RAMEX: a proposed rain mapping experiment using microwave oxygen and water vapor sounding channels

The proposed baseline RAin Mapping EXperiment (RAMEX) would measure global precipitation over land and sea with 9-km resolution at nadir using 14 channels near 118 and 183 GHz, and with 18-km resolution using eight additional channels near 54 GHz. Rms instantaneous precipitation retrieval accuracies of ~33 percent relative to NEXRAD have been demonstrated over land for rain rates over 4 mm/hr using only 50-km resolution Advanced Microwave Sounding Unit (AMSU) polar satellite data near 54 and 183 GHz. NAST-M passive microwave aircraft data in the 54- and 118-GHz oxygen bands, and other considerations, suggest that the RAMEX rain rate accuracy should be superior and that there is hope that snow rate might be estimated similarly. The nominal 31-kg, 83-W, 86-kbps RAMEX sensor designed for the nadir Express pallet of the international Space Station would continuously map an 1180-km swath reaching 57-degrees latitude. A follow-on global precipitation mapping constellation of six slightly larger instruments at 833-km altitude could provide a wider swath with similar spatial resolution and global 2-hr repeat coverage with similar performance