The primary GPM instruments are the Dual-frequency Precipitation Radar (DPR) (active remote sensor) and GPM Microwave Imager (GMI) (passive remote sensor).

The DPR measures the 3D structure of precipitation, provides quantitative estimates of the precipitation particle size distribution, and provides estimates of rainfall rates to the scientific community. These measurements are accomplished by using the differential attenuation of microwave energy between the Ku-band (operating at 13.6 GHz) and the Ka-band (operating at 35.5 GHz) frequencies covering a swath of 245 km (Ku) (152 miles) and 125 km (Ka) (78 miles) at a vertical resolution of 250 m and a horizontal resolution of ~5 km.

The GMI is a radiometer that uses a set of 13 optimized channels measuring microwave energy at frequencies ranging from 10 to 183 GHz at resolutions ranging from 5 to 25 km and covers a swath of 885 Km (550 miles). These frequencies help to retrieve heavy, moderate, and light precipitation measurements to derive surface precipitation rates. 

Learn more:

• Dual-frequency Precipitation Radar (DPR)
• GPM Microwave Imager (GMI)