The IR channel senses radiation emitted by the earth’s surface as a function of temperature. You can see various surface features such as land, snow, and water that have large temperature differences. This happens along the coastline when the water is warmer or cooler than the adjoining land surface. When the land and water are almost the same temperature, the coastline is no longer distinct.

Areas of snow will appear light gray in comparison to snow-free land areas, which appear to get darker as the land warms during the day. Another clue for identifying snow on satellite imagery is that snow areas are stationary while clouds are in motion.