Satellite Eyes - Seeing Beyond the RainbowSatellites like Landsat can have sensors which "see" in visible light, but they may also be able to record radiation (such as infrared) that it is beyond our capability to see.
The Electromagnetic Spectrum
Visible light is
only one kind of electromagnetic radiation that satellites can monitor.
Infrared and radar are also part of the electromagnetic spectrum, and
each represents radiation in a different wavelength. For example, yellow
light has a longer wavelength than blue, and red is longer than yellow.
Infrared and radar wavelengths are longer still. By collecting data in
different regions of the spectrum, satellites can reveal information that
would go undetected by our eyes alone.
Thermal infrared image from the Heat Capacity Mapping Mission (HCMM). This scene covers 15 times the area of a Landsat frame but can only resolve features larger than 600 meters (about 1900 feet). The warmest areas of the region, which show up in the lightest tones, are the deserts of Arizona and Mexico. Thermal imagery can reveal important information on the temperature and properties of surface materials. (26k jpg)
image from the Seasat mission. The smooth surface of the dune field appears
dark, while the rough texture and orientation of the mountains give them
a brighter appearance. The light and dark patterns in the Sea are due
to variations in the water surface caused by the blowing wind. (45k jpg)
Digital images of the Capitol area of Washington, D.C., from three different spectral bands are combined into a "false-color" composite. The colors are called "false" because any primary color can be assigned to any band. Thus, vegetation can be featured in red by assigning this color to a near infrared band. Vegetation is very reflective in the near infrared and, therefore, has high brightness values in this band.
Images processed at the Center for Earth and Planetary Studies