A software package for the transformation of atmospheric and illumination conditions (TASIC) has been implemented on the Canada Centre for Remote Sensing's Image Analysis System. This package offers three different transformations: (1) transformation to reflectance units; (2) transformation of illumination conditions; and (3) transformation to radiance units under standard atmospheric and illumination conditions.

Atmospheric parameters can be derived from four different sources. allowing users considerable flexibility. In particular, the method of obtaining atmospheric information from the LANDSAT signals from clear water bodies (Ahern et al. 1977 a, b) has been incorporated as one of the options. It offers high accuracy without the requirement of additional information derived from ground observations.

The TASIC procedure, including the acquisition of two-dimensional atmospheric information, is described in detail. Examples are given demonstrating the removal of atmospheric and solar illumination variations in a sequence of six LANDSAT images of the same area obtained between May and September 1976.

Systematic errors introduced by the uncertainty in the absolute calibration of the LANDSAT multispectral scanner are the most significant errors. The radiative transfer model used in the TASIC software also introduces significant systematic errors. Random errors are less important in the present procedures.

It is estimated that 60 to 90 percent of the variations due to atmospheric and illumination changes can be removed using the TASIC algorithm.

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