Infrared satellite imagery is an important remote sensing tool for meteorologists. Infrared (IR) satellite images are simply a picture from above of the temperature of clouds or other features at or above the surface of the earth. Usually, when areas appear colored, as in the yellow area on the image below, that indicates mid or high level clouds which have cold tops. In this example from Thursday evening, however, the yellow area is actually being detected in an area of clear skies. The temperatures being detected are from extremely cold air at the surface (notice the -17F observation near the middle).
If you were to look at a topographic image of this area, you would also notice that the area with the coldest temperatures is also an area of lower terrain. Colder air is denser and tends to settle in valleys and other low spots.
Other features that cause sharp temperature differences at or near the surface can also be detected with IR satellite, such as wild fires. Here is an example of a wild fire detected on IR satellite in New Jersey in 1995.