Radar instruments can operate in any type of weather and day or night. They record data either on film or convert light to electrical signals that are recorded digitally. Making observations in the light bandwiths beyond the visible part of the spectrum requires the use of detectors rather than film. These detectors are sensitive to reflected or emitted electromagnetic radiation in other parts of the spectrum and usually record the received signals digitally for transmission back to receivers on the Earth. Data from the various spectral regions can be used to complement one another and give a fuller, more accurate picture of Earth from space.
All matter emits energy at thermal infrared wavelengths.
This fact was recognized early by the military for reconnaissance applications in the 1950s, and has attained a high degree of sophistication, as witnessed by the startling images we saw from aircraft cockpits during the Desert Storm War. Ghostlike images of soldiers running from glowing tanks and radiant missiles homing in on buildings and vehicles are examples of how this phenomenon is exploited for military purposes. The wide area coverage and coarse spatial resolution of these weather satellite instruments are ideal for monitoring cloud patterns and ocean temperatures. Their routine use for weather prediction dramatically affects our everyday lives, and makes it less likely that we will leave the house without an umbrella. We are all familiar with the animated satellite cloud images shown on our local evening news programs.