GPM Microwave Imager (GMI). Microwave radiometers are versatile instruments, and when properly configured, can be used to infer a wide variety of phenomena in addition to precipitation, such as atmospheric moisture and temperature profiles, soil moisture, and sea surface temperature. To measure precipitation, the radiometer detects microwave energy emitted and scattered by rain and ice particles contained within clouds. This radiation continuously "upwells" from within clouds and is lost to space, but when intercepted and detected by a radiometer in Earth orbit, can provide useful information on the phase (liquid vs. solid), intensity and vertical distribution of precipitation. Several channels on board the radiometer measure microwave radiation at different wavelengths. Certain wavelengths are more sensitive to scattering or emission of microwave energy, and each wavelength is tuned to provide precipitation information within different vertical layers in the atmosphere.

Plans are in place to use microwave radiometers on several satellite missions that will be in orbit during the GPM era. NASA will procure two nearly identical GMI instruments from industry, one instrument to be placed on Core, and the other on the NASA constellation satellite. GMI will be designed to make simultaneous measurements in several microwave frequencies (e.g., 10.7, 19.3, 21, 37, 89 GHz), giving the instrument the capability to measure a variety of rainfall rates and related environmental parameters. Additional, there are plans to provide experimental, higher frequency channels (165 and 183 GHz) that have the needed sensitivity to detect light rain and snow frequently found at Earth's higher latitudes.

GPM Dual Frequency Radar (DFR). Detailed measurements of cloud structure and precipitation characteristics will be made with the Dual Frequency Precipitation Radar (DPR). JAXA is providing this instrument for GPM. The DPR is comprised of two, essentially independent radars operating in the microwave region of the electromagnetic spectrum. One radar transmits microwave energy in the Ku-Band (13.6 GHz) and is referred to as the Precipitation Radar (PR)-U. The other radar operates in the Ka-Band (35.55 GHz) and is referred to as the PR-A. Weather radar operates by measuring the amount of energy scattered back to the radar by precipitation. At the two different radar frequencies of the DFR, it is possible to infer information regarding rain rate, cloud type, solid vs. liquid precipitation, and the size of precipitation particles. The design of both radars builds upon the legacy of TRMM's Precipitation Radar (PR), but greatly extends its capabilities by incorporating new technologies and modifications for an expanded set of frequencies.