Extraction of target-specific spectral reflectance from remote observations

The usual goal of aircraft and satellite remote sensing is to extract information which is directly related to ground targets in spite of atmospheric degradation which often complicates target identification and classification. Empirical algorithms which attempt to characterize targets by their spectral shape (slope, curvature, etc.) have been successful under special conditions, but fail when spectral variations in the solar or atmospheric parameters overwhelm those of the target reflectance. It is possible to derive an algorithm based on derivatives of the radiative transfer equation. This makes it possible to define the conditions under which a derivative algorithm will be insensitive to atmospheric effects and allows estimation of expected errors. This paper describes the development of the "derivative ratio algorithm," based on derivatives of a simple radiative transfer equation. The limiting conditions of the algorithm are derived and demonstrated using examples of reflectance spectra of turbid water and an ash leaf.