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Example of leaf and soil spectra. The REIP is the point of maximum slope in the spectrum of a leaf. A healthy leaf has a broader spectral absorption in the red (680 nm) and REIP occurs at a longer wavelength, as compared to a stressed leaf. 

Example of leaf and soil spectra. The REIP is the point of maximum slope in the spectrum of a leaf. A healthy leaf has a broader spectral absorption in the red (680 nm) and REIP occurs at a longer wavelength, as compared to a stressed leaf. 

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High spatial resolution airborne imagery was acquired in California's Napa Valley in 1993 and 1994 as part of the Grapevine Remote sensing Analysis of Phylloxera Early Stress (GRAPES) project. Investigators from NASA, the University of California, the California State University, and Robert Mondavi Winery examined the application of airborne digita...

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... NDVI highlights differences in vegetation canopy reflectance. Healthy vegetation has strong absorbance characteristics in the red portion of the electromagnetic spectrum (EMS), while also reflecting strongly in the NIR portion of the EMS. These properties are due to the interaction of light with the chlorophyll in the plant tissue, Figure 1. Subtle changes in vegetation vigor or leaf chlorophyll composition result in subtle alterations in absorbance and reflectance characteristics. These characteristics are then highlighted in the NDVI. The index is near zero for bare soil, but can be close to 1.0 for a dense, healthy canopy. The NDVI was used because it lessens the influence of solar illumination, angular influences, slope, and viewing geometry. It performs consistently between sensors, for different flights, and within the images. NDVI is also correlated to leaf area index (LAI), or canopy leaf amount, and biomass (Tucker 1979). The index compensates for brightness differences and highlights the spectral differences between pixels. Absolute NDVI's were not directly comparable because of year-to-year differences in non- canopy variables and non-phylloxera related growth effects. Non-canopy variables include calibration differences (the CASI data were calibrated to radiance versus the raw EO Camera data), atmospheric conditions (weather conditions and aerosol concentration), and solar illumination angle differences. Year to year plant growth differences could be also be a response to other factors, including other plant stresses, changes in management practices, and increased rainfall (i.e., more irrigation) in 1994. However, if the range of NDVI values within the images is represented by classes, then relative values (classes) in the images from the same areas on ...

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