GPM Microwave Imager (GMI) Level 1B (L1B) Algorithm Theoretical Basis Document (ATBD) (Version 4)

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This document describes the GMI Level 1B algorithm developed by PPS. It consists of physical bases and mathematical equations for GMI calibration, as well as after-launch activities. The document also presents high-level software design. Parts of this document are from the Remote Sensing Systems (RSS) GMI Calibration ATBD and the BATC Calibration Data Book as contributed by the BATC GMI manufactory contract. The GMI L1B geolocation algorithm is described in a separate Geolocation Toolkit ATBD.

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GPM Combined Radar-Radiometer Precipitation Algorithm Theoretical Basis Document (ATBD) (Version 4)

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The GPM Combined Radar-Radiometer Algorithm performs two basic functions: first, it provides, in principle, the most accurate, high resolution estimates of surface rainfall rate and precipitation vertical distributions that can be achieved from a spaceborne platform, and it is therefore valuable for applications where information regarding instantaneous storm structure are vital.

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IMERG Early/Late Run Precipitation Anomalies

Beginning on April 6, anomalies in the input SSMIS F17 precipitation estimates were detected in the IMERG Early and Late runs.  These anomalies manifest as episodic “swath shaped” areas of high precipitation over land which appear to affect most orbits to some degree.  The root cause is degradation in the 37 GHz V polarization channel.  On April 13 the issue was somewhat mitigated but we continue to monitor the situation.  Please let us know if you detect these (or other anomalies) in the IMERG Early and Late Runs after April 13.

V04 Processing for GPM Near-Realtime (NRT) is Scheduled to Begin

Late on March 2, 2016, the GPM NRT system will begin using V04 algorithms for:

  • Level 1B GMI
  • Level 1C GMI
  • Level 1 Radar
  • Level 2 Radar
  • Level 2 Combined

V04 is the first version that uses GPM as the calibrator for the constellation rather than TRMM. The GPROF database is built using the combined observations. GMI is extremely well calibrated and the brightness temperatures in 1B and 1C are an important improvement over those in V03.

Positional Algorithm Issue with GMI 85GHz

One of our scientists noticed that the 85GHz H and V channels have missing values in ascending passes just south of 20 deg S. In that region it appears consistently since 10:45UTC which is the earliest we checked. The other channels seem fine.

The counts for the 85GHz channels appear to be fine as is the geolocation. However both the 1B and 1 Base files have the missing values in that area. We are checking what is causing the algorithm to list the values as missing.

Please keep this in mind when using those channels.

Delay in Some GMI and Combined

Starting at 16:33 UTC July 6 a filled log directory led to sh commands failing on redirecting logs to be created in that directory. A typo in the cleanup routine failed to clean our all the files after the normal 4 days. As a result they have been accumulating since the beginning of the mission.  It is unexpected that the sh failed when it could not redirect anymore.  

Initial IMERG Products Released

PPS is re-releasing the first public version IMERG products The Integrated Multi-satellitE Retrievals for GPM (IMERG) merges precipitation estimates from passive microwave sensors, geo-IR, and monthly surface precipitation gauge analysis data (where available) to provide half-hourly and monthly precipitation estimates and related fields on a 0.1° lat./long. grid over the domain 60°N-S.

GMI Production Halted for Deep Space Calibration

On December 8, 2014 and December 10, 2014 the GPM MOC will conduct deep space calibrations maneuvers that will assist in physically verifying GMI calibration changes and also help in further characterization of the GMI instrument itself.

Special processing is required for the data collected during the DSC. Therefore, PPS production of Standard GMI products will be halted on Dec 8 at 20:30 UTC. Processing will resume during normal business hours on Dec 9.


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