IMERG V07 (at Long Last) and What Comes Next

The U.S. Global Precipitation Measurement (GPM) mission Science Team provides gridded global estimates of surface precipitation rate and related information at the 0.1° half-hour resolution with the Integrated Multi-satellitE Retrievals for GPM (IMERG) products. This presentation will briefly summarize the major upgrades included in Version 07 IMERG, such as improved input precipitation datasets; improved bias thanks to four upgrades in processing; and improved time continuity in precipitation features due to changes to the Kalman filter that approximately preserve the local histogram of precipitation rates and that better account for differences in sensor performance. A long-standing offset in the geolocation that shifted grid values 0.1° to the east in the latitude band 70°N-S has been corrected. Other changes in V07 include an update to the precipitation phase specification for improved consistency with current input datasets, and a climatological gauge adjustment to the near-real-time Early and Late products. Finally, an innovative forward encoding scheme (Satellite Precipitation Estimates Error Detection, or SPEEDe) uncovered 162 orbits of GPROF estimates that were defective, leading to a second retrospective processing of the Final Run (designated V07B). By the time of the workshop the Early and Late Runs will also have migrated to V07B.

Early evaluations of V07B IMERG Final Run show improved behavior in most cases, including improved continuity across the TRMM/GPM data boundary. For V08 development, we will further improve continuity, focusing on the TRMM/GPM transition, the orbit boosts for both TRMM and GPM, and homogeneity of the constellation record. We will address redesigning the Kalman filter, developing a SAPHIR dataset that is more consistent with other microwave estimates, and refining quality control for microwave and infrared input datasets. Important long-term issues include: 1) accommodating the new generation of SmallSats in a multi-satellite framework, 2) developing the next passive-active calibration system, and 3) strategizing the right context for producing future multi-satellite datasets.