What's the difference between landmask.dat, landmask_null.dat, landmask_dilated_25.dat, and watermask.dat in $SDSROOT/data/common? 

From a previous thread (here), it sounds like landmask_null.dat incorporates inland waterways somehow.  Is this correct?  And the other three?

The difference between landmask.dat and landmask_null.dat, is that landmask_null.dat will cause SeaDAS to treat every single pixel as ocean in case you want to process inland lakes and rivers that may otherwise be masked. I believe you need to set proc_land=1 when running l2gen for this to work. (See this post.)

Here is more info on the landmasks: http://oceancolor.gsfc.nasa.gov/forum/oceancolor/topic_show.pl?pid=232

RE watermask.dat, this is the shallow water mask input file used for setting the l2_flags bit to indicate shallow water (defined as 30m) areas.

Thanks, Mike!