Many of which are already available using the GARP program. Detected wavelengths around 3.9 um. Is near enough to the visible that it detects a component of reflected sunlight, during the daytime of course.
Ice clouds appear dark.
When used with the 10.7 um imagery, regions with super-cooled water clouds can be determined. Can even observe smaller scale features missed by the synoptic network. The actual layer which is 'viewed' changes depending on moisture and temperature characteristics of the atmosphere. Generally drier and warmer conditions result in viewing lower into the atmosphere. Need to be looped to get the full amount of information.