U.S. patent application number 13/890499 was filed with the patent office on 2013-09-26 for plant treatment based on a water invariant chlorophyll index.
The applicant listed for this patent is Kyle H. Holland. Invention is credited to Kyle H. Holland.
Application Number | 20130250280 13/890499 |
Document ID | / |
Family ID | 43622746 |
Filed Date | 2013-09-26 |
United States Patent
Application |
20130250280 |
Kind Code |
A1 |
Holland; Kyle H. |
September 26, 2013 |
PLANT TREATMENT BASED ON A WATER INVARIANT CHLOROPHYLL INDEX
Abstract
A method and system of treating plants is provided. The method
includes measuring optical properties of a plant using a plurality
of spectral bands. The method further includes calculating in a
computational device at least two vegetative indexes using the
optical properties, each of the at least two vegetative indexes
correlating to one or more plant growth parameters. The method
further includes calculating in the computational device a water
invariant chlorophyll index from at least two vegetative indexes
using the plurality of spectral bands. The also provides for
treating one or more of the plants based on the water invariant
chlorophyll index.
Inventors: |
Holland; Kyle H.; (Lincoln,
NE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Holland; Kyle H. |
Lincoln |
NE |
US |
|
|
Family ID: |
43622746 |
Appl. No.: |
13/890499 |
Filed: |
May 9, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12896460 |
Oct 1, 2010 |
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13890499 |
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12108371 |
Apr 23, 2008 |
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12896460 |
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10703256 |
Nov 7, 2003 |
7408145 |
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12108371 |
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60925831 |
Apr 23, 2007 |
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Current U.S.
Class: |
356/51 |
Current CPC
Class: |
G01N 2201/1244 20130101;
G01N 21/31 20130101; G01N 21/55 20130101; G01N 2021/8466 20130101;
G01N 2021/3155 20130101; G01J 3/10 20130101; G01N 21/3563 20130101;
G01J 3/36 20130101; G01N 2021/635 20130101 |
Class at
Publication: |
356/51 |
International
Class: |
G01N 21/55 20060101
G01N021/55 |
Claims
1. A method for measuring a plant's reflectance, comprising the
steps of: (a) modulating a light source comprised of one or more
LEDS that emit light in the spectral range of 350 nm to 480 nm
having a phosphorescent coating, and (b) detecting light
originating from the light source reflected off of the plant in the
presence of ambient light in one or more spectrally sensitive
photodetectors.
2. The method of claim 1, wherein the phosphor coating comprises
one or more rare earth elements selected from the group consisting
of cerium, yttrium, terbium, gadolinium, and europium.
3. The method of claim 1 further comprising monitoring and
stabilizing intensity of the light source.
4. The method of claim 1 further comprising calculating a
vegetation index using detected light.
5. The method of claim 2 further comprising performing spectral
selectivity using a narrowband optical filter.
6. The method of claim 5 wherein the narrowband optical filter is
configurable.
7. The method of claim 5 further comprising reducing specular
reflections using polarizing filters.
8. The method of claim 1 further comprising performing spectral
selectivity using a linear variable filter.
9. The method of claim 1 further comprising performing spectral
selectivity using a diffraction grating.
10. The method of claim 1 wherein the ambient light is
sunlight.
11. The method of claim 1 wherein the phosphor re-emits light from
an LED light source.
12. The method of claim 1 wherein the phosphor emits low color
temperature white light.
13. The method of claim 1 wherein the phosophor emits green,
yellow, orange, or red light.
14. The method of claim 1 further comprising mounting the light
sensor on a moving vehicle.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Divisional application of U.S. patent
application Ser. No. 12/896,460 filed Oct. 1, 2010, which is a
Continuation-in-part application of U.S. patent application Ser.
No. 12/108,371 filed Apr. 23, 2008, which is a continuation-in-part
of U.S. patent application Ser. No. 10/703,256 filed Nov. 7, 2003,
which is now U.S. Pat. No. 7,408,145 issued on Aug. 5, 2008 and
which also claims priority to U.S. Provisional Application No.
60/925,831 filed Apr. 23, 2007, all of which are herein
incorporated by reference in their entireties.
FIELD OF THE INVENTION
[0002] This invention relates to a structure and a method for
determining changes in the chlorophyll status of a plant via remote
sensing of the plant's reflectance spectrum spanning from
approximately 400 nm to 1200 nm.
BACKGROUND OF THE INVENTION
[0003] Techniques to remotely measure crop status have historically
include the use of a spectroradiometer and other instruments
(Bausch et al. 1994; Chappelle et al. 1992; Maas and Dunlap, 1989),
aerial photography (Benton et al, 1976), and satellite imagery.
[0004] The techniques listed above are not without their
limitations. For example, early research by Resource21.TM.
determined that during the optimal fly over times between 10 a.m.
and 11 a.m. for satellite imaging, cloud cover had adverse affects
on visibility. It was found that during the 10 a.m. to 11 a.m. time
frame, fields in Colorado were visible approximately 80% of the
time while eastern Nebraska fields were visible approximately 50%
of the time. This trend in decreased visibility continued the
farther east that data was collected. Also, spatial resolution for
satellite imagery is poor (Landsat, 20 meter and panchromatic, 10
meter). Similar problems plague aerial photographic methods as
well. While aerial imagery has better spatial resolution (typically
less than 3 meters) than satellite imaging, partial cloud cover can
shade sections of fields giving biased or incorrect reflectance
measurements. Both techniques, however, suffer from the need for
extensive data processing (performed by third party providers at
high cost and long lead time) and geo-referencing issues. Even with
spectroradiometric methods using sunlight as the ambient light
source, cloud cover and time of day (8 a.m. to 8 p.m.) demands
limit the mainstream acceptance of the technology for addressing
the nitrogen rate over-loading problem.
[0005] Vehicle-mounted, active sensing technologies overcome the
limitations of the passive technologies listed above by utilizing
artificially generated light to irradiate a plant canopy and
measure a portion of this light that is reflected off the canopy,
much like the passive sensing instrumentation. Active sensors can
have either steady-state or modulated light sources. With
steady-state light illumination, care must be taken to adequately
shield the measurement scene (typically a leaf) from ambient light
such as in the case of spectrophotometric measurements utilizing a
halogen lamp. However, sensors with modulated light sources can be
operated without concern for ambient background illumination. With
a modulated active sensor, the modulated radiation is reflected
from the target and measured by the sensor's detection hardware.
Electrical circuits within the sensor are able to differentiate
between the modulated portion of the reflectance and ambient
background light. This unique feature of active sensors is why they
can operate equally well under all lighting conditions. Active
sensors are sometimes referred to as real-time or on-the-go
sensors. This simply means that the data or measurements produced
by the sensors can be utilized immediately for performing
agricultural operations such as applying herbicide or
fertilizer.
[0006] Active plant canopy sensors have a long history dating back
almost 70 years. One of the earliest active electro-optical sensors
was developed by Ferte and Balp (U.S. Pat. No. 2,177,803). This
sensor was designed to be spectrally sensitive to a plant's
carotenoid peak located at 550 nm for the intended purpose of
detecting plants and selective thinning. The detection system
utilized two phototubes each fitted with spectrally selective
filters. One filter was colored with methyl green pigment to give
the associated detector a spectral sensitivity to vegetation with a
spectral peak located at 535 nm while the other filter was colored
with rhodamine B to create a notch filter to block green light. The
interplay between the optical signals sensed by the detection
circuitry was utilized by the system to activate a plant thinning
device.
[0007] Another early active sensor was developed by Marihart (U.S.
Pat. No. 2,682,132). This particular sensor was vehicle mounted and
was developed for the selective application of herbicides and
fertilizer. The sensing system utilized a modulated light source
consisting of a fluorescent lamp and a phototube connected to an
inductor-capacitor tuned amplifier to measure light reflected from
the plant canopy. Spectral selectivity was performed via the use of
color filters in front of either the detector or the light
source.
[0008] In 1969, Palmer et al. developed a sugar beet singling and
thinning system to automatically thin plant populations. This
instrument incorporated four optically modulated sensors connected
to a PDP-8 minicomputer mounted to a tractor/mower. Plant
distribution was detected via two photomultiplier tubes fitted with
optical band pass filters inside each sensor. The center
wavelengths for the filters were 630 nm and 810 nm with each filter
having an apparent bandwidth of roughly 60 nm. The minicomputer was
programmed to create a 2-dimensional "kill map" of plants to be
eliminated. When a plant to be eliminated was detected, the system
would respond by spraying the plant with a non-selective
herbicide.
[0009] During the time period spanning from 1975 to 2002, fully
solid-state plant status and weed sensors were developed. These
sensors utilized LED's to actively illuminate plant canopies in
order to overcome the limitations of lamp-based and passive
illumination methods. Henderson and Grafton (U.S. Pat. No.
3,902,701) developed one of the first active sensor instruments to
use LED's as an illumination source. The instrument was designed to
be mobile with an intended use to measure leaf reflectance
characteristics and relate this reflectance to plant health and
status. Stafford et al. (1989) developed a portable handheld sensor
to measure turf moisture content. This instrument contained two
near infrared (NIR) monochromatic LED's with one LED source
emitting 940 nm light and the other 1150 nm light. Subsequently,
Beck and Vyse (U.S. Pat. No. 5,292,702) developed an active weed
sensor, much like the Henderson sensor, incorporating two LED light
sources with one LED source emitting 670 nm light and the other 750
nm light (WeedSeeker by Patchen, Ukiah, Calif.). Stone et al. (U.S.
Pat. No. 6,596,996) developed a dual wavelength active light
sensor, essentially a form of the Henderson and Beck patents, for
the purpose of quantitative biomass determination while Holland
(U.S. Pat. No. 7,408,145) developed a plant biomass sensor
utilizing a novel polychromatic LED light source. For all the
aforementioned solid state sensors, the light sources were
modulated and detected reflectance signals were demodulated
synchronously. Reusch in European Patent EP 1 429 594 and his paper
submitted to the 6.sup.th European Conference on Precision
Agriculture discloses a technique to use halogen and flash lamp
techniques for active illumination. The instrumentation taught in
these documents are similar to the instrument disclosed by Palmer
and Owens (1969). It should be noted concerning spectral
selectivity, that Holland (U.S. Pat. No. 7,408,145) describes a
device that addresses the concerns Reusch has argued regarding LED
technology.
SUMMARY OF THE INVENTION
[0010] The new sensor of the present invention overcomes the
time-of-day and fair weather limitations of passive technologies by
incorporating its own radiant source and by rejecting the influence
of ambient light on the measured canopy reflectance. Unlike passive
sensor technology, this sensor will be able to operate under
completely dark or full sun conditions.
[0011] Additionally, the new sensor apparatus is an improvement
both in performance and cost over competing active-sensor
technologies commercially available. Furthermore it improves on
prior art by allowing sensors to be developed that have wavelength
selectivity, improved light source performance and life, and
detection means and signal processing.
[0012] As discussed above, the invention presented here will be
advantageous in a number of commercial applications. For
site-specific agricultural applications, the developed sensor would
allow the producer to reduce the amount of nitrogen fertilizer
applied to a crop or facilitate spoon-feeding the crop during the
growing season, thus having the potential for lowering production
costs and enhancing environmental quality. Also, by being able to
determine the appropriate fertilizer needs of the crop at any given
location in the field, the producer can apply only the fertilizer
needed to prevent yield loss or degradation of product quality
(i.e., protein content in wheat and barley or sugar content in
sugar beets). Subsequently, decreased fertilizer rates will
substantially lower nitrogen runoff and leaching losses, which will
improve the health of our watersheds, waterways, lakes, and oceans.
In addition, data produced by the sensor may be used to produce
relative yield maps for forecasting crop production. As for turf
grass applications, the sensor technology would allow turf managers
to map changes occurring on turf landscapes or for monitoring the
status of turf quality.
[0013] When incorporated into variable rate applicator and/or
sprayers systems, the present invention significantly reduces the
use of fertilizers by precisely applying agricultural products to
individual plants to be treated or eliminated. Moreover, the
present invention is operable under a wide variety of conditions
including cloudy conditions, bright sunlight, artificial
illumination, or even total darkness. The advantage to the producer
is that field operations do not have to be timed to daytime
sunlight hours for operation.
[0014] All embodiments of the invention can be used in two primary
ways. The first method of use includes the application of the
invention to handheld instrumentation. Here the invention is
utilized to measure plant canopies held in hand by a producer, turf
manager, researcher, and the like. The invention may include the
use of GPS for geo-referencing data collected by the invention. A
second method of use includes applications where the sensor is
mounted on a moving object such as a tractor, mower, center
pivot/linear irrigator, or the like. Again, data may be
geo-referenced using GPS for mapping and data layer (GPS maps, soil
maps, etc.) integration. Problem areas can be logged and reviewed
later by the producer or land manager for analysis and site
management decisions.
[0015] An object of the invention is to provide a sensor for
remotely sensing plant status using biophysical and biochemical
properties of the plant thereby allowing selective monitoring,
elimination, or treatment of individual plants.
[0016] This and other objects of the invention will be made
apparent to those skilled in the art upon a review of this
specification, the associated drawings and the appended claims.
According to one aspect of the present invention, a method of
treating plants is provided. The method includes measuring optical
properties of a plant using a plurality of spectral bands. The
method further includes calculating in a computational device at
least two vegetative indexes using the optical properties, each of
the at least two vegetative indexes correlating to one or more
plant growth parameters. The method further includes calculating in
the computational device a water invariant chlorophyll index from
at least two vegetative indexes using the plurality of spectral
bands. The also provides for treating one or more of the plants
based on the water invariant chlorophyll index.
[0017] According to another aspect of the present invention, a
method of treating plants includes measuring optical properties of
one or more plants across a plurality of spectral bands, and
calculating in a computational device at least two vegetative
indexes using the optical properties, each of the at least two
vegetative indexes correlating to one or more plant growth
parameters. The method further includes calculating in the
computational device a water invariant chlorophyll index from at
least two vegetative indexes using the plurality of spectral bands.
The method also includes treating the plants based on the water
invariant chlorophyll index.
[0018] According to another aspect of the present invention, a
system for treating plants includes an optical sensing system
configured to measure optical properties of one or more plants
across a plurality of spectral bands. The system also includes an
applicator for selectively applying treatment to the plants. The
system also includes an intelligent control or controller which is
operatively connected to the optical sensing system and the
applicator and configured to (a) calculate at least two vegetative
indexes using the optical properties, each of the at least two
vegetative indexes correlating to one or more plant growth
parameters, (b) calculate a water invariant chlorophyll index from
at least two vegetative indexes using the plurality of spectral
bands, and (c) control the applicator to provide for selectively
applying treatment to the plants based on the water invariant
chlorophyll index.
[0019] According to another aspect of the present invention, a
method for measuring a plant's reflectance is provided. The method
includes modulating a light source comprised of one or more LEDS
that emit light in the spectral range of 350 nm to 480 nm having a
phosphorescent coating, and detecting light originating from the
light source reflected off of the plant in the presence of ambient
light in one or more spectrally sensitive photodetectors.
[0020] According to another aspect of the present invention, a
method of treating plants includes measuring optical properties of
a plant using at least three spectral bands, determining by a
computational device a treatment for one or more of the plants
using the optical properties, and applying the treatment to the one
or more of the plants.
[0021] According to another aspect of the present invention, a
system for treating plants includes an optical sensing system
configured to measure optical properties of one or more plants
across a plurality of spectral bands, an applicator for selectively
applying treatment to the plants, and a controller operatively
connected to the optical sensing system and the applicator and
configured to control the application of the treatment based on
properties of the one or more plants determined from the optical
properties, and one or more indexes that relate the properties of
the one or more plants to the optical properties.
[0022] According to another aspect of the present invention, a
method of treating plants includes measuring optical properties of
a plant using a plurality of spectral bands, and calculating in a
computational device at least two vegetative indexes using the
optical properties, each of the at least two vegetative indexes
correlating to one or more plant growth parameters, wherein a first
of the vegetative indexes is used for low leaf area index and a
second of the vegetative indexes is used for a high leaf area
index.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 illustrates plant reflectance curves over the visible
and near infrared portion of the spectrum with the red-edge portion
of the spectrum emphasized.
[0024] FIG. 2 illustrates the effect of nitrogen rate on the plant
reflectance curve over the visible and near infrared portion of the
spectrum.
[0025] FIG. 3 shows a diagram of the inventions mechanical
enclosure.
[0026] FIG. 4 shows the functional block diagram of a typical
sensor embodiment.
[0027] FIG. 5 show the structure of phosphor coated LED.
[0028] FIG. 6 show the emission spectra for 6500K (cool), 3000K
(warm) and orange phosphor LED's.
[0029] FIG. 7 shows schematically a circuit used to instrument the
inventions light source.
[0030] FIG. 8 shows diagrammatically a sensor based mapping
system.
[0031] FIG. 9 shows diagrammatically a sensor based variable-rate
applicator system.
[0032] FIG. 10 illustrates the necessary sensor-to-spray nozzle
separation for compensating for plant canopy periodicity and random
leaf orientation.
DETAILED DESCRIPTION
[0033] The following contains a description for a sensor that
remotely measures plant canopy chlorophyll content independent of
soil reflectance and ambient illumination levels. The sensor can be
used in stand-alone instrumentation configurations or in a network
of sensors mounted to a vehicle or moving apparatus for on-the-go
remote sensing applications. The following description of the
invention is meant to be illustrative and not limiting. Other
embodiments will be obvious in view of this invention.
[0034] The positive relationship between leaf greenness and crop
nitrogen (N) status means it should be possible to determine crop N
requirements based on reflectance data collected from the crop
canopy (Walberg et al., 1982; Girardin et al., 1985; Hinzman et
al., 1986; Dwyer et al., 1991) and leaves (McMurtrey et al., 1994),
see FIG. 1. Plants with increased levels of N typically have more
chlorophyll (Inada, 1965; Rodolfo and Peregrina, 1962; Al-Abbas et
al., 1974; Wolfe et al., 1988) and greater rates of photosynthesis
(Sinclair and Horie, 1989). Hence, plants that appear a darker
green are perceived to be healthier than N deficient plants and as
such healthier plants reflectance less light in the visible portion
of the spectrum (400 to 700 nm) and reflect more light in the near
infrared (>700 nm), see FIG. 2.
[0035] Chlorophyll in leaves absorbs strongly in the blue 3 and red
4 regions of the spectrum (460 nm and 670 nm) and as the
wavelengths increase past 670 nm the leaves begin to strongly
reflect infrared light, see FIG. 2. The transition region between
the photosynthetic portion 1 (400 nm to 670 nm) and the biomass
portion 2 (>780 nm) of a plant's reflectance spectrum is
sometimes referred to as the red-edge region 5. It has been
reported in literature that the wavelength where the maxima of the
derivative 6 for the red-edge band occurs is strongly correlated to
changes in the chlorophyll status of a plant. Guyot and Baret
(1988) developed an algebraic relationship expressing the
wavelength of the red-edge inflection point (REIP) 6, sometimes
referred to as the red edge position (REP), using four reflectance
bands spanning from 670 nm to 780 nm. The usefulness of measuring
red-edge reflectance spectra, and subsequently determining the
inflection point's wavelength position, is that the chlorophyll
status of the plant can be measured independently of soil
background interference. That is, the chlorophyll status as denoted
by shifts in the red-edge inflection point, is independent of the
slope of the vegetative reflectance curve and has reduced
sensitivity to soil and biomass reflectance characteristics. Shifts
in the value of the inflection point are directly related to the
chlorophyll status (and water content) of the plant with
chlorophyll content being closely related to nutrient status.
Another useful red edge parameter is the red well position 7 (RWP).
This is the point on the vegetation reflectance curve that
represents the plants minimum reflectance, i.e., the wavelength of
maximum chlorophyll absorption. This parameter, like the REIP, is
also useful in determining changes in a plant's chlorophyll status.
Other vegetative indices are also available for plant N status
determination that solely rely on visible wavebands (400 nm to 700
nm). For example the Visible Atmospherically Resistant Index (V
ARI) utilizes reflectances at 550 nm (green light) and 670 nm (red
light). Indices of this form can provide significant information
pertaining to crop phenology.
[0036] The general embodiment of the invention can be utilized to
measure plant vegetation reflection. In this embodiment, a
low-color temperature white LED emitter(s) provide coincident beam
of light; the beam of light is substantially in the vegetative
reflectance spectrum (400 nm to 900 nm) and is sequenced on and
off. The light source may be composed most preferably of one or
more white LED emitters. The emitted LED beam illuminates a surface
area on the plant's canopy, which may include bare ground and
desired plants. The reflected light signals are then detected by an
array of spectrally sensitive photo detectors fitted with filters.
In a second embodiment, a high-color temperature white LED
emitter(s) provide coincident beam of light; the beam of light is
substantially in the vegetative reflectance spectrum (400 nm to 750
nm) and is sequenced on and off. The light source may be composed
most preferably of one or more white LED emitters. As with the
first embodiment, the LED beam illuminates a surface area on the
plant's canopy, which may include bare ground and desired plants.
The reflected light signals are then detected by an array of
spectrally sensitive photo detectors fitted with filters. Each
embodiment utilizes a controller for analyzing reflectance signals
measured by the instruments and, assuming a plant is detected,
responds by activating a device to take some action with respect to
the plant or stores the analyzed signal with corresponding DGPS
position in the controller's memory for later analysis. A number of
actions may be taken by the controller. If the plant is a crop that
is determined to be lacking in nutrient, the desired action may be
to apply fertilizer.
[0037] Additionally, if the plant under test is a turf landscape,
such as found on golf courses and sporting fields, plant
chlorophyll and/or biomass may be mapped and geo-located using GPS
for later, comparative analysis.
[0038] In the first embodiment listed above, the visible wave bands
(540 nm to 680 nm) and the long wave near infrared bands (760 nm to
900 nm) may be utilized to calculate classic biomass vegetative
indexes such as normalized difference vegetative index (NDVI),
simple ratio index (SRI), etc. . . . . Additionally other unique
vegetative indices, sensitive to chlorophyll can be formulated
utilizing the wavebands along the red edge. For example, one could
use a 730 nm LED and a 780 nm LED to illuminate the canopy in order
to measure a plant's chlorophyll content. The reflectance ratio of
these two wavebands is proportional to the chlorophyll status of
the plant. Albeit, this ratio may be somewhat sensitive to soil
background interference, it will produce good data for canopies
with LAI's greater than 2, that is, canopies that have more
complete closure.
[0039] Prior art cited in U.S. Pat. No. 3,910,701 teaches the use
of multiple LED wavelengths for plant status determination and the
use of wavelength differentials (slopes) for comparative
determination of plant status. This art, however, makes no
distinction on the use the red-edge portion of a plant's
reflectance spectrum for qualitative chlorophyll assessment. Prior
art cited in U.S. Pat. No. 5,789,741 make no distinction with
respect to chlorophyll content measurement but rather refer to
changes in the slope of the vegetative reflectance spectrum as
being indicative of the presence or absence of plant material as
compared with soil background reflectivity. The resultant
measurement made by the invention of '741 will be heavily
influenced by soil background interference. Furthermore, this
invention does not incorporate the spectral reflectance around the
red-edge portion of vegetative reflectance curve but rather detects
slope changes as they deviate from the soil background line (but
still heavily influenced by soil background interference); one
slope calculated from 600 nm to 670 nm and the other from 670 nm to
780 nm. As such, one trained in the art will note that data
produced by this method (U.S. Pat. No. 5,789,741) offers limited
benefit over biomass calculation methodologies via data produced by
prior art referenced in U.S. Pat. Nos. 5,296,702, 5,389,781,
5,585,626 and 6,596,996. Reusch teaches a device in European Patent
that uses flash lamp and halogen technology light source
technology. However, these light source technologies suffer from a
number of problems. It is rather impractical to utilize
incandescent or halogen lamps due to the need to mechanical
modulate light emitting from light sources of this type. Flash lamp
technology could be utilized, however, but their use will be
limited in performance due to the low modulation and demodulation
rates that are achievable with such an illumination system
(typically less than 100 Hz). Both lamp technologies suffer from
rather short working lifetimes as well as having potentially poor
spectral stability. The problems associated with flash lamp
technology include, but are not limited too, are: poor mechanical
stability short lifetime typically less than 3000 to 7000 hrs, poor
spectral stability; although lamps, may deliver repeatable total
energy, spectral band energy may fluctuate from flash to flash,
poor modulation performance typically less than 100 flashes per
second, high cost; cost factors associated with high energy flash
lamps will limit commercial applicability, low modulation rates
will result in poor signal-to-noise performance.
[0040] The problems associated with halogen lamp technology
include, but not limited too, are: poor mechanical stability, short
lifetime; typically less than 1000 to 2000 hrs, poor spectral
stability; partly due to envelope plating from filament
evaporation, can not be easily modulated (electrical modulation
limits modulation rates to less than 2 Hz). Typically one would
have to modulate via mechanical means for example by chopping the
light using a slotted disc. Mechanical modulation schemes are both
costly and unreliable, especially in high vibration environments
such as those found on farm vehicles. Also, to note, both flash and
halogen lamp technologies require substantially more power to
operate than competing LED technologies.
[0041] While each of the two embodiments previously discussed have
different spectral bands of illumination, the fundamental
electronic instrumentation required to realize the two devices
share many common features and in many ways are essentially the
same. A discussion of the electro-optic elements required to
realize each of the embodiments follows.
[0042] FIG. 3 shows a diagram of the sensor enclosure. The
enclosure facilitates the protection of the electronic circuitry
while providing optical emission and reception ports for the light
source and the light detector components, respectively, of the
sensor. Port 30 in FIG. 3 is the emitter port of the sensor while
port 31 is the detector port of the sensor. Detector port 31 can
also be a plurality of ports to facilitate multiple detector
channels or the light can be split into multiple beams internally
to the housing for multiple detector channels.
[0043] Port 30 and port 31 can facilitate various types of optical
components to concentrate and collect optical energy. The type of
optics used by the sensor can include lens, mirrors, optical flats,
filters, and diffusers. The type of optics selected for the emitter
and detector optics depends on the application; that is, the
required field of view, the height the sensor will be operated
above the plant canopy, the required cost of the sensor all may
play a part in the design of the sensor's optical arrangement. The
sensor can operate at a distance of 1/2 foot and up to 10 s of feet
from the plant canopy or surface of interest but is not limited to
this specific range. To those skilled in the art it should be
readily apparent that fore optics on the emission side and the
detection side can take on many forms.
[0044] For example, a useful optically adaptation on the detector
side of the optical arrangement would be to encapsulate the
detector optics (filters and detectors). The outer optical surface
would have a convex surface spaced from the plane of the photodiode
so as to create an afocal or nearly afocal optical arrangement.
This preferred mode of construction improves the optical energy
collection performance of the filter/diode combination while
sealing the optical path from dust and water vapor
condensation.
[0045] On the emission side of the sensor, there are a number of
ways in which to shape and direct the light beam emitting from the
sensor body. For instance, if one wishes to generate a line pattern
from the sensors light source, preferably a bank of LEDs, one could
place a cylindrical lens in front of this light source spaced
appropriately so as to image a line of illumination in the field of
view of the detection optics.
[0046] Alternately, a circular or ellipsoidal area of irradiance
can be produced using only the encapsulation optics of an LED or an
array of LEDs. In this instance, the beam pattern produced by the
source is defined by the spatial irradiance distribution of each
individual LED. No additional collimation or focusing optics is
incorporated. Encapsulated LEDs can be purchased commercially that
have spatial distribution angles of 4 degrees to almost 180
degrees. Most preferably, it is best to collimate the light emitted
from an LED in order to maintain a light beam with localized
irradiance over distance. In this case the LED or LED array would
be spaced an appropriate distance from a convex lens (or concave
mirror) to form an afocal or nearly afocal optical system. The
resulting optical system will produce a light beam that will be
collimated along the optical axis of the light source resulting in
areas of illumination with high radiance.
[0047] FIG. 4 shows a system diagram typical for the many
embodiments of the invention. The sensor is composed of optics to
facilitate optical energy collimation and collection, a modulated
light source 41 comprised of one or many banks of polychromatic
LEDs and/or monochromatic LEDs with associated modulated driver and
power control electronics 42, single or multichannel photodetector
array 43, high-speed preamplifier(s) with ambient light
cancellation 44, a phase sensitive signal conditioning 45 and data
acquisition circuitry 46, and a microcontrol unit (MCU) or digital
signal processor (DSP) 47 and an input/output interface 48 to
communicate sensor data to an operator or controller. These system
elements will be discussed in the following.
[0048] The light source for the invention is most preferably
composed of low-color temperature phosphor coated light emitting
diode(s). The structure of a phosphor LED is shown in FIG. 5. Here
LED die 50 is coated with a phosphorescent compound that remits
light via excitation by LED 51. The emission spectrum of phosphor
coated LED's can be described as having a polychromatic emission
spectrum, in that, the emission spectrum can be classified as
having at least two peaks with the first one (shortest wavelength)
having a first center wavelength (CWL1) due to the emission peak of
the LED and at least a second longer-wave emission center
wavelength peak (CWL 2) due to the reradiation of the LED light by
the phosphor coating. Depending on the phosphor composition, other
peaks in the emission spectrum may be present. Phosphor coated
LED's are convenient light sources for this type of invention for a
number of reasons. First, white light emitting LED's are available
have spectral emission characteristics that are useful for making
plant biomass and pigment measurements. These LED's can be
constructed to have color temperatures that span from deep violet
(400 nm) to near infrared (900 nm). Second, LED's, in general, are
extremely easy to use and can be modulated to megahertz
frequencies. Relatively simple electronic driver circuits can be
implemented and easily controlled by sensor controller
electronics.
[0049] Last, LED's have long lifetimes and are rugged. The typical
LED will operate between 80,000 and 100,000 hours depending on the
quiescent device power and operating temperature range. White light
LED's using phosphor coatings over UV or blue LED emitters can have
lifetimes of 40,000 to 80,000 hours. Most white light emitting
LED's in production today are based on an InGaN-GaN structure, and
emit blue light of wavelengths between 450 nm-470 nm blue GaN.
These GaN-based, InGaN-active-layer LED's are covered by a
yellowish phosphor coating usually made of cerium-doped yttrium
aluminum garnet (Ce3+:YAG) crystals which have been powdered and
bound in a polymer or silicone adhesive. The LED chip emits blue
light, part of which is efficiently converted to a broad spectrum
centered at about 580 nm (yellow) by the Ce3+:YAG. The emission
color of Ce3+:Y AG emitters can be modified by substituting the
cerium with other rare earth elements such as terbium and
gadolinium and can even be further adjusted by substituting some or
all of the aluminum in the YAG with gallium. Due to the spectral
characteristics of the diode, the red and green colors of objects
in its blue yellow light are not as vivid as in broad-spectrum
light. Manufacturing variations and varying thicknesses in the
phosphor make the LED's produce light with different color
temperatures, from warm yellowish to cold bluish. Spectrum of a
white LED clearly showing blue light which is directly emitted by
the GaN-based LED (peak at about 465 nanometers) and the more
broadband stokes shifted light emitted by the Ce3+:YAG phosphor
which extends from around 500 to 700 nanometers. White LEDs can
also be made by coating near ultraviolet emitting LEDs with a
mixture of high efficiency europium based red and blue emitting
phosphors plus green emitting copper and aluminum doped zinc
sulfide (ZnS:Cu, Al). This is a method analogous to the way
fluorescent lamps work. The spectrum of a white LED is easily
modified to create other colors by modifying the elemental
components in the phosphor coating. For example, an orange,
broad-band LED can be created to emit longer wavelengths of
light--higher intensities of red and NIR--by using a phosphor
coating containing a mixture of gadolinium, aluminum, oxygen and
cerium (Gd.sub.3Al.sub.50.sub.12:Ce) over a 470 nm LED die. FIG. 6
shows the spectral graphs for cool white (6500K) 60, warm white
(3000K) 61 and orange phosphor coated LED 62 emitters. Note in the
graphs that the warm white and orange phosphor LED's exhibit a
strong stokes shift to longer wavelengths. Good emitter output
intensities in the red and NIR portions of the spectrum can be
obtained for plant active plant canopy reflectance instruments or
other active sensing instruments. Additionally, an NIR LED can be
added to the device to further extend near infrared performance to
longer wavelengths. It should be noted that there are numerous
other methods, that one skilled in the art, can create different
spectral outputs for LED devices (using green, yellow and red
phosphor compounds) having the basic structure of the white
phosphor LED.
[0050] In order to achieve good output stability with respect to
thermal and aging effects, the LED sources should be adequately
driven and monitored. The output intensity of LED's is very
temperature dependent. Depending on the material type, an LED's
output can drift between 0.4%/C and 1%/C. FIG. 7 shows
schematically a circuit that provides active power control for the
light source and an output intensity signal for monitoring and
calibration. Control voltage 70 sets the output power of light
source 71. Photodiode 72, an Infineon SFH203 (Munich, Germany),
samples part of the output intensity of light source 71 and feeds
this signal via amplifier 73 to servo amplifier 74. Modulation of
the output signal is performed using transistor 77. Furthermore,
the output of amplifier 73 can be utilized to monitor the light
source intensity for purposes of calibration and diagnostics. The
performance of this circuit has provided output intensity control
of approximately 0.05%/C over the operating range of the invention.
Many techniques have been discussed in literature detailing methods
on maintaining and stabilizing light sources for photometric type
measurements including the method presented here. For example,
photodiode 52 can also be an array of spectrally sensitive diodes
that can be utilized to monitor the same spectral bands as
multi-channel photo detector array 43. In this case, each device
will have a corresponding amplifier and associated detection
circuitry for measuring light source spectral intensity
fluctuations. Furthermore, this array of spectrally sensitive
photodiodes could be designed so that spectral fluctuations in the
blue, green and red portions of the emission spectrum of the light
source are monitored. The resultant signals could then be utilized
to correct for the overall spectral changes of the light source via
mathematical curve fitting. These adjustments would account for
output intensity and spectral changes of the light source. As those
skilled in the art will note, there are numerous techniques and
methodologies for light source power monitor/stabilization for
photometric measurements discussed in engineering and scientific
literature.
[0051] The detectors used in the invention are most preferably
silicon photodiodes however other detector technologies such as
GaAsP and the like, may be utilized as well. Silicon detectors have
a typical photosensitivity spanning from 200 nm (blue enhanced) to
1200 nm. Band shaping of the detectors is performed using filtering
materials such as colored filter glass, interference filters,
polarizing filters or dichroic filters. Combinations of the
aforementioned filter techniques can be combined in order to
band-shape the radiation impinging on the photo detector surface.
For example, an interference filter can be used to select a narrow
bandwidth of light. In this situation, one could choose to use a 10
nm interference filters to select a band of interest within the
vegetative reflectance spectrum. The use of polarizing filters may
be incorporated to reduce the influence of specular reflections
from the plant canopy. This is particularly useful for minimizing
the effect of dew and water on a plant's reflectance characteristic
as well as reducing specular reflection effects due to glossy leaf
surfaces. Utilizing an array of photodetectors fitted with
interference or edge filters would provide the wavelength selection
needed to realize the embodiment's of this invention As one trained
in the art will see, there are numerous ways in which various
optical filters can be utilized to shape and control the light
impinging on a photo detector or photo detector array. A unique
configuration pertaining to embodiment two involves the use of
linear diode array detector and diffraction grating (or linear
variable filter (LVF) technology). The diffraction grating (or LVF)
separates incoming, modulated light in to many wavelengths. By
configuring embodiment one with a diffraction grating (or
LVF)/linear array combination sensitive to the red edge region of
the vegetative reflectance curve, plant chlorophyll concentrations
can be measured mostly independent of soil background interference.
The potential for filter configurability by an operator of the
invention is possible. By specifically constructing the housing in
FIG. 3 to support user insertion and removal of filters, the
invention can support in-field configurability This is advantageous
from the stand point that spectral selection can be easily changed
when the application of the instrument is changed. Filter sets can
be selected to cover all the useful vegetative indices that may be
encountered for a particular agricultural landscape. For example, a
filter set of red, green and NIR spectral filters can be utilized
for nitrogen management (green, NIR filters) or soil mapping/weed
mapping/herbicide application (red, NIR filters). The green and red
band filters can be easily swapped depending on the field operation
to be performed. Calibration constants for each filter combination
can be stored internally in the sensor's on-board memory or
recalibration can be easily performed via an integrating sphere or
reflectance panel.
[0052] Referring once again to FIG. 4, both embodiments of the
invention utilize a phase sensitive detector subsystem (PSD) 45 and
analog-to-digital converter 46 (ADC) after each photo detector. The
PSDs, sometimes referred to as lock-in amplifiers, are utilized by
the invention to extract and further amplify the very small signals
detected and amplified by the photodetector preamplifier(s). PSDs
are often used in applications where the signal to be measured is
very small in amplitude and buried in noise. Detection is carried
out synchronously with modulation of the light sources. Phase
sensitive detection is one of many types of band narrowing
techniques that can be utilized to measure small signals. As will
be apparent to those skilled in the art, other methods include the
use of averaging techniques, discriminators and direct digital
conversion/processing. With respect to direct digital
conversion/processing, the phase sensitive acquisition component
can be performed internally to a MCU or DSP by directly sampling
the output of the photodiode amplifiers and performing the band
pass and PSD functions digitally. By performing these operations in
the digital domain, the temperature drift of the phase detector,
common to analog techniques, can be eliminated. The invention
performs the synchronous modulation/demodulation at a carrier
frequency of 250 kHz. It should be noted that the operation of the
invention is not limited to this particular modulation rate and can
operate at other modulation frequencies as well with as much
effectiveness. Additionally, this rate can be increased or
decreased as dictated by the application. The MCU or DSP samples
the output of a PSD 45 utilizing ADC 46. The resolution of the ADC
is most preferably 12 bits. Each channel can sampled using a
dedicated ADC or one ADC can be utilized to sample all channels via
a multiplexer.
[0053] Once the detected optical signals are amplified, demodulated
and quantified, the MCU or DSP 47 can calculate chlorophyll content
and/or a vegetative relationship based on the reflectance values
sensed.
[0054] When the sensor is fitted with a low-color temperature white
LED source or long wave colored phosphor LED light source
(utilizing green, yellow, orange or red phosphors or combinations
thereof), calculations for plant chlorophyll status based multiple
red-edge reflectance spectra can be performed a number ways. For
the situation where the instrumentation has been designed to
measure four or more reflectance values along the red edge,
polynomial fitting may be used to fit the curve represented by the
reflectance points. Subsequently, the resulting polynomial may be
differentiated to find the red-edge inflection point value. The
resulting wavelength will be proportional to relative shifts in the
chlorophyll status of the plant. When four reflectance values are
measured, the four reflectances having the center wavelengths of
670 nm, 700 nm, 740 nm and 780 nm, a preferred method is the
four-point interpolation method. This method has the following
mathematical for
.rho. i = .rho. 1 + .rho. 4 2 ##EQU00001## .lamda. i = .lamda. 2 +
( .lamda. 3 - .lamda. 2 ) .rho. i - .rho. 2 .rho. 3 - .rho. 2
##EQU00001.2##
[0055] Where .lamda..sub.1, .lamda..sub.2, .lamda..sub.3 and
.lamda..sub.4 are wavelengths 670 nm, 700 nm, 740 nm and 780 nm,
respectively, and .rho..sub.1, .rho..sub.2, .rho..sub.3 and .sub.P4
are reflectances at the corresponding wavelengths, respectively.
Additionally, another red edge parameter, the red well position
RWP, may be calculated using these same wavebands. The RWP
interpolation has the following mathematical form
.lamda. 0 = .lamda. 1 + ( .lamda. 2 - .lamda. 1 ) .rho. i - .rho. 2
.rho. 3 - .rho. 2 ##EQU00002##
The RWP represent the wavelength position of a plants minimum
reflectance in the red, or rather the position of maximum
chlorophyll absorption. The RWP functions in a similar fashion as
the REIP for predicting relative changes in plan chlorophyll
status.
[0056] Other mathematical techniques for determining the REIP and
RWP include Lagrangian interpolation, inverted-Gaussian modeling,
regression modeling, etc. . . . . As will be apparent to one
skilled in the art, the list of the aforementioned methods is not
exhaustive and other common approaches to determining the REIP and
RWP wavelength positions may be formulated or found in
literature.
[0057] In another useful red-edge sensor embodiment, three
reflectance bands, with one band reflectance band the in the red
edge portion of a plant's vegetation reflectance spectra (680 nm to
760 nm), are utilized in a sensor that can distinguish between both
plant nutrient and water stresses via the Canopy Chlorophyll
Content Index (CCCI). The sensor utilizes two particular vegetation
indexes. They are a Normalized Difference Red-Edge (NDRE) index
which has the following mathematical form:
NDRE = .rho. 3 - .rho. 2 .rho. 3 - .rho. 2 ##EQU00003##
and a standard Normalized Difference Vegetation Index (NDVI) which
has the form:
NDVI = .rho. 3 - .rho. 1 .rho. 3 + .rho. 1 ##EQU00004##
[0058] Where .rho..sub.1, .rho..sub.2 and .rho..sub.3 are
reflectances at wavelengths 670 nm, 720 nm and 800 nm (an alternate
combination can include wavebands 550 nm, 720 nm and 800 nm; it
should be note that there numerous waveband combinations). The NDVI
as an estimate of percent plant cover and the NDRE as an indicator
of plant chlorophyll content. The CCCI formula utilizes both the
NDVI and NDRE indexes to calculate the impact of water and nutrient
on a crop or plant.
[0059] Another embodiment of the disclosed invention utilizes a
high-color temperature white LED source and detects reflectances in
two visible wavebands. Nitrogen relationships in crop can be
measured utilizing the two wavelength V ARI vegetation index. This
particular index utilizes reflectance information measured at two
visible band wavelengths and has the functional form:
VARI = .rho. 2 - .rho. 1 .rho. 2 + .rho. 1 ##EQU00005##
[0060] In the above relationship, .rho..sub.1 and .rho..sub.2 are
the reflectances measured at 670 nm and 550 nm respectively. In
this embodiment the need for near infrared spectral emission is not
required and the subsequent sensing device will perform well for
detecting nitrogen stresses differentially in field crops.
[0061] Another embodiment of the disclosed invention utilizes a
high-color temperature white LED source and detects reflectances in
three visible wavebands. Nitrogen relationships in crop can be
measured utilizing the three wavelength VARI vegetation index. This
particular indicee utilizes reflectance information measured at two
visible band wavelengths and has the functional form:
VARI = .rho. 2 - .rho. 1 .rho. 2 + .rho. 1 - .rho. 3
##EQU00006##
[0062] In the above relationship, .rho..sub.1, .rho..sub.2 and
.rho..sub.3 are the reflectances measured at 670 nm and 550 nm and
470 nm respectively. As it was in the previous embodiment, the need
for near infrared spectral emission is not required and the
subsequent sensing device will perform well for detecting nitrogen
stresses differentially in field crops or for providing
phonological information pertaining to a plant.
[0063] Yet other embodiments of the disclosed invention might
utilize simple ratio indexes for determining nitrogen relationships
in the crop Multiple ratios can be determined simultaneously
utilizing three spectral wavebands. This is demonstrated below
as:
SRI 1 = .rho. 2 .rho. 1 and SRI 2 = .rho. 2 .rho. 3
##EQU00007##
[0064] In the above relationship, .rho..sub.1, .rho..sub.2 and
.rho..sub.3 are the reflectances measured at 670 nm and 780 nm and
730 nm respectively. Here, the vegetation indexes give exceptional
sensitivity over a wide range of leaf area indexes (LAI) or
biomasses. For small, early growth stage plants SRI 1 would be
utilized in the invention to give added sensitivity to the VRA
system while at later growth stages (high LAIs) SRI 2 would be
utilized for added sensitivity to high biomass crops. Other indexes
(for example VARI, NDVI, chlorophyll index (CI=SRI-1), etc. . . . )
can be utilized as well with one index sensitive to low biomass
crops and the other to high biomass crops. The invention can
process these indexes simultaneously with the VRA system enabled to
use one or the other or both if needed for a particular field
operation.
[0065] Still two other embodiments of the disclosed invention
utilizes a low-color temperature white LED source or long wave
colored phosphor LED source (utilizing green, yellow, orange or red
phosphors or combinations thereof) and detects reflectances in two
and three wavebands. Crop status can also be measured utilizing the
two or three wavelength red-edge VARI vegetation index. The
particular indices utilize reflectance information measured at one
or two visible wavelengths and one red edge wavelength. The indices
have the functional forms:
VARI ( Red_Edge _ 2 _Band ) = .rho. 2 - .rho. 1 .rho. 2 + .rho. 1
##EQU00008## VARI ( Red_Edge _ 3 _Band ) = .rho. 2 - 1.7 .times.
.rho. 1 + 0.7 .times. .rho. 3 .rho. 2 + 2.3 .times. .rho. 1 - 1.3
.times. .rho. 3 ##EQU00008.2##
[0066] In the above relationship, .rho..sub.1, .rho..sub.2 and
.rho..sub.3 are the reflectances measured at 670 nm, 710 nm and 470
nm respectively. As will be apparent to one skilled in the art,
there numerous other combinations of wavebands and indices that the
principles of this inventive instrument can incorporate.
[0067] Data calculated by the sensor's processing component is
communicated to an operator or system controller via input/output
interface 48. In the case of a handheld instrument, the I/O
interface may take the form of a keypad and display. If the
invention is incorporated into a sprayer or mapping system having
several sensors networked together, the I/O interface will most
preferably be a networkable serial port such a as RS485 port or CAN
2.0b port.
Applications of Use-Methods
[0068] FIG. 8 show a block diagram of the invention incorporated
into a system that is used to map plant status. Elements of the
system include sensor array 80, sensor controller 81, and GPS 82.
The sensor array 80 may also be referenced throughout as an example
of an optical sensing system and the sensor controller 81 may be
referenced simply as a controller 81. The controller 81 may be
operatively connected to an applicator.
[0069] The role of the sensor in this system is to measure the
chlorophyll status and/or biomass properties of the plant being
mapped. Data produced by the sensor are collected by the system
controller for storage and later analysis. Each sensor point is
geo-referenced using the GPS connected the system controller. There
are two primary ways in which mapping can be performed the system.
First, the map collected by the system can be all-inclusive, that
is, every data point measured by the sensor can be stored away in
the controller's memory for later retrieval and analysis. Second,
the sensor/controller can be programmed with a defined set of rules
so as to distinguish poor performing regions of a landscape from
good or healthy regions and vice versa and store only the poor
performing regions. This mode of operation saves storage space in
the controller and reduces the amount of data processing that has
to be performed. As an example, the mapping systems could be
mounted to the mower machinery for a golf course. When the course
personnel perform their weekly mowing operations, the mapping
systems would scout for problem areas of the turf. For turf
management operations, this mode would be most useful because
regions of turf that are suffering from stress (disease, water,
nutrient, and so forth) or are beginning to suffer. The mapping
systems would flag affected areas for the turf manager to scout out
visually.
[0070] FIG. 9 show a block diagram of the invention incorporated
into a system that is used for applying an agricultural product.
Elements of the system include sensor array 90 (or optical sensing
system), sensor controller 91, GPS 92, fertilizer controller 93,
sprayer pumps/actuators 94 and ground speed sensor 95. The
functions of the sensor controller 91 and the fertilizer controller
93 may be combined as a single controller. The sprayer
pumps/actuators 94 may form at least a part of an applicator. For
applying an agricultural product.
[0071] The agricultural product may be either in liquid or solid
form and may be, but not limited to, a nutrient, mineral, herbicide
or fungicide or a combination of the aforementioned materials. The
variable rate control system can be mounted to a commercial sprayer
or tractor mounted sprayer system. GPS can be incorporated in the
system when a map is required of plant canopy characteristics for
later analysis. In addition, to mapping plant characteristics,
material dispensation rates can be mapped as well. GPS is also
required when applying fertilizer referenced to an N sufficient
reference strip. In this situation, a region of the field is given
an N-rate that totally meets the needs of the crop to grow without
loss of yield and apply a lower amount of pre-emergent fertilizer
(only the amount to initially cause the crop to grow) to the
remainder of the field. At a time later in the growing season, the
producer will apply a second treatment to the remainder of the
field using the sensor readings for the N sufficient region of the
field. Readings from the N insufficient parts of the field will be
compared with readings from the N sufficient regions of the field.
The controller will use the sensor measurements to calculate the
appropriate rate of fertilizer to apply to the N insufficient
portion of the field in order to prevent yield loss. As mentioned
earlier, the growth stage of the plant will have an impact on the
usefulness of a particular vegetation index based on the selection
of the spectral components utilized to perform the index
calculation. For example, and NDVI or other vegetation index based
on red and near infrared light will be most effective at
quantifying plant biomass at low leaf area indexes (LAI), that is,
small plants where as an NDRE (same mathematical form as and NDVI)
based on red-edge and near infrared spectral components will have
be most effective at quantifying plant biomass at high LAIs. As
such the system disclosed can automatically (or set manually) to
switch between vegetation indexes that are either sensitive to low
LAI or high LAI plants in order to optimize system sensitivity to
plant biomass and to optimally apply agrochemicals. This is
important because many vegetation indexes tend to have poor or
limited sensitivity to crops at either low biomasses or high
biomasses (stated otherwise as low LAI or high LAI).
[0072] FIG. 10 shows an applicator example with the sensor
stood-off from the spray nozzles. When designing variable rate
application system, the obvious approach is to physically locate
the sensor close or next to the sprayer nozzle. However, because of
the random orientation of most plant canopies the sensor should be
separated from the sprayer nozzles by a distance D 100. This allows
the sensing instrument to collect data on a portion of the crop, so
as to average the spatial variability, before applying an
agricultural product. The separation distance D between the sensor
and sprayer nozzles should most preferably be greater than 3 feet.
In operation, the variable rate system will collect data for D feet
and apply an agricultural product over D feet while sensing the
next D separation distance. Another strength of a red-edge
measurement sensor, as disclosed above, is that the measurement
made by the instrument is relatively invariant with respect to
varying plant population. This is critical for making N fertilizer
recommendations on fields that have had crops planted utilizing
variable rate seeding techniques. With a biomass sensor, a seed
rate map would have to be utilized in conjunction with the variable
rate application algorithm in order to compensate for changes in
plant biomass resulting from the seeding operation.
[0073] The benefits of a system such as the one just described are
both economic and environmental. By using less fertilizer and only
applying it where the crop needs it, the producer can lower his use
of fertilizer and thus lower his production cost. Additionally, by
using less fertilizer and only applying it where the crop needs it,
reduced run-off and leaching into our watershed occurs. Because the
present invention produces its own source of light, the
measurements that it makes is not influenced by ambient light
conditions. Applicator equipment fitted with sensors of this type
can be operated around the clock at night and under full sun.
[0074] According to another aspect of the present invention a Water
Invariant Chlorophyll Index (WICI) is provided to assist in
minimizing the effect of water stress when making a chlorophyll
type measurement. It has been tested on dryland corn and wheat
although may be used for other types of crops as well.
[0075] Below are two examples of WICI's. The basic form of a WICI
index is comprised of the ratio of two DVI's (Difference Vegetation
Index) using a minimum of three spectral bands shown below
WICI 1 = DVI | .lamda. 2 .lamda. 3 DVI | .lamda. 1 .lamda. 3 =
.rho. 3 - .rho. 2 .rho. 3 - .alpha. .rho. 1 ##EQU00009## WICI 2 =
DVI | .lamda. 2 .lamda. 3 DVI | .lamda. 1 .lamda. 2 = .rho. 3 -
.rho. 2 .rho. 2 - .alpha. .rho. 1 ##EQU00009.2##
where .rho..sub.1, .rho..sub.2 and .rho..sub.3 represent the
reflectances at 670 nm, 730 nm and 800 nm,
[0076] .alpha. is a scalar (0.ltoreq..alpha..ltoreq.2).
[0077] It is theorized that better delta matching can be obtained
while still preserving the information content of the red band via
the use of scalar a. On test data this appeared to be the case.
[0078] WICI 1 was designed specifically for use in cereals while
WICI 2 was designed for use in corn.
[0079] The concept involves the assumption that a plant under short
term water stress will have reflectance offsets that are nearly
identical for wavebands closely located together. Consider WICI 1
shown in the below equation with water stress offsets added.
WICI 1 = ( .rho. 3 + .delta. w 3 ) - ( .rho. 2 + .delta. w 2 ) (
.rho. 3 + .delta. w 2 ) - ( .rho. 1 + .delta. w 1 )
##EQU00010##
where .delta..sub.w1, .delta..sub.w2, and .delta..sub.w3 are the
water stress reflectances for each spectral band. If we assume
that
.delta..sub.w1.apprxeq..delta..sub.w2.apprxeq..delta..sub.w3.apprxeq..de-
lta..sub.w
and substitute the right hand of the above equation into the
previous equation and rearrange terms, we obtain the following
equation.
WICI 1 = ( .rho. 3 + .delta. w 3 ) - ( .rho. 2 + .delta. w 2 ) (
.rho. 3 + .delta. w 2 ) - ( .rho. 1 + .delta. w 1 ) = ( .rho. 3 +
.delta. w ) - ( .rho. 2 + .delta. w ) ( .rho. 3 + .delta. w ) - (
.rho. 1 + .delta. w ) = ( .rho. 3 - .rho. 2 ) + ( .delta. w -
.delta. w ) ( .rho. 3 - .rho. 1 ) + ( .delta. w - .delta. w ) = (
.rho. 3 - .rho. 2 ) ( .rho. 3 - .rho. 1 ) ##EQU00011##
[0080] Note also, that in certain circumstances, the delta terms
may be other mutual offset phenomena, for example, soil back
ground. In addition to the representative examples of computations
for calculating WICI, the present invention contemplates other
variations. For example, more than three spectral bands may be used
in the calculations, or multiple WICI's may be separately computed
and combined.
[0081] The resulting WICI, once calculated, may be used to assist
in determining the proper treatment for a plant. The treatment may
involve applying agrochemicals using an applicator. The process of
making the measurements, the calculations, and the treatment may be
part of a real-time process is performed onboard an agricultural
implement within the field. In such a process, a system may be used
which includes an optical system which includes one or more optical
sensors, an applicator for applying treatment, and a controller
operatively connected to the optical system and the applicator
which performs calculations and controls the applicator.
[0082] Although various embodiments have been described, the
present invention contemplates numerous variations. For example,
although a water invariant chlorophyll index is described, the
present invention contemplates that other types of water indexes
may be used, including that described in Zygielbaum et al. (2009),
"Non-destructive detection of water stress and estimation of
relative water content in maize", Geophysical Research Letters,
Vol. 36, L12403, herein incorporated by reference in its entirety.
In addition, other types of indexes may be used to assist in
determining the proper treatment for plants. This may include a
Chlorophyll Content Index (CCCI), such as that described in Barnes
et al. (2000), Coincident detection of crop water stress, nitrogen
status, and canopy density using ground-based multispectral data,
Proc. 5th Intern. Conf. on Precision Agriculture and Other Resource
Management, 38 TRANSACTIONS OF THE ASAE, herein incorporated by
reference in its entirety.
[0083] Although various embodiments of this invention have been
described in detail above, those skilled in the art will readily
appreciate that many modifications are possible in the embodiments
given without materially departing from the novel teachings and
advantages of this invention. Accordingly, various modifications,
adaptations, and combinations or various features of the described
embodiments can be practiced without departing from the scope of
the invention as set forth in the claims.
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