Transcript Dr. Ken Sudduth

Comparison of Commercial Crop
Canopy Sensors
Ken Sudduth
Newell Kitchen
Scott Drummond
USDA-ARS, Columbia, Missouri
Missouri VR-N
research
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Began on-farm research using canopy sensors in
2004
Field-length sensor-controlled strips and imbedded
small plots to define N response variability across
landscapes
Data were collected with GreenSeeker and Crop
Circle ACS-210; N application based on CC data
ARS-Missouri
system
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Implemented on a
Spra-Coupe
Used a “binary
nozzle” concept
with 3 different
valve manifolds
Spra-Coupe application system
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Drop nozzles with 1x, 2x, and 4x orifice plates were
installed in row middles to cover 6-row strip plots
Nominal application rates:
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1x = 30 lb N/acre
4x = 120
5x = 150
2x = 60
6x = 180
3x = 90
7x = 210
Are Crop Circle and GreenSeeker
sensor readings different?

They’re not identical, but since they follow a straight
line, we can use either one – if the rate equation is
adjusted correctly
GS = 1.24 CC - 0.903
GS = 1.24 CC - 0.903
0.6
GreenSeeker Row 5
GreenSeeker Row 2
0.6
0.4
0.2
0
0.4
0.2
0
0
0.2
0.4
Crop Circle Row 2
0.6
0
0.2
0.4
Crop Circle Row 5
0.6
Comparison of application rates –
Not much difference
Crop
Circle
Crop
Circle
Sensor 3
4349250
4349200
4349150
N Rates
GreenSeeker
Ntech Sensor 2
4349250
4349200
4349150
1
2
3
4
5
6
7
Missouri VR-N
research

Most of our early data analysis and interpretation
was with Crop Circle (ACS-210) data – how do
GreenSeeker and Topcon CropSpec sensors
compare?
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A 2009 study comparing commercial sensors gave
unexpected results
Study was redesigned and repeated in 2010
Three commercial sensors were compared based on:
 Relative NDVI
 Temporal stability
 Correlation to SPAD and crop height
Materials and methods - Sensors
Holland Scientific
Crop Circle ACS-210
Topcon
CropSpec
NTech
GreenSeeker
Materials and methods - Sensors
Holland Scientific
Crop Circle
ACS-210
NTech Industries
GreenSeeker
Model 505
Topcon CropSpec
Visible
wavelength
590 ± 5.5 nm
660 ± 15 nm
735 ± 5 nm
NIR wavelength
880 ± 10 nm
770 ± 15 nm
805 ± 5 nm
Height above
target
0.25 to 2.1 m
0.6 to 1.6 m
2 to 4 m
View direction
Nadir
Nadir
Oblique, 45 to
55º
32º x 6º
61 x 1.5 cm
(~ constant over
height range)
2 to 4 m wide
(~ proportional to
height above
target)
Field of view /
sensing footprint
Holland Scientific
Crop Circle
ACS-210
NTech Industries
GreenSeeker
Model 505
Topcon CropSpec
Visible
wavelength
590 ± 5.5 nm
660 ± 15 nm
735 ± 5 nm
NIR wavelength
880 ± 10 nm
770 ± 15 nm
805 ± 5 nm
Height above
target
0.25 to 2.1 m
0.6 to 1.6 m
2 to 4 m
View direction
Nadir
Nadir
Oblique, 45 to
55º
32º x 6º
61 x 1.5 cm
(~ constant over
height range)
2 to 4 m wide
(~ proportional to
height above
target)
Field of view /
sensing footprint
Materials
and
methods Sensors
Sensor geometry as used in previous field research:
Crop Circle and GreenSeeker on rows 2 and 5 of 6row pass; CropSpec from adjacent runs
Data collected at 10 Hz from Crop
Circle and GreenSeeker; 1 Hz from
CropSpec
Data collection
plots
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Response blocks with
8 N rates
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Reflectance data collected multiple times
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0 to 235 kg/ha on 34 kg/ha increments applied soon after
planting (0 to 210 lb/ac on 30 lb/ac increments)
Each plot 12 rows (9 m) wide by 15 m long
Two data passes with 6-row machine in each plot
2.5 m of data trimmed from each end, leaving center 10 m
Corn height ~ 1 to 1.5 m
Pass averages calculated and used for analysis
Auxiliary data collection
Corn height
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60
Indicator of total biomass
SPAD chlorophyll
meter reading
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Indicator of leaf N
concentration
from Sudduth et al., 2010
n = 48
R2 = 0.84
SPAD Reading
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50
40
30
2
3
4
Leaf N, %
5
Results
Comparing Crop Circle and GreenSeeker
relative NDVI
Comparing Crop Circle and CropSpec
relative NDVI
Mean crop height = 0.9 m
Mean crop height = 1.4 m
Different sensed areas
Crop Circle and GreenSeeker at 10 Hz (~60 points/sensor/plot)
CropSpec at 1 Hz (~6 points/sensor/plot)
Comparing relative NDVI
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GreenSeeker and Crop Circle highly
correlated
More differences between CropSpec and
the two nadir sensors
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Sensed area of the two sensors
Data not collected simultaneously (generally
from adjacent run, < 5 min time difference)
Slope and offset considerations
Temporal stability
of sensor data
Temporal stability of sensor data
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Data from all three sensors exhibited stability over a
period of >7 hours (r ≥ 0.92)
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Possible reasons for temporal differences:
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GreenSeeker slightly more variable over time
Driving misalignment between runs (nadir sensors)
Sensor variations (ambient light effects)
Ambient condition changes (leaf surface moisture, plant
alignment due to wind, etc.)
Physiological changes in the plants
Effects were not large in this study
Relating sensor
data to SPAD
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CropSpec most strongly
related to SPAD
Relating sensor
data to crop height
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GreenSeeker and Crop
Circle more strongly
related to corn height
Sensors vs. biophysical data
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CropSpec more predictive of SPAD (N)
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Oblique view minimized height/distance effect
Sensed lower leaves where N was more strongly expressed
Crop Circle and GreenSeeker more predictive of
height (biomass)
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Effects of distance and also mixed soil/plant scene
Summary
In a comparison of three commercial crop canopy sensors:
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Pass-average relative NDVIs from all three sensors were
strongly correlated
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Relative NDVI from all sensors was stable over time
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Highest correlation between Crop Circle and GreenSeeker
Slightly more temporal variability with GreenSeeker
Relative NDVI from all sensors was related to both crop
height (biomass) and SPAD (N concentration)
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CropSpec data most strongly affected by SPAD
CC and GS more strongly affected by crop height/biomass
Summary
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Can CropSpec data be used in existing algorithms
developed for Crop Circle or GreenSeeker?
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Appropriate slope and offset compensation would be required
Additional field research is needed to determine stability of slope
and offset values over different crop conditions
Because effects of biophysical parameters are different
for CropSpec than for Crop Circle and GreenSeeker
better results may be obtained with sensor-specific
algorithms
2011 Sensor comparison
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Very narrow range in
2011 sensor data
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Similar growth stage
and crop height to
2010 data
2012--- #1?#
240
Missouri
algorithm
graphically
Nrate, lbs N/acre
200
160
120
Crop Circle V6-V7
GreenSeeker V6-V7
Crop Circle V8-V10
GreenSeeker V8-V10
80
40
0.8
1.2
1.6
Ratiotarget/Ratioreference
2
2.4
Missouri algorithm developed from
previous plot research
Equations for calculating N rates (lbs N/acre) from active canopy sensors
Corn Growth Stage
Sensor Type
V6-V7 (1 to 1.5-ft tall corn)
V8-V10 (2 to 4-ft tall corn)
Crop Circle
(330 x ratiotarget / ratioreference) - 270
(250 x ratiotarget / ratioreference) - 200
GreenSeeker
(220 x ratiotarget / ratioreference) - 170
(170 x ratiotarget / ratioreference) - 120
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Notes:
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Maximum N rate should not exceed 220 lbs N/acre.
For V6-V7 corn, the value of ratioreference should not exceed 0.37 for
Crop Circle and 0.30 for GreeenSeeker. Set this as a ceiling.
For V8-V10 corn, the value of ratioreference should not exceed 0.25 for
Crop Circle and 0.18 for GreeenSeeker. Set this as a ceiling.