Rainfall is also a major source of energy that drives the circulation of the atmosphere. Surprisingly, tropical rainfall comprises more than two-thirds of global rainfall. TRMM is the first mission dedicated to measuring tropical and subtropical rainfall through microwave and visible infrared sensors, and includes the first spaceborne rain radar. These new measurements will increase our knowledge of how rainfall releases heat energy to drive atmospheric circulation. Multi-year science data sets yielded by TRMM will be vastly more informative than any now available.
Additional satellites built for studying the Earth are soon to follow.
Slated for launch in 1998, the AM-1 spacecraft is to characterize clouds, aerosol, and the Earth's radiation balance. AM-1 is to cross the equator in the morning hours. The Landsat 7 is set for a 1998 liftoff as well. It will study land surface features and changes using high-resolution imagery. A PM-1 spacecraft is targeted for launching in 2000, geared to study clouds, precipitation and radiative balance.