In the infrared channel, the satellite senses infrared energy at many wavelengths. This laboratory exercise concentrates only on the infrared wavelength interval of 10.2 to 11.2 micrometers. Energy from this wavelength interval is sensed as heat.

The earth’s surface absorbs about half of the incoming solar energy. Clouds and the atmosphere absorb a much smaller degree of solar energy. The earth’s surface, clouds, and the atmosphere then re-emit part of this absorbed solar energy as heat. The satellite senses heat in the infrared wavelength of 10.2 to 11.2 micrometers.

As some of this re-emitted energy passes up through the atmosphere, clouds and atmospheric gasses absorb a portion of the energy. The energy can then be re-emitted in the same wavelength range. Thus, the infrared channel is sensing radiation emitted by the earth’s surface, earth's atmosphere, and cloud tops.

A major advantage of the IR channel is that it can sense energy at night, so we have 24-hour access to this imagery. This is a disadvantage of the VIS channel which requires daylight and cannot "see" at night.

The IR image above gives us temperature information of the surface and cloud tops as a result of radiation being sensed by the satellite. You will learn to interpret imagery in the remainder of this section.