IMERG V07 Technical Documentation

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The Integrated Multi-satelliE Retrievals for GPM (*IMERG*) is the unified U.S. algorithm that provides the multi-satellite precipitation product for the U.S. GPM team. The precipitation estimates from the various precipitation-relevant satellite passive microwave (PMW) sensors comprising the GPM constellation (which includes those during the Tropical Rainfall Measuring Mission [TRMM] era) are computed using the 2021 version of the Goddard Profiling Algorithm (GPROF2021), then gridded, intercalibrated to the GPM Combined Radar Radiometer Analysis product (with Global Precipitation Climatology Project [GPCP] climatological calibration), and combined into half-hourly 0.1°×0.1° fields. These are provided to the Climate Prediction Center (CPC) Morphing-Kalman Filter (CMORPH-KF) quasi-Lagrangian time interpolation procedure and the re-calibration procedure applied to the Precipitation Estimation from Remotely Sensed Information using Artificial Neural Networks (PERSIANN) Dynamic Infrared–Rain Rate (PDIR) infrared (IR) precipitation retrievals. In parallel, the Modern-Era Retrospective analysis for Research and Applications, Version 2 (MERRA2) and Goddard Earth Observing System Forward Processing (GEOS FP) precipitation (PRECTOT), total precipitable liquid water (TQL), and total precipitable water vapor (TQV) fields are used in the CMORPH-KF quasi-Lagrangian time interpolation procedure. The PDIR estimates are computed (supported by an asynchronous re-calibration cycle) and sent to the CMORPH-KF quasi-Lagrangian time interpolation procedure. The Kalman Filter (KF) quasi-Lagrangian time interpolation (supported by an asynchronous KF weights updating cycle) uses the PMW and IR estimates to create half-hourly estimates. The IMERG system is run twice in near-real time

• “Early” multi-satellite product ~4 hr after observation time and
• “Late” multi-satellite product ~14 hr after observation time,

and once after the monthly gauge analysis is received

• “Final” satellite-gauge product ~3.5 months after the observation month.

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