Earth Science research at NASA has turned space-based observing technology and scientific expertise to the study of our home planet. Planet Earth is an integrated system of land, ocean, atmosphere, ice, and biological processes. From the vantage point of space, we are beginning to understand how these processes work and how they interact.
In order to support the intermediate and long term goals of understanding the Earth, NASA has developed numerous radio sensors designed to fly onboard spacecraft. These sensors may be passive or active in operation. They allow global "pictures" to be taken of the Earth on a daily basis in a wide range of frequencies. Passive sensors emit no energy; instead, they measure the natural emissions of the Earth's various features and its atmosphere at specific frequencies in order to provide a description of the earth's environment. Active sensors are spaceborne radars that provide information on the geological structure of the Earth and the state of and movement of Earth's oceans. The data collected by these sensors is transmitted by radio links to facilities on earth, either directly or through relay satellites.