Integrated Multi-satellite Retrievals for GPM (IMERG)

"Rainfall estimates combining data from all passive-microwave instruments in the GPM Constellation. This algorithm is intended to intercalibrate, merge, and interpolate “all” satellite microwave precipitation estimates, together with microwave-calibrated infrared (IR) satellite estimates, precipitation gauge analyses, and potentially other precipitation estimators at fine time and space scales for the TRMM and GPM eras over the entire globe. The system is run several times for each observation time, first giving a quick estimate (IMERG "early run") and successively providing better estimates as more data arrive (IMERG "late run"). The final step uses monthly gauge data to create research-level products (IMERG "final run")." (National Aeronautics and Space Administration, 2019)