[remote sensing]
A computed value within a raster dataset that is an arithmetic calculation of different spectral bands used to mitigate illumination effects of the terrain and accentuate phenomena based on spectral signature curves. For example, Normalized Difference Vegetation Index (NDVI) is a common calculation correlated with vegetation vigor [(NIR – Red) / (NIR +Red)]. Many image indices require that the gray levels in bands be transformed to either radiance or reflectance for inputs.