A recent addition to the RAW_SCREEN process is the module
that flags pixels which are potentially affected by the Data Multiplexer
Unit (DMU) corruption which arose in late 1994. The DMU corruption of
the raw image is such that pixels between a certain DN range may be
assigned erroneously a DN value of 159. A raw image screening algorithm
using statistical methods was developed by VILSPA which singles out
images that have abnormally high numbers of pixels at DNs of 159 and
thus are likely to have been affected by the DMU problem. This image
screening process is only run on images taken after October of 1994.
There is no way to tell which specific pixels with DN=159 have been
affected by the DMU corruption. As a result, in images which the
screening process has identified as suspect, all pixels with DN
values of 159 are flagged (with 
flag=-8) as possibly being
corrupted.