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REMOTE SENSING

Sensitivity of Narrow-Band and Broad-Band Indices for Assessing Nitrogen Availability and Water Stress in an Annual Crop

^a Center for Precision Agric. Systems, Washington State Univ., 24106 N. Bunn Rd., Prosser, WA 99350
^b Geography Dep., Univ. of California, Santa Barbara, CA 93106-4060

^* Corresponding author (eileen_perry{at}wsu.edu).

We evaluated a suite of vegetation indices to detect treatment differences in nutrient and water availability in corn for areas larger and smaller than the ground sample diameter (GSD) from both a portable spectrometer and the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS). The ANOVA results for a N trial showed that indices based on the chlorophyll red-edge were more sensitive to differences in N treatment than those based on the visible and near infrared (NIR) regions only. Classifications of pixels for a spatial detection study using unfertilized strips with widths of 6 m, 12 m, 18 m, and 24 m were performed and scored as the percentage of correctly classified pixels. Generally, the indices using the red-edge produced more accurate detections, although none of the indices could detect nutrient stress in the 6-m strips based on 15-m imagery. A water stress study was set up in another location of the same field by withholding irrigation water. While the indices based on the chlorophyll red-edge outperformed others for N application detection, the visible and NIR indices differentiated water stress the best.

Abbreviations: AVIRIS, Airborne Visible/Infrared Imaging Spectrometer • CCCI, Canopy Chlorophyll Content Index • EWT, Equivalent Water Thickness • GSD, ground sample diameter • INT, integrated TCARI/OSAVI • LAI, leaf area index • MCARI, Modified Chlorophyll Absorption in Reflectance Index • NDVI, Normalized Difference Vegetation Index • NDWI, Normalized Difference Water Index • NIR, near infrared • NNDVI, Narrow-Band NDVI • NIR Rededge, Reciprocal Reflectance Red-edge • OSAVI, Optimized Soil Adjusted Vegetation Index • PRI, Photochemical Reflectance Index • R, reflectance • RVSI, Red-edge Vegetation Stress Index • TCARI, Transformed Chlorophyll Absorption in Reflectance Index • VARI, Visible Atmospherically Resistant Index • WDRVI, Wide Dynamic Range Vegetation Index • WI, Water Index

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Received for publication September 12, 2007.