Yield Estimation from Hyperspectral Imagery Using Spectral Angle Mapper (SAM)
2008
Yang, Chenghai | Everitt, J. H. | Bradford, Joe M.
Vegetation indices (VIs) derived from remotely sensed imagery are commonly used to estimate crop yields. Spectral angle mapper (SAM) provides an alternative approach to quantifying the spectral differences among all pixels in an image and therefore has the potential for mapping yield variability. The objective of this study was to apply the SAM technique to airborne hyperspectral imagery for mapping yield variability. Airborne hyperspectral imagery was acquired from two grain sorghum fields in south Texas, and yield data were collected using a grain yield monitor. SAM images were generated from the hyperspectral images based on six reference spectra extracted directly from the hyperspectral images and four reflectance spectra measured on the ground. Statistical analysis showed that the ten SAM images for each field produced similar correlation coefficients with yield. For comparison, all 5151 possible narrow-band normalized difference vegetation indices (NDVIs) were derived from the 102-band images and related to yield. Results showed that the SAM images based on the soil reference spectra provided higher correlation coefficients with yield than 75% and 92% of the 5151 narrow-band NDVIs for fields 1 and 2, respectively. Like an NDVI image, a SAM image can be easily generated from a hyperspectral image to characterize the spatial variability in yield. Moreover, since the best NDVI typically varies with yield datasets, a SAM image based on a single reference spectrum can be a better representation of yield variability if actual yield data are not available for the identification of the best NDVI. The results from this study indicate that the SAM technique can be used alone or in conjunction with other VIs for yield estimation from hyperspectral imagery.
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