Lessons Learned in V07 IMERG
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Date
2023-04-03
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Citation of Original Publication
Huffman, George, et al. "Lessons Learned in V07 IMERG" EGU General Assembly 2023, EGU23-2961 (Vienna, Austria & Online, 23–28 April 2023). https://doi.org/10.5194/egusphere-egu23-2961.
Rights
This work was written as part of one of the author's official duties as an Employee of the United States Government and is therefore a work of the United States Government. In accordance with 17 U.S.C. 105, no copyright protection is available for such works under U.S. Law.
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Public Domain Mark 1.0
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Abstract
The Global Precipitation Measurement (GPM) mission combines passive microwave (PMW) and
infrared (IR) satellite data, together with other data to create the Integrated Multi-satellitE
Retrievals for (IMERG) precipitation product on a (nearly) global 0.1° half-hour grid. Experience
with Version 06 datasets revealed deficiencies that the algorithm team has addressed in creating
the new Version 07 datasets.
Input precipitation estimates from the Goddard Profiling (GPROF) algorithm (which retrieves
precipitation from passive microwave sensor data), the GPM Combined Radar-Radiometer
Algorithm (CORRA), and the new Precipitation Estimation from Remotely Sensed Information Using
Artificial Neural Networks–Dynamic Infrared Rain Rate (PDIR) algorithm (retrieving precipitation
from IR data) all represent advances over the V06 inputs. For V07, several issues have been
addressed, and many algorithm improvements have been implemented. These include refining
the Kalman filter to approximately preserve the local histogram of precipitation rates (Scheme for
Histogram Adjustment with Ranked Precipitation Estimates in the Neighborhood, or SHARPEN),
and applying the Kalman filter even when a PMW overpass occurs. Furthermore, a long-standing
bug 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 a hierarchical selection among motion vector
sources to address deficiencies in the precipitation propagation near orography, an update to the
precipitation phase specification for improved consistency with current inputs, and climatological
adjustment of the near-real-time Early and Late Runs to the Final Run (which includes monthly
precipitation gauge analyses). Extensive development work was directed at unexpected biases in
the V06 products, leading to 1) calibrations that now employ the entire swath widths of CORRA
and GPROF GPM Microwave Imager (GMI) precipitation estimates (rather than spatially coincident
data), and 2) coarsening the CORRA resolution to approximately match the GPROF-GMI footprint
scale. The latter provides more consistent histograms for building the calibrations.
It is anticipated that the retrospective analysis for V07 will be well underway at the time of the
meeting. Changes between V06 and V07 will illustrate the cumulative result of the improvements
implemented in V07. The current status of processing and plans for future development will also
be discussed.