April 16 MAS tri-spectral analysis

Tri-spectral brightness temperarture differencing can be used to differentiate thermodynamic phase of clouds. This figure demonstrates the technique. A scatter diagram of 8-11 micron versus 11-12 micron brightness temperature differences from a section of the 16 April 1996 MAS data set shows a distinct arch pattern (top). This is indicative of ice cloud. The red points clustered with values < -2 K are clear scenes; they appear in the warmest section of the image when overlaid (bottom). The green areas are beginning to be influenced by the cirrus cloud, with the points clustering in a line from the clear region with a slope > 1. As the cloud becomes more opaque, less and less of the atmosphere and surface are observed, and the cloud signal reaches a maximum in the 8-11 micron brightness temperature difference, and then begins to bend back towards the origin (e.g. a black cloud). This simple technique has proven effective in identifying single layer, single phase cloud over fairly uniform backgrounds.