Removing the influence of the atmosphere is a critical pre-processing step in analyzing images of surface reflectance. Properties such as the amount of water vapor, distribution of aerosols, and scene visibility must be known. Because direct measurements of these atmospheric properties are rarely available, they must be inferred from the image pixels. Hyperspectral images in particular provide enough spectral information within a pixel to independently measure atmospheric water vapor absorption bands. Atmospheric properties are then used to constrain highly accurate models of atmospheric radiation transfer to produce an estimate of the true surface reflectance.

The Atmospheric Correction Module provides two atmospheric correction modeling tools for retrieving spectral reflectance from multispectral and hyperspectral radiance images: QUick Atmospheric Correction (QUAC®) and Fast Line-of-sight Atmospheric Analysis of Spectral Hypercubes (FLAASH®). You must have a separate license for the ENVI Atmospheric Correction Module; contact your sales representative for more information.

QUAC and FLAASH were developed by Spectral Sciences, Inc., under sponsorship from the U.S. Air Force Research Laboratory. Spectral Sciences has developed several modern atmospheric radiation transfer models, and has worked extensively on MODTRAN since the model’s inception in 1989.