Satellites are playing an ever-increasing role in estimating precipitation over remote areas. Improving satellite retrievals of precipitation requires increased understanding of its passive microwave signatures over different land surfaces. Snow-covered surfaces are notoriously difficult to interpret because they exhibit both emission from the land below and scattering from the ice crystals. Using data from the Global Precipitation Measurement (GPM) satellite, we demonstrate that microwave brightness temperatures of rain and snowfall transition from a scattering to an emission regime from summer to winter, due to expansion of less emissive snow cover. Evidence suggests that the combination of low- (10–19 GHz) and high-frequency (89–166 GHz) channels provides the maximum amount of information for snowfall detection. The results demonstrate that, using a multifrequency matching method, the probability of snowfall detection can even be higher than rainfall—chiefly because of the information content of the low-frequency channels that respond to the (near) surface temperature.
Bibliographical noteFunding Information:
The authors acknowledge the support (NNX16AO56G) from the NASA Precipitation Measurement Missions through R. Kakar. GPM data (version 4) are provided courtesy of the NASA Precipitation Processing System at the Goddard Space Flight center (https://pmm.nasa.gov/data-access/). The MERRA-2 and MODIS data are from the Goddard Earth Sciences and Information Service Center (https://disc.sci.gsfc.nasa.gov/mdisc/) and the Land Processes Distributed Active Archive Center by the USGS (https://lpdaac.usgs.gov/data_access/data_pool). The authors would like to thank Zeinab Takbiri for her help, Pierre Kirstetter at the University of Oklahoma for providing us the MRMS data, and Efi Foufoula-Georgiou at the University of California-Irvine for her support and offered insights.
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