Note: Descriptions are shown in the official language in which they were submitted.
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MEASURING SOIL LIGHT RESPONSE
TECHNICAL FIELD
This invention relates to soil measurement probes and to methods of measuring
the
response of soil to light in situ.
s BACKGROUND
Various probes have been developed for measuring or viewing soils in situ
(i.e., in a
subsurface environment), rather than bringing the soil to the surface for
analysis. Some
probes include sensors that measure probe loads or physical soil properties.
Someprobes
feature windows through which laser light is transmitted into the soil, such
as for measuring a
fluorescence response. Miniature video cameras have also been installed in
probes, for
viewing images of the soil in situ.
SUMMARY
The invention features measuring the response of soil in situ to light of
multiple,
discrete wavelengths, with which the soil is illuminated in succession by a
soil measurement
15 probe.
According to one aspect of the invention, a soil measurement probe has a
housing, a
window, a light source, and a photo-detector. Preferably, the probe also has a
light manifold.
In some embodiments, the probe also has an electrical connector at an upper
end of the
housing, for interfacing with a data transmission cable extending down to the
probe from the
2o ground surface. Preferably, the probe defines an internal passage extending
through its
length and forming a pass-through for wires from down-probe sensors.
The housing defines a force axis and an interior cavity and has an outer
surface
exposed for sliding contact with soil as the housing is moved through the soil
along its force
axis. Preferably, the housing also has a buckling strength sufficient to
withstand an
25 unsupported axial load of at least two tons (18 kilonewtons) applied along
the force axis.
In some applications, the housing is a generally cylindrical body with a
closed
downhole end. However, different housing shapes are also envisioned. For
example, in
some embodiments, the housing is shaped to cleave the soil as it is moved
laterally through
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the soil. In embodiments where the housing is a generally cylindrical body
with a closed
downhole end, the downhole end preferably includes a force sensor configured
to measure
soil-applied load as the probe is advanced through the soil along the force
axis. More
preferably, the downhole end includes a first force sensor responsive to
normal load applied
parallel to the force axis at a distal tip of the probe, and a second force
sensor responsive to
shear stress applied to the outer probe surface behind the tip.
The window is mounted in an opening in the outer surface of the probe and
provides
optical communication between the soil and the interior cavity. In some
embodiments, the
window has an outer surface substantially flush with the outer surface of the
probe. The
outer surface of the probe preferably has a flat region at this point to
facilitate contact
between the soil and the window. More preferably, this flat region is open at
its lower end,
thus providing an unobstructed path for soil approaching the window. In some
embodiments,
the window is a sapphire disk. Sapphire is preferred for its exceptional
hardness and superior
abrasion resistance in cooperation with its good optical properties.
The light source is located within the interior cavity and directed toward the
window
for illuminating the soil in situ alternately with light of a first wavelength
and with light of a
second wavelength. In some embodiments, the light source is controllable to
selectively
illuminate the soil with the first and second wavelengths in succession. In a
preferred
embodiment, the first and second wavelengths correspond to visible colors,
preferably with
2o each corresponding to a different one of red, green and blue visible
colors. In some
embodiments, the light source is also controllable to selectively illuminate
the soil with a
third wavelength to the exclusion of the first and second wavelengths. More
preferably, the
first, second and third wavelengths correspond to visible colors of red, green
and blue.
However, it is envisioned that other wavelengths of light could be used.
2s In some embodiments, the light sburce is provided by separate light
emitters, with
one light emitter configured to emit light at the first wavelength, and
another light emitter
configured to emit light at the second wavelength. Preferably, these light
emitters are light-
emitting diodes.
The photo-detector is also located within the interior cavity and directed
toward the
so window. As the soil is illuminated by the light source, the photo-detector
responds to light of
each of the first and second wavelengths reflected from the soil. In some
embodiments, the
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photo-detector is a light-responsive integrated circuit that outputs a signal
with a frequency
that varies with light intensity.
In embodiments of the probe with the light manifold, the light manifold
defines an
illumination channel positioned to direct light from the light source to an
interior surface of
the window. The light manifold also defines a reflection channel spaced. apart
from the
illumination channel.and positioned to provide an optical path from the
interior surface of the
window to the photo-detector. This configuration of the light manifold blocks
direct
incidence of transmitted light upon the photo-detector.
In some embodiments, the probe also has a controller adapted to trigger the
light
1 o source to emit light at the first wavelength, then to cease to emit light
at the first wavelength,
and to subsequently emit light at the second wavelength. The controller can be
connected to
the light source via a length of cable extending from the housing. Preferably,
the controller
triggers distinct emissions of each of the first and second wavelengths within
a total elapsed
time of less than about one second. More preferably, the controller is adapted
to trigger the
15 light source while the probe is advancing through the soil.
According to another aspect of the invention, a soil measurement probe has a
housing, a window, an illumination means, and a photo-detector. The housing
defines a push
axis and an interior cavity. The housing also has an outer surface exposed for
sliding contact
with soil as the housing is pushed through the soil along its push axis. The
window is
2o mounted' in an opening in the outer surface of the probe and provides
optical communication
between the soil and the interior cavity. The photo-detector is disposed
within the interior
cavity, directed toward the window, and responds to light of each of multiple
wavelengths as
reflected from the soil in situ. In some embodiments, the probe also has a
controller adapted
to trigger the illumination means to emit light at the a first wavelength,
then to cease to emit
25 light at the first wavelength, and to subsequently emit light at the a
second wavelength, then
to cease to emit light at the second wavelength, and to subsequently emit
light at the a third
wavelength.
The illumination means is disposed within the interior cavity and directed
toward the
window, for illuminating the soil in situ with the multiple light wavelengths
in succession. In
so some embodiments, the multiple wavelengths are a first, a second, and a
third wavelength
corresponding to the visible colors of red, green, and blue. The illumination
means
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preferably illuminates the soil with each of the wavelengths in succession
within an overall
time period of less than about one second. In some cases, the illumination
means is a light-
emitting diode assembly capable of emitting multiple, discrete wavelengths.
According to another aspect of the invention, a soil measurement probe has a
housing, a window, a light source, and a sense means. The housing defines a
push axis and
an interior cavity. The housing also has an outer surface exposed for sliding
contact with soil
as the housing is pushed through the soil along its push axis. The window is
mounted in an
opening in the outer surface of the probe and provides optical communication
between the
soil and the interior cavity. The light source is disposed within the interior
cavity and
1 o directed toward the window for illuminating the soil in situ alternately
with light of a first
wavelength and with light of a second wavelength. The first and second
wavelengths each
preferably corresponds to a different one of red, green and blue visible
colors. Preferably, the
light source is light-emitting diodes. In some embodiments, the probe also has
a controller
adapted to trigger the light source to emit light at the first wavelength,
then to cease to emit
15 light at the first wavelength, and to subsequently emit light at the second
wavelength. .
The sense means is disposed within the interior cavity and directed toward the
window, for sensing light of each of the first and second wavelengths as
reflected from the
soil in situ. In some cases, the sense means is a light-responsive integrated
circuit.
According to another aspect of the invention, a method is provided for
measuring
2o color response of soil. The method includes advancing a probe from a ground
surface
through subsurface soil, shining a light of a first wavelength into the soil
ih situ through a
window in a side surface of the probe, measuring a first amount of light
reflected by the soil
back into the probe in response to shining the light of the first wavelength;
then, after
extinguishing the light of the first wavelength, shining a light of a second
wavelength into the
25 soil in situ through the window, and measuring a second amount of light
reflected by the soil
back into the probe in response to shining the light of the second wavelength.
Each of the
first and second wavelengths preferably corresponds to a different one of red,
green and blue
visible colors. For some applications, the method also includes shining a
light of a third
wavelength into the soil in situ through the window and measuring a third
amount of light
so reflected by the soil back into the probe in response to shining the light
of the third
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wavelength. In some embodiments, the method also includes deriving a numeric R-
G-B
representation of color of the soil.
The sensor and method described herein can provide a relatively inexpensive
means
of gathering soil data across a field for the compilation of a soil color map.
Such a map can
provide an indication of the distribution of nutrient holding capacity or
organic matter.
composition, for example, in agricultural applications. The components can be
fashioned to
fit within a relatively small diameter, for direct pushes of probes by
hydraulic rams, or even
fashioned into the soil-contacting surfaces of plow blades or other farm
implements.
Additional sensors are readily incorporated, for the simultaneous mapping of
multiple soil
1 o properties.
The details of one or more embodiments of the invention are set forth in the
accompanying drawings and the description below. Other features, objects, and
advantages
of the invention will be apparent from the description and drawings, and from
the claims.
DESCRIPTION OF DRAWINGS
Fig. 1 is a profile view of a test vehicle using a soil probe to measure soil
properties
in situ.
Fig. 2 is a side view of a soil light response probe.
Fig.3 is a cross-sectional view of the soil light response probe, taken along
line 3-3 in
2o Fig. 2.
Fig. 4 is an enlarged cross-sectional view of the color sensor portion of the
soil light
response probe of Fig. 2.
Fig. 5 is a perspective view of the light manifold of the soil light response
probe.
Fig. 6 is a flow chart illustrating the operation of the soil light response
probe.
Fig. 7 illustrates the operation of a color sensing plow.
Like reference symbols in the various drawings indicate like elements.
DETAILED DESCRIPTION
Fig. 1 illustrates a test vehicle 16 adapted to collect in-field subsurface
data. Vehicle
16 includes a push system 23 for pushing cone penetrometer (CPT) probes 18 or
other
3o invasive sensors from the ground surface 114 into the soil 110 along a
selected path, either
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vertical or angled, at the end of a string of hollow push rods 17. These
probes can contain
sensors, known in the art, that are responsive to various soil properties. In
many cases,
signals from such sensors are relayed electrically or wirelessly up to the
push vehicle 16 for
logging and analysis. Penetrometer sensors can be used to measure or derive
soil
compaction, grain size, moisture, temperature and resistivity, as well as
other chemical and
physical properties. Some such sensors are available from Geoprobe Systems,
Inc., of
Salina, Kansas, and Applied Research Associates Inc., of South Royalton,
Vermont. A probe
controller 19 on-board vehicle 16 collects data from deployed sensors 18, with
data from in-
ground sensors correlated with depth as determined from a depth gage 22, and
communicates
1 o the data to an acquisition laptop computex 24, which also receives
geographic position from
an on-board global positioning system (not shown). The on-board data
acquisition computer
is also capable of integrating data collected from sensors with pre-existing
data for the site to
develop a site map, and/or relaying raw or processed data off-site via mobile
telecommunications link, as described in pending patent application number
09/998,863,
published as US2003/0083819 A1.
Fig. 2 shows the exterior of a soil light response probe 21 for use with the
test vehicle
16 shown in. Fig. 1. Probe 21 includes a housing 30, a window 38 mounted in an
opening in
the housing, and a conical tip 48 to facilitate penetration into the ground.
'The window 38 is
mounted in an opening 40 in a flat area 39 machined in the outer diameter of
the body of the
2o housing. The window is substantially flush with the flat area 39. This
insures that soil is in
contact with the window 38, for better illumination. The housing 30 is of
robust design and
constructed of hardened steel to withstand the high loads and abrasion that
result from being
pushed into the ground up to about six feet by a hydraulic ram system:
As shown in Fig. 3, housing 30 defines a push or force axis 32. Housing 30 has
an
upper section'30a and a lower section 30b, held together by a slip fit and a
dog-point set
screw 58. Housing 30 also has an outer surface 34 exposed for sliding contact
with soil as
the housing 30 is pushed or pulled through the soil. An interior cavity 36 of
the probe
contains a light source 42, a photo-detector 44, and a circuit board 66. The
window 38 in the
probe shown in Figs. 2 and 3 provides optical communication between the soil
and the
3o interior cavity 36 of the probe 21. The light source 42 is directed toward
the window 38 for
illuminating the soil in situ alternately with light of three discrete
wavelengths. The photo-
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detector 44, also directed toward the window 38, is responsive to light of
these three
wavelengths as reflected from the soil ifa situ. The light source 42 is
connected to the circuit
board 66 by four leads 43 (Fig. 4).
A suitable light source 42 is available from LEDtronics, Inc.,
http://www.ledtronics:com/, as part number DIS-1024-005A. This light source
package
contains three light-emitting diodes (LEDs), a red LED operating at a
wavelength of about
660 nanometers, a green LED operating at a wavelength of about 586 nanometers,
and a blue
LED operating at a wavelength of about 430 nanometers, in a single, 4-wire LED
package. ,
Other light sources 42, providing different numbers or wavelengths of emitted
light,
including non-visible wavelengths in the infrared range or ultraviolet range,
are also
envisioned. The light source should be capable of independent emission of each
of the
desired wavelengths.
A suitable photo-detector 44 is available from Texas Instruments;
http://www.ti.coml,
as part number TSL230A. This device outputs a signal with a frequency that is
proportional
15 t0 the amount of light incident on the sensing element. Other devices, such
as the Burr-
Brown OPT301 integrated optical sensor, which produces a voltage output
proportional to
the amount of light incident on the sensing element, are also suitable.
A suitable window 38 is available from Edmund Industrial Optics,
http://www.edmundoptics.com/, as part number NT43-630, whichis a 10.15
millimeter
2o diameter and 1.4 millimeter thick sapphire disk. Sapphire is preferred for
its exceptional
hardness and superior abrasion resistance in coordination with its good
optical properties.
The window may be secured directly in a bore in the housing wall with epoxy.
The light source 42 and the photo-detector 44 are mounted on the circuit board
66,
which is held in place within the internal cavity by being secured in a slot
in an upper sleeve
2s 60, and may be held in the slot using epoxy. A set screw 56 secures the
upper sleeve in
place after the circuit board 66 and upper sleeve 60 are inserted into the
housing 30 and
rotated to position light source 42 and photo-detector 44 in alignment with
window 38.
Associated wiring 68 extends from the circuit board 66 to an electrical
connector 70 at an
upper end of the housing 30. The electrical connector interfaces with a
data/pover
3o transmission cable 26 (Fig. 1) extending down to the probe from the ground
surface.
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Probe 21 also includes a geotechnical sensor section at its lower end. O-rings
50 are
used to seal the geotechnical sensor section. The geotechnical sensor section
includes strain
gages to measure soil-applied load as the probe is advanced through the soil,
as known in the
field of cone penentrometers. One set of strain gages 52 measures shear stress
applied to a
sleeve 46 immediately behind the removable tip 48. A second set of strain
gages 54
measures the normal load applied to tip 48 parallel to the probe axis as the
probe is pushed
into the soil. Associated wiring 62 extends from the strain gages 52, 54 to an
electrical
connector 64 at an upper end of the housing 30. Wiring 62 is preferably
coaxial cable to
minimize interference with data signals. Electrical connector 64 interfaces
with data/power
1o transmission cable 26 (Fig. 1) extending down to the probe from the ground
surface.
As shown in Fig. 4, transmitted light 74 from light source 42 is directed
toward
window 38 through channel 78 of light manifold 72. Reflected light 76 (i.e.,
light reflected
by the soil) is directed toward photo-detector 44 through channel 80 of light
manifold 72.
Light manifold 72 blocks direct incidence of transmitted light 74 upon the
photo-detector 44.
15 As shown on Fig. 5, light manifold 72 has an arcuate upper surface 84 that
mounts
snugly against an inner surface 86 (Fig. 4) of the upper section of the probe
housing. Light
manifold 72 is machined from a solid piece of aluminum and defines an undercut
cavity 86
for placement of the photo-detector, and a bore 82 into which the light source
is mounted.
Light manifold 72 also defines a transmitted light channel 78 leading from
bore 82 to upper
2o surface 84, and a separate, reflected light channel 80 leading back from
upper surface 84 to
cavity 86. As their names imply, transmitted light 74 is directed toward the
window through
the transmitted light channel, and reflected light 76 is directed toward the
photo-detector
through the reflected light channel.
A microprocessor associated with probe controller 19 (Fig. 1) operates probe
21 to
2s perform the steps shown in Fig. 6. The microprocessor turns on each of the
colors in the
LED package (one at a time, in sequence) while recording the output of the
photo. sensor,
thus measuring an amount of light reflected from the soil at each of the three
wavelengths of
light that the LED package produces.. The microprocessor also measures the
output from the
tip and sleeve load sensors. After power up, the microprocessor turns on only
the red LED
3o and records the amount of reflected light for approximately 0.125 seconds.
Next, the
microprocessor turns on only the green LED and records the amount of reflected
light for
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approximately 0.125 seconds. Next, the microprocessor turns on only the blue
LED and
records the amount of reflected light for approximately 0.125 seconds. The
microprocessor
then records the probe depth and the output from the strain gages. The
microprocessor
checks the battery voltage and sounds an alert signal if the battery voltage
is low. The
microprocessor then transmits the data as a digital sequence to the data
acquisition computer.
Under normal operating conditions, this cycle is repeated on an ongoing basis
until the
system is powered down.
Refernng back to Fig. 1, an ultrasonic distance measurement device 22 mounted
on
the vehicle monitors the depth of the sensor in the ground and the
microprocessor logs the
io output of the depth sensor to correlate all measurements to depth. The
system is powered by
a battery, and the battery voltage is 'also monitored by the microprocessor.
As data is
collected, the data is sent out by the microprocessor as plain text over a
serial interface line
(RS-232) 28 to a personal computer.24. The personal computer is used to record
the data,
display the data graphically, and apply any calibration factors or unit
conversions.
Referring to Fig.7, a color sensor plow 100 measures soil color properties
while
traveling horizontally through soil 110 along a force axis 102. A window 3~ is
mounted in
an opening in the body 104 of the plow. Preferably, the window 3~ is
positioned on a plow
blade 106 so as to be in substantially continuous contact with the soil 110
without receiving
direct impact load of the soil 110 while plowing. Wiring 112 provides data and
power
2o transmission between a controller on a tractor (not shown) pulling the
color sensor plow I00
Alternatively, sensor components in the plow body 104 could be powered by a
local battery
with data transmitted wirelessly.
The color sensor described above may also be combined in a single probe with
other
sensors, such as those responsive to soil density, texture, moisture,
resistivity, temperature or
imagery. The output from the various sensors is preferably correlated to depth
or field
position (such as with a depth gage and/or a global positioning system) so as
to enable the
association of sensor output with vertical and/or lateral position in the
soil. The color sensor
can also be deployed in a probe driven into the soil to shallow depths by
hand. In addition to
pushing the probe into the soil, it is also conceivable that a device
containing the color sensor
3o can be hammered into the subsurface or dragged at a given depth
horizontally across a field.
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In some applications, the color sensor is pushed into the soil at various
locations
across a field so as to create vertical color profiles. In agricultural
applications, these color
profiles typically will be created to a depth of approximately two meters. At
select locations,
soil can be removed from the ground in the form of a core sample directly
adjacent to the
location of the color sensor profile. The core can be analyzed by sending
various sections to
a laboratory to determine soil organic carbon content, nutrient levels
(nitrogen, phosphorous,
potassium), and color. These results are then used to calibrate the output of
the color sensor
to one of those measured properties for a particular site. Likewise, sections
of the core can
be analyzed for soil texture (grain size), bulk density and moisture for the
purpose of
1 o calibrating the sensors on the probe that are intended to indicate these
soil properties. Cores
only need to be taken at a few locations in order.to calibrate sensor response
for a given type
of soil. Core,samples or other objects of a known color can be held against
the color sensor
window to determine probe calibration factors. The probe can also be
calibrated with the
Munsell soil color chart. Each standard Munsell color chip can be placed over
the window
15 and the color of the chip plotted in three-dimensional R-G-B space. When
the probe is later
employed to obtain an R-G-B value of soil color in situ, the field R-G-B
values are plotted
into the same color space and a minimum distance-to-mean algorithm employed to
determine
which of the Munsell chips is closest to the field color measurement in
Euclidean space. The
output of the algorithm can be the identification of the closest Munsell soil
color, or a
2o weighted function of the three or four closest Munsell samples. Once a
database of sensor
response to specific soil types is determined, further core sampling may not
be necessary for
acceptable accuracy.
It has been shown in research studies that the percent soil organic matter in
a soil is
nearly linearly related to soil color within a given landscape. See, for
example, Shulze et al:,
25 "The Significance Of Organic Matter In Determining Soil Color", Soil Sci.
Soe. Amer,
Special Publ., No. 31, pp 71-90 (1993). Fertilizers and other nutrients have a
positive ionic
charge and are thus chemically adsorbed and held onto negatively charged
organic matter
particles. The more organic matter that a soil contains, both in concentration
and volume, the
higher the nutrient holding capacity. In addition, the texture and density of
a soil impacts the
3o ability of the soil to physically hold moisture. Since the nutrients are
often dissolved into soil
water, they will migrate through the soil with the water. By measuring the
soil texture and
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density, it is also possible to determine the physical nutrient holding
capacity of the soil
environment.
Once the vertical soil organic matter and nutrient holding capacity is
determined at
selected areas in a field, the conditions that exist between observations can
be interpreted.
r
This can be accomplished using a variety of spatial statistical routines that
estimate
conditions across the site in three dimensions. The resulting map can be
imported into
applications that utilize the information for decision support. For example,
the data can be
employed to modify the distribution of materials applied by a variable rate
fertilizer
applicator. Organic matter distribution data may also be employed to calculate
an overall
1 o carbon sequestration amount for a given field, such as for determining
carbon credits in a
carbon emission control program.
A number of embodiments of the invention have been described. Nevertheless, it
will
be understood that various modifications may be made without departing from
the spirit and
scope of the invention. Accordingly, other embodiments are within the scope of
the
1.5 following claims.
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