Comments on different CZCS ringing mask algorithms

SeaDAS Mueller algorithm

1. The SeaDAS implementation follows the Mueller algorithm but also requires at least 3 bright target pixels before applying the mask.
2. Also, it does not calculate the excess brightness in the previous 50 pixels, only the previous contiguous set of pixels above the threshold (with an upper limit of 50).

SeaDAS Evans and Gordon 94 'Mueller' ringing mask

1. This uses the Lwn in band 2 (520 nm) downstream of a bright (in 750 nm Lt) target to determine the ringing mask using a threshold (> 0.7 is masked) and then a gradient (> 0.1 is masked), followed by a nextra 20 masked pixels.
2. The algorithm, as coded, does not appear to add the extra 20 pixel masking that Evans and Gordon specify. This is not an oversight, but a code error.

Watson Gregg's Evans and Gordon 94 'Mueller' ringing mask

1. One difference with E+G is that the Lt_750 / cos(solz) is used instead of Lt_750 to determine bright target. E+G discuss this as a possible change in the cloud mask
2. The logic in the code could miss applying the ring mask to some pixels. If a bright target occurs in extra added pixels (those 20 pixels after where the threshold and gradient tests are done), no ring mask will be computed for it.