In support of NASA's rain measuring missions, the radar group at JPL designed and built the Airborne Rain MApping Radar (ARMAR) in the early 90's, and in 2001 we completed the 2nd-generation Airborne Precipitation Radar (APR-2). While ARMAR was a single-frequency system designed to emulate TRMM's PR, APR-2 is a dual-frequency radar designed to emulate the GPM core satellite's Ku- and Ka-band radars.

APR-2 is a dual-frequency (13 GHz & 35 GHz), Doppler, dual-polarization radar system. It has a downward looking antenna that performs cross track scans, covering a swath that is +/- 25 to each side of the aircraft path. Additional features include: simultaneous dual-frequency, matched beam operation at 13.4 and 35.6 GHz (same as GPM Dual-Frequency Precipitation Radar), simultaneous measurement of both like- and cross-polarized signals at both frequencies, Doppler operation, and real-time pulse compression (calibrated reflectivity data can be produced for large areas in the field during flight, if necessary).