The first section in JetStream, The Atmosphere, provided information about the Earth-Atmosphere energy balance. That section refers to the total combined energy received from the sun and emitted by the earth and atmosphere.
However, not all wavelengths of electromagnetic radiation from the sun reach the earth and not all wavelengths emitted by the earth reach into space. The atmosphere absorbs some this energy while allowing other wavelengths to pass through.
The places where energy passes through are called "atmospheric windows". We use these "windows" in remote sensing to peer into the atmosphere from which we can obtain much information concerning the weather.
Most of the sun's energy comes from visible light and the near infrared portion of the electromagnetic spectrum. All of the outgoing energy emitted by the earth is infrared.
The dips in the incoming and outgoing energy are where the atmosphere absorbs energy. Some of the incoming energy is absorbed by the atmosphere whereas most of the infrared energy emitted by the earth is absorbed.
Taking advantage of these "windows", we look at the atmosphere at various wavelengths. Each of these channels where chosen to provide different views of the earth.
The different channels we use to peer into the atmosphere are based upon the technology at the time each satellite was built and their particular orbit.