The shortwave IR channel is in a wavelength region where significant radiation comes from both solar and terrestrial infrared emission. At 3.7 µm, water and ice have different reflective properties. This difference can be used to detect snow and ice on the ground during daytime and distinguish water clouds from ice clouds.

By differencing the 3.7- and 11-µm channel brightness temperatures, a product can be generated that helps with the detection of fog and stratus at night. The change in emissivity for water droplets from 3.7 to 11 µm is significant when compared with emissivity changes for ice particles. This results in an observed brightness temperature difference between the 3.7- and 11-µm channels that can be easily computed, displayed, and then used to identify water clouds. Because these channels only see brightness temperatures at cloud top, surface observations or at least a thorough knowledge of local effects is needed to infer the presence of fog and stratus clouds.

This difference product can also aid in identifying supercooled water clouds. First, water clouds are identified using the 3.7/11-µm channel difference product. Then the 11-µm channel cloud-top brightness temperatures can be used to help identify clouds that contain supercooled water and therefore pose a risk for aviation icing.