H11O-01
PRECIPITATION ESTIMATION USING COMBINED RADAR AND MICROWAVE RADIOMETER OBSERVATIONS FROM GPM- IMPROVEMENTS AND INITIAL VALIDATION

Monday, 14 December 2015: 08:00
3022 (Moscone West)
William S Olson1, Mircea Grecu2, Stephen J Munchak3, Kwo-Sen Kuo4, Benjamin T Johnson5, Ziad S Haddad6, Lin Tian7, Liang Liao7, Bartie L Kelley8 and Sarah Ringerud9, (1)Joint Center for Earth Systems Technology, Baltimore, MD, United States, (2)NASA/Goddard Space Flight Ctr, Greenbelt, MD, United States, (3)Colorado State University, Fort Collins, CO, United States, (4)Earth System Science Interdisciplinary Center, COLLEGE PARK, MD, United States, (5)NOAA College Park, College Park, MD, United States, (6)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (7)Morgan State University, Greenbelt, MD, United States, (8)Science Systems and Applications, Inc., Lanham, MD, United States, (9)NASA Goddard Space Flight Center, Greenbelt, MD, United States
Abstract:
In recent satellite missions, spaceborne radar observations, sometimes in combination with passive microwave radiometer measurements, are being used to estimate vertical profiles of precipitation rates. Launched in 2014, the Global Precipitation Measurement (GPM) mission core satellite observatory features a dual-frequency radar operating at 13.6 and 35.5 GHz (Ku and Ka bands) and a microwave radiometer with thirteen channels from 10 - 183 GHz. The use of combined radar and radiometer observations should yield the most accurate estimates of precipitation profiles from space, and these estimates will ultimately serve as a crucial reference for cross-calibrating passive microwave precipitation estimates from the GPM radiometer constellation. And through the microwave radiometer estimates, the combined algorithm calibration will ultimately be propagated to GPM infrared-microwave multisatellite estimates of surface rainfall.

The GPM combined precipitation estimation algorithm performs initial estimates (an “ensemble”) of precipitation profiles based upon an observed Ku-band reflectivity profile and different a priori assumptions concerning the size distributions of the precipitation particles and the profiles of cloud water and water vapor in the atmospheric column. The initial ensemble of profiles is then updated using a filter that embodies the physics relating precipitation to the observed Ka reflectivity profile, Ku and Ka path-integrated attenuation (derived from radar surface backscatter measurements), and microwave radiances. The final, filtered ensemble of profiles is consistent with all the available radar-radiometer data and a priori information.

Since the GPM launch, the combined radar-radiometer algorithm has been improved to more specifically account for the effects of radar non-uniform beamfilling, multiple-scattering of radar pulses, the different resolutions of the radar and radiometer observations, interrelated radar and passive microwave surface properties, and precipitation particle single-scattering properties. These and other changes lead to estimates of surface rainfall rates that compare favorably with ground-based, raingauge-calibrated radar estimates of rain rates. Algorithm improvements and validation will be discussed at the meeting.

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