The gist is that current microwave radiometer detection sees an overlap of frequencies for wet snow, sleet and refreezing precip; and also doesn't account for snowflake size or water content. The new GPM satellite is due to launch in 2014 carrying a radar developed by the JAEA which will use active scanning in two frequencies to get a better idea of the precip type, in the meantime NASA and EnvCan are deploying a fleet of aircraft and surface stations to fine tune the radiometer design.
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Above the clouds at 33,000 feet, a third plane, NASA Dryden's airborne laboratory DC-8, carries NASA Goddard-developed Conical Scanning Millimeter-wave Imaging Radiometer (CoSMIR) radiometer and NASA's Jet Propulsion Laboratory-developed Airborne Precipitation Radar-2 (APR-2). Together these two instruments simulate the instruments that the GPM satellite will carry into orbit.
The datasets will complement current measurements made by radiometers on Earth-observing satellites Aqua and Soumi NPP and the Cloud Profiling Radar on CloudSat.
"What we can do with all these measurements is learn these relationships between what the radar and the radiometer sees, what's in the cloud, and what's falling out," says Skofronick-Jackson.
The GCPEx campaign, running from January 17 through February 29, is on its way to filling in that picture.