The TMI instrument on the TRMM satellite measures microwaves emitted from the Earth's land and water. By comparing emission from different microwave frequencies, the characteristics of ice and water in the atmosphere can be determined. For example, 85 GHz microwaves are scattered by ice crystals in tropical cyclones, making cyclone rain bands appear 'colder' than the surrounding areas. By comparing 85 GHz temperatures in different polarizations with other frequency band measurements, accurate measurements of rainfall in the atmosphere can be made. This animation shows four days of TMI 85 GHz measurements, one orbit at a time. Hurricane Katrina was in the Gulf of Mexico at the time and clearly shows up in the measurements.
GCMD keywords can be found on the Internet with the following citation:
Olsen, L.M., G. Major, K. Shein, J. Scialdone, S. Ritz, T. Stevens, M. Morahan, A. Aleman, R. Vogel, S. Leicester, H. Weir, M. Meaux, S. Grebas, C.Solomon, M. Holland, T. Northcutt, R. A. Restrepo, R. Bilodeau, 2013. NASA/Global Change Master Directory (GCMD) Earth Science Keywords. Version 220.127.116.11.0