Commission errors, however, create algorithm havoc and must be minimized. After pass one processing, descriptive statistics are calculated from the cloud category using band 6. These include mean temperature, standard deviation, and distribution skew. New band 6 thresholds are developed from these statistics for use during pass two. Only the thermal band is examined during this pass to capture the remaining clouds.
Image pixels that fall below the new threshold qualify.
After processing, the pass one and two cloud cover scores are compared. Extreme differences are indicative of cloud signature corruption. When this occurs, the pass two results are ignored and the cloud score reverts to the pass one result. During processing, a cloud cover mask is created. After the two passes through the data, a filter is applied to the mask to fill in cloud holes.