Comparison of Commercial Crop Canopy Sensors
Ken SudduthNewell Kitchen
Scott DrummondUSDA-ARS, Columbia, Missouri
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
Missouri VR-N research
ARS-Missourisystem
Implemented on a Spra-Coupe
Used a “binary nozzle” concept with 3 different valve manifolds
Spra-Coupe application system
Drop nozzles with 1x, 2x, and 4x orifice plates were installed in row middles to cover 6-row strip plots
Nominal application rates: 1x = 30 lb N/acre 2x = 60 3x = 90 4x = 120 5x = 150 6x = 180 7x = 210
Are Crop Circle and GreenSeeker sensor readings different?
0 0.2 0.4 0.6C rop C irc le R ow 2
0
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0.4
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Gre
enS
ee
ker
Ro
w 2
0 0.2 0.4 0.6C rop C irc le R ow 5
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Gre
enS
ee
ker
Ro
w 5
G S = 1.24 C C - 0.903 G S = 1.24 C C - 0.903
They’re not identical, but since they follow a straight line, we can use either one – if the rate equation is adjusted correctly
Comparison of application rates – Not much difference
4349150
4349200
4349250
4349150
4349200
4349250
N tech Sensor 2
C rop C ircle Sensor 3
N R ates
1 2 3 4 5 6 7
Crop Circle
GreenSeeker
Most of our early data analysis and interpretation was with Crop Circle (ACS-210) data – how do GreenSeeker and Topcon CropSpec sensors compare?
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
Missouri VR-N research
Materials and methods - Sensors
Topcon CropSpec
NTechGreenSeeker
Holland Scientific Crop Circle ACS-210
Topcon CropSpec
NTechGreenSeeker
Holland Scientific Crop Circle ACS-210
Materials and methods - Sensors
Holland Scientific
Crop Circle ACS-210
NTech Industries
GreenSeekerModel 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 NadirOblique, 45 to
55º
Field of view / sensing footprint
32º x 6º
61 x 1.5 cm(~ constant over height
range)
2 to 4 m wide(~ proportional to height above
target)
Materials and methods - Sensors
Holland Scientific
Crop Circle ACS-210
NTech Industries
GreenSeekerModel 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 NadirOblique, 45 to
55º
Field of view / sensing footprint
32º x 6º
61 x 1.5 cm(~ constant over height
range)
2 to 4 m wide(~ proportional to height above
target)
Sensor geometry as used in previous field research: Crop Circle and GreenSeeker on rows 2 and 5 of 6-row pass; CropSpec from adjacent runs
Data collected at 10 Hz from Crop Circle and GreenSeeker; 1 Hz from CropSpec
Data collection plots
Response blocks with 8 N rates
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
Reflectance data collected multiple times Corn height ~ 1 to 1.5 m
Pass averages calculated and used for analysis
Auxiliary data collection
Corn height Indicator of total biomass
SPAD chlorophyll meter reading
Indicator of leaf N concentration
2 3 4 5Leaf N, %
30
40
50
60
SP
AD
Rea
din
g
n = 48R2 = 0.84
from Sudduth et al., 2010
Results
Comparing Crop Circle and GreenSeeker relative NDVI
0.2 0.4 0.6 0.8 1 1.2NDVI Crop Circle
0.2
0.4
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0.8
1
1.2
ND
VI G
reen
See
ker
Y = 1.11 * X - 0.0994n = 64R2 = 0.99
0.2 0.4 0.6 0.8 1 1.2NDVI Crop Circle
0.2
0.4
0.6
0.8
1
1.2
ND
VI G
reen
See
ker
Y = 1.38 * X - 0.365n = 64R2 = 0.90
16 July, 1450 Data Run 23 July, 944 Data Run
Comparing Crop Circle and CropSpec relative NDVI
0.2 0.4 0.6 0.8 1 1.2NDVI Crop Circle
0.2
0.4
0.6
0.8
1
1.2
ND
VI C
ropS
pec
Y = 1.27 * X - 0.346n = 55R2 = 0.73
0.2 0.4 0.6 0.8 1 1.2NDVI Crop Circle
0.2
0.4
0.6
0.8
1
1.2
ND
VI C
ropS
pec
Y = 0.544 * X - 0.471n = 64R2 = 0.64
16 July, 1450 Data Run 23 July, 944 Data Run
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)
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Corn Height 0.65m Corn Height 1.25m
Comparing relative NDVI
GreenSeeker and Crop Circle highly correlated
More differences between CropSpec and the two nadir sensors
Sensed area of the two sensors Data not collected simultaneously
(generally from adjacent run, < 5 min time difference)
Slope and offset considerations
0.2 0.4 0.6 0.8 1 1.2NDVI Crop Circle
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0.4
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1.2
ND
VI G
reen
See
ker
0.2 0.4 0.6 0.8 1 1.2NDVI GreenSeeker
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ND
VI C
rop
Spe
c
0.2 0.4 0.6 0.8 1 1.2NDVI Crop Circle
0.2
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0.8
1
1.2
ND
VI C
ropS
pec
Y = 0.544 * X - 0.471n = 64R2 = 0.64
Y = 1.38 * X - 0.365n = 64R2 = 0.90
Y = 0.752 * X + 0.143n = 64R2 = 0.55
16 July, 1450 Data Run
0.2 0.4 0.6 0.8 1 1.2GreenSeeker NDVI, 944 run
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Gre
enS
eeke
r N
DV
I
1217 run1452 run 903 run
0.2 0.4 0.6 0.8 1 1.2Crop Circle NDVI, 944 run
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Cro
p C
ircle
ND
VI
0.2 0.4 0.6 0.8 1 1.2CropSpec NDVI, 944 run
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Cro
pSp
ec N
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1:1 line
1:1 line1:1 line
Temporal stability of sensor data
Temporal stability of sensor data
Data from all three sensors exhibited stability over a period of >7 hours (r ≥ 0.92)
GreenSeeker slightly more variable over time Possible reasons for temporal differences:
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
30 35 40 45 50 55 60SPAD Reading
0.2
0.4
0.6
0.8
1
1.2
ND
VI C
rop
Spe
c
Y = 0.0250 * X - 0.349n = 64R2 = 0.90
30 35 40 45 50 55 60SPAD Reading
0.2
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0.8
1
1.2
ND
VI G
reen
See
ker
Y = 0.0165 * X + 0.140n = 64R2 = 0.70
30 35 40 45 50 55 60SPAD Reading
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0.8
1
1.2
ND
VI
Cro
p C
ircle
Y = 0.0151 * X + 0.207n = 64R2 = 0.73
Relating sensor data to SPAD
CropSpec most strongly related to SPAD
0.8 1.2 1.6 2Corn Height (m)
0.2
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1
1.2
ND
VI
Cro
p C
ircle
Y = 0.381 * X + 0.359n = 64R2 = 0.82
0.8 1.2 1.6 2Corn Height (m)
0.2
0.4
0.6
0.8
1
1.2
ND
VI C
ropS
pec
Y = 0.472 * X + 0.133n = 64R2 = 0.54
0.8 1.2 1.6 2Corn Height (m)
0.2
0.4
0.6
0.8
1
1.2
ND
VI G
reen
See
ker
Y = 0.430 * X + 0.289n = 64R2 = 0.83
Relating sensor data to crop height
GreenSeeker and Crop Circle more strongly related to corn height
Sensors vs. biophysical data
CropSpec more predictive of SPAD (N) Oblique view minimized height/distance effect Sensed lower leaves where N was more strongly
expressed Crop Circle and GreenSeeker more predictive
of height (biomass) Effects of distance and also mixed soil/plant scene
Summary
In a comparison of three commercial crop canopy sensors:
Pass-average relative NDVIs from all three sensors were strongly correlated
Highest correlation between Crop Circle and GreenSeeker Relative NDVI from all sensors was stable over time
Slightly more temporal variability with GreenSeeker Relative NDVI from all sensors was related to both crop
height (biomass) and SPAD (N concentration) CropSpec data most strongly affected by SPAD CC and GS more strongly affected by crop height/biomass
Summary
Can CropSpec data be used in existing algorithms developed for Crop Circle or GreenSeeker?
Appropriate slope and offset compensation would be required Additional field research is needed to determine stability of
slope and offset values over different crop conditionsBecause 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
Very narrow range in 2011 sensor data
Similar growth stage and crop height to 2010 data
2012--- #1?#
0.6 0.8 1NDVI Crop Circle
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0.8
1
ND
VI G
reen
See
ker
2010 data2011 data
0.8 1.2 1.6 2 2.4R atio ta rget/R atio re ference
40
80
120
160
200
240
Nra
te, l
bs N
/acr
e
Crop C ircle V6-V7G reenSeeker V6-V7Crop C ircle V8-V10G reenSeeker V8-V10
Missouri algorithm graphically
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
Notes: 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.