of reflected signals
present in one pixel, however, the phase difference between the
phase with respect to a first radio wave receiving point and the
phase with respect to a second radio wave receiving point is not
zero.
[0013] There has thus been a problem in that a reflected signal
with a phase difference between the phase with respect to a first
radio wave receiving point and the phase with respect to a second
radio wave receiving point not being zero cannot be suppressed.
[0014] The present invention has been made to solve such problems
as described above, and an object thereof is to provide a radar
image processing device and a radar image processing method capable
of also suppressing a reflected signal with the difference between
phases with respect to radio wave receiving points different from
each other not being zero.
Solution to Problem
[0015] A radar image processing device according to the present
invention includes processing circuitry performing a process of:
calculating a phase shift component in a first axis direction on a
two-dimensional inclined surface included in the first radar image
and the second radar image, the first axis being an axis of the
inclined surface inclined with respect to a ground-range direction;
calculating a phase on a surface parallel to the inclined surface
with respect to the inclined surface; and calculating a phase
difference in each of a plurality of reflected signals present in
each of pixels included in first and second radar images, the phase
difference being a difference between phases with respect to the
respective radio wave receiving points from a phase shift component
calculated and a phase calculated; calculating each of phase
rotation amounts in a plurality of pixels included in the second
radar image from each phase difference calculated; and rotating
phases in a plurality of pixels included in the second radar image
on a basis of the respective rotation amounts calculated, and
calculating a difference between pixel values of pixels being
complex numbers at corresponding pixel positions among a plurality
of pixels included in the first radar image and a plurality of
pixels resulting from phase rotation included in the second radar
image.
Advantageous Effects of Invention
[0016] According to the present invention, a radar image processing
device has a configuration including: processing circuitry
performing a process of: calculating a phase shift component in a
first axis direction on a two-dimensional inclined surface included
in the first radar image and the second radar image, the first axis
being an axis of the inclined surface inclined with respect to a
ground-range direction; calculating a phase on a surface parallel
to the inclined surface with respect to the inclined surface; and
calculating a phase difference in each of a plurality of reflected
signals present in each of pixels included in first and second
radar images, the phase difference being a difference between
phases with respect to the respective radio wave receiving points
from a phase shift component calculated and a phase calculated;
calculating each of phase rotation amounts in a plurality of pixels
included in the second radar image from each phase difference
calculated; and rotating phases in a plurality of pixels included
in the second radar image on a basis of the respective rotation
amounts calculated, and calculating a difference between pixel
values of pixels being complex numbers at corresponding pixel
positions among a plurality of pixels included in the first radar
image and a plurality of pixels resulting from phase rotation
included in the second radar image. The radar image processing
device according to the present invention is therefore capable of
also suppressing a reflected signal from a scatterer with the
difference between phases with respect to the radio wave receiving
points different from each other not being zero.
BRIEF DESCRIPTION OF DRAWINGS
[0017] FIG. 1 is a configuration diagram illustrating a radar image
processing device 10 according to a first embodiment.
[0018] FIG. 2 is a configuration diagram illustrating a phase
processing unit 12 of the radar image processing device 10
according to the first embodiment.
[0019] FIG. 3 is a configuration diagram illustrating an image
processing unit 13 of the radar image processing device 10
according to the first embodiment.
[0020] FIG. 4 is a hardware configuration diagram illustrating
hardware of each of the phase processing unit 12 and the image
processing unit 13.
[0021] FIG. 5 is a hardware configuration diagram of a computer in
a case where the phase processing unit 12 and the image processing
unit 13 are implemented by software, firmware, or the like.
[0022] FIG. 6 is a flowchart illustrating processing of the phase
processing unit 12.
[0023] FIG. 7 is an explanatory diagram illustrating an inclined
surface 51, a parallel surface 52, and imaging parameters.
[0024] FIG. 8 is an explanatory diagram illustrating the relation
of a spacing .DELTA.sl of pixels in a slant-range direction, the
range Sw of radar images (a first radar image, a second radar
image) and the distance sl from a position in the slant-range
direction corresponding to the center position of the radar image
to the observation area.
[0025] FIG. 9 is a flowchart illustrating processing of the image
processing unit 13.
[0026] FIG. 10 is an explanatory diagram illustrating suppression
of reflected signals present in one pixel in a case where the
phases in pixels included in the second radar image are not rotated
by a phase rotating unit 33.
[0027] FIG. 11 is an explanatory diagram illustrating suppression
of reflected signals present in one pixel in a case where the
phases in pixels included in the second radar image are rotated by
the phase rotating unit 33.
[0028] FIG. 12 is a configuration diagram illustrating an image
processing unit 13 of a radar image processing device 10 according
to a second embodiment.
[0029] FIG. 13 is a hardware configuration diagram illustrating
hardware of each of a phase processing unit 12 and the image
processing unit 13.
[0030] FIG. 14 is an explanatory diagram illustrating a plurality
of reflected signals present in one pixel in a case where only two
radar images are included in a radar image group 2.
[0031] FIG. 15 is an explanatory diagram illustrating a plurality
of reflected signals present in one pixel in a case where two or
more radar images are included in a radar image group 2.
[0032] FIG. 16 is a configuration diagram illustrating an image
processing unit 13 of a radar image processing device 10 according
to a third embodiment.
[0033] FIG. 17 is a hardware configuration diagram illustrating
hardware of each of a phase processing unit 12 and the image
processing unit 13.
[0034] FIG. 18 is a configuration diagram illustrating an image
processing unit 13 of a radar image processing device 10 according
to a fourth embodiment.
[0035] FIG. 19 is a hardware configuration diagram illustrating
hardware of each of a phase processing unit 12 and the image
processing unit 13.
[0036] FIG. 20 is a configuration diagram illustrating an image
processing unit 13 of a radar image processing device 10 according
to a fifth embodiment.
[0037] FIG. 21 is a hardware configuration diagram illustrating
hardware of each of a phase processing unit 12 and the image
processing unit 13.
DESCRIPTION OF EMBODIMENTS
[0038] Embodiments for carrying out the invention will now be
described with reference to the accompanying drawings for more
detailed explanation of the invention.
First Embodiment
[0039] FIG. 1 is a configuration diagram illustrating a radar image
processing device 10 according to a first embodiment.
[0040] In FIG. 1, a radar 1 is a synthetic aperture radar (SAR), a
real aperture radar, or the like, and is mounted on a platform for
observing the Earth, etc. The radar 1 takes a radar image, and
acquires parameters when taking the radar image. The platform can
be a satellite, an aircraft, or the like.
[0041] The radar 1 images an observation area from a radio wave
receiving point, and then images the observation area again when
the platform is at a radio wave receiving point near the
aforementioned radio wave receiving point.
[0042] In a case of repeat-pass imaging, when the platform is a
satellite, the radar 1 images an observation area from a radio wave
receiving point, the platform then orbits the Earth, and the radar
1 images the same observation area again to acquire a radar image
when the platform has returned to a radio wave receiving point near
the aforementioned radio wave receiving point. When the platform is
an aircraft, the platform is flown to repeatedly pass the same
path, and the radar 1 images one observation area when the platform
is at substantially the same radio wave receiving points to acquire
radar images.
[0043] In a case of single-pass imaging, a plurality of radars 1
are mounted on one platform, and the plurality of radars 1 image
one observation area from a radio wave receiving point to acquire
radar images. In this case, the plurality of the radars 1 are
installed at different positions on the platform.
[0044] In addition, a plurality of radars 1 having equal imaging
parameters such as a wavelength are mounted on different platforms
from each other, and each of the plurality of radars 1 image one
observation area from a radio wave receiving point to acquire radar
images.
[0045] Thus, the radars 1 image the same observation area twice
from the respective radio wave receiving points, which are
different from each other, to acquire two radar images; a first
radar image and a second radar image.
[0046] Hereinafter, the position of the platform when the first
radar image is taken will be referred to as a first radio wave
receiving point, and the position of the platform when the second
radar image is taken will be referred to as a second radio wave
receiving point.
[0047] The first radar image and the second radar image have an
equal resolution. Thus, the pixel positions of a plurality of
pixels included in a first radar image and those of a plurality of
pixels included in a second radar image are expressed in the same
manner by (pixel,line).
[0048] "pixel" is a variable representing the position of a pixel
in a slant-range direction in each of a first radar image and a
second radar image, and "line" is a variable representing the
position of a pixel in an azimuth direction in each of a first
radar image and a second radar image.
[0049] The radar 1 transmits a radar image group 2 including a
first radar image and a second radar image to the radar image
processing device 10.
[0050] The radar 1 transmits an imaging parameter group 3 including
a first imaging parameter associated with the first radar image and
a second imaging parameter associated with the second radar image
to the radar image processing device 10.
[0051] The radar image group 2 is an image group including a first
radar image and a second radar image.
[0052] The types of polarization used in imaging a first radar
image and in imaging a second radar image are not limited, and each
of a first radar image and a second radar image may thus be any of
a single-polarization radar image, a dual-polarization radar image,
and a quad-polarization radar image.
[0053] Each of a first radar image and a second radar image is a
radar image showing intensity distribution of radio waves emitted
by the radar 1, then reflected by an observation area, and received
by the radar 1.
[0054] A plurality of pixels included in a first radar image and a
plurality of pixels included in a second radar image each have a
complex pixel value.
[0055] A complex pixel value includes information indicating the
distance between the radar 1 and a scatterer present in the
observation area, and also information indicating phase shift
occurring when a radio wave emitted by the radar 1 is reflected by
a scatterer. Hereinafter, a "pixel value" has a value of a complex
number unless otherwise noted.
[0056] An imaging parameter group 3 is a parameter group including
a first imaging parameter and a second imaging parameter.
[0057] The first imaging parameter includes position information on
the orbit of the platform and sensor information when a first radar
image is taken by the radar 1.
[0058] The second imaging parameter includes position information
on the orbit of the platform and sensor information when a second
radar image is taken by the radar 1.
[0059] The position information on the orbit is information
indicating the latitude, the longitude, and the altitude of the
platform when a first radar image or a second radar image is taken
by the radar 1. Thus, the position information on the orbit is used
as information indicating a first radio wave receiving point or a
second radio wave receiving point.
[0060] The sensor information includes information indicating an
off-nadir angle .theta. of the radar 1 when a first radar image or
a second radar image is taken, information indicating a wavelength
a, of a radio wave emitted from the radar 1, and information
indicating an average R of distances from the radar 1 to an
observation area.
[0061] The radar image processing device 10 includes a radar image
acquiring unit 11, a phase processing unit 12, and an image
processing unit 13.
[0062] The radar image acquiring unit 11 acquires each of a radar
image group 2 and an imaging parameter group 3 transmitted from the
radar 1.
[0063] The radar image acquiring unit 11 outputs the radar image
group 2 to the image processing unit 13, and outputs the imaging
parameter group 3 to the phase processing unit 12.
[0064] The phase processing unit 12 acquires the imaging parameter
group 3 output from the radar image acquiring unit 11, and the
inclination angle .alpha. of a two-dimensional inclined surface 51
with respect to a ground-range direction (see FIG. 7).
[0065] The phase processing unit 12 also acquires the distance
.alpha. between the inclined surface 51 and a parallel surface 52
that is a surface parallel to the inclined surface 51 (see FIG.
7).
[0066] Details of the inclined surface 51 and the parallel surface
52 will be described later.
[0067] The phase processing unit 12 performs a process of
calculating a phase shift component .phi.(x) in an x-axis (first
axis) direction on the inclined surface 51 by using the first
imaging parameter, the second imaging parameter, and the
inclination angle .alpha..
[0068] The phase processing unit 12 performs a process of
calculating a phase .phi.(z.sub.0) on the parallel surface 52 with
respect to the inclined surface 51 by using the first imaging
parameter, the second imaging parameter, the inclination angle
.alpha., and the distance z.sub.0.
[0069] The phase processing unit 12 performs a process of
calculating, in each of a plurality of reflected signals present in
each of pixels included in the first and second radar images, a
phase difference .DELTA..phi.(x,z.sub.0) between the phase with
respect to the first radio wave receiving point and the phase with
respect to the second radio wave receiving point.
[0070] The image processing unit 13 acquires the radar image group
2 output from the radar image acquiring unit 11, and each phase
difference .DELTA..phi.(x,z.sub.0) output from the phase processing
unit 12.
[0071] The image processing unit 13 performs a process of
calculating each of phase rotation amounts
exp[j.DELTA..phi.(x,z.sub.0)] in a plurality of pixels included in
the second radar image from each phase difference
.DELTA..phi.(x,z.sub.0) output from the phase processing unit
12.
[0072] The image processing unit 13 performs a process of rotating
the phases in the plurality of pixels included in the second radar
image on the basis of the respective calculated rotation amounts
exp[j.DELTA..phi.(x,z.sub.0)].
[0073] The image processing unit 13 performs a process of
calculating a difference between pixel values of pixels at
corresponding pixel positions among a plurality of pixels included
in the first radar image and among a plurality of pixels obtained
by phase rotation included in the second radar image.
[0074] FIG. 2 is a configuration diagram illustrating the phase
processing unit 12 of the radar image processing device 10
according to the first embodiment.
[0075] FIG. 3 is a configuration diagram illustrating the image
processing unit 13 of the radar image processing device 10
according to the first embodiment.
[0076] FIG. 4 is a hardware configuration diagram illustrating
hardware of each of the phase processing unit 12 and the image
processing unit 13.
[0077] In FIG. 2, a phase shift component calculating unit 21 is
implemented by a phase shift component calculating circuit 41
illustrated in FIG. 4, for example.
[0078] The phase shift component calculating unit 21 acquires the
imaging parameter group 3 output from the radar image acquiring
unit 11, and the inclination angle .alpha..
[0079] The phase shift component calculating unit 21 performs the
process of calculating the phase shift component .phi.(x) in the
x-axis direction on the inclined surface 51 by using the first
imaging parameter, the second imaging parameter, and the
inclination angle .alpha..
[0080] The phase shift component calculating unit 21 outputs the
phase shift component .phi.(x) in the x-axis direction to a phase
difference calculating unit 23.
[0081] A phase calculating unit 22 is implemented by a phase
calculating circuit 42 illustrated in FIG. 4, for example.
[0082] The phase calculating unit 22 acquires the imaging parameter
group 3 output from the radar image acquiring unit 11, the
inclination angle .alpha., and the distance z.sub.0.
[0083] The phase calculating unit 22 performs the process of
calculating the phase .phi.(z.sub.0) on the parallel surface 52
with respect to the inclined surface 51 by using the first imaging
parameter, the second imaging parameter, the inclination angle
.alpha., and the distance z.sub.0.
[0084] The phase calculating unit 22 outputs the phase
.phi.(z.sub.0) to the phase difference calculating unit 23.
[0085] The phase difference calculating unit 23 is implemented by a
phase difference calculating circuit 43 illustrated in FIG. 4, for
example.
[0086] The phase difference calculating unit 23 performs the
process of calculating, in each of a plurality of reflected signals
present in each of pixels included in the first and second radar
images, the phase difference .DELTA..phi.(x,z.sub.0) from the phase
shift component .phi.(x) and the phase .phi.(z.sub.0).
[0087] The phase difference .DELTA..phi.(x,z.sub.0) is a phase
difference in each of the reflected signals, between the phase of
the reflected signal with respect to the first radio wave receiving
point and the phase of the reflected signal with respect to the
second radio wave receiving point.
[0088] The phase difference calculating unit 23 outputs each phase
difference .DELTA..phi.(x,z.sub.0) to the image processing unit
13.
[0089] In FIG. 3, a rotation amount calculating unit 31 is
implemented by a rotation amount calculating circuit 44 illustrated
in FIG. 4, for example.
[0090] The rotation amount calculating unit 31 performs the process
of calculating each of phase rotation amounts
exp[j.DELTA..phi.(x,z.sub.0)] in a plurality of pixels included in
the second radar image from each phase difference
.DELTA..phi.(x,z.sub.0) output from the phase difference
calculating unit 23.
[0091] The rotation amount calculating unit 31 outputs each
rotation amount exp[j.DELTA..phi.(x,z.sub.0)] to a phase rotating
unit 33.
[0092] A difference calculating unit 32 includes the phase rotating
unit 33 and a difference calculation processing unit 34.
[0093] The phase rotating unit 33 is implemented by a phase
rotating circuit 45 illustrated in FIG. 4, for example.
[0094] The phase rotating unit 33 acquires the second radar image
from the radar image group 2 output from the radar image acquiring
unit 11.
[0095] The phase rotating unit 33 performs the process rotating the
phases in the plurality of pixels included in the second radar
image on the basis of the respective rotation amounts
exp[j.DELTA..phi.(x,z.sub.0)] output from the rotation amount
calculating unit 31.
[0096] The phase rotating unit 33 outputs a second radar image
including a plurality of pixels obtained by phase rotation to the
difference calculation processing unit 34.
[0097] The difference calculation processing unit 34 is implemented
by a difference calculation processing circuit 46 illustrated in
FIG. 4, for example.
[0098] The difference calculation processing unit 34 acquires the
first radar image from the radar image group 2 output from the
radar image acquiring unit 11, and acquires the second radar image
output from the phase rotating unit 33.
[0099] The difference calculation processing unit 34 performs the
process of calculating a difference .DELTA.S(pixel,line) between
pixel values of pixels at corresponding pixel positions among a
plurality of pixels included in the first radar image and among a
plurality of pixels obtained by phase rotation included in the
second radar image.
[0100] The difference .DELTA.S(pixel,line) corresponds to a pixel
of a suppressed image in which unnecessary reflected signals from
the scatterer are suppressed.
[0101] The difference calculation processing unit 34 outputs the
suppressed image including the respective differences .DELTA.s
(pixel, line) to the outside of the unit.
[0102] In FIG. 2, it is assumed that each of the phase shift
component calculating unit 21, the phase calculating unit 22, and
the phase difference calculating unit 23, which are components of
the phase processing unit 12, is implemented by such dedicated
hardware as illustrated in FIG. 4.
[0103] In addition, in FIG. 3, it is assumed that each of the
rotation amount calculating unit 31, the phase rotating unit 33,
and the difference calculation processing unit 34, which are
components of the image processing unit 13, is implemented by such
dedicated hardware as illustrated in FIG. 4.
[0104] Specifically, the phase processing unit 12 and the image
processing unit 13 are assumed to be implemented by the phase shift
component calculating circuit 41, the phase calculating circuit 42,
the phase difference calculating circuit 43, the rotation amount
calculating circuit 44, the phase rotating circuit 45, and the
difference calculation processing circuit 46.
[0105] Note that each of the phase shift component calculating
circuit 41, the phase calculating circuit 42, the phase difference
calculating circuit 43, the rotation amount calculating circuit 44,
the phase rotating circuit 45, and the difference calculation
processing circuit 46 may be a single circuit, a composite circuit,
a programmed processor, a parallel-programmed processor, an
application specific integrated circuit (ASIC), a
field-programmable gate array (FPGA), or a combination thereof, for
example.
[0106] The components of the phase processing unit 12 and the
components of the image processing unit 13 are not limited to those
implemented by dedicated hardware. The phase processing unit 12 and
the image processing unit 13 may be implemented by software,
firmware, or a combination of software and firmware.
[0107] The software or firmware is stored in a memory of a computer
in the form of programs. The computer refers to hardware for
executing programs, and may be a central processing unit (CPU), a
central processor, a processing unit, a computing unit, a
microprocessor, a microcomputer, a processor, or a digital signal
processor (DSP), for example.
[0108] FIG. 5 is a hardware configuration diagram of a computer in
a case where the phase processing unit 12 and the image processing
unit 13 are implemented by software, firmware, or the like.
[0109] In the case where the phase processing unit 12 is
implemented by software, firmware, or the like, programs for
causing a computer to perform procedures of the phase shift
component calculating unit 21, the phase calculating unit 22, and
the phase difference calculating unit 23 are stored in a memory
61.
[0110] In addition, in the case where the image processing unit 13
is implemented by software, firmware, or the like, programs for
causing a computer to perform procedures of the rotation amount
calculating unit 31, the phase rotating unit 33, and the difference
calculation processing unit 34 are stored in the memory 61.
[0111] A processor 62 of the computer thus executes the programs
stored in the memory 61.
[0112] In addition, FIG. 4 illustrates an example in which each of
the components of the phase processing unit 12 and the components
of the image processing unit 13 is implemented by dedicated
hardware, and FIG. 5 illustrates an example in which the phase
processing unit 12 and the image processing unit 13 are implemented
by software, firmware, or the like.
[0113] The implementations are not limited to the above, and some
components of the phase processing unit 12 and some components of
the image processing unit 13 may be implemented by dedicated
hardware and others may be implemented by software, firmware, and
the like, for example.
[0114] Next, the operation of the radar image processing device 10
illustrated in FIG. 1 will be explained.
[0115] The radar 1 transmits a radar image group 2 including a
first radar image and a second radar image, and an imaging
parameter group 3 including a first imaging parameter and a second
imaging parameter to the radar image processing device 10.
[0116] The radar image acquiring unit 11 acquires each of the radar
image group 2 and the imaging parameter group 3 transmitted from
the radar 1.
[0117] The radar image acquiring unit 11 outputs the radar image
group 2 to the image processing unit 13, and outputs the imaging
parameter group 3 to the phase processing unit 12.
[0118] The pixel values of the pixels included in radar images (the
first radar image, the second radar image) are complex numbers that
are expressed as in the following formula (1).
S(pixel,line)=Av(pixel,line)exp[j.PSI.(pixel,line)] (1)
[0119] In the formula (1), Av(pixel,line) represents the amplitude
of a pixel at a pixel position (pixel,line).
[0120] .PSI.(pixel,line) represents the phase (argument) of a pixel
at a pixel position (pixel,line).
[0121] j is a symbol representing an imaginary unit.
[0122] The phase processing unit 12 performs a process of
calculating a phase difference .DELTA..phi.(x,z.sub.0).
[0123] FIG. 6 is a flowchart illustrating the processing of the
phase processing unit 12.
[0124] The processing of the phase processing unit 12 will now be
explained in detail with reference to FIG. 6.
[0125] The phase shift component calculating unit 21 acquires the
imaging parameter group 3 output from the radar image acquiring
unit 11, and the inclination angle .alpha. (step ST1 in FIG.
6).
[0126] The phase calculating unit 22 acquires the imaging parameter
group 3 output from the radar image acquiring unit 11, the
inclination angle .alpha., and the distance z.sub.0 (step ST2 in
FIG. 6).
[0127] The inclination angle .alpha. is a parameter set in advance
by a user, and expressed as in FIG. 7, for example.
[0128] The distance z.sub.0 is a parameter set in advance by a
user, and expressed as in FIG. 7, for example.
[0129] Each of the inclination angle .alpha. and the distance
z.sub.0 may be provided to the phase calculating unit 22 by manual
operation made by a user, or may be provided to the phase
calculating unit 22 from an external device, which is not
illustrated, for example.
[0130] FIG. 7 is an explanatory diagram illustrating the inclined
surface 51, the parallel surface 52, and the imaging
parameters.
[0131] In FIG. 7, the inclined surface 51 is a two-dimensional
surface included in common in the first radar image and the second
radar image.
[0132] The direction of the x axis, which is the first axis, of the
inclined surface 51 is a direction inclined by the inclination
angle .alpha. with respect to the ground-range direction, and the
direction of a second axis of the inclined surface 51 is the
azimuth direction (the depth direction from the sheet surface of
FIG. 7).
[0133] The parallel surface 52 is a surface parallel to the
inclined surface 51 and at a distance of z.sub.0 from the inclined
surface 51.
[0134] In a case where the inclined surface 51 is a flat roof of a
building built vertically on a horizontal ground surface, for
example, the inclination angle .alpha. is set to 0 degrees.
[0135] In a case where the inclined surface 51 is a wall surface of
a building built vertically on a horizontal ground surface, for
example, inclination angle .alpha. is set to 90 degrees.
[0136] P.sub.1 represents the first radio wave receiving point, and
P.sub.2 represents the second radio wave receiving point.
[0137] The first radio wave receiving point P.sub.1 is a center
position on the orbit of the platform when the first radar image is
taken, and the second radio wave receiving point P.sub.2 is a
center position on the orbit of the platform when the second radar
image is taken.
[0138] B.sub.1,2 represents a distance component, in a direction
perpendicular to the direction (hereinafter referred to as a
"slant-range direction") of a radio wave emitted by the radar 1, of
the distance between the first radio wave receiving point P.sub.1
and the second radio wave receiving point P.sub.2.
[0139] .theta. is an off-nadir angle, which is an angle between a
vertically downward direction from the platform and the slant-range
direction.
[0140] R represents an average of the distance between the first
radio wave receiving point P.sub.1 and the observation area and the
distance between the second radio wave receiving point P.sub.2 and
the observation area.
[0141] The distance component B.sub.1,2, the off-nadir angle
.theta., and the average R of the distances are information
included in the imaging parameters.
[0142] Sw represents a range of the first radar image and a range
of the second radar image that capture an observation object.
[0143] The range Sw of the first radar image and the range Sw of
the second radar image are the same to each other.
[0144] Herein, because the distance between the first radio wave
receiving point P.sub.1 and the observation area and the distance
between the second radio wave receiving point P.sub.2 and the
observation area are long, the phase shift component calculating
unit 21 assume that each of the off-nadir angle .theta. and the
average R of the distances does not change.
[0145] Specifically, the off-nadir angle .theta. included in the
first imaging parameter and the off-nadir angle .theta. included in
the second imaging parameter are the same value.
[0146] In addition, the average R of the distances included in the
first imaging parameter and the average R of the distances included
in the second imaging parameter are the same value.
[0147] In addition, a pixel at a pixel position (pixel,line) among
a plurality of pixels included in the first radar image and a pixel
at a pixel position (pixel,line) among a plurality of pixels
included in the second radar image are pixels at the same pixel
position.
[0148] FIG. 8 is an explanatory diagram illustrating the relation
of a spacing .DELTA.sl of pixels in the slant-range direction, the
range Sw of radar images (the first radar image, the second radar
image) and the distance sl from a position in the slant-range
direction corresponding to the center position of the radar image
to the observation area.
[0149] In FIG. 8, the distance from a position in the slant-range
direction corresponding to a near range of the radar image to a
position in the slant-range direction corresponding to the center
position of the radar image is (Sw/2)sin 0.
[0150] Thus, the distance sl is expressed as in the following
formula (2).
s l = .DELTA. sl .times. pixel - S w 2 sin .theta. ( 2 )
##EQU00001##
[0151] Each of the spacing .DELTA.sl and the range Sw of the radar
images is information included in the imaging parameters.
[0152] In addition, the relation between a position x in the x-axis
direction on the inclined surface 51 and the distance sl based on
the center position of the radar image is expressed as in the
following formula (3).
sl=x sin(.theta.-.alpha.) (3)
[0153] The following formula (4) is satisfied on the basis of the
formula (2) and the formula (3).
x sin ( .theta. - .alpha. ) = .DELTA. sl .times. pixel - Sw 2 sin
.theta. ( 4 ) ##EQU00002##
[0154] The phase shift component calculating unit 21 calculates the
position x on the inclined surface 51 corresponding to a pixel
position "pixel" in the slant-range direction in the radar image by
substituting the position "pixel" into the formula (4).
[0155] A plurality of reflected signals from scatterers are present
in the pixel at the position "pixel" substituted into the formula
(4).
[0156] The position "pixel" substituted into the formula (4) may be
provided to the phase shift component calculating unit 21 by manual
operation made by a user, or may be provided to the phase shift
component calculating unit 21 from an external device, which is not
illustrated, for example.
[0157] The phase shift component calculating unit 21 calculates the
phase shift component .phi.(x) at the position x in the x-axis
direction on the inclined surface 51 by using the distance
component B.sub.1,2, the off-nadir angle .theta., the average R of
the distances, the wavelength .lamda. of the emitted radio wave,
the inclination angle .alpha., and an observation path parameter p
(step ST3 in FIG. 6).
[0158] The observation path parameter p is a parameter indicating
whether the observation path when the radar image is taken is
repeat pass or single pass, which is p=2 in the case of repeat pass
or p=1 in the case of single pass. The observation path parameter p
may be provided to the phase shift component calculating unit 21
and the phase calculating unit 22 by manual operation made by a
user, or may be provided to the phase shift component calculating
unit 21 and the phase calculating unit 22 from an external device,
which is not illustrated, for example.
[0159] The following formula (5) is a formula for calculating the
phase shift component .phi.(x) used by the phase shift component
calculating unit 21.
.phi. ( x ) = ( 2 p .pi. B 1 , 2 cos ( .theta. - .alpha. ) .lamda.
R ) x ( 5 ) ##EQU00003##
[0160] The phase shift component calculating unit 21 outputs the
phase shift component .phi.(x) in the x-axis direction to the phase
difference calculating unit 23.
[0161] The phase calculating unit 22 calculates the phase
.phi.(z.sub.0) on the parallel surface 52 with respect to the
inclined surface 51 by using the distance component B.sub.1,2, the
off-nadir angle .theta., the average R of the distances, the
wavelength .lamda. of the emitted radio wave, the inclination angle
.alpha., the distance z.sub.0, and the observation path parameter p
(step ST4 in FIG. 6).
[0162] The following formula (6) is a formula for calculating the
phase .phi.(z.sub.0) used by the phase calculating unit 22.
.rho. ( z 0 ) = ( 2 p .pi. B 1 , 2 .lamda. R sin ( .theta. -
.alpha. ) ) z 0 ( 6 ) ##EQU00004##
[0163] The phase calculating unit 22 outputs the phase
.phi.(z.sub.0) to the phase difference calculating unit 23.
[0164] The phase difference calculating unit 23 calculates, in each
of a plurality of reflected signals present in each of pixels
included in the first and second radar images, the phase difference
.DELTA..phi.(x,z.sub.0) by using the phase shift component .phi.(x)
and the phase .phi.(z.sub.0) (step ST5 in FIG. 6).
[0165] The phase difference .DELTA..phi.(x,z.sub.0) is a phase
difference, in each of the reflected signals, between the phase of
the reflected signal with respect to the first radio wave receiving
point P.sub.1 and the phase of the reflected signal with respect to
the second radio wave receiving point P.sub.2.
[0166] The following formula (7) is a formula for calculating the
phase difference .DELTA..phi.(x,z.sub.0) used by the phase
difference calculating unit 23.
.DELTA..PHI.(x,z.sub.0)=.PHI.(x)+.rho.(z.sub.0) (7)
[0167] The phase difference calculating unit 23 outputs each phase
difference .DELTA..phi.(x,z.sub.0) to the image processing unit
13.
[0168] The image processing unit 13 performs a process of acquiring
a suppressed image.
[0169] FIG. 9 is a flowchart illustrating the processing of the
image processing unit 13.
[0170] The processing of the image processing unit 13 will now be
explained in detail with reference to FIG. 9.
[0171] The rotation amount calculating unit 31 acquires each phase
difference .DELTA..phi.(x,z.sub.0) output from the phase difference
calculating unit 23.
[0172] The rotation amount calculating unit 31 calculates each of
phase rotation amounts exp[j.DELTA..phi.(x,z.sub.0)] in a plurality
of pixels included in the second radar image from each phase
difference .DELTA..phi.(x,z.sub.0) (step ST11 in FIG. 9).
[0173] The rotation amount calculating unit 31 outputs each
rotation amount exp[j.DELTA..phi.(x,z.sub.0)] to the phase rotating
unit 33.
[0174] The phase rotating unit 33 acquires the second radar image
from the radar image group 2 output from the radar image acquiring
unit 11.
[0175] The phase rotating unit 33 performs the process rotating the
phases in the plurality of pixels included in the second radar
image on the basis of the respective rotation amounts
exp[j.DELTA..phi.(x,z.sub.0)] output from the rotation amount
calculating unit 31 (step ST12 in FIG. 9).
[0176] The following formula (8) is a formula representing the
process of rotating a phase performed by the phase rotating unit
33.
S.sub.2'(pixel,line)=S.sub.2(pixel,line)exp[j.DELTA.(x,z.sub.0)]
(8)
[0177] In the formula (8), S.sub.2(pixel,line) represents the pixel
value of a pixel included in the second radar image output from the
radar image acquiring unit 11, and S.sub.2'(pixel,line) represents
the pixel value of a pixel included in the second radar image
obtained by rotation of the phase in the pixel by the phase
rotating unit 33.
[0178] The phase rotating unit 33 outputs a second radar image
including a plurality of pixels obtained by phase rotation to the
difference calculation processing unit 34.
[0179] The difference calculation processing unit 34 acquires the
first radar image from the radar image group 2 output from the
radar image acquiring unit 11, and acquires the second radar image
including a plurality of pixels obtained by the phase rotation and
output from the phase rotating unit 33.
[0180] The difference calculation processing unit 34 calculates a
difference .DELTA.S(pixel,line) between pixel values of pixels at
corresponding pixel positions among a plurality of pixels included
in the first radar image and among a plurality of pixels obtained
by phase rotation included in the second radar image (step ST13 in
FIG. 9).
[0181] The following formula (9) is a formula for calculating the
difference .DELTA.S(pixel,line) used by the difference calculation
processing unit 34.
.DELTA.S(pixel,line)=S.sub.1(pixel,line)-S.sub.2'(pixel,line)
(9)
[0182] In the formula (9), S.sub.1(pixel,line) represents the pixel
value of a pixel included in the first radar image.
[0183] The difference calculation processing unit 34 outputs the
suppressed image including the respective differences .DELTA.s
(pixel, line) to the outside of the unit.
[0184] Here, FIG. 10 is an explanatory diagram illustrating
suppression of reflected signals present in one pixel in a case
where the phases in the pixels included in the second radar image
are not rotated by the phase rotating unit 33.
[0185] In FIG. 10, regarding a reflected signal assigned with "1",
the distance from the scatterer that scatters the reflected signal
to the first radio wave receiving point P.sub.1 and the distance
from the scatterer that scatters the reflected signal to the second
radio wave receiving point P.sub.2 are equal to each other. Thus,
regarding the reflected signal assigned with "1", the phase
difference .DELTA..phi.(x,z.sub.0) between the phase with respect
to the first radio wave receiving point P.sub.1 and the phase with
respect to the second radio wave receiving point P.sub.2 is
zero.
[0186] Because the difference .DELTA.S(pixel,line) for the
reflected signal assigned with "1" is thus zero, the reflected
signal assigned with "1" is suppressed.
[0187] Regarding a reflected signal assigned with "2", the distance
from the scatterer that scatters the reflected signal to the first
radio wave receiving point P.sub.1 and the distance from the
scatterer that scatters the reflected signal to the second radio
wave receiving point P.sub.2 are not equal to each other. Thus,
regarding the reflected signal assigned with "2", the phase
difference .DELTA..phi.(x,z.sub.0) between the phase with respect
to the first radio wave receiving point P.sub.1 and the phase with
respect to the second radio wave receiving point P.sub.2 is other
than zero.
[0188] Because the difference .DELTA.S(pixel,line) for the
reflected signal assigned with "2" is thus other than zero, the
reflected signal assigned with "2" is not suppressed.
[0189] Regarding a reflected signal assigned with "3" as well, the
distance from the scatterer that scatters the reflected signal to
the first radio wave receiving point P.sub.1 and the distance from
the scatterer that scatters the reflected signal to the second
radio wave receiving point P.sub.2 are not equal to each other.
Thus, regarding the reflected signal assigned with "3", the phase
difference .DELTA..phi.(x,z.sub.0) between the phase with respect
to the first radio wave receiving point P.sub.1 and the phase with
respect to the second radio wave receiving point P.sub.2 is other
than zero.
[0190] Because the difference .DELTA.S(pixel,line) for the
reflected signal assigned with "3" is thus other than zero, the
reflected signal assigned with "3" is not suppressed.
[0191] FIG. 11 is an explanatory diagram illustrating suppression
of reflected signals present in one pixel in a case where the
phases in pixels included in the second radar image are rotated by
the phase rotating unit 33.
[0192] Regarding a reflected signal assigned with "1", as
illustrated in FIG. 10, the distance from the scatterer that
scatters the reflected signal to the first radio wave receiving
point P.sub.1 and the distance from the scatterer that scatters the
reflected signal to the second radio wave receiving point P.sub.2
are equal to each other. Thus, regarding the reflected signal
assigned with "1", the phase difference .DELTA..phi.(x,z.sub.0)
between the phase with respect to the first radio wave receiving
point P.sub.1 and the phase with respect to the second radio wave
receiving point P.sub.2 is zero, and the phase rotation amount
exp[j.DELTA..phi.(x,z.sub.0)] calculated by the rotation amount
calculating unit 31 is zero.
[0193] Regarding the reflected signal assigned with "1", because
the phase rotation amount exp[j.DELTA..phi.(x,z.sub.0)] is zero,
the phase is not rotated by the phase rotating unit 33 as
illustrated in FIGS. 10 and 11. Thus, because the phase difference
.DELTA..phi.(x,z.sub.0) is still zero for the reflected signal
assigned with "1", the difference .DELTA.S(pixel,line) is zero, and
the reflected signal assigned with "1" is thus suppressed.
[0194] Regarding a reflected signal assigned with "2", as
illustrated in FIG. 10, the distance from the scatterer that
scatters the reflected signal to the first radio wave receiving
point P.sub.1 and the distance from the scatterer that scatters the
reflected signal to the second radio wave receiving point P.sub.2
are not equal to each other. Thus, regarding the reflected signal
assigned with "2", the phase difference .DELTA..phi.(x,z.sub.0)
between the phase with respect to the first radio wave receiving
point P.sub.1 and the phase with respect to the second radio wave
receiving point P.sub.2 is other than zero. Thus, the phase
rotation amount exp[j.DELTA..phi.(x,z.sub.0)] calculated by the
rotation amount calculating unit 31 is other than zero.
[0195] Regarding the reflected signal assigned with "2" resulting
from phase rotation, as illustrated in FIG. 11, the distance to the
first radio wave receiving point P.sub.1 and the distance to the
second radio wave receiving point P.sub.2 are not equal to each
other even after the rotation by the rotation amount
exp[j.DELTA..phi.(x,z.sub.0)] by the phase rotating unit 33. Thus,
regarding the reflected signal assigned with "2" resulting from the
phase rotation, the phase difference .DELTA..phi.(x,z.sub.0)
between the phase with respect to the first radio wave receiving
point P.sub.1 and the phase with respect to the second radio wave
receiving point P.sub.2 is other than zero.
[0196] Because the difference .DELTA.S(pixel,line) for the
reflected signal assigned with "2" resulting from the phase
rotation is thus other than zero, the reflected signal assigned
with "2" resulting from the phase rotation is not suppressed.
[0197] Regarding a reflected signal assigned with "3", as
illustrated in FIG. 10, the distance from the scatterer that
scatters the reflected signal to the first radio wave receiving
point P.sub.1 and the distance from the scatterer that scatters the
reflected signal to the second radio wave receiving point P.sub.2
are not equal to each other. Thus, regarding the reflected signal
assigned with "3", the phase difference .DELTA..phi.(x,z.sub.0)
between the phase with respect to the first radio wave receiving
point P.sub.1 and the phase with respect to the second radio wave
receiving point P.sub.2 is other than zero. Thus, the phase
rotation amount exp[j.DELTA..phi.(x,z.sub.0)] calculated by the
rotation amount calculating unit 31 is other than zero.
[0198] Regarding the reflected signal assigned with "3", as
illustrated in FIG. 11, the distance to the first radio wave
receiving point P.sub.1 and the distance to the second radio wave
receiving point P.sub.2 have become equal to each other as a result
of the rotation by the rotation amount
exp[j.DELTA..phi.(x,z.sub.0)] by the phase rotating unit 33. Thus,
regarding the reflected signal assigned with "3" resulting from the
phase rotation, the phase difference .DELTA..phi.(x,z.sub.0)
between the phase with respect to the first radio wave receiving
point P.sub.1 and the phase with respect to the second radio wave
receiving point P.sub.2 is zero.
[0199] Because the difference .DELTA.S(pixel,line) for the
reflected signal assigned with "3" resulting from the phase
rotation is thus zero, the reflected signal assigned with "3"
resulting from the phase rotation is suppressed.
[0200] In the first embodiment described above, the radar image
processing device 10 has a configuration including the phase
difference calculating unit 23 that calculates a phase difference,
which is the difference between the phases with respect to the
radio wave receiving points different from each other, of each of a
plurality of reflected signals present in one pixel, and the
rotation amount calculating unit 31 that calculates each of the
phase rotation amounts in a plurality of pixels included in the
second radar image from the respective phase differences, in which
the difference calculating unit 32 rotates the phases in the
plurality of pixels included in the second radar image on the basis
of the respective rotation amounts, and calculates a difference
between pixel values of pixels at corresponding pixel positions
among the plurality of pixels included in the first radar image and
the plurality of pixels obtained by the phase rotation included in
the second radar image. The radar image processing device 10 is
therefore capable of also suppressing a reflected signal with the
difference between phases with respect to the radio wave receiving
points different from each other not being zero.
Second Embodiment
[0201] The first embodiment presents an example in which the radar
image processing device 10 acquires a radar image group 2 including
a first radar image and a second radar image, and outputs a
suppressed image.
[0202] In a second embodiment, a radar image processing device 10
that acquires a radar image group 2 including two or more radar
images capturing the same observation area taken from radio wave
receiving points different from each other, and outputs a
suppressed image will be described.
[0203] In the radar image processing device 10 of the second
embodiment, the phase processing unit 12 and the image processing
unit 13 perform processes on each combination of two radar images
included in the radar image group 2. In this case, one radar image
included in each combination will be referred to as a first radar
image, and the other radar image included in the combination will
be referred to as a second radar image.
[0204] Specifically, the phase shift component calculating unit 21,
the phase calculating unit 22, and the phase difference calculating
unit 23 repeat the process of calculating the phase difference
.DELTA..phi..sub.i(x,z.sub.0) until the process of calculating the
phase difference .DELTA..phi..sub.i(x,z.sub.0) is completed for all
of the combinations i of two radar images. Symbol i is a variable
representing a combination of two radar images.
[0205] The rotation amount calculating unit 31, the phase rotating
unit 33, and the difference calculation processing unit 34 repeat
the process of calculating the difference
.DELTA.S.sub.i(pixel,line) until the process of calculating the
difference .DELTA.S.sub.i(pixel,line) is completed for all of the
combinations i of two radar images.
[0206] The radar image processing device 10 in the second
embodiment has a configuration as illustrated in FIG. 1, that is
similar to the radar image processing device 10 of the first
embodiment.
[0207] The phase processing unit 12 in the second embodiment has a
configuration as illustrated in FIG. 2, that is similar to the
phase processing unit 12 of the first embodiment.
[0208] Note that the radar image group 2 includes two or more radar
images, and the imaging parameter group 3 includes two or more
imaging parameters.
[0209] FIG. 12 is a configuration diagram illustrating an image
processing unit 13 of the radar image processing device 10
according to the second embodiment.
[0210] FIG. 13 is a hardware configuration diagram illustrating
hardware of each of the phase processing unit 12 and the image
processing unit 13.
[0211] In FIGS. 12 and 13, reference numerals that are the same as
those in FIGS. 3 and 4 represent the same or corresponding
components, and the description thereof will thus not be
repeated.
[0212] An image combining unit 35 is implemented by an image
combining circuit 47 illustrated in FIG. 13, for example.
[0213] The image combining unit 35 acquires a weight parameter
w.sub.i used for generation of a suppressed image.
[0214] The image combining unit 35 performs a process of combining
differences .DELTA.S.sub.i(pixel,line) at corresponding pixel
positions among the respective differences calculated for the
respective combinations i by the difference calculation processing
unit 34 by using the weight parameter w.sub.i.
[0215] The image combining unit 35 outputs a suppressed image
including the respective differences S.sub.sup(pixel, line)
resulting from the combining to the outside of the unit.
[0216] In FIG. 2, it is assumed that each of the phase shift
component calculating unit 21, the phase calculating unit 22, and
the phase difference calculating unit 23, which are components of
the phase processing unit 12, is implemented by such dedicated
hardware as illustrated in FIG. 13.
[0217] In addition, in FIG. 12, it is assumed that each of the
rotation amount calculating unit 31, the phase rotating unit 33,
the difference calculation processing unit 34, and the image
combining unit 35, which are components of the image processing
unit 13, is implemented by such dedicated hardware as illustrated
in FIG. 13.
[0218] Specifically, the phase processing unit 12 and the image
processing unit 13 are assumed to be implemented by the phase shift
component calculating circuit 41, the phase calculating circuit 42,
the phase difference calculating circuit 43, the rotation amount
calculating circuit 44, the phase rotating circuit 45, the
difference calculation processing circuit 46, and the image
combining circuit 47.
[0219] Note that each of the phase shift component calculating
circuit 41, the phase calculating circuit 42, the phase difference
calculating circuit 43, the rotation amount calculating circuit 44,
the phase rotating circuit 45, the difference calculation
processing circuit 46, and the image combining circuit 47 may be a
single circuit, a composite circuit, a programmed processor, a
parallel-programmed processor, an ASIC, an FPGA, or a combination
thereof, for example.
[0220] The components of the phase processing unit 12 and the
components of the image processing unit 13 are not limited to those
implemented by dedicated hardware. The phase processing unit 12 and
the image processing unit 13 may be implemented by software,
firmware, or a combination of software and firmware.
[0221] In the case where the phase processing unit 12 is
implemented by software, firmware, or the like, programs for
causing a computer to perform procedures of the phase shift
component calculating unit 21, the phase calculating unit 22, and
the phase difference calculating unit 23 are stored in a memory 61
illustrated in FIG. 5.
[0222] In addition, in the case where the image processing unit 13
is implemented by software, firmware, or the like, programs for
causing a computer to perform procedures of the rotation amount
calculating unit 31, the phase rotating unit 33, the difference
calculation processing unit 34, and the image combining unit 35 are
stored in the memory 61.
[0223] A processor 62 of the computer thus executes the programs
stored in the memory 61.
[0224] Next, the operation of the radar image processing device 10
will be explained.
[0225] The phase processing unit 12 performs a process of
calculating the phase difference .DELTA..phi..sub.i(x,z.sub.0) for
each combination i of two radar images among the two or more radar
images included in the radar image group 2.
[0226] The phase shift component calculating unit 21 acquires a
combination of two imaging parameters associated with the two radar
images from the imaging parameter group 3 output from the radar
image acquiring unit 11.
[0227] Herein, one radar image included in the combination i will
be referred to as a first radar image, and the other radar image
included in the combination i will be referred to as a second radar
image.
[0228] A radio wave receiving point for a first radar image
included in one combination and a radio wave receiving point for a
first radar image included in another combination are different
from each other. Herein, however, for convenience of explanation,
both of such radio wave receiving points will be referred to as
first radio wave receiving points P.sub.1.
[0229] In addition, a radio wave receiving point for a second radar
image included in one combination and a radio wave receiving point
for a second radar image included in another combination are
different from each other. Herein, however, for convenience of
explanation, both of such radio wave receiving points will be
referred to as second radio wave receiving points P.sub.2.
[0230] An imaging parameter associated with the first radar image
will be referred to as a first imaging parameter, and an imaging
parameter associated with the second radar image will be referred
to as a second imaging parameter.
[0231] In addition, the phase shift component calculating unit 21
acquires the inclination angle .alpha..
[0232] The phase calculating unit 22 acquires the first imaging
parameter, the second imaging parameter, the inclination angle
.alpha., and the distance z.sub.0.
[0233] The phase shift component calculating unit 21 calculates the
position x on the inclined surface 51 corresponding to a pixel
position "pixel" in the slant-range direction in the radar image by
substituting the position "pixel" into the formula (4).
[0234] The pixel at the position "pixel" substituted into the
formula (4) is a pixel in which a plurality of reflected signals
from scatterers are present.
[0235] The phase shift component calculating unit 21 calculates the
phase shift component .phi..sub.i(x) in the x-axis direction on the
inclined surface 51 by using the distance component B.sub.1,2, the
off-nadir angle .theta., the average R of the distances, the
wavelength .lamda. of the emitted radio wave, the inclination angle
.alpha., and the observation path parameter p.
[0236] The following formula (10) is a formula for calculating the
phase shift component .phi..sub.i(x) used by the phase shift
component calculating unit 21.
.phi. i ( x ) = ( 2 p .pi. B 1 2 cos ( .theta. - .alpha. ) .lamda.
R ) x ( 10 ) ##EQU00005##
[0237] The phase shift component calculating unit 21 outputs the
phase shift component .phi..sub.i(x) in the x-axis direction to the
phase difference calculating unit 23.
[0238] The phase calculating unit 22 calculates the phase
.rho..sub.i(z.sub.0) on the parallel surface 52 with respect to the
inclined surface 51 by using the distance component B.sub.1,2, the
off-nadir angle .theta., the average R of the distances, the
wavelength .lamda. of the emitted radio wave, the inclination angle
.alpha., the distance z.sub.0, and the observation path parameter
p. The same applies to the phase .rho..sub.i(z.sub.0) in any
combination.
[0239] The following formula (11) is a formula for calculating the
phase .rho..sub.i(z.sub.0) used by the phase calculating unit
22.
.rho. i ( z 0 ) = ( 2 p .pi. B 1 , 2 .lamda. R sin ( .theta. -
.alpha. ) ) z 0 ( 11 ) ##EQU00006##
[0240] The phase calculating unit 22 outputs the phase
.rho..sub.i(z.sub.0) to the phase difference calculating unit
23.
[0241] The phase difference calculating unit 23 calculates, in each
of a plurality of reflected signals present in one pixel in each
combination i, a phase difference .DELTA..phi..sub.i(x,z.sub.0)
between the phase with respect to the first radio wave receiving
point P.sub.1 and the phase with respect to the second radio wave
receiving point P.sub.2 by using the phase shift component
.phi..sub.i(x) and the phase .rho..sub.i(z.sub.0).
[0242] The following formula (12) is a formula for calculating the
phase difference .DELTA..phi..sub.i(x,z.sub.0) used by the phase
difference calculating unit 23.
.DELTA..PHI..sub.i(x,z.sub.0)=.PHI..sub.i(x)+.rho..sub.i(z.sub.0)
(12)
[0243] The phase difference calculating unit 23 outputs each phase
difference .DELTA..phi..sub.i (x,z.sub.0) to the image processing
unit 13.
[0244] The rotation amount calculating unit 31 acquires each phase
difference .DELTA..phi..sub.i (x,z.sub.0) output from the phase
difference calculating unit 23.
[0245] The rotation amount calculating unit 31 calculates, for each
combination i, each of phase rotation amounts
exp[j.DELTA..phi..sub.i (x,z.sub.0)] in a plurality of pixels
included in the second radar image from each phase difference
.DELTA..phi..sub.i(x,z.sub.0).
[0246] The rotation amount calculating unit 31 outputs each
rotation amount exp[j.DELTA..phi..sub.i(x,z.sub.0)] to the phase
rotating unit 33.
[0247] The phase rotating unit 33 acquires the second radar image
included in the combination i from the radar image group 2 output
from the radar image acquiring unit 11.
[0248] The phase rotating unit 33 performs the process of rotating
the phases in the plurality of pixels included in the acquired
second radar image on the basis of the respective rotation amounts
exp[j.DELTA..phi..sub.i (x,z.sub.0)] output from the rotation
amount calculating unit 31.
[0249] The following formula (13) is a formula representing the
process of rotating a phase performed by the phase rotating unit
33.
S.sub.2'(pixel,line)=S.sub.2(pixel,line)exp[j.DELTA..PHI..sub.i(x,z.sub.-
0)] (13)
[0250] The phase rotating unit 33 outputs a second radar image
including a plurality of pixels obtained by phase rotation to the
difference calculation processing unit 34.
[0251] The difference calculation processing unit 34 acquires the
first radar image included in the combination i from the radar
image group 2 output from the radar image acquiring unit 11, and
acquires the second radar image including a plurality of pixels
obtained by the phase rotation and output from the phase rotating
unit 33.
[0252] The difference calculation processing unit 34 calculates the
difference .DELTA.S.sub.i(pixel,line) between pixel values of
pixels at corresponding pixel positions among a plurality of pixels
included in the acquired first radar image and among a plurality of
pixels obtained by phase rotation included in the acquired second
radar image.
[0253] The following formula (14) is a formula for calculating the
difference .DELTA.S.sub.i(pixel,line) used by the difference
calculation processing unit 34.
.DELTA.S.sub.i(pixel,line)=S.sub.1(pixel,line)-S.sub.2'(pixel,line)
(14)
[0254] The difference calculation processing unit 34 outputs each
difference .DELTA.S.sub.i(pixel,line) to the image combining unit
35.
[0255] The rotation amount calculating unit 31, the phase rotating
unit 33, and the difference calculation processing unit 34 repeat
the process of calculating the difference
.DELTA.S.sub.i(pixel,line) until the process of calculating the
difference .DELTA.S.sub.i(pixel,line) is completed for all of the
combinations i of two radar images.
[0256] The image combining unit 35 acquires a weight parameter
w.sub.i used for generation of a suppressed image.
[0257] The weight parameter w.sub.i may be provided to the image
combining unit 35 by manual operation made by a user, or may be
provided to the image combining unit 35 from an external device,
which is not illustrated.
[0258] The image combining unit 35 combines differences
.DELTA.S.sub.i(pixel,line) at corresponding pixel positions among
the respective differences calculated for the respective
combinations i by the difference calculation processing unit 34 by
using the weight parameter w.sub.i.
[0259] The image combining unit 35 outputs a suppressed image
including the respective differences S.sub.sup (pixel, line)
resulting from the combining to the outside of the unit.
[0260] For the method of combining the differences
.DELTA.S.sub.i(pixel,line) in all the combination, a method of
obtaining an arithmetic mean or a method of obtaining a geometric
mean can be used.
[0261] In a case where the method of obtaining an arithmetic mean
is used, the image combining unit 35 combines the differences
.DELTA.S.sub.i(pixel,line) in all the combinations by the following
formula (15).
S sup ( pixel , line ) = 1 N i N w i .DELTA. S i ( pixel , line ) (
15 ) ##EQU00007##
[0262] In a case where the method of obtaining a geometric mean is
used, the image combining unit 35 combines the differences
.DELTA.S.sub.i(pixel,line) in all the combinations by the following
formula (16).
S sup ( pixel , line ) = { i N .DELTA. S i ( pixel , line ) w i } 1
/ N ( 16 ) ##EQU00008##
[0263] In the formulas (15) and (16), N represents the number of
combinations of two radar images.
[0264] Here, FIG. 14 is an explanatory diagram illustrating a
plurality of reflected signals present in one pixel in a case where
only two radar images are included in the radar image group 2 like
the radar image processing device 10 of the first embodiment.
[0265] In the case where only two radar images are included in the
radar image group 2, a plurality of null points may be formed as a
result of the process of calculating the differences
.DELTA.S.sub.i(pixel, line) performed by the difference calculation
processing unit 34 as illustrated in FIG. 14.
[0266] In the example of FIG. 14, null points are formed in all of
a reflected signal assigned with "1", a reflected signal assigned
with "2", and a reflected signal assigned with "3".
[0267] Thus, in the example of FIG. 14, all of the reflected signal
assigned with "1", the reflected signal assigned with "2", and the
reflected signal assigned with "3" are suppressed.
[0268] FIG. 15 is an explanatory diagram illustrating a plurality
of reflected signals present in one pixel in a case where two or
more radar images are included in the radar image group 2 like the
radar image processing device 10 of the second embodiment.
[0269] In FIG. 15, the number of radar images included in the radar
image group 2 is M, and P.sub.M represents the position of the
platform when an M-th radar image is taken.
[0270] Because the number of radar images included in the radar
image group 2 is two or larger and the image combining unit 35
combines the differences .DELTA.S.sub.i(pixel,line) at
corresponding pixel positions, the number of null points that are
formed is reduced as compared with that in the case where the
number of radar images is two.
[0271] In the example of FIG. 15, the number of null points that
are formed is one, and no null point is formed in the reflected
signal assigned with "2".
[0272] In the second embodiment described above, the radar image
processing device 10 has a configuration including the image
combining unit 35 that combines differences
.DELTA.S.sub.i(pixel,line) at corresponding pixel positions among
the respective differences calculated for the respective
combinations i by the difference calculation processing unit 34.
The radar image processing device 10 is therefore capable of
reducing the number of null points that are formed, which can
prevent reflected signals that need to be maintained from being
suppressed.
Third Embodiment
[0273] The second embodiment presents an example in which the radar
image processing device 10 output the differences
S.sub.sup(pixel,line) obtained by the combining as a suppressed
image.
[0274] In a third embodiment, a radar image processing device 10
that calculates an image in which a plurality of reflected signals
present in one pixel are extracted from the differences
S.sub.sup(pixel,line) resulting from the combining by the image
combining unit 35 will be described.
[0275] The radar image processing device 10 in the third embodiment
has a configuration as illustrated in FIG. 1, that is similar to
the radar image processing device 10 of the first or second
embodiment.
[0276] The phase processing unit 12 in the third embodiment has a
configuration as illustrated in FIG. 2, that is similar to the
phase processing unit 12 of the first or second embodiment.
[0277] Note that the radar image group 2 includes two or more radar
images, and the imaging parameter group 3 includes two or more
imaging parameters.
[0278] FIG. 16 is a configuration diagram illustrating an image
processing unit 13 of the radar image processing device 10
according to the third embodiment.
[0279] FIG. 17 is a hardware configuration diagram illustrating
hardware of each of the phase processing unit 12 and the image
processing unit 13.
[0280] In FIGS. 16 and 17, reference numerals that are the same as
those in FIGS. 3, 4, 12, and 13 represent the same or corresponding
components, and the description thereof will thus not be
repeated.
[0281] An extraction image calculating unit 36 is implemented by an
extraction image calculating circuit 48 illustrated in FIG. 17, for
example.
[0282] The extraction image calculating unit 36 acquires the first
radar image from the radar image group 2 output from the radar
image acquiring unit 11, and acquires the respective differences
S.sub.sup(pixel,line) resulting from the combining output from the
image combining unit 35.
[0283] The extraction image calculating unit 36 performs a process
of calculating an image in which a plurality of reflected signals
present in one pixel are extracted on the basis of the pixel values
of a plurality of pixels included in the first radar image and the
respective differences S.sub.sup(pixel,line) resulting from the
combining.
[0284] In FIG. 2, it is assumed that each of the phase shift
component calculating unit 21, the phase calculating unit 22, and
the phase difference calculating unit 23, which are components of
the phase processing unit 12, is implemented by such dedicated
hardware as illustrated in FIG. 17.
[0285] In addition, in FIG. 16, it is assumed that each of the
rotation amount calculating unit 31, the phase rotating unit 33,
the difference calculation processing unit 34, the image combining
unit 35, and the extraction image calculating unit 36, which are
components of the image processing unit 13, is implemented by such
dedicated hardware as illustrated in FIG. 17.
[0286] Specifically, the phase processing unit 12 and the image
processing unit 13 are assumed to be implemented by the phase shift
component calculating circuit 41, the phase calculating circuit 42,
the phase difference calculating circuit 43, the rotation amount
calculating circuit 44, the phase rotating circuit 45, the
difference calculation processing circuit 46, the image combining
circuit 47, and the extraction image calculating circuit 48.
[0287] The components of the phase processing unit 12 and the
components of the image processing unit 13 are not limited to those
implemented by dedicated hardware. The phase processing unit 12 and
the image processing unit 13 may be implemented by software,
firmware, or a combination of software and firmware.
[0288] Next, the operation of the radar image processing device 10
will be explained.
[0289] Note that the radar image processing device 10 is similar to
the radar image processing device 10 of the second embodiment
except that the extraction image calculating unit 36 is included,
and thus, only the operation of the extraction image calculating
unit 36 will be explained here.
[0290] The extraction image calculating unit 36 acquires the first
radar image from the radar image group 2 output from the radar
image acquiring unit 11, and acquires the respective differences
S.sub.sup(pixel,line) resulting from the combining output from the
image combining unit 35.
[0291] The extraction image calculating unit 36 calculates a pixel
value S.sub.ext(pixel,line) of a pixel in which a plurality of
reflected signals are present from the pixel values of a plurality
of pixels included in the first radar image and the respective
differences S.sub.sup(pixel,line) resulting from the combining.
[0292] The following formula (17) is a formula for calculating the
pixel value S.sub.ext(pixel,line) used by the extraction image
calculating unit 36.
S.sub.ext(pixel,line)=S.sub.i(pixel,line)/S.sub.sup(pixel,line)
(17)
[0293] The extraction image calculating unit 36 outputs, to the
outside of the unit, an image including the pixel having the pixel
value S.sub.ext(pixel, line) as an image in which a plurality of
reflected signal present in one pixel are extracted.
[0294] In the third embodiment described above, the radar image
processing device 10 has a configuration including the extraction
image calculating unit 36 that calculates an image in which a
plurality of reflected signals present in one pixel are extracted
on the basis of the pixel values of a plurality of pixels included
in the first radar image and the respective differences
S.sub.sup(pixel,line) resulting from the combining. The radar image
processing device 10 is therefore capable of outputting not only a
suppressed image in which reflected signals are suppressed but also
an extraction image in which reflected signals are extracted.
Fourth Embodiment
[0295] In a fourth embodiment, a radar image processing device 10
that calculates, as an interference phase
.DELTA..gamma..sub.C1,C2(pixel,line), the phase at each pixel
position from the difference .DELTA.S.sub.C1(pixel,line) at each
pixel position in a first combination C1 and the difference
.DELTA.S.sub.C2(pixel,line) at each pixel position in a second
combination C2 will be described.
[0296] The radar image processing device 10 in the fourth
embodiment has a configuration as illustrated in FIG. 1, that is
similar to the radar image processing device 10 of the first,
second, or third embodiment.
[0297] The phase processing unit 12 in the fourth embodiment has a
configuration as illustrated in FIG. 2, that is similar to the
phase processing unit 12 of the first, second, or third
embodiment.
[0298] Note that, the radar image group 2 includes three or more
radar images capturing the same observation area taken from radio
wave receiving points different from each other, and the imaging
parameter group 3 includes three or more imaging parameters.
[0299] FIG. 18 is a configuration diagram illustrating the image
processing unit 13 of the radar image processing device 10
according to the fourth embodiment.
[0300] FIG. 19 is a hardware configuration diagram illustrating
hardware of each of the phase processing unit 12 and the image
processing unit 13.
[0301] In FIGS. 18 and 19, reference numerals that are the same as
those in FIGS. 3, 4, 12, 13, 16, and 17 represent the same or
corresponding components, and the description thereof will thus not
be repeated.
[0302] In the radar image processing device 10 of the fourth
embodiment, a combination of any two radar images included in the
radar image group 2 will be referred to as a first combination C1.
In addition, a combination of any two radar images included in the
radar image group 2 will be referred to as a second combination
C2.
[0303] The two radar images included in the first combination C1
and the two radar images included in the second combination C2 are
different from each other. Note that, one of the two radar images
included in the first combination C1 may be the same as any one of
the two radar images included in the second combination C2.
[0304] In the radar image processing device 10 of the fourth
embodiment, the difference calculation processing unit 34
calculates the difference .DELTA.S.sub.C1(pixel,line) at each pixel
position in the first combination C1, and the difference
.DELTA.S.sub.C2(pixel,line) at each pixel position in the second
combination C2.
[0305] The interference phase calculating unit 37 is implemented by
an interference phase calculating circuit 49 illustrated in FIG.
19, for example.
[0306] The interference phase calculating unit 37 acquires the
differences .DELTA.S.sub.C1(pixel,line) at the respective pixel
positions calculated for the first combination C1, and the
differences .DELTA.S.sub.C2(pixel,line) at the respective pixel
positions calculated for the second combination C2 by the
difference calculation processing unit 14.
[0307] The interference phase calculating unit 37 calculates, as
interference phases .DELTA..gamma..sub.C1,C2(pixel,line), the
phases at the respective pixel positions from the differences
.DELTA.S.sub.C1(pixel,line) and the differences
.DELTA.S.sub.C2(pixel,line).
[0308] In FIG. 2, it is assumed that each of the phase shift
component calculating unit 21, the phase calculating unit 22, and
the phase difference calculating unit 23, which are components of
the phase processing unit 12, is implemented by such dedicated
hardware as illustrated in FIG. 19.
[0309] In addition, in FIG. 18, it is assumed that each of the
rotation amount calculating unit 31, the phase rotating unit 33,
the difference calculation processing unit 34, and the interference
phase calculating unit 37, which are components of the image
processing unit 13, is implemented by such dedicated hardware as
illustrated in FIG. 19.
[0310] Specifically, the phase processing unit 12 and the image
processing unit 13 are assumed to be implemented by the phase shift
component calculating circuit 41, the phase calculating circuit 42,
the phase difference calculating circuit 43, the rotation amount
calculating circuit 44, the phase rotating circuit 45, the
difference calculation processing circuit 46, and the interference
phase calculating circuit 49.
[0311] The components of the phase processing unit 12 and the
components of the image processing unit 13 are not limited to those
implemented by dedicated hardware. The phase processing unit 12 and
the image processing unit 13 may be implemented by software,
firmware, or a combination of software and firmware.
[0312] Next, the operation of the radar image processing device 10
will be explained.
[0313] The phase processing unit 12 performs a process of
calculating the phase differences .DELTA..phi..sub.C1(x,z.sub.0)
for the first combination C1, and a process of calculating the
phase differences .DELTA..phi..sub.C2(x,z.sub.0) for the second
combination C2.
[0314] The process of calculating a phase difference performed by
the phase processing unit 12 will now be explained in detail.
[0315] First, the phase shift component calculating unit 21
acquires a combination of two imaging parameters associated with
the two radar images included in the first combination C1 from the
imaging parameter group 3 output from the radar image acquiring
unit 11.
[0316] Herein, one radar image included in the first combination C1
will be referred to as a first radar image, and the other radar
image included in the first combination C1 will be referred to as a
second radar image.
[0317] In addition, an imaging parameter associated with the first
radar image will be referred to as a first imaging parameter, and
an imaging parameter associated with the second radar image will be
referred to as a second imaging parameter.
[0318] In addition, the phase shift component calculating unit 21
acquires the inclination angle .alpha..
[0319] The phase calculating unit 22 acquires the first imaging
parameter, the second imaging parameter, the inclination angle
.alpha., and the distance z.sub.0.
[0320] The phase shift component calculating unit 21 calculates the
position x on the inclined surface 51 corresponding to a pixel
position "pixel" in the slant-range direction in the radar image by
substituting the position "pixel" into the formula (4).
[0321] The phase shift component calculating unit 21 calculates the
phase shift component .phi..sub.C1(x) in the x-axis direction on
the inclined surface 51 for the first combination C1 by using the
distance component B.sub.1,2, the off-nadir angle .theta., the
average R of the distances, the wavelength .lamda. of the emitted
radio wave, the inclination angle .alpha., and the observation path
parameter p.
[0322] The following formula (18) is a formula for calculating the
phase shift component .DELTA..phi..sub.i(x) used by the phase shift
component calculating unit 21.
.phi. C 1 ( x ) = ( 2 p .pi. B 1 , 2 cos ( .theta. - .alpha. )
.lamda. R ) x ( 18 ) ##EQU00009##
[0323] The phase shift component calculating unit 21 outputs the
phase shift component .DELTA..phi..sub.i(x) in the x-axis direction
to the phase difference calculating unit 23.
[0324] Subsequently, the phase shift component calculating unit 21
acquires a combination of two imaging parameters associated with
the two radar images included in the second combination C2 from the
imaging parameter group 3 output from the radar image acquiring
unit 11.
[0325] Herein, one radar image included in the second combination
C2 will be referred to as a first radar image, and the other radar
image included in the second combination C2 will be referred to as
a second radar image.
[0326] In addition, an imaging parameter associated with the first
radar image will be referred to as a first imaging parameter, and
an imaging parameter associated with the second radar image will be
referred to as a second imaging parameter.
[0327] In addition, the phase shift component calculating unit 21
acquires the inclination angle .alpha..
[0328] The phase calculating unit 22 acquires the first imaging
parameter, the second imaging parameter, the inclination angle
.alpha., and the distance z.sub.0.
[0329] The phase shift component calculating unit 21 calculates the
position x on the inclined surface 51 corresponding to a pixel
position "pixel" in the slant-range direction in the radar image by
substituting the position "pixel" into the formula (4).
[0330] The phase shift component calculating unit 21 calculates the
phase shift component .phi..sub.C2(x) in the x-axis direction on
the inclined surface 51 for the second combination C2 by using the
distance component B.sub.1,2, the off-nadir angle .theta., the
average R of the distances, the wavelength .lamda. of the emitted
radio wave, the inclination angle .alpha., and the observation path
parameter p.
[0331] The following formula (19) is a formula for calculating the
phase shift component .phi..sub.C2(x) used by the phase shift
component calculating unit 21.
.phi. C 2 ( x ) = ( 2 p .pi. B 1 , 2 cos ( .theta. - .alpha. )
.lamda. R ) x ( 19 ) ##EQU00010##
[0332] The phase shift component calculating unit 21 outputs the
phase shift component .phi..sub.C2(x) in the x-axis direction to
the phase difference calculating unit 23.
[0333] The phase calculating unit 22 calculates the phases
.rho..sub.C1(z.sub.0) and .rho..sub.C2(z.sub.0) on the parallel
surface 52 with respect to the inclined surface 51 by using the
distance component B.sub.1,2, the off-nadir angle .theta., the
average R of the distances, the wavelength .lamda. of the emitted
radio wave, the inclination angle .alpha., the distance z.sub.0,
and the observation path parameter p.
[0334] The following formula (20) is a formula for calculating the
phases .rho..sub.C1(z.sub.0) and .rho..sub.C2(z.sub.0) used by the
phase calculating unit 22.
.rho. C 1 ( z 0 ) = .rho. C 2 ( z 0 ) = ( 2 p .pi. B 1 , 2 .lamda.
R sin ( .theta. - .alpha. ) ) z 0 ( 20 ) ##EQU00011##
[0335] The phase calculating unit 22 outputs the phases
.rho..sub.C1(z.sub.0) and .rho..sub.C2(z.sub.0) to the phase
difference calculating unit 23.
[0336] The phase difference calculating unit 23 acquires the
respective phase shift components .phi..sub.C2(x) and
.DELTA..phi..sub.i(x) output from the phase shift component
calculating unit 21, and acquires the respective phases
.rho..sub.C1(z.sub.0) and .rho..sub.C2(z.sub.0) output from the
phase calculating unit 22.
[0337] The phase difference calculating unit 23 calculates, for the
first combination C1, the phase difference
.DELTA..phi..sub.C1(x,z.sub.0) in each of a plurality of reflected
signals present in one pixel by using the phase shift component
.DELTA..phi..sub.i(x) and the phase .rho..sub.C1(z.sub.0).
[0338] The following formula (21) is a formula for calculating the
phase difference .DELTA..phi..sub.C1(x,z.sub.0) used by the phase
difference calculating unit 23.
.DELTA..PHI..sub.C1(x,z.sub.0)=.PHI..sub.C1(x)+.rho..sub.C1(z.sub.0)
(21)
[0339] The phase difference calculating unit 23 outputs each phase
difference .DELTA..phi..sub.C1(x,z.sub.0) to the image processing
unit 13.
[0340] Subsequently, the phase difference calculating unit 23
calculates, for the second combination C2, the phase difference
.DELTA..phi..sub.C2(x,z.sub.0) in each of a plurality of reflected
signals present in one pixel by using the phase shift component
.phi..sub.C2(x) and the phase .rho..sub.C2(z.sub.0).
[0341] The following formula (22) is a formula for calculating the
phase difference .DELTA..phi..sub.C2(x,z.sub.0) used by the phase
difference calculating unit 23.
.DELTA..PHI..sub.C2(x,z.sub.0)=.PHI..sub.C2(x).rho..sub.C2(z.sub.0)
(22)
[0342] The phase difference calculating unit 23 outputs each phase
difference .DELTA..phi..sub.C2(x,z.sub.0) to the image processing
unit 13.
[0343] The rotation amount calculating unit 31 acquires the
respective phase differences .DELTA..phi..sub.C1(x,z.sub.0) and
.DELTA..phi..sub.C2(x,z.sub.0) output from the phase difference
calculating unit 23.
[0344] The rotation amount calculating unit 31 calculates, for the
first combination C1, each of phase rotation amounts
exp[j.DELTA..phi..sub.C1(x,z.sub.0)] in a plurality of pixels
included in the second radar image from each phase difference
.DELTA..phi..sub.C1(x,z.sub.0).
[0345] The rotation amount calculating unit 31 outputs each
rotation amount exp[j.DELTA..phi..sub.C1(x,z.sub.0)] to the phase
rotating unit 33.
[0346] Subsequently, the rotation amount calculating unit 31
calculates, for the second combination C2, each of phase rotation
amounts exp[j.DELTA..phi..sub.C2(x,z.sub.0)] in a plurality of
pixels included in the second radar image from each phase
difference .DELTA..phi..sub.C2(x,z.sub.0).
[0347] The rotation amount calculating unit 31 outputs each
rotation amount exp[jA.phi..sub.C2(x,z.sub.0)] to the phase
rotating unit 33.
[0348] The phase rotating unit 33 first acquires the second radar
image included in the first combination C1 from the radar image
group 2 output from the radar image acquiring unit 11.
[0349] The phase rotating unit 33 performs the process of rotating
the phases in the plurality of pixels included in the acquired
second radar image on the basis of the respective rotation amounts
exp[j.DELTA..phi..sub.C1(x,z.sub.0)] output from the rotation
amount calculating unit 31.
[0350] The following formula (23) is a formula representing the
process of rotating a phase performed by the phase rotating unit
33.
S.sub.2'(pixel,line)=S.sub.2(pixel,line)exp[j.DELTA..PHI..sub.C1(x,z.sub-
.0)] (23)
[0351] The phase rotating unit 33 outputs a second radar image
including a plurality of pixels obtained by phase rotation to the
difference calculation processing unit 34.
[0352] Subsequently, the phase rotating unit 33 acquires the second
radar image included in the second combination C2 from the radar
image group 2 output from the radar image acquiring unit 11.
[0353] The phase rotating unit 33 performs the process of rotating
the phases in the plurality of pixels included in the acquired
second radar image on the basis of the respective rotation amounts
exp[j.DELTA..phi..sub.C2(x,z.sub.0)] output from the rotation
amount calculating unit 31.
[0354] The following formula (24) is a formula representing the
process of rotating a phase performed by the phase rotating unit
33.
S.sub.2'(pixel,line)=S.sub.2(pixel,line)exp[j.DELTA..PHI..sub.C2(x,z.sub-
.0)] (24)
[0355] The phase rotating unit 33 outputs a second radar image
including a plurality of pixels obtained by phase rotation to the
difference calculation processing unit 34.
[0356] The difference calculation processing unit 34 acquires the
first radar image included in the first combination C1 from the
radar image group 2 output from the radar image acquiring unit
11.
[0357] The difference calculation processing unit 34 also acquires
the second radar image including a plurality of pixels obtained by
the phase rotation on the first combination C1 output from the
phase rotating unit 33.
[0358] The difference calculation processing unit 34 calculates the
difference .DELTA.S.sub.C1(pixel,line) between pixel values of
pixels at corresponding pixel positions among a plurality of pixels
included in the acquired first radar image and among a plurality of
pixels obtained by phase rotation included in the acquired second
radar image.
[0359] The following formula (25) is a formula for calculating the
difference .DELTA.S.sub.C1(pixel,line) used by the difference
calculation processing unit 34.
.DELTA.S.sub.C1(pixel,line)=S.sub.1(pixel,line)-S.sub.2'(pixel,line)
(25)
[0360] The difference calculation processing unit 34 outputs each
difference .DELTA.S.sub.C1(pixel,line) to the interference phase
calculating unit 37.
[0361] Subsequently, the difference calculation processing unit 34
acquires the first radar image included in the second combination
C2 from the radar image group 2 output from the radar image
acquiring unit 11.
[0362] The difference calculation processing unit 34 also acquires
the second radar image including a plurality of pixels obtained by
the phase rotation on the second combination C2 output from the
phase rotating unit 33.
[0363] The difference calculation processing unit 34 calculates the
difference .DELTA.S.sub.C2(pixel,line) between pixel values of
pixels at corresponding pixel positions among a plurality of pixels
included in the acquired first radar image and among a plurality of
pixels obtained by phase rotation included in the acquired second
radar image.
[0364] The following formula (26) is a formula for calculating the
difference .DELTA.S.sub.C2(pixel,line) used by the difference
calculation processing unit 34.
.DELTA.S.sub.C2(pixel,line)=S.sub.1(pixel,line)-S.sub.2'(pixel,line)
(26)
[0365] The difference calculation processing unit 34 outputs each
difference .DELTA.S.sub.C2(pixel,line) to the interference phase
calculating unit 37.
[0366] The interference phase calculating unit 37 acquires the
differences .DELTA.S.sub.C1(pixel,line) at the respective pixel
positions calculated for the first combination C1 by the difference
calculation processing unit 14.
[0367] The interference phase calculating unit 37 also acquires the
differences .DELTA.S.sub.C2(pixel,line) at the respective pixel
positions calculated for the second combination C2 by the
difference calculation processing unit 14.
[0368] The interference phase calculating unit 37 calculates, as
interference phases .DELTA..gamma..sub.C1,C2(pixel,line), the
phases at the respective pixel positions from the differences
.DELTA.S.sub.C1(pixel,line) and the differences
.DELTA.S.sub.C2(pixel,line) by using the following formula (27) or
formula (28).
.DELTA..gamma..sub.C1,C2=<(.DELTA.S.sub.C1/.DELTA.S.sub.C2)
(27)
.DELTA..gamma..sub.C1,C2=<.DELTA.S.sub.C1-<.DELTA.S.sub.C2
(28)
[0369] In the formula (27) and the formula (28), < is a symbol
representing the argument of a complex number.
[0370] The interference phases .DELTA..gamma..sub.C1,C2(pixel,line)
are the phases of only the reflected signals remaining without
being suppressed among a plurality of reflected signals present in
one pixel.
[0371] The interference phase calculating unit 37 outputs the
interference phases .DELTA..gamma..sub.C1,C2(pixel,line) to the
outside of the unit.
[0372] For example, when signals reflected by a ground surface and
signals reflected by the roof of a building are present in one
pixel, the signals reflected by the ground surface are suppressed
by the phase processing unit 12 and the image processing unit 13,
and only the signals reflected by the roof of the building remain.
Thus, the interference phases .DELTA..gamma..sub.C1,C2(pixel,line)
are calculated as the phases of the signals reflected by the roof
of the building.
[0373] In the fourth embodiment described above, the radar image
processing device 10 has a configuration including the interference
phase calculating unit 37 that calculates, as an interference phase
.DELTA..gamma..sub.C1,C2(pixel,line), the phase at each pixel
position from the difference .DELTA.S.sub.C1(pixel,line) in the
first combination C1 and the difference .DELTA.S.sub.C2(pixel,line)
in the second combination C2. The radar image processing device 10
is therefore capable of obtaining the phases of reflected signals
in a state in which unnecessary reflected signals from a scatterer
are suppressed.
Fifth Embodiment
[0374] In a fifth embodiment, a radar image processing device 10
that estimates the position of a scatterer present in an
observation area by using interference phases
.DELTA..gamma..sub.C1,C2(pixel,line) calculated by the interference
phase calculating unit 37 will be described.
[0375] The radar image processing device 10 has a configuration as
illustrated in FIG. 1, that is similar to that in the first
embodiment.
[0376] The phase processing unit 12 has a configuration as
illustrated in FIG. 2, that is similar to that in the first,
second, or third embodiment.
[0377] FIG. 20 is a configuration diagram illustrating the image
processing unit 13 of the radar image processing device 10
according to the fifth embodiment.
[0378] FIG. 21 is a hardware configuration diagram illustrating
hardware of each of the phase processing unit 12 and the image
processing unit 13.
[0379] In FIGS. 20 and 21, reference numerals that are the same as
those in FIGS. 3, 4, 12, 13, 16 to 19 represent the same or
corresponding components, and the description thereof will thus not
be repeated.
[0380] A position estimating unit 38 is implemented by a position
estimating circuit 50 illustrated in FIG. 21, for example.
[0381] The position estimating unit 38 estimate the position of a
scatterer present in an observation area by using the interference
phases .DELTA..gamma..sub.C1,C2(pixel,line) calculated by the
interference phase calculating unit 37.
[0382] In FIG. 2, it is assumed that each of the phase shift
component calculating unit 21, the phase calculating unit 22, and
the phase difference calculating unit 23, which are components of
the phase processing unit 12, is implemented by such dedicated
hardware as illustrated in FIG. 21.
[0383] In addition, in FIG. 20, it is assumed that each of the
rotation amount calculating unit 31, the phase rotating unit 33,
the difference calculation processing unit 34, the interference
phase calculating unit 37, and the position estimating unit 38,
which are components of the image processing unit 13, is
implemented by such dedicated hardware as illustrated in FIG.
21.
[0384] Specifically, the phase processing unit 12 and the image
processing unit 13 are assumed to be implemented by the phase shift
component calculating circuit 41, the phase calculating circuit 42,
the phase difference calculating circuit 43, the rotation amount
calculating circuit 44, the phase rotating circuit 45, the
difference calculation processing circuit 46, the interference
phase calculating circuit 49, and the position estimating circuit
50.
[0385] The components of the phase processing unit 12 and the
components of the image processing unit 13 are not limited to those
implemented by dedicated hardware. The phase processing unit 12 and
the image processing unit 13 may be implemented by software,
firmware, or a combination of software and firmware.
[0386] Next, the operation of the radar image processing device 10
will be explained.
[0387] Note that the radar image processing device 10 is similar to
the radar image processing device 10 of the fourth embodiment
except that the position estimating unit 38 is included, and thus,
only the operation of the position estimating unit 38 will be
explained here.
[0388] Herein, for convenience of explanation, a radio wave
receiving point for a first radar image included in a first
combination C1 will be referred to as a radio wave receiving point
P.sub.a, and a radio wave receiving point for a second radar image
included in the first combination C1 will be referred to as a radio
wave receiving point P.sub.b.
[0389] In addition, a radio wave receiving point for a first radar
image included in a second combination C2 will be referred to as a
radio wave receiving point P.sub.c, and a radio wave receiving
point for a second radar image included in the second combination
C2 will be referred to as a radio wave receiving point P.sub.d.
[0390] The position estimating unit 38 acquires the interference
phases .DELTA..gamma..sub.C1,C2(pixel,line) output from the
interference phase calculating unit 37.
[0391] The position estimating unit 38 also acquires the respective
phase differences .DELTA..phi..sub.C1(x,z.sub.0) and
.DELTA..phi..sub.C2(x,z.sub.0) output from the phase difference
calculating unit 23.
[0392] The position estimating unit 38 estimates the position z-hat
of a scatterer present in an observation area by using the
interference phases .DELTA..gamma..sub.C1,C2(pixel,line) and the
respective phase differences .DELTA..phi..sub.C1(x,z.sub.0) and
.DELTA..PHI..sub.C2(x,z.sub.0) output from the phase difference
calculating unit 23, as expressed in the following formula
(29).
[0393] Because the symbol "{circumflex over ( )}" cannot be typed
above the character "z" in the description due to electronic
filing, it is described in such a manner as z-hat herein.
z ^ = R sin ( .theta. - .alpha. ) [ .lamda. ( B a , c + B b , d ) 2
p .pi. { 2 .angle. .DELTA. .gamma. C 1 , C 2 - .DELTA..phi. C 1 ( x
, z 0 ) + .DELTA. .phi. C 2 ( x , z 0 ) } - cos ( .theta. - .alpha.
) x R ] ( 29 ) ##EQU00012##
[0394] In the formula (29), B.sub.a,c represents a distance
component, in a direction perpendicular to the slant-range
direction, of the distance between the radio wave receiving point
P.sub.a and the radio wave receiving point P.sub.c.
[0395] B.sub.b,d represents a distance component, in a direction
perpendicular to the slant-range direction, of the distance between
the radio wave receiving point P.sub.b and the radio wave receiving
point P.sub.d.
[0396] R represents an average of the distances between each of the
radio wave receiving point P.sub.a, the radio wave receiving point
P.sub.b, the radio wave receiving point P.sub.c, and the radio wave
receiving point P.sub.d and the observation area.
[0397] The distance component B.sub.a,c, the distance component
B.sub.b,d, the off-nadir angle .theta., and the average R of the
distances are information included in the imaging parameter.
[0398] Symbol x represents the position on the inclined surface 51
associated with the position "pixel", and is output from the phase
shift component calculating unit 21.
[0399] The position z-hat of the scatterer is the distance (height)
in a z-axis direction from the inclined surface 51 to a signal
reflecting surface of the scatterer.
[0400] The position estimating unit 38 outputs the estimated
position z-hat of the scatterer to the outside of the unit.
[0401] Herein, the two radar images included in the first
combination C1 and the two radar images included in the second
combination C2 are different from each other. The combinations,
however, are not limited thereto, and one of the two radar images
included in the first combination C1 may be the same as one of the
two radar images included in the second combination C2.
[0402] For example, the second radar image included in the first
combination C1 and the second radar image included in the second
combination C2 may be the same radar image.
[0403] In the case where the second radar image included in the
first combination C1 and the second radar image included in the
second combination C2 may be the same radar image, B.sub.b,d=0 is
obtained, and the formula (29) used for estimation of the position
z-hat is simplified as in the following formula (30).
z ^ = R sin ( .theta. - .alpha. ) [ .lamda. B a , c 2 p .pi. { 2
.angle..DELTA. .gamma. C 1 , C 2 - .DELTA..phi. C 1 ( x , z 0 ) +
.DELTA..phi. C 2 ( x , z 0 ) } - cos ( .theta. - .alpha. ) x R ] (
30 ) ##EQU00013##
[0404] In the fifth embodiment described above, the radar image
processing device 10 has a configuration including the position
estimating unit 38 that estimates the position z-hat of a scatterer
present in an observation area by using the interference phases
.DELTA..gamma..sub.C1,C2(pixel,line) calculated by the interference
phase calculating unit 37. The radar image processing device 10 is
therefore capable of obtaining the position of a scatterer present
in an observation area.
[0405] Note that the embodiments of the present invention can be
freely combined, any components in the embodiments can be modified,
and any components in the embodiments can be omitted within the
scope of the invention of the present application.
INDUSTRIAL APPLICABILITY
[0406] The present invention is suitable for a radar image
processing device and a radar image processing method that
calculate differences between a plurality of pixels included in a
first radar image and a plurality of pixels obtained by phase
rotation included in a second radar image.
REFERENCE SIGNS LIST
[0407] 1: radar, 2: radar image group, 3: imaging parameter group,
10: radar image processing device, 11: radar image acquiring unit,
12: phase processing unit, 13: image processing unit, 21: phase
shift component calculating unit, 22: phase calculating unit, 23:
phase difference calculating unit, 31: rotation amount calculating
unit, 32: difference calculating unit, 33: phase rotating unit, 34:
difference calculation processing unit, 35: image combining unit,
36: extraction image calculating unit, 37: interference phase
calculating unit, 38: position estimating unit, 41: phase shift
component calculating circuit, 42: phase calculating circuit, 43:
phase difference calculating circuit, 44: rotation amount
calculating circuit, 45: phase rotating circuit, 46: difference
calculation processing circuit, 47: image combining circuit, 48:
extraction image calculating circuit, 49: interference phase
calculating circuit, 50: position estimating circuit, 51: inclined
surface, 52: parallel surface, 61: memory, 62: processor
* * * * *