are ndvi readings sensors dependent?
DESCRIPTION
Are NDVI Readings Sensors Dependent?. Tremblay, N., Z. Wang, B. Ma, C. Bélec and P. Vigneault St-Jean-sur-Richelieu, Quebec. Yara FieldScan (N-Sensor). Yara FieldScan (N-Sensor). GreenSeeker. Justifications. Variable N Rates Based on vegetation indices (e.g. NDVI) - PowerPoint PPT PresentationTRANSCRIPT
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Are NDVI Readings Sensors Dependent?
Tremblay, N., Z. Wang, B. Ma, C. Bélec and P. VigneaultSt-Jean-sur-Richelieu, Quebec
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Yara FieldScan (N-Sensor)
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Yara FieldScan (N-Sensor)
TouchScreen
Card DriveSpreader Controller
Irradiance Sensor
Left Sensors Right Sensors
Cab Top Mounted
In Cab Section
PC
DGPS or GPS (optional)
S2S1
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GreenSeeker
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Justifications
• Variable N Rates– Based on vegetation indices (e.g. NDVI)– Algorithms under development
• Importance of univariate population statistics in the design of fertilization algorithms (Pena-Yewtukhiw et al., 2006)– Divide the population into classes, and then treat each class
with a particular rate of fertilizer N• Are NDVI readings (therefore, the algorithms) sensors
dependent?
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Outfit For Devices Comparison v. 2007
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Sensors Sampling Density on Summer Wheat 2005
Yara FieldScan GreenSeeker
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Yara FieldScan Scanning Area as Compared to GreenSeeker Positions
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Yara FieldScan NDVI and GreenSeeker NDVI in Wheat
0.0 0.2 0.4 0.6 0.8 1.0NDVI_Yara
0.0
0.2
0.4
0.6
0.8
1.0N
DV
I_G
S
0.0 0.2 0.4 0.6 0.8 1.0NDVI_Yara
0.0
0.2
0.4
0.6
0.8
1.0
ND
VI_
GS
0.0 0.2 0.4 0.6 0.8 1.0NDVI_Yara
0.0
0.2
0.4
0.6
0.8
1.0
ND
VI_
GS
ZG
S23
(30
DA
S)
ZG
S30
(33
DA
S)
ZG
S41
(40
DA
S)
2005
0.0 0.2 0.4 0.6 0.8 1.0NDVI_Yara
0.0
0.2
0.4
0.6
0.8
1.0
ND
VI_
GS
ZG
S33
(42
DA
S) 2006
0.77
0.41
0.86
0.47
0.90
0.46
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Variability in Wheat Field 2006
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Wheat
• CV of NDVI values decreased with growth stages and were lower with the Yara FieldScan
• Yara FieldScan saturated earlier• However, in 2006, for NDVI lower than 0.5:
– NDVI_Yara’s CV: 26 % – NDVI_GS’s CV: 31 %
• GreenSeeker showed no progression with growth stage
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Yara FieldScan
• 50-100 m²/s• Scan at an
oblique view zenith angle (64° on average)
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Oblique vs nadir views
• Plant Chl concentration better predicted from oblique-looking reflectance measurements (Demetriades-Shah and Court, 1987)– Soil reflectance is reduced
• Spot area of oblique angle (45°) greater by 50 % (Poss et al., 2006)
• Saturates at lower values than nadir directions (Myneni and Williams, 1994)
• Likely more sensitive to canopy conditions at early stages
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Corn 2005
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Yara FieldScan NDVI and GreenSeeker NDVI in Corn
0.0 0.2 0.4 0.6 0.8 1.0NDVI_Yara
0.0
0.2
0.4
0.6
0.8
1.0N
DV
I_G
S
0.0 0.2 0.4 0.6 0.8 1.0NDVI_Yara
0.0
0.2
0.4
0.6
0.8
1.0
ND
VI_
GS
0.0 0.2 0.4 0.6 0.8 1.0NDVI_Yara
0.0
0.2
0.4
0.6
0.8
1.0
ND
VI_
GS
Ear
ly V
5 (4
2 D
AS
) V
5 (4
8 D
AS
)
V4
(43
DA
S)
20062005
0.32
0.30
0.64
0.47
x1.6 x2.0
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Yara Devices
• N-Sensor• FieldScan
– 550, 660, 700, 740, and 780 nm• N-Sensor ALS
Reusch et al., 2002
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Vegetation Indices and Saturation
• GreenSeeker
• NDVI from Yara FieldScan tend to saturate because of geometry• Optimized vegetation index
– VIopt = 100*(lnR780-lnR740), Reusch (2005) – Larger CV than NDVI on wheat
• ZGS 23 (8 vs 6 %)• ZGS 30 (8 vs 3 %)• ZGS 41 (9 vs 1 %)
– Other version: VIopt = 100*(lnR760-lnR730), Jasper et al. (2006)
http://www.ntechindustries.com/lit/gs/DataSheet_GS_Sensor.pdf
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Conclusions
• More similarities between sensors with corn than wheat• NDVI from Yara FieldScan saturated earlier
– Oblique view– Potentially more sensitivity at early stages; less at late stages– Let’s try GreenSeeker looking forward on small corn for more
sensitivity at early stages– Opportunities for more adapted indices from other bands
• Notably different NDVI population statistics depending on crop features and growth stages– Implications for algorithms development
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Acknowledgements
• M.Y. Bouroubi• GAPS program (Agriculture and Agri-Food Canada)• Summer students• synAgri for aSEC data collection• Éric Thibault (Pleine Terre s.e.n.c.)• Growers Landry, Bieri and Martel
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For more information: –Contact Nicolas Tremblay: [email protected] –web: http://res2.agr.ca/stjean/personnel/tremblay_e.htm
Thank You !