U.S. patent application number 11/597513 was filed with the patent office on 2007-12-20 for method of and an apparatus for determining information relating to a projectile, such as a golf ball.
Invention is credited to Fredrik Tuxen.
Application Number | 20070293331 11/597513 |
Document ID | / |
Family ID | 34956418 |
Filed Date | 2007-12-20 |
United States Patent
Application |
20070293331 |
Kind Code |
A1 |
Tuxen; Fredrik |
December 20, 2007 |
Method of and an Apparatus for Determining Information Relating to
a Projectile, Such as a Golf Ball
Abstract
An apparatus and a method of providing information relating to a
projectile, such as a sports ball, such as a golf ball. The
apparatus and method provide better estimations of e.g. the landing
point of the projectile or its position in general in that an
oscillating signal caused e.g. by multiple path reflections of the
radiation, is identified and may be removed in order to generate
the "true" signal used for the landing point determination. This
oscillating signal may be used for quantifying an error of the
landing point determination or may be used for providing
information relating to the surroundings of the projectile during
its flight.
Inventors: |
Tuxen; Fredrik; (Horsholm,
DK) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 8910
RESTON
VA
20195
US
|
Family ID: |
34956418 |
Appl. No.: |
11/597513 |
Filed: |
May 23, 2005 |
PCT Filed: |
May 23, 2005 |
PCT NO: |
PCT/DK05/00336 |
371 Date: |
July 31, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60574231 |
May 26, 2004 |
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Current U.S.
Class: |
473/199 |
Current CPC
Class: |
G01S 13/88 20130101;
G01S 7/352 20130101; G01S 2013/462 20130101; G01S 13/583 20130101;
G01S 13/4418 20130101 |
Class at
Publication: |
473/199 |
International
Class: |
A63B 69/36 20060101
A63B069/36 |
Claims
1-68. (canceled)
69. A method of determining information relating to a projectile,
the method comprising: receiving electromagnetic radiation emitted
from or reflected by the projectile at least partly while it is in
flight, and providing a corresponding signal, generating an altered
signal by removing, from the provided signal, an oscillating
signal, and determining the information relating to the projectile
from the altered signal.
70. A method according to claim 69, wherein the generating step
comprises performing an averaging operation comprising averaging
the provided signal over a predetermined time period.
71. A method according to claim 69, wherein the generating step
comprises tracking the oscillating signal and subtracting the
oscillating signal from the provided signal.
72. A method according to claim 69, wherein the generating step
comprises generating the altered signal for a predetermined period
of time after, that the provided signal reaches zero.
73. A method according to claim 69, wherein the receiving step
comprises receiving the radiation from at least two different
directions.
74. A method according to claim 69, wherein the determining step
comprises determining a parameter of the projectile at a first
point in time and estimating, from the determined parameter, the
parameter at a second, later, point in time.
75. A method according to claim 74, wherein the estimation is
performed using a predetermined relation between the parameter and
time.
76. A method according to claim 74, wherein the parameter
determined is a distance between a means receiving the radiation
and the projectile.
77. A method according to claim 69, wherein the corresponding
signal provided is a signal representing an intensity of the
radiation received and wherein the determining step comprises
determining a distance between a means receiving the radiation and
the projectile.
78. A method according to claim 69, wherein the generating step
comprises generating the altered signal, until the altered signal
fulfils a predetermined criterion, the determining step comprising
providing, as the information, an estimate of a landing point of
the projectile.
79. A method according to claim 78, wherein the determining step
comprises providing as the information an estimate of a distance
between the landing point of the projectile and a predetermined
target.
80. A method according to claim 78, wherein the determining step
comprises providing as the information an estimate of a deviation
from a predetermined direction and a determined direction of the
projectile.
81. A method according to claim 80, wherein the determining step
further comprises determining a launch position of the projectile,
the determined direction of the projectile being a direction
between the launch position and the landing point.
82. A method according to claim 78, wherein the generating step
comprises performing a filtering using a time constant larger than
a period of the oscillating signal and wherein the determining step
comprises determining the landing point as a point where the signal
level has decreased a predetermined amount.
83. A method of determining information relating to a projectile,
the method comprising: receiving electromagnetic radiation emitted
from or reflected by the projectile at least partly while it is in
flight, and providing a corresponding signal, identifying whether
an amplitude of the provided signal varies more than a
predetermined threshold, determining the information from the
corresponding signal, and quantifying an uncertainty of the
determination of the information from the variation of the
amplitude.
84. A method according to claim 83, wherein the generating step
comprises performing an averaging operation comprising averaging
the provided signal over a time period larger than a predetermined
time period.
85. A method according to claim 83, further comprising a step of
generating an altered signal by removing an oscillating signal from
the provided signal, the method further comprising the step of
determining further information from the altered signal.
86. A method according to claim 85, wherein the generating step
comprises tracking the oscillating signal and subtracting the
oscillating signal from the provided signal.
87. A method according to claim 85, wherein the generating step
comprises generating the altered signal for a predetermined period
of time after, that the provided signal reaches zero.
88. A method according to claim 83, wherein the receiving step
comprises receiving the radiation from at least two different
directions.
89. A method according to claim 83, wherein the determining step
comprises determining a parameter of the projectile at a first
point in time and estimating, from the determined parameter, the
parameter at a second, later, point in time.
90. A method according to claim 89, wherein the estimation is
performed using a predetermined relation between the parameter and
time.
91. A method according to claim 89, wherein the parameter
determined is a distance between a means receiving the radiation
and the projectile.
92. A method according to claim 83, wherein the corresponding
signal provided is a signal representing an intensity of the
radiation received and wherein the determining step comprises
determining a distance between a means receiving the radiation and
the projectile.
93. A method of determining information relating to the
surroundings of a projectile, the method comprising: receiving
electromagnetic radiation emitted from or reflected by the
projectile at least partly while it is in flight, and providing a
corresponding signal, generating an altered signal by isolating,
from the provided signal, an oscillating signal, and determining,
as the information and from the altered signal, an angle to
vertical of, and/or a distance to, a surface over which the
projectile flies and/or a reflection coefficient of the radiation
of a surface over which the projectile flies.
94. A method according to claim 69, wherein the step of providing
the corresponding signal comprises providing a signal representing
an intensity or power of the received radiation within a
predetermined frequency/wavelength interval.
95. A method according to claim 69, the method further comprising
the initial step of providing electromagnetic radiation toward the
projectile while in flight.
96. A method of determining a distance between a projectile and a
radiation receiver, the method comprising the steps of: receiving
electromagnetic radiation emitted from or reflected by the
projectile at least partly while it is in flight, determining an
intensity of the radiation received and a distance between the
receiver and the projectile at a first point in time, determining,
at a second, later point in time, a second intensity of the
radiation received, and determining from a mathematical relation
between the first and second intensities determined, a distance, at
the second point in time, between the receiver and the
projectile.
97. An apparatus for determining information relating to a
projectile, the apparatus comprising: means for receiving
electromagnetic radiation emitted from or reflected by the
projectile at least partly while it is in flight, and for providing
a corresponding signal, means for generating an altered signal by
removing, from the provided signal, an oscillating signal, and
means for determining the information relating to the projectile
from the altered signal.
98. An apparatus according to claim 97, wherein the generating
means are adapted to perform an averaging operation comprising
averaging the provided signal over a predetermined time period.
99. An apparatus according to claim 97, wherein the generating
means are adapted to track the oscillating signal and subtract the
oscillating signal from the provided signal.
100. An apparatus according to claim 97, wherein the generating
means are adapted to generate the altered signal for a
predetermined period of time after, that the provided signal
reaches zero.
101. An apparatus according to claim 97, wherein the receiving
means are adapted to receive the radiation from at least two
different directions.
102. An apparatus according to claim 97, wherein the determining
means are adapted to determine a parameter of the projectile at a
first point in time and estimate, from the determined parameter,
the parameter at a second, later, point in time.
103. An apparatus according to claim 102, wherein the determining
means are adapted to perform the estimation using a predetermined
relation between the parameter and time.
104. An apparatus according to claim 102, wherein the determining
means are adapted to determine a parameter being a distance between
the receiving means and the projectile.
105. An apparatus according to claim 97, wherein the receiving
means are adapted to provide the corresponding signal representing
an intensity of the radiation received and wherein the determining
means are adapted to determine a distance between the receiving
means and the projectile.
106. An apparatus according to claim 97, wherein the generating
means are adapted to generate the altered signal, until the altered
signal fulfils a predetermined criterion, the determining means
being adapted to provide, as the information, an estimate of a
landing point of the projectile.
107. An apparatus according to claim 106, wherein the determining
means are adapted to provide as the information an estimate of a
distance between the landing point of the projectile and a
predetermined target.
108. An apparatus according to claim 106, wherein the determining
means are adapted to provide as the information an estimate of a
deviation from a predetermined direction and a determined direction
of the projectile.
109. An apparatus according to claim 108, wherein the determining
means further comprise means for determining a launch position of
the projectile, the determining means being adapted to provide the
determined direction of the projectile as a direction between the
launch position and the landing point.
110. An apparatus according to claim 105, wherein the generating
means comprise means for filtering the provided signal using a time
constant larger than a period of the oscillating signal, the
determining means being adapted to determine a landing point as a
point where the signal level has decreased a predetermined
amount.
111. An apparatus of determining information relating to a
projectile, the apparatus comprising: means for receiving
electromagnetic radiation emitted from or reflected by the
projectile at least partly while it is in flight, and for providing
a corresponding signal, means for identifying whether an amplitude
of the provided signal varies more than a predetermined threshold,
means for determining the information from the corresponding
signal, and means for quantifying an uncertainty of the
determination of the information from the variation of the
amplitude.
112. An apparatus according to claim 111, wherein the generating
means are adapted to perform an averaging operation comprising
averaging the provided signal over a time period larger than a
predetermined time period.
113. An apparatus according to claim 111, further comprising means
for generating an altered signal by removing an oscillating signal
from the provided signal, the determining means being adapted to
provide additional information relating to the projectile from the
altered signal.
114. An apparatus according to claim 111, wherein the generating
means are adapted to track the oscillating signal and subtract the
oscillating signal from the provided signal.
115. An apparatus according to claim 113, wherein the generating
means are adapted to generate the altered signal for a
predetermined period of time after, that the provided signal
reaches zero.
116. An apparatus according to claim 111, wherein the receiving
means are adapted to receive the radiation from at least two
different directions.
117. An apparatus according to claim 111, wherein the determining
means are adapted to determine a parameter of the projectile at a
first point in time and estimate, from the determined parameter,
the parameter at a second, later, point in time.
118. An apparatus according to claim 117, wherein the determining
means are adapted to perform an estimation using a predetermined
relation between the parameter and time.
119. An apparatus according to claim 117, wherein the determining
means are adapted to determine a parameter being a distance between
a means receiving the radiation and the projectile.
120. An apparatus according to claim 111, wherein the receiving
means are adapted to provide a corresponding signal representing an
intensity of the radiation received and wherein the determining
means are adapted to determine a distance between the receiving
means receiving the radiation and the projectile.
121. An apparatus of determining information relating to the
surroundings of a projectile, the apparatus comprising: means for
receiving electromagnetic radiation emitted from or reflected by
the projectile at least partly while it is in flight, and for
providing a corresponding signal, means for generating an altered
signal by isolating, from the provided signal, an oscillating
signal, and means for determining, as the information and from the
altered signal, an angle to vertical of, and/or a distance to, a
surface over which the projectile flies and/or a reflection
coefficient of the radiation of a surface over which the projectile
flies.
122. An apparatus according to claim 97, wherein the receiving
means are adapted to provide the corresponding signal as a signal
representing an intensity or power of the received radiation within
a predetermined frequency/wavelength interval.
123. An apparatus according to claim 97, the apparatus further
comprising means for providing electromagnetic radiation toward the
projectile while in flight.
124. An apparatus of determining a distance between a projectile
and a radiation receiver, the apparatus comprising: means for
receiving electromagnetic radiation emitted from or reflected by
the projectile at least partly while it is in flight, means for
determining an intensity of the radiation received and a distance
between the receiver and the projectile at a first point in time,
means for determining, at a second, later point in time, a second
intensity of the radiation received, and means for determining from
a mathematical relation between the first and second intensities
determined, a distance, at the second point in time, between the
receiver and the projectile.
125. A method of determining information relating to a projectile,
the method comprising: receiving electromagnetic radiation emitted
from or reflected by the projectile at least partly while it is in
flight, and providing a corresponding signal, determining an
expected oscillation of the provided signal, and determining the
information from a deviation between the corresponding signal and
the expected oscillation.
126. An apparatus of determining information relating to a
projectile, the apparatus comprising: means for receiving
electromagnetic radiation emitted from or reflected by the
projectile at least partly while it is in flight, and for providing
a corresponding signal, means for determining an expected
oscillation of the provided signal, and means for determining the
information from a deviation between the corresponding signal and
the expected oscillation.
127. A method according to claim 69, wherein: the receiving step
comprises receiving radiation at a plurality of spatially displaced
positions and providing a provided signal for each position, the
generating step comprises generating an altered signal for each
provided signal, and the determining step comprises determining the
information on the basis of all provided signals.
128. A method according to claim 83, wherein: the receiving step
comprises receiving radiation at a plurality of spatially displaced
positions and providing a provided signal for each position, the
identifying step is performed for each provided signal, the
determining step comprises determining the information on the basis
of all provided signals, and the quantifying step is performed on
the basis of the variation of the amplitudes of all provided
signals.
129. A method according to claim 91, wherein: the receiving step
comprises receiving radiation at a plurality of spatially displaced
positions and providing a provided signal for each position, the
generating step is performed for at least two of the provided
signals, and the determining step comprises determining the
information on the basis of all generated, altered signals.
130. A method according to claim 96, wherein: the receiving step
comprises receiving radiation at a plurality of spatially displaced
positions and providing a provided signal for each position, the
steps of determining intensities comprises determining the
intensities at each position, and the step of determining the
distance comprises determining the distance on the basis of all
intensities determined.
131. A method according to claim 125, wherein: the receiving step
comprises receiving radiation at a plurality of spatially displaced
positions and providing a provided signal for each position, the
step of determining the expected oscillation comprises determining
an expected oscillation for at least one of the positions, and the
step of determining the information comprises determining the
information on the basis of the deviation between at least one pair
of an expected oscillation and the corresponding provided
signal.
132. An apparatus according to claim 97, wherein: the receiving
means comprise a plurality of spatially displaced receiving means
each adapted to provide a provided signal, the generating means
area adapted to generate an altered signal for each receiving
means, and the determining means are adapted to determine the
information on the basis of all provided signals.
133. An apparatus according to claim 111, wherein: the receiving
means comprise a plurality of spatially displaced receiving means
each adapted to provide a provided signal, the identifying means
performed for each provided signal, the determining means are
adapted to determine the information on the basis of all provided
signals, and the quantifying means is adapted to perform the
quantification on the basis of the variation of the amplitudes of
all provided signals.
134. An apparatus according to claim 119, wherein: the receiving
means comprise a plurality of spatially displaced receiving means
each adapted to provide a provided signal, the generating means is
adapted to generate an altered signal for each of at least two of
the provided signals, and the determining means is adapted to
determine the information on the basis of all generated, altered
signals.
135. An apparatus according to claim 124, wherein: the receiving
means comprise a plurality of spatially displaced receiving means
each adapted to provide a provided signal, the means for
determining intensities are adapted to determine the intensities at
each receiving means, and the means for determining the distance is
adapted to determine the distance on the basis of all intensities
determined.
136. An apparatus according to claim 126, wherein: the receiving
means comprise a plurality of spatially displaced receiving means
each adapted to provide a provided signal, the means for
determining the expected oscillation is adapted to determine an
expected oscillation for at least one of the receiving means, and
the means for determining the information is adapted to determine
the information on the basis of a deviation between at least one
pair of an expected oscillation and the corresponding provided
signal.
137. A method according to claim 83, wherein the step of providing
the corresponding signal comprises providing a signal representing
an intensity or power of the received radiation within a
predetermined frequency/wavelength interval.
138. A method according to claim 93, wherein the step of providing
the corresponding signal comprises providing a signal representing
an intensity or power of the received radiation within a
predetermined frequency/wavelength interval.
139. A method according to claim 83, the method further comprising
the initial step of providing electromagnetic radiation toward the
projectile while in flight.
140. A method according to claim 93, the method further comprising
the initial step of providing electromagnetic radiation toward the
projectile while in flight.
141. An apparatus according to claim 106, wherein the generating
means comprise means for filtering the provided signal using a time
constant larger than a period of the oscillating signal, the
determining means being adapted to determine a landing point as a
point where the signal level has decreased a predetermined
amount.
142. An apparatus according to claim 111, wherein the receiving
means are adapted to provide the corresponding signal as a signal
representing an intensity or power of the received radiation within
a predetermined frequency/wavelength interval.
143. An apparatus according to claim 121, wherein the receiving
means are adapted to provide the corresponding signal as a signal
representing an intensity or power of the received radiation within
a predetermined frequency/wavelength interval.
144. An apparatus according to claim 111, the apparatus further
comprising means for providing electromagnetic radiation toward the
projectile while in flight.
145. An apparatus according to claim 121, the apparatus further
comprising means for providing electromagnetic radiation toward the
projectile while in flight.
Description
[0001] The present invention relates to a method and an apparatus
for determining information relating to a projectile, such as a
rifle projectile, a missile or, a sports ball, such as a golf ball,
or another object adapted to be launched. The information relates
to the projectile at least partly while the projectile is in
flight. In a number of embodiments, the information sought may be
the actual path taken by the projectile, the deviation thereby from
a predetermined path, the landing point, or the like.
[0002] A number of apparatus and methods are known for determining
information from flying projectiles. Such apparatus may comprise
the providing of transmitting equipment inside the projectile or
e.g. a bat used for hitting a sports ball. Other equipment uses a
radar for receiving radiation from the projectile, such as from a
golf ball, and for determining information from the projectile.
However, such apparatus is not able to determine the actual landing
point of the ball in that, normally, the radar is turned off, lacks
sensitivity, or the measurement stopped before the ball lands.
[0003] Golf radars are described in: WO03/032006, WO 91/06348, U.S.
Pat. Nos. 5,700,204, 6,547,671, 5,092,602, 4,509,052, 3,798,644,
6,133,946, 5,489,099, 6,244,971, 6,456,232, and 5,495,249 as well
as in JP-A-6126015 and 8266701.
[0004] A problem encountered using radar or the like on a flying
projectile is that of the radiation transmitted from the projectile
to the receiver may take multiple paths. Such multiple paths will
have different path lengths, whereby the signals from the
individual paths will interfere with each other. This interference
will influence rather drastically on the final result, such as a
determination of a velocity or position of the projectile.
[0005] Especially the determination of a landing point of the
projectile is difficult in that the radiation from the projectile
will experience also the ground especially when close to the
ground, where the detection is critical. At this point, the
interference of the signals will be large, whereby the signal will
vary and actually reaches zero even though the projectile is still
in flight. In this respect, it should be noted that the signal
needs not actually reach zero, but it will be smaller than a
detection threshold, whereby it will "formally" be zero in the
sense that it is not detectable within the detection limit.
[0006] This multi-path problem may be solved by preventing
radiation from all but one such path from reaching the detector.
This, however, may be difficult to obtain especially when the
projectile is close to the ground and is far away from the
detector.
[0007] This problem is seen both in golf, cricket and baseball,
where balls are hit large distances and where, such as for training
purposes or entertainment purposes, it is desired to know where the
ball landed or other characteristics of the ball flight path.
[0008] One aspect of the invention relates to another manner of
handling the multi-path situation. This aspect relates to a method
of determining information relating to a projectile, the method
comprising: [0009] receiving electromagnetic radiation emitted from
or reflected by the projectile at least partly while it is in
flight, and providing a corresponding signal, [0010] generating an
altered signal by removing, from the provided signal, an
oscillating signal, and [0011] determining the information relating
to the projectile from the altered signal.
[0012] In the present context, normally, the radiation
emitted/reflected from the projectile takes more than one path
toward the receiver, whereby the radiation received has the same
frequency/wavelength or is within a predetermined wavelength
interval. In this manner, wavelength filtering may be provided in
order to filter away noise caused by radiation outside this
frequency or this interval.
[0013] The oscillating signal may be caused (at least partly) by
the radiation taking more than one path, where the radiation from
the multiple paths interfere and cause the oscillating signal.
[0014] Also, that the radiation is received at least partly while
the projectile is in flight relates to the fact that radiation
received and information derived from the projectile before flying
or after having landed may be very valuable in combination with the
radiation received (and information derived) during the flight.
[0015] This oscillation is caused by the projectile moving, whereby
the path lengths in the different paths vary and cause, together
with the wavelength of the radiation, an oscillation of the
resulting signal received.
[0016] The oscillating signal is continuous and may, but need not,
be sinusoidal. In fact, the oscillation would, if caused by this
multi-path effect, increase in amplitude over time and it will also
change in frequency. The amplitude will depend on the reflection of
the surroundings, normally the ground. The oscillation will depend
on the shape of the surroundings (path length difference) as well
as the projectile trajectory and relative position of the receiver.
For a golf ball trajectory, the frequency of the oscillating signal
is, for a receiver placed a couple of meters behind the launch
point, normally in the interval of 0.5-10 Hz. For riffle
projectiles, missiles or artillery projectiles the frequency of the
oscillating signal is slightly lower, normally in the interval of
0.1-2 Hz.
[0017] Naturally, any type of radiation may be used, such as
visible light, IR, NIR, UV, Microwaves or radio waves may be used.
Also sound, such as ultrasound may be used.
[0018] The corresponding signal may be a signal representing signal
strength, a frequency, a wavelength, intensity, a phase or any
other characteristic of the radiation received. Normally, the
corresponding signal represents this characteristic over a period
of time.
[0019] The information derived relating to the projectile may be
the position thereof, the velocity, spin, rotation, height,
acceleration, path, or the like.
[0020] In the present context, the removal of the oscillating
signal from the corresponding signal may be a coherent adding of
the unwanted signal shifted 180 degrees in phase or any other
manner of taking away the oscillating signal from the other
signal.
[0021] The resulting, altered signal will be a smooth signal,
representing the actual position and movement of the
projectile.
[0022] In one embodiment, the generating step comprises performing
an averaging operation comprising averaging the provided signal
over a predetermined time period. Averaging over a period of time
larger than a full period or variation (of a non-periodical signal)
of the oscillating signal will average out the oscillating signal
and provide an altered signal with components having a frequency
lower than a signal having a period of the averaging time period.
This is one manner of removing the oscillating signal.
[0023] Another manner is one wherein the generating step comprises
tracking the oscillating signal and subtracting the oscillating
signal from the provided signal. This tracking may be obtained on
the basis of a knowledge of the frequency (or frequency interval)
of the oscillating signal. In this manner, the signal may be
identified and tracked, whereby subtraction is easy.
[0024] As mentioned above, the provided signal may, due to
interference, reach zero even though the actual signal desired--the
altered signal--has not reached zero. Thus, one embodiment relates
to a method where the generating step comprises generating the
altered signal for a predetermined period of time after, that the
provided signal reaches zero. If the provided signal subsequently
rises above zero, the providing of the altered signal may continue,
until the provided signal has not increased over zero for the
predetermined point in time. In this manner, any interference will
not untimely stop the determination.
[0025] As mentioned above, the oscillating signal may be caused by
interference from multiple paths. Thus, the receiving step may
comprise receiving the radiation from at least two different
directions or paths.
[0026] In one embodiment, the determining step comprises
determining a parameter of the projectile at a first point in time
and estimating, from the determined parameter, the parameter at a
second, later, point in time. One manner of performing this
estimation is to perform it using a predetermined relation between
the parameter and time. In that situation, the parameter will have
a predetermined course or development over time. One such parameter
is a distance between a means receiving the radiation and the
projectile. When monitoring the parameter, such as the distance, at
a first point in time or during a first period of time, it is
possible to predict the parameter/distance at a later point in
time.
[0027] When the corresponding signal provided is a signal
representing an intensity of the radiation received, the
determining step may comprise determining a distance between a
means receiving the radiation and the projectile. This is due to
the fact that the intensity emitted or reflected by the projectile
may be independent of an orientation of the projectile or it is a
priori known, whereby the intensity/signal strength received will
relate to the distance between the projectile and the receiver.
Naturally, if a radiation/sound emitter is used, the distance
between the projectile and the emitter should also be taken into
account.
[0028] A particularly interesting embodiment is one which is able
to determine the landing point or landing spot of the projectile.
Hitherto, landing point determination has been performed on the
basis of knowledge of only part of the path or the projectile
during flight. This, however, has presented uncertainties in the
determination. One reason for the prior art techniques not putting
emphasis on the signals from a projectile close to the ground may
be the above-mentioned oscillating multiple-path signals.
[0029] In this embodiment, the generating step comprises generating
the altered signal, until the altered signal fulfils a
predetermined criterion, the determining step further comprising
providing, as the information, an estimate of a landing point of
the projectile.
[0030] Thus, now that it is possible to actually remove the
oscillating signal, which in multiple-path situations is the
strongest, when the projectile is close to the ground, it is
possible to keep providing a reliable altered signal. Then, the
certain criterion is preferably related to a situation where it is
probable that the projectile has, in fact, landed.
[0031] In this situation, the landing point of the projectile will
normally be the spot of impact between the projectile and the
ground. In the situation where the projectile subsequently bounces
back up and again hits the ground, the landing point is the first
point of impact.
[0032] The predetermined criterion will relate to what the provided
and actual signals represent. When these signals represent a signal
strength or amplitude, the predetermined criteria may be an
absolute or a relative signal strength/intensity/amplitude, a
predetermined absolute or relative drop/increase of the
strength/intensity/amplitude, a predetermined course or development
over time.
[0033] One particular manner is to have the determining step
comprise performing a filtering using a time constant larger than a
period of the oscillating signal, and to determine a landing point
as a point where the signal level has decreased a predetermined
amount, such as 3 dB.
[0034] The frequency or period of the oscillating signal depends on
both the trajectory of the projectile as well as the height thereof
above the ground (or the distance to the reflecting surface) and
the velocity of the projectile. Thus, a golf ball may give rise to
a period in the interval of 0.5-10 Hz, whereas a projectile
launched by a rifle or a handgun may give rise to longer periods,
such as 0.1-2 Hz, again depending on the actual trajectory.
[0035] One manner of using this landing point is one where the
determining step comprises providing as the information an estimate
of a distance between the landing point of the projectile and a
predetermined target. This may be useful for practising hitting a
target, such as a flag on a golf course, where it may then be
desirable to also know the distance, and often also the direction
and height difference, from the target to the receiver. Thus, using
this set-up, it is possible to determine the actual distance
between the target and the landing point without having to travel
to the target area.
[0036] Another manner of using the landing point information is to
have the determining step comprise providing as the information an
estimate of a deviation from a predetermined direction and a
determined direction of the projectile. This determined direction
may e.g. be determined from the landing point.
[0037] This deviation may be an angular deviation between the two
directions, but the deviation may also be determined as a 3
dimensional distance between the intended and the actual directions
at the distance of the landing point of the projectile.
[0038] In order to determine the actual path/direction of the
projectile, it is desired that the determining step further
comprises determining a launch position of the projectile, the
determined direction of the projectile being a direction between
the launch position and the landing point. A number of manners
exist of determining the launch position of the projectile. One
method is to simply dictate this position in relation to the
receiver.
[0039] The launch position may be a position where the projectile
leaves the ground plane, as would be the case for a golf ball, it
might be a position from where the projectile leaves a launch pad,
such as a rifle, or it may be a position where the projectile is
impacted in order to initiate its path, such as where it is hit by
a hand, a bat, or the like.
[0040] A second aspect relates to e.g. the use of the provided
signal even though the oscillating signal forms part thereof. This
aspect relates to a method of determining information relating to a
projectile, the method comprising: [0041] receiving electromagnetic
radiation emitted from or reflected by the projectile at least
partly while it is in flight, and providing a corresponding signal,
[0042] identifying whether an amplitude of the provided signal
varies more than a predetermined threshold, [0043] determining the
information from the corresponding signal, and [0044] quantifying
an uncertainty of the determination of the information from the
variation of the amplitude.
[0045] Thus, the oscillating signal is accepted, and an uncertainty
of the information is quantified on the basis of the
strength/intensity/amplitude of the oscillating signal. This
quantification is a standard technique in statistical analysis.
[0046] Naturally, the oscillating signal could also be removed by
the method further having a step of generating the altered signal
by removing from the provided signal an oscillating signal, the
method further comprising the step of determining further
information from the altered signal. The information determined
from the altered signal may be that described in relation to the
first aspect. Thus, his generating step could comprise performing
an averaging operation comprising averaging the provided signal
over a time period larger than a predetermined time period or
tracking the oscillating signal and subtracting the oscillating
signal from the provided signal.
[0047] As mentioned above, the generating step could generate the
altered signal for a predetermined period of time after, that the
provided signal reaches zero, in order to more precisely determine
e.g. a landing point.
[0048] The oscillating signal may be caused by multiple-path
problems caused when the receiving step comprises receiving the
radiation from at least two different directions or paths.
[0049] Also, the determining step could comprise determining a
parameter of the projectile at a first point in time and
estimating, from the determined parameter, the parameter at a
second, later, point in time. This estimation may be performed
using a predetermined relation between the parameter and time, and
the parameter determined may be a distance between a means
receiving the radiation and the projectile.
[0050] The corresponding signal provided may be a signal
representing an intensity of the radiation received. Then, the
determining step could comprise determining a distance between a
means receiving the radiation and the projectile.
[0051] A third aspect of the invention relates to the use of the
oscillating signal for providing information. This aspect relates
to a method of determining information relating to the surroundings
of a projectile, the method comprising: [0052] receiving
electromagnetic radiation emitted from or reflected by the
projectile at least partly while it is in flight, and providing a
corresponding signal, [0053] generating an altered signal by
isolating, from the provided signal, an oscillating signal, and
[0054] determining, as the information and from the altered signal,
In one situation, an angle to vertical of, and/or a distance to, a
surface over which the projectile flies and/or a reflection
coefficient of the radiation of a surface over which the projectile
flies.
[0055] When the oscillating signal relates to a multiple-path
situation, it should be remembered that one path may be that
directly between the projectile and the receiver, but that the
others must have experienced at least one reflection from or by the
surroundings. This reflection provides information about the
reflecting coefficient and the angle of, and/or a distance to, the
point of reflection. During flight of the projectile, this point
will also move in the surroundings.
[0056] This may be combined with knowledge, such as provided using
the first or second aspects, of the position of the projectile.
[0057] A fourth aspect relates to a method of determining a
distance between a projectile and a radiation receiver, the method
comprising the steps of: [0058] receiving electromagnetic radiation
emitted from or reflected by the projectile at least partly while
it is in flight, [0059] determining an intensity of the radiation
received and a distance between the receiver and the projectile at
a first point in time, [0060] determining, at a second, later point
in time, a second intensity of the radiation received, and [0061]
determining from a mathematical relation between the first and
second intensities determined, a distance, at the second point in
time, between the receiver and the projectile.
[0062] This is especially interesting, if it may be assumed that
the emission or reflection from the projectile toward the receiver
is constant, in that the difference between the intensities may
then simply only relate to the difference in distance. In that
situation, the mathematical relation is simple.
[0063] A situation which may complicate the matter slightly is that
where the receiver(s), or any transmitter providing the radiation,
have an angle dependent emission or sensitivity/gain, in which the
angle or position of the projectile also has to be taken into
account. This, however, is a known procedure e.g. in radar
technology.
[0064] Naturally, if a transmitter is used for providing the
radiation/sound toward the projectile, the distance between the
transmitter and the projectile also has to be taken into
account.
[0065] The first point in time may be a point in time before, at,
or after launch of the projectile where the position of the
projectile is known.
[0066] The present distance determination may be used for
determining the actual distance to the projectile or it may be used
for checking another distance measurement.
[0067] In any of the above aspects, the step of providing the
corresponding signal could comprise providing a signal representing
an intensity or power of the received radiation within a
predetermined frequency/wavelength interval. In that manner, a
filtering of unrelated radiation/sound may be performed.
[0068] Also, the method according to any of the above aspects may
further comprise the initial step of providing electromagnetic
radiation toward the projectile while in flight. In that manner,
the wavelength/frequency of the radiation/sound as well as the
intensity/signal strength thereof may be controlled.
[0069] A fifth aspect relates to, as the first aspect, the removal
of the oscillating. In particular, the fifth aspect relates to an
apparatus for determining information relating to a projectile, the
apparatus comprising: [0070] means for receiving electromagnetic
radiation emitted from or reflected by the projectile at least
partly while it is in flight, and for providing a corresponding
signal, [0071] means for generating an altered signal by removing,
from the provided signal, an oscillating signal, and [0072] means
for determining the information relating to the projectile from the
altered signal.
[0073] The present receiving means may be a single receiving means
or be multiple receiving means positioned in predetermined
positions in relation to each other in order for the receiving
means to be able to e.g. determine from where the radiation is
received.
[0074] The receiving means may be adapted to receive the
radiation/sound at multiple positions and thereby be adapted to
provide an altered signal for each receiving means. This may
provide additional information, such as three-dimensional or
two-dimensional information relating to the projectile.
[0075] Again, radiation of any wavelength and e.g. sound may be
used for the present determination.
[0076] In one embodiment, the generating means are adapted to
perform an averaging operation comprising averaging the provided
signal over a predetermined time period. In this manner, when the
predetermined time period exceeds a period of the oscillating
signal, this signal may be averaged out.
[0077] Also, the generating means may be adapted to track the
oscillating signal and subtract the oscillating signal from the
provided signal. This also makes it possible to remove the
oscillating signal. In fact, it makes it possible to also derive
the oscillating signal and derive information there from--see
below.
[0078] Preferably, the generating means are adapted to generate the
altered signal for a predetermined period of time after, that the
provided signal reaches zero. In this manner, when the oscillating
signal has a large amplitude compared to that of the altered
signal, the determination of the altered signal may be continued
even though the oscillating signal extinguishes it for a period of
time.
[0079] As mentioned above, the receiving means are preferably
adapted to receive the radiation from at least two different
directions. The receiving means need not be angle sensitive in that
the interference is removed by the present generating means.
However, if the oscillating signal is caused by multiple paths of
the radiation, its detection requires detection of the radiation
from these paths.
[0080] In one embodiment, the determining means are adapted to
determine a parameter of the projectile at a first point in time
and to estimate, from the determined parameter, the parameter at a
second, later, point in time. In one situation, the determining
means are adapted to perform the estimation using a predetermined
relation between the parameter and time. This relation may be
provided empirically or may be determined on the basis of a theory.
One parameter to determine is a distance between the receiving
means and the projectile.
[0081] The receiving means may be adapted to provide the
corresponding signal representing an intensity/signal
strength/amplitude of the radiation received. Then, the determining
means may be adapted to determine a distance between the receiving
means and the projectile. This is especially so, if the
reflection/emission characteristics of the projectile are known or
even constant, which makes the distance determination easier.
[0082] In a particularly interesting embodiment, the generating
means are adapted to generate the altered signal, until the altered
signal fulfils a predetermined criterion, the determining means
being adapted to provide, as the information, an estimate of a
landing point of the projectile. As mentioned above, this enables
the method and apparatus to make a better estimation of the landing
point. Also, the criteria may be determined within a wide variety
of possibilities depending on the situation.
[0083] Then, the determining means could be adapted to provide, as
the information, an estimate of a distance between the landing
point of the projectile and a predetermined target. In this manner,
it may be desired to know the positional relation between the
receiver and the target. This relation may also comprise a height
difference between the receiver and the target.
[0084] Alternatively or in addition, the determining means could be
adapted to provide as the information an estimate of a deviation
from a predetermined direction and a determined direction of the
projectile. Different types of deviations are described above. This
provides another type of coordinate system in which the projectile
path is analyzed. This type of analysis may be desired in order to
evaluate the difference between an aiming direction and the actual
direction of the projectile.
[0085] Especially in the last situation, the determining means
could further comprise means for determining a launch position of
the projectile, the determining means being adapted to provide the
determined direction of the projectile as a direction between the
launch position and the landing point. Determining the launch
position instead of dictating it provides a better
user-friendliness and facilitates use of the apparatus in field
operations where fixed positions are not usual.
[0086] As mentioned above, one manner of removing the oscillating
signal is to perform a suitable averaging. One manner of averaging
is to have the generating means comprise means for filtering the
provided signal using a time constant larger than a period of the
oscillating signal, the determining means being adapted to
determine a landing point as a point where the signal level has
decreased a predetermined amount, such as 3 dB.
[0087] A sixth aspect relates to an apparatus of determining
information relating to a projectile, the apparatus comprising:
[0088] means for receiving electromagnetic radiation emitted from
or reflected by the projectile at least partly while it is in
flight, and for providing a corresponding signal, [0089] means for
identifying whether an amplitude of the provided signal varies more
than a predetermined threshold, [0090] means for determining the
information from the corresponding signal, and [0091] means for
quantifying an uncertainty of the determination of the information
from the variation of the amplitude.
[0092] As is the case in the second aspect, this means that the
oscillating signal need not be removed but that the results (the
information) take this "error" signal into account.
[0093] Then, the generating means may be adapted to perform an
averaging operation comprising averaging the provided signal over a
time period larger than a predetermined time period. This may then
be used for quantifying the oscillating signal and the
uncertainty.
[0094] Naturally, the fifth and sixth aspects may be combined,
whereby the sixth aspect may also comprise generating means for
generating an altered signal by removing an oscillating signal from
the provided signal, the determining means being adapted to provide
additional information relating to the projectile from the altered
signal.
[0095] Then, the generating means may be adapted to track the
oscillating signal and subtract the oscillating signal from the
provided signal. Also, the generating means could be adapted to
generate the altered signal for a predetermined period of time
after, that the provided signal reaches zero.
[0096] In general, the receiving means are preferably adapted to
receive the radiation from at least two different directions.
[0097] In one embodiment, the determining means are adapted to
determine a parameter of the projectile at a first point in time
and estimate, from the determined parameter, the parameter at a
second, later, point in time. Then, the determining means may be
adapted to perform an estimation using a predetermined relation
between the parameter and time. Also, the determining means are
preferably adapted to determine a parameter being a distance
between a means receiving the radiation and the projectile.
[0098] In a preferred embodiment, the receiving means are adapted
to provide a corresponding signal representing an intensity of the
radiation received and wherein the determining means are adapted to
determine a distance between the receiving means receiving the
radiation and the projectile.
[0099] As the third aspect, a seventh aspect relates to the use of
the oscillating signal. This embodiment relates to an apparatus of
determining information relating to the surroundings of a
projectile, the apparatus comprising: [0100] means for receiving
electromagnetic radiation emitted from or reflected by the
projectile at least partly while it is in flight, and for providing
a corresponding signal, [0101] means for generating an altered
signal by isolating, from the provided signal, an oscillating
signal, and [0102] means for determining, as the information and
from the altered signal, an angle to vertical of, and/or a distance
to, a surface over which the projectile flies and/or a reflection
coefficient of the radiation of a surface over which the projectile
flies.
[0103] Naturally, this may be combined with a means for providing
information relating to a position of the projectile. This means
may be one according to any of the first, second, fifth, and sixth
aspects.
[0104] In any of the fifth-seventh aspects, as well as the eighth
aspect mentioned below, the receiving means are preferably adapted
to provide the corresponding signal as a signal representing an
intensity or power of the received radiation within a predetermined
frequency/wavelength interval and/or the apparatus preferably
further comprises means for providing electromagnetic radiation
toward the projectile while in flight,
[0105] An eighth aspect of the invention relates to an apparatus of
determining a distance between a projectile and a radiation
receiver, the apparatus comprising: [0106] means for receiving
electromagnetic radiation emitted from or reflected by the
projectile at least partly while it is in flight, [0107] means for
determining an intensity of the radiation received and a distance
between the receiver and the projectile at a first point in time,
[0108] means for determining, at a second, later point in time, a
second intensity of the radiation received, and [0109] means for
determining from a mathematical relation between the first and
second intensities determined, a distance, at the second point in
time, between the receiver and the projectile.
[0110] This aspect relates to the fourth aspect mentioned
above.
[0111] A ninth aspect relates to a method of determining
information relating to a projectile, the method comprising: [0112]
receiving electromagnetic radiation emitted from or reflected by
the projectile at least partly while it is in flight, and providing
a corresponding signal, [0113] determining an expected oscillation
of the corresponding signal, and [0114] determining the information
from a deviation between the corresponding signal and the expected
oscillation.
[0115] When the oscillation relates to the multipath problem stated
above, the oscillation may be estimated from e.g. knowledge of the
path of the projectile. This deviation may be calculated from
parameters relating to the projectile, its path and/or surroundings
of the projectile. Then, both the signal strength and the amplitude
oscillation may be determined and compared to the provided signal.
Deviations there from may be caused by deviations in the path of
the projectile compared to that used in the estimation. Such a
deviation in the path of the projectile may be that the projectile
has, in fact, actually landed.
[0116] In that manner, the information may be derived from a
deviation, such as a deviation between the corresponding signal and
the estimated oscillation.
[0117] The estimated oscillation may be an estimate of the
amplitude or period/frequency of the provided signal as a function
of time.
[0118] The deviation may be a deviation in intensity/signal
strength or in the phase of the estimated signal compared to the
estimated oscillation. Other types of deviations or other criteria
which the deviation should fulfil are described further above.
[0119] In addition, a step of identifying whether the amplitude of
the provided signal varies more than a predetermined threshold may
be added in order to determine whether an oscillation large enough
is present for it to be taken into account. Also, the presence of
this variation may be an indication of that the projectile is close
to the ground.
[0120] An interesting piece of information to derive is the landing
point of the projectile. This may be estimated (as the information)
from the deviation in that the provided signal will drop, when the
projectile has landed. Then, the provided signal will deviate from
the estimated oscillation which does not foresee the drop. Then,
e.g. a drop of the signal of a predetermined amount may be used for
determining the landing point. The actual landing point may be
determined on the basis of knowledge of the trajectory of the
projectile while flying.
[0121] It should be remembered that the provided signal may, when
the oscillation is large, actually become lower than the detection
threshold (become zero). However, the estimation of the variation
may take this into account, whereby this will not interfere with
the correct determination of the information, such as the landing
point.
[0122] A tenth aspect relates to an apparatus of determining
information relating to a projectile, the apparatus comprising:
[0123] means for receiving electromagnetic radiation emitted from
or reflected by the projectile at least partly while it is in
flight, and for providing a corresponding signal, [0124] means for
determining an expected oscillation of the provided signal, and
[0125] means for determining the information from a deviation
between the corresponding signal and the expected oscillation.
[0126] The advantages described in relation to the ninth aspect
relate equally to this aspect.
[0127] An especially interesting embodiment or group of embodiments
is one where a plurality of receiving means are used or the
radiation is determined at a plurality of displaced positions. In
this manner, the different detections may be used for deriving
additional information.
[0128] This additional information may relate to the position of
the projectile in that the angle(s) of incident radiation may now
be determined, such as by measuring an amplitude or phase
difference between the radiation determined at a plurality of
positions. Preferably, the positional relationship between the
positions is known.
[0129] In addition, the plurality of determinations of the
radiation may also, or optionally, be used for providing further
statistics in the measurement in that a mathematical operation may
be performed (e.g. on information that may be provided from e.g. a
single determination) in order to increase the certainty of the
determination.
[0130] The above-mentioned oscillating signal may, in addition to
vary the amplitude of the signal received, cause a determination of
the angle detected (using the radiation received at a plurality of
positions) to be uncertain. Thus, the removal or tracking of the
oscillating signal will also improve the certainty on an angle
determination--and thereby on the position determination. This is
important in a number of situations, such as when wishing to
determine the landing point of the projectile.
[0131] Preferably, in the method of the first aspect: [0132] the
receiving step comprises receiving radiation at a plurality of
spatially displaced positions and providing a provided signal for
each position, [0133] the generating step comprises generating an
altered signal for each provided signal, and [0134] the determining
step comprises determining the information on the basis of all
provided signals.
[0135] Naturally, the filtering, averaging etc. described above may
be performed on each individual signal or after combining the
signals.
[0136] The altered signals may, for a number of the provided
signals, be identical. However, there may also be differences
between the provided signals in that e.g. phase shifts may be
caused by the different positions for the detection.
[0137] In this context, a spatial displacement simply means that
the radiation is received at a plurality of different positions.
These positions may have differing heights over a ground plane and
may have different angles to the trajectory of the projectile.
Naturally, different displacements give different advantages
depending on the directions or angles preferably determined.
[0138] The determination may then be the determination of a
position, angle, velocity, or any other of the above-mentioned
types of information relevant to a flying or landing projectile.
The information may also be a combination of this information, such
a trajectory and a landing point in time so that the landing point
position may be determined.
[0139] In the second aspect, preferably: [0140] the receiving step
comprises receiving radiation at a plurality of spatially displaced
positions and providing a provided signal for each position, [0141]
the identifying step is performed for each provided signal, [0142]
the determining step comprises determining the information on the
basis of all provided signals, and [0143] the quantifying step is
performed on the basis of the variation of the amplitudes of all
provided signals.
[0144] Naturally, the quantifying step may be a quantification
based on each individual position, which quantifications are then
subsequently assembled into a single, overall uncertainty.
Alternatively, it may be determined initially as the overall
uncertainty.
[0145] In the third aspect, preferably: [0146] the receiving step
comprises receiving radiation at a plurality of spatially displaced
positions and providing a provided signal for each position, [0147]
the generating step is performed for at least two of the provided
signals, and [0148] the determining step comprises determining the
information on the basis of all generated, altered signals.
[0149] As mentioned above, the oscillating signals need not be
different at all positions, whereby it may not be required to
actually determine or track (derive or remove) the oscillating
signal individually for each position.
[0150] In the fourth aspect, preferably: [0151] the receiving step
comprises receiving radiation at a plurality of spatially displaced
positions and providing a provided signal for each position, [0152]
the steps of determining intensities comprises determining the
intensities at each position, and [0153] the step of determining
the distance comprises determining the distance on the basis of all
intensities determined.
[0154] In this embodiment, a distance estimate may be derived for
each position, which estimates are then subsequently merged (such
as averaged). Alternatively, a single distance is determined from
the intensities (which may then alternatively be merged prior to
the determination of the distance).
[0155] In the fifth aspect, preferably: [0156] the receiving step
comprises receiving radiation at a plurality of spatially displaced
positions and providing a provided signal for each position, [0157]
the step of determining the expected oscillation comprises
determining an expected oscillation for at least one of the
positions, and [0158] the step of determining the information
comprises determining the information on the basis of the deviation
between at least one pair of an expected oscillation and the
corresponding provided signal.
[0159] As mentioned above, an expected oscillation may be relevant
to a plurality of the positions, whereby it is not required to
determine an expected oscillation individually for each
position.
[0160] From the deviation of the oscillation of one pair of an
expected oscillation and the corresponding provided signal, certain
information, such as a landing time, may be derived. However, it is
preferred that an expected oscillation is actually determined for a
plurality of the positions. Then, the deviation will be performed
on a number of such pairs. In that manner, a better estimation of
e.g. the angle and thereby position of the projectile may be
obtained, whereby a better estimation of the landing spot position
is obtained.
[0161] In the sixth aspect, preferably: [0162] the receiving means
comprise a plurality of spatially displaced receiving means each
adapted to provide a provided signal, [0163] the generating means
area adapted to generate an altered signal for each receiving
means, and [0164] the determining means are adapted to determine
the information on the basis of all provided signals.
[0165] This is parallel to the above-mentioned preferred embodiment
of the first aspect.
[0166] In the seventh aspect, preferably: [0167] the receiving
means comprise a plurality of spatially displaced receiving means
each adapted to provide a provided signal, [0168] the identifying
means performed for each provided signal, [0169] the determining
means are adapted to determine the information on the basis of all
provided signals, and [0170] the quantifying means is adapted to
perform the quantification on the basis of the variation of the
amplitudes of all provided signals.
[0171] This is parallel to the above-mentioned preferred embodiment
of the second aspect.
[0172] In the eight aspect, preferably: [0173] the receiving means
comprise a plurality of spatially displaced receiving means each
adapted to provide a provided signal, [0174] the generating means
is adapted to generate an altered signal for each of at least two
of the provided signals, and [0175] the determining means is
adapted to determine the information on the basis of all generated,
altered signals.
[0176] This is parallel to the above-mentioned preferred embodiment
of the third aspect.
[0177] In the ninth aspect, preferably: [0178] the receiving means
comprise a plurality of spatially displaced receiving means each
adapted to provide a provided signal, [0179] the means for
determining intensities are adapted to determine the intensities at
each receiving means, and [0180] the means for determining the
distance is adapted to determine the distance on the basis of all
intensities determined.
[0181] This is parallel to the above-mentioned preferred embodiment
of the fourth aspect.
[0182] In the tenth aspect, preferably: [0183] the receiving means
comprise a plurality of spatially displaced receiving means each
adapted to provide a provided signal, [0184] the means for
determining the expected oscillation is adapted to determine an
expected oscillation for at least one of the receiving means, and
[0185] the means for determining the information is adapted to
determine the information on the basis of a deviation between at
least one pair of an expected oscillation and the corresponding
provided signal.
[0186] This is parallel to the above-mentioned preferred embodiment
of the fifth aspect.
[0187] It is clear that the above aspects relate to overlapping
effects and technologies, whereby any two or more thereof may be
combined in order to obtain even better products.
[0188] In the following, a preferred embodiment will be described
with reference to the drawing, wherein:
[0189] FIG. 1 shows the positioning of the radar relative to the
tracking object trajectory as well as a reflective surface,
[0190] FIG. 2 shows an example of a ball trajectory with reference
to the radar position,
[0191] FIG. 3 shows the received signal intensity of the different
received signals,
[0192] FIG. 4 is a vector diagram showing the multipath signal
adding with the direct reflected signal,
[0193] FIG. 5 shows the process flow to isolate and quantify the
multipath signal,
[0194] FIG. 6 shows schematically the position of the transmitter
and receivers of the system,
[0195] FIG. 7 shows the normalized received signal intensity in
both presence and absence of multipath signals,
[0196] FIG. 8 shows the output of the sliding RMS detector in both
presence and absence of multipath signals,
[0197] FIG. 9 shows an electronic functional block diagram of the
system,
[0198] FIG. 10 shows the received signal intensity of two different
receivers, and
[0199] FIG. 11 shows elevation angle measurement derived from the
monopulse phase.
[0200] In the preferred embodiment of the present invention, the
transmitter 27 is a continuous wave (CW) signal being emitted from
an antenna 15 co-located with at least one receiving antenna, i.e.
a CW Doppler radar. In the preferred embodiment, the receiver
consists of at least three separate receiving antennas 16-18,
enabling use of the well known monopulse measuring principle to
measure the angle to the projectile, see "Introduction to Radar
Systems" Third Edition, Merril I. Skolnik, which is incorporated
herein as reference. An electrical functional block diagram of the
system is shown in FIG. 9.
[0201] In the preferred embodiment, the projectile is a sports
ball, a special interest is related to the case of a golf ball,
where there is high commercial interest of being able to measure
the exact trajectory, including precise determination of the
landing point. In the following description the measuring object in
flight will be referred to as a ball, but can be any type of a
solid object traveling through the air, such as projectiles,
missiles, airplanes and other sports balls.
[0202] The antennas can be arranged as shown in FIG. 6, but many
other combinations are possible. The receiving antennas 16 and 17
are vertically spaced a distance DV, where as the receiving
antennas 17 and 18 are horizontally spaced a distance DH. In this
way the phase difference .DELTA.V between the signal from a ball
recorded by receiving antennas 16 and 17 will be directly related
to the vertical angle E from the radar to the ball through [eq. 1].
The phase difference .DELTA.H between receiving antennas 17 and 18
will consequently be directly related to the horizontal angle A
from the radar to the ball through [eq. 2].
.DELTA.V=2n*DV/.lamda.*sin(E) [eq. 1] [0203] , where .lamda. is the
radar wavelength .DELTA.H=2n*DV/.lamda.*sin(A) [eq. 2]
[0204] In the preferred embodiment of the present invention, the
phase differences between receiving antennas 16-18 are measured by
using the phase-phase monopulse principle on the recorded signals.
However, many other standard techniques can be used for this, like
the amplitude-amplitude monopulse principle, as outlined in the
publication "Introduction to Radar Systems" Third Edition, Merril
I. Skolnik, which is incorporated herein as reference again.
[0205] The radar return signal from a CW Doppler radar consists of
a number of continuous signals x(t) corresponding each to the
relative position and movement of the reflective objects in front
of the radar. In the following the situation only one reflective
object, the ball, is considered, but the description holds as well
for multiple reflective objects. In this case the received signal
z.sub.rx(t) of one of the receivers 16-18 only consist of the
direct reflected signal x(t) from the ball, see [eq. 3].
z.sub.rx(t)=x(t) [eq. 3]
[0206] The amplitude of the x(t), a(t) is determined by the radar
cross section of the ball as well as the distance from the radar
and radar gain in the specific direction of the ball, see [eq. 4].
|x(t)|.sup.2=a(t).sup.2=Ptx*Gtx*Grx*RCS*.lamda..sup.2/((4*n).sup.3*R.sup.-
4) [eq. 4] [0207] , where: [0208] Ptx is the transmitted power
[0209] Gtx is the transmitting antenna gain in direction of ball
[0210] Grx is the receiving antenna gain in direction of ball
[0211] RCS is the radar cross section of ball [0212] .lamda. is the
the radar wavelength [0213] R is the distance from radar to
ball
[0214] In most practical situations not only the direct reflected
signal, R, 5 is received from the ball 1, flying along a trajectory
40 between a launch position 38 and a landing point 39, also a
multipath reflected signal, Rmp, 6 is received, see FIG. 1. The
resulting received signal z.sub.rx(t) can be described by [eq. 5].
z.sub.rx(t)=x(t)+x.sub.mp(t)=x(t)*(1+e.sub.mp(t)) [eq. 5] [0215] ,
where: [0216] x(t) is the received signal of the direct reflected
ray 5 from the ball 1 [0217] x.sub.mp(t)=x(t)*e.sub.mp(t) received
signal of the multipath reflected ray 6 from the ball 1. [0218]
e.sub.mp(t) is the modulation of the multipath reflected signal 6
relative to the direct reflected signal 5.
[0219] In the following only one multipath signal will be
considered, but the general principles are also applicable on
multiple multipath signals.
[0220] The multipath reflected signal 6 will be highly correlated
with the direct reflected signal 5, but will include a modulation,
described by e.sub.mp(t). e.sub.mp(t) will depend on the geometry
and reflection characteristics of the ball and the reflecting point
4. e.sub.mp(t), where the reflecting point is on a reflecting
surface (illustrated by a horizontal line) can be described by [eq.
6].
e.sub.mp(t)=
(.delta.RCS*.rho..sub.g*dG)*(R/Rmp).sup.2*exp(-j*2n*dR/.lamda.)=a.sub.mp(-
t)*exp((.phi..sub.mp(t)) [eq. 6]
[0221] , where: [0222] .delta.RCS is the reflection difference in
multipath geometry compared to direct reflection [0223] .rho..sub.g
is the reflection coefficient of the ground [0224] dG is the radar
gain difference for the incoming multipath reflected ray [0225] dR
is the path length difference between multipath ray 6 and direct
reflected ray 5. [0226] .lamda. is the wavelength of the radio
wave
[0227] For an object propagating in a stationary environment, i.e.
multipath reflection point 4 does not jump around, the modulation
signal e.sub.mp(t) will be a slowly varying oscillating signal
dictated by the variation of the path length difference dR.
[0228] The path length difference dR can be mathematically
expressed from the geometry in FIG. 1 by [eq. 7]. dR=Rmp-R=R(
(1+4*y*hr/R.sup.2)-1) [eq. 7] [0229] , where: [0230] hr is the
height of the receiving antenna above the reflecting surface [0231]
y is the height of the ball above the reflecting surface
[0232] Assuming a ball trajectory (see FIG. 2), observed by a radar
2, the received power over time will be as shown in FIG. 3. In FIG.
3, 7 is the received power |x(t)|.sup.2 from the direct reflected
ray 5 alone, graph 8 is the received power |x.sub.mp(t)|.sup.2 from
the multipath reflected ray 6 alone. The resulting received power
|z.sub.rx(t)|.sup.2 (graph 9) shows an oscillating signal around
the power received from the direct reflected ray, graph 7. It is
realized that the oscillation of 9 is directly related to the
variation of e.sub.mp(t) coherently adding with a unity vector
representing the normalized direct reflected signal x(t), as can be
seen in the vector diagram in FIG. 4.
[0233] The period, Tmp, of the oscillation of 9 is given by when dR
changes .lamda.. Tmp is typically in the interval of 0.1-2 seconds
for sports ball trajectories with radar 2 placed close to some part
of the trajectory.
[0234] If more receivers are present like in FIG. 9, the heights hr
of the individual receiving antennas are in general not the same.
This means that dR is slightly different at a given point in time
for the different receivers, this introduces a phase difference of
the oscillating signal power between the different receivers in the
multipath scenario. In FIG. 10 the received power
|z.sub.rx(t)|.sup.2 for receiving antenna 17 is plotted as 9
together with the received power |z.sub.rx(t)|.sup.2 for receiving
antenna 16 which also plotted as 35. In FIG. 10 the received power
|x(t)|.sup.2 from the direct reflected ray 5 alone is shown as 7
for comparison.
[0235] Due to the phase difference of the oscillating signals of
the different receivers, the monopulse phase difference will be
distorted in a multipath scenario. In FIG. 11 the vertical angle 36
derived from [eq. 1] is shown for the case of only the direct
reflected ray 5, and also the vertical angle 37 in the case of
presence of multipath signals is shown.
[0236] Determination of Presence of Multipath Signals
[0237] The process of detecting the presence of multipath signals
in the received signal z.sub.rx(t) is shown in FIG. 5.
[0238] First the tracking is established 10 as normally done with
Doppler radars, i.e. tracking the Doppler frequency generated by
the moving ball over time. From the recorded data of the at least
three receivers, the three dimensional position is calculated 11
without knowing whether a multipath signal is present or not. The
range R to the ball is calculated as an integration of the tracked
Doppler frequency from launch time and adding the assumed distance
between the radar and the launch position 38. The vertical and
horizontal angles are calculated from [eq. 1] and [eq. 2]. If a
multipath signal is present this will introduce an error in the
three dimensional position through distortion on the vertical (and
horizontal) angle as illustrated in FIG. 11. Heavy filtering
(averaging) is done on the angles to reduce the negative influence
on the three dimensional position, the time constant on the angle
filtering should be higher than the period of the oscillation
Tmp.
[0239] All the three received signals are then normalized 12 for
the known time variation of the direct reflected signal power as
can be derived from [eq. 4].
[0240] The normalization equation is:
z.sub.n,rx(t)=z.sub.rx(t)*R.sup.2/ (Gtx*Grx*RCS) [eq. 8] [0241] ,
where: [0242] Gtx is the transmitting antenna gain in direction of
ball 1 [0243] Grx is the receiving antenna gain in direction of
ball 1 [0244] RCS is the radar cross section of ball 1
[0245] In the case of a spherical symmetrical ball, like golf
balls, tennis balls, baseballs, cricket balls and similar, the
radar cross section RCS of the ball is to a very high degree
constant independent of orientation of the ball relative to the
radar. In this case RCS in [eq. 8] can be omitted.
[0246] In FIG. 7 the normalized signal power |z.sub.n,rx(t)|.sup.2
is shown. The trace 19 corresponds to the normalized signal power
without multipath 7, and the trace 20 corresponds to the normalized
signal power with multipath 9. The oscillation of 20 is clearly an
indication of multipath.
[0247] It is noted that the detection of oscillation of power of
the normalized signal z.sub.n,rx(t) can be done in number of
different ways. In the following only one of the preferred methods
are outlined, but many other standard methods may be applied.
[0248] To isolate the multipath signal 13 a sliding
root-mean-square (RMS) detector on the normalized signal
z.sub.n,rx(t) is used. The RMS detector is performed over a time
corresponding to the expected period of the oscillation Tmp, and is
calculated according to [eq. 9].
RMS.sub.Tmp(t)=(E{|z.sub.n,rx(t)|.sup.2}.sub.t.+-.Tmp/2-E{|z.sub.n,rx(t)|-
}.sup.2.sub.t.+-.Tmp/2)/( 2*E{|z.sub.n,rx(t)|}.sub.t.+-.Tmp/2) [eq.
9]
[0249] In FIG. 8 the sliding RMS detector RMS.sub.Tmp(t) is shown.
The trace 25 corresponds to the normalized signal power without
multipath 7, and the trace 26 corresponds to the normalized signal
power with multipath 9.
[0250] To quantify the magnitude of the multipath signal, the
output of the sliding RMS detector can be used directly. In fact
the value of RMS.sub.Tmp(t) is directly an estimation of
a.sub.mp(t) in [eq. 6]. To quantify whether multipath signals is
present or not, the output of the RMS detector is compared with a
predetermined threshold 14.
[0251] The sliding RMS detector as outlined above must in general
be applied separately on all the three received signals, since the
amplitude of the oscillation need not be the same for all the
receiving signals.
[0252] Once the magnitude of the multipath signal a.sub.mp(t) is
known, the tracking and smoothing filters can be adjusted to
tolerate the errors caused by the multipath signals. The worst case
error in the phase differences in [eq. 1] and [eq. 2] are given by:
.DELTA.V.sub.err,W.C..apprxeq.2*A tan(a.sub.mp(t))
.DELTA.H.sub.err,W.C..apprxeq.2*A tan(a.sub.mp(t))
[0253] Using these error margins in the tracking and smoothing
filters will enable the ball to be tracked more robust and provide
more accurate flight path data.
[0254] To detect when the ball has actually landed 39, the
knowledge of the multipath level is used.
[0255] When the ball is about to land, the signal level of the
direct reflected ray 5 is normally at a minimum, due to maximum
distance between ball 1 and radar 2. Further more, the power of the
received multipath signal 6 will be only slightly smaller than the
direct reflected signal 5, since the ground reflection coefficient
.rho..sub.g is close to 1.0 for parallel incident rays.
Consequently the total received signal z.sub.rx(t) can reach a
minimum that might be under the detection limit, even though the
ball has not landed. The minimum signal level in the landing
scenario happens exactly when the phase of the multipath signal is
180 degrees out of phase with the direct reflected signal, i.e.
when .phi..sub.mp(t)=-n. This happens exactly the time Tmp/2 before
the ball actually lands. Consequently the tracking is always
continued at least Tmp/2 after the signal level has dropped below
the detection limit when multipath is detected as explained above.
If the signal reappears after this dropout, it will only reappear
for Tmp/2 seconds. These reappearing data are merged with the
previous track.
[0256] The landing point is determined as being the last
measurement point including any merging of reappearing signals. If
the detection of the measurement point is done by frequency
analysis, which extend over some data points, the time for landing
is being determined as being when the signal level has dropped 3 dB
relative to the expected power variation taking into account the
multipath influence. By adding the three received signals before
detecting the measurement points an increase in signal-to-noise
ratio is gained, which will give a more accurate determination of
the landing time. The final three dimensional landing point is
calculated by evaluating the smoothed trajectory data at the
landing time determined above. The relative phase of the multipath
signal .phi..sub.mp(t) can be estimated in a number of different
ways. One method is to detect the zero-crossings 21 and 22 (in dB)
and minimum 23 and maximum 24 of the normalized signal power
|z.sub.n,rx(t)|.sup.2 like 20 in FIG. 7. The minimum represent
.phi..sub.mp(t) equal to .+-.n, the maximum .phi..sub.mp(t) equal
to 0 and finally the zero crossings close to .+-.n/2. This gives
two solutions for the slope of the phase .phi..sub.mp(t), an
upwards and a downwards slope. The slope is determined from the
sign of the derivative of dR with respect to time, which is
calculated from the measured trajectory during step 11. The final
estimation of .phi..sub.mp(t) is done by fitting a smooth curve to
the found phase points above.
[0257] The estimation of the phase of the multipath signal must be
carried out separately for each of the receiving signals
[0258] Removal of Multipath Signal
[0259] Once the presence of the multipath signal has been detected
and the relative multipath signal e.sub.mp(t) has been estimated,
it is possible to remove the multipath signal from the received
signals by altering the receiver signal according to [eq. 10].
x.sub.est(t)=z.sub.rx(t)/(1+ .sub.mp(t)) [eq. 10]
[0260] Then the three dimensional position can be re-calculated
from the altered receiver signals x.sub.est(t). The trajectory data
derived from the altered receiver signals will to a high degree be
cleaned for multipath distortion on the vertical and horizontal
angles. Further the altered signal will not experience the
oscillation, and possible dropouts just before landing, thus given
a much better accuracy on the estimation of landing time and
thereby more accurate landing position.
[0261] Range and RCS Measurement from Signal Power Level
[0262] In the following all the receiver signals are either cleaned
for oscillating signals as explained above [eq. 10], or averaged
out the oscillation in the normalized z.sub.n,rx(t) similar to [eq.
8] and then inverse normalization of [eq. 6] to get z.sub.rx(t), or
the level of the multipath signal is below a certain limit not to
affect the received power level according to [eq. 3].
[0263] In relation to range measurement of Doppler radar signals,
all previous inventions have analyzed the radar return from a
single fixed frequency Doppler radar only for the frequency shift
generated by the apparent velocity Vr of the ball moving in front
of the radar, or more precisely the change in range over time
(sometimes denoted range rate), mathematically dR/dt.
[0264] To calculate the distance R to the ball, all previous
Doppler radar inventions have integrated the range rate Vr from a
known reference point. Consequently the distance R is a derived
measurement from the directly measured range rate Vr and it
requires a fix point.
[0265] The present invention presents a novel method to actually
measure the distance R to the ball by proper analyzing of the radar
return signal from a Doppler radar. The distance R is measured
independently from the measured range rate.
[0266] The direct measured distance R in a Doppler radar system can
be used in many different applications and scenarios. More
generally speaking the direct measured range adds a new independent
measured parameter for a Doppler radar.
[0267] The present invention measures the distance R to the ball by
measuring the signal level Prx corresponding to the tracking
object. The preferred method to measure the signal level of a given
tracking object is by frequency analyzing methods, but other
methods may also be applied.
[0268] The distance R to the ball is calculated from the received
signal level Prx by using the radar equation inversely:
R=((Ptx/Prx*Gtx*Grx*.lamda..sup.2)/(4n).sup.3*RCS).sup.0.25 [eq.
11]
[0269] All the parameters on the right hand side above, are system
parameters that are known except for the radar cross section RCS of
the ball.
[0270] The antenna gain of the Doppler radar in the transmitter Gtx
and receiver Grx can vary inside the coverage volume of the radar.
However, if the sighting angle to the target is known, this
inaccuracy can be removed by using the known radiation pattern of
the transmitting and receiving antennas.
[0271] In a monopulse Doppler radar system, the sighting angle to
the target can be measured independently of the range rate Vr and
the distance R. This means that in such a system the only unknown
on the right hand side of [eq. 11] is the RCS.
[0272] Equation [eq. 11] can be simplified to [eq. 12], where M is
the measured signal level adjusted for system parameters.
R=M*RCS.sup.0.25 ,
M=((Ptx/Prx*Gtx*Grx*L*.lamda..sup.2)/(4n).sup.3).sup.0.25 [eq.
12]
[0273] In some cases the RCS of the ball is known a priori. In this
case [eq. 12] can be used directly to measure the distance R.
[0274] In other cases only the relative level of RCS is known when
viewing the ball from different aspect angles, i.e.
RCS=RCSo*func((.phi.,.theta.) where RCSo is unknown. In this case
[eq. 12] can be rewritten to [eq. 13], where M' includes the known
func((.phi.,.theta.).sup.0.25 variation of the RCS.
R=M'*RCSo.sup.0.25 , M'=M*func((.phi.,.theta.).sup.0.25 [eq.
13]
[0275] In this case the ball is observed at minimum two different
distances, see [eq. 14-15] where the relative change in distance is
measured by integration of the measured range rate Vr.
R(n)=M'(n)*RCSo.sup.0.25 [eq. 14]
R(n+1)=R(n)+.DELTA.R=M'(n+1)*RCSo.sup.0.25 , .DELTA.R=int(n,n+1,Vr)
[eq. 15]
[0276] RCSo can now be calculated from [eq. 16]:
RCSo=(.DELTA.R/(M'(n+1)-M'(n))).sup.4 [eq. 16]
[0277] After having found RCSo, [eq. 13] is used directly to
measure the distance R.
[0278] Spherically shaped targets are a special interesting group
of targets. This type of targets includes also targets that are
nearly spherical. Examples include small projectiles, calibration
spheres and most sporting balls (golf ball, base ball, foot/soccer
ball, tennis ball, cricket ball etc.). The spherically shaped
targets has the advantage that the RCS is constant independent of
orientation of target (func((.phi.,.theta.)=1), and that it is
relatively simple to theoretically predict the RCS from given
dimensions and material characteristics.
[0279] Reflection Coefficient and Position of Reflection Point
[0280] When the relative phase .phi..sub.mp(t) of the multipath
signal has been estimated as outlined above, the variation of dR
over time is also known through [eq. 6]. When dR is known, [eq. 7]
can be used to estimate the height hr of the radar 2 above the
reflection point, where R and y are taken from the measured three
dimensional position of the ball. The only assumption is that the
reflecting surface is horizontal.
[0281] When the height hr is known, also the angle Emp in FIG. 1
can be found, this means that the reflection point can be
positioned three dimensionally.
[0282] By also having the estimation of the relative amplitude
a.sub.mp(t) of the multipath signal, the reflection coefficient
.rho..sub.g of the reflecting surface can be estimated using [eq.
6] inversely.
* * * * *