GOES Sounder Longwave IR (channel-8 minus channel-6) Difference

This product is the temperature difference between two longwave IR channels of the GOES Sounder, channel-8 (11 µm) a "clean" window channel and channel-6 (12 µm) a "dirty" window with some atmospheric absorption. The temperature difference between these channels is usually positive, with small negative differences possible. Larger positive differences (dark areas) are usually caused by differential transmission thru semi-transparent ice clouds, such as cirrus; and smaller positive differences (lighter gray areas) are normally observed over land. These smaller differences are the result of differential absorption usually due to low-level moisture, with more moisture causing more difference between the channels (darker as opposed to lighter areas). However moisture is not the only cause of a difference between the channels. Small differences between the channels may also be the result of ground surfaces with low emissivity (less than the assumed emissivity of 1.0) or may be the result of surface temperature inversions. These inversion sometimes cause negative differences between the channels (the whitest areas).