The CZCS instrument normally delivers a voltage response to the light intensity in a scene in a linear manner, making it useful for scientific work. However, if it encounters a very bright source, such as cloud tops and some land features, the detectors will not give accurate measures of the far less intense down-scan features. This ringing needs to be either corrected or masked from processing.
Several masking techniques used in past processings were examined. They fall into 2 categories:
Based on the tests of both methods, it was decided to use the Mueller ringing mask in CZCS processing. In the process of examining the methods, several problems were also found in the previous algorithmic implementations.
As was mentioned before, the Mueller mask works very well with bright clouds but over-corrects frequently off of coastal sites. The technique was modified to apply the mask based on the amount of saturation in the other visible bands. This modification was found to mask ringing well while retaining more samples in coastal regions. This was the masking algorithm adopted for the processing.