Daily rainfall detection and estimation over land using microwave surface emissivities
Birman, Camille ; Karbou, Fatima ; Mahfouf, Jean-François
Surface emissivities computed at 89 GHz from AMSU-A, AMSU-B and SSMI/S instruments are used to detect rain events and to estimate a daily precipitation rate over land surfaces. This new retrieval algorithm, called EMIssivity Rainfall Retrieval (Emirr), is evaluated over France and compared to several other precipitation products. The precipitation detection is performed using temporal changes of daily surface emissivities. A statistical fit, derived from a rainfall analysis product using raingauge and radar data, is devised to estimate a daily precipitation rate from surface emissivities. Rain retrievals are evaluated over a one year period in 2010 against other precipitation products including rain gauge measurements. The Emirr algorithm allows a reasonable detection of rainy events from daily surface emissivities. The number of rainy days and the daily rainfall rates compare well with estimates from other precipitation products. However, the algorithm tends to overestimate low precipitation amounts and to underestimate higher ones, with reduced performances in the presence of snow. Despite such limitations, this new method is very promising and provides a demonstration of the potential use of the 89 GHz surface emissivities to infer relevant information (occurrence and amounts) on daily precipitation over land surfaces.
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