The “Lee Sigma” filter for filtering intensity data implements the “improved Lee sigma filter” algorithm given by [1].
The “improved Lee Sigma” filter for filtering polarimetric data implements the “extended Lee sigma filter” given by [2].
[1] Lee J S, Wen J H, Ainsworth T L, et al. Improved Sigma filter for speckle filtering of SAR imagery. IEEE Transactions on Geoscience Remote Sensing 2009; 47(1): 202-213.
[2] Lee, J. S., Ainsworth , T. L., Wang, Y. & Chen, K. S. 2015. Polarimetric SAR Speckle Filtering and the Extended Sigma Filter. IEEE Transactions on Geoscience and Remote Sensing, 53, 1150-1160.