Comparisons of rainrates from Near-Realtime Late-Run IMERG and MRMS (Q3)
IMERGIntegrated Multi-Satellite Retrievals for GPM (IMERG) 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 and successively providing better estimates as more data arrive. The final step uses monthly gauge data to create research-level products. Background information and references are provided to describe the context and the relation to other similar missions. Issues involved in understanding the accuracies obtained from the calculations are discussed. Throughout, a baseline Day-1 product is described, together with options and planned improvements that might be instituted before or after launch depending on maturity and project constraints. The IMERG gridded estimates are on a 30-minute temporal resolution and a 0.1-degree by 0.1-degree spatial resolution extending from 180W to 180E and 60S to 60N. For more information about IMERG, downlad IMERG_ATBD_V4.4.pdf This study utilizes the IMERG Late Run data, which is the near-realtime product in the IMERG suite of products that runs about 16 hours after observationtime. The IMERG Late Run data is now available at https://storm-pps.gsfc.nasa.gov/storm, or ftp://jsimpson.pps.eosdis.nasa.gov. Currently the late product is 16 hours behind realtime. This might improve over the course of the next Several months depending upon the input data latency and statistics requirements. Thanks to George Huffman and David T. Bolvin for providing near-realtime Late-Run IMERG data.
Comparisons with MRMS (or called Q3)The comparisons are conducted over the CONUS (20N-50N, 125W-65W) using gauge-calibrated(GC) IMERG, uncalibrated(UC) IMERG and MRMS data during the commonly available periods:
V03E: Mar 2015 - May 2016
V04A: Mar 2014 - May 2016
Note: Comparison for V04A will be done soon. There is no back end gauge correction for V04A IMERG Late-Run, so the cal and uncal fields are the same.