Microwave radiation reaching the SSM/I and AMSU sensors results from atmospheric, cloud, and surface contributions within the 19 to 200 GHz portion of the microwave spectrum. These contributions are made up of complex interactions including emission by water vapor, emission and scattering by water and ice in clouds, as well as emission and scattering by ocean and land surfaces. By selecting the frequencies at the top of the graphic, you can see corresponding illustrations and image examples that emphasize how these individual contributions vary. This variation with frequency is what makes retrieval of the many meteorological parameters such as water vapor, rain rate, and snow cover possible.

One of the biggest strengths of microwave measurements from space is that atmospheric phenomena -- such as clouds, precipitation, temperature, and moisture -- and surface features are detected and discriminated in the presence of clouds. Keep this in mind as you review the individual products and applications in later sections.

Another advantage of microwave sensing is that frequencies below 200 GHz are relatively insensitive to cirrus clouds. This lack of sensitivity to cirrus removes a significant constraint present in visible and infrared remote sensing applications.