Algorithm Information Documents

  • GPM GPROF (Level 2) Algorithm Theoretical Basis Document (ATBD) (Version 4)
    Keywords:
    Publication Date:
    08/01/2014
    Abstract / Summary:

    This ATBD describes the Global Precipitation Measurement (GPM) passive microwave rainfall algorithm, which is a parametric algorithm used to serve all GPM constellation radiometers. The output parameters of the algorithm are enumerated in Table 1. It is based upon the concept that the GPM core satellite, with its Dual Frequency Radar (DPR) and GPM Microwave Imager (GMI), will be used to build a consistent a-priori database of cloud and precipitation profiles to help constrain possible solutions from the constellation radiometers.


    In particular, this document identifies sources of input data and output from the retrieval algorithm and describes the physical theory upon which the algorithm is based. The document includes implementation details, as well as the assumptions and limitations of the adopted approach. Because the algorithm is being developed by a broad team of scientists, this document additionally serves to keep each developer abreast of all the algorithm details and formats needed to interact with the code. The version number and date of the ATBD will therefore always correspond to the version number and date of the algorithm – even if changes are trivial.

  • GPM/DPR Level 2 Algorithm Theoretical Basis Document (ATBD)
    Keywords:
    Publication Date:
    10/01/2018
    Abstract / Summary:

    The objective of the level 2 DPR algorithms is to generate from the level 1 DPR products radaronly derived meteorological quantities on an instantaneous FOV (field of view) basis. A subset of the results will be used by the level 2 combined radar-radiometer algorithm and the level 3 combined and radar-only products. 

    The general idea behind the algorithms is to determine general characteristics of the precipitation, correct for attenuation and estimate profiles of the precipitation water content, rainfall rate and, when dual-wavelength data are available, information on the particle size distributions in rain and snow. It is particularly important that dual-wavelength data will provide better estimates of rainfall and snowfall rates than the TRMM PR data by using the particle size information and the capability of estimating, even in convective storms, the height at which the precipitation transitions from solid to liquid.

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    GPM Integrated Multi-Satellite Retrievals for GPM (IMERG) Algorithm Theoretical Basis Document (ATBD) v5.2
    Publication Date:
    02/07/2018
    Abstract / Summary:

    This document describes the algorithm and processing sequence for the Integrated Multi-satellitE Retrievals for GPM (IMERG).  This 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.

  • GPM Combined Radar-Radiometer Precipitation Algorithm Theoretical Basis Document (ATBD) (Version 03)
    Publication Date:
    11/30/2011
    Abstract / Summary:

    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 precipitation distributions that can be achieved from a spaceborne platform, and it is therefore valuable for applications where information regarding instantaneous storm structure are vital. Second, long-term accumulation of combined algorithm estimates will yield a single common reference dataset that will be used to “cross-calibrate” rain rate estimates from all of the passive microwave radiometers in the GPM constellation. The cross-calibration of the radiometer estimates is crucial for developing a consistent, high-time-resolution precipitation record for climate science and prediction model validation applications. Because of the Combined Algorithm’s essential roles as accurate reference and calibrator, the GPM Project is supporting a Combined Algorithm Team to implement and test the algorithm prior to launch. In the pre-launch phase, GPM-funded science investigations may lead to significant improvements in algorithm function, but the basic algorithm architecture has been formulated. This algorithm architecture is largely consistent with the successful TRMM Combined Algorithm design, but it has been updated and modularized to take advantage of improvements in the representation of physics, new climatological background information, and model- based analyses that may become available at any stage of the mission. This document presents a description of the GPM Combined Algorithm architecture, scientific basis, inputs/outputs, and supporting ancillary datasets.

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    GPM Microwave Imager (GMI) Level 1B Algorithm Theoretical Basis Document (ATBD) (Version 3)
    Keywords:
    Publication Date:
    11/01/2010
    Abstract / Summary:

    This document describes the GMI Level 1B algorithm. It consists of physical bases and mathematical equations for GMI calibration, as well as pre-launch and post-launch activities. The document also presents high-level software design. However, detailed software descriptions will be presented separately in the Level 1B Software Design Document. Parts of this document are from the RSS GMI Calibration ATBD as contributed by the Ball Aerospace GMI manufactory contract. The GMI L1B geolocation algorithm is described in a separate Geolocation Toolkit (GeoTK) ATBD.

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    GPM Level 1C Algorithm Theoretical Basis Document (ATBD) (Version 4)
    Keywords:
    Publication Date:
    04/01/2016
    Abstract / Summary:

    Level 1C (L1C) algorithms are a collection of algorithms that produce common calibrated brightness temperature products for the Global Precipitation Measurement (GPM) Core and Constellation satellites.

    This document describes the GPM Level 1C algorithms. It consists of physical and mathematical bases for orbitization, satellite intercalibration, and quality control, as well as the software architecture and implementation for the Level 1C algorithms.

    The Level 1C algorithms transform equivalent Level 1B radiance data into Level 1C products. The input source data are geolocated and radiometric calibrated antenna temperature (Ta) or brightness temperature (Tb). The output Level 1C products are common intercalibrated brightness temperature (Tc) products using the GPM Microwave Imager (GMI) as the reference standard.

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