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

0.2

0.4

0.6

Gre

enS

ee

ker

Ro

w 2

0 0.2 0.4 0.6C rop C irc le R ow 5

0

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0.6

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

0.6

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)

0

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9

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

0.2

0.4

0.6

0.8

1

1.2

ND

VI G

reen

See

ker

0.2 0.4 0.6 0.8 1 1.2NDVI GreenSeeker

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1

1.2

ND

VI C

rop

Spe

c

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

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

0.2

0.4

0.6

0.8

1

1.2

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

0.2

0.4

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1

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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

DV

I

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

0.4

0.6

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

0.2

0.4

0.6

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

0.4

0.6

0.8

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

0.6

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.