GPM Documents

  • Download File:
    GPM Mission Brochure
    Publication Date:
    11/01/2013
    Abstract / Summary:

    This 17 page flyer provides an overview of the GPM Mission. It describes the technologies used to measure precipitation and the missions scientific goals and societal applications.

    Excerpt:

    "The Global Precipitation Measurement (GPM) mission is an international partnership co-led by NASA and the Japan Aerospace Exploration Agency (JAXA). The mission centers on the deployment of the GPM Core Observatory and consists of a network, or constellation, of additional satellites that together will provide next-generation global observations of precipitation from space. The GPM Core Observatory will carry an advanced radar/radiometer system and serve as a reference standard to unify precipitation measurements from all satellites that fly within the constellation."

    Table of Contents:

    • Precipitation Measurement Science
    • Global Precipitation Measurement Mission
    • GPM Core Observatory
    • GMI: GPM Microwave Imager
    • DPR: Dual-frequency Precipitation Radar
    • Spacecraft Design
    • Ground System and Data
    • GPM Mission Applications: A Global Understanding for a Better Future
  • MC3E Summary from The Earth Observer, January 2012
    Publication Date:
    02/01/2012
    Abstract / Summary:

    This excerpt from the NASA Earth Observer publication provides and in-depth summary of the Midlatitude Continental Convective Clouds Experiment (MC3E), which took place from April 22nd - June 6th 2011 in central Oklahoma. The overarching goals of the field effort were to provide a complete three-dimensional characterization of precipitation microphysics in the context of improving the reliability of GPM precipitation retrievals over land, and to advance understanding of the primary physical components that form the basis for models that simulate convection and clouds.

  • A Ground Validation Network for the Global Precipitation Measurement Mission
    Publication Date:
    03/01/2011
    Abstract / Summary:

    A prototype Validation Network (VN) is currently operating as part of the Ground Validation System for NASA’s Global Precipitation Measurement (GPM) mission. The VN supports precipitation retrieval algorithm development in the GPM prelaunch era. Postlaunch, the VN will be used to validate GPM spacecraft instrument measurements and retrieved precipitation data products.

    The period of record for the VN prototype starts on 8 August 2006 and runs to the present day. The VN database includes spacecraft data from the Tropical Rainfall Measuring Mission (TRMM) precipitation radar (PR) and coincident ground radar (GR) data from operational meteorological networks in the United States, Australia, Korea, and the Kwajalein Atoll in the Marshall Islands. Satellite and ground radar data products are collected whenever the PR satellite track crosses within 200 km of a VN ground radar, and these data are stored permanently in the VN database. VN products are generated from coincident PR and GR observations when a significant rain event occurs.

    The VN algorithm matches PR and GR radar data (including retrieved precipitation data in the case of the PR) by calculating averages of PR reflectivity (both raw and attenuation corrected) and rain rate, and GR reflectivity at the geometric intersection of the PR rays with the individual GR elevation sweeps. The algorithm thus averages the minimum PR and GR sample volumes needed to “matchup” the spatially coincident PR and GR data types. The result of this technique is a set of vertical profiles for a given rainfall event, with coincident PR and GR samples matched at specified heights throughout the profile.

    VN data can be used to validate satellite measurements and to track ground radar calibration over time. A comparison of matched TRMM PR and GR radar reflectivity factor data found a remarkably small difference between the PR and GR radar reflectivity factor averaged over this period of record in stratiform and convective rain cases when samples were taken from high in the atmosphere. A significant difference in PR and GR reflectivity was found in convective cases, particularly in convective samples from the lower part of the atmosphere. In this case, the mean difference between PR and corrected GR reflectivity was −1.88 dBZ. The PR–GR bias was found to increase with the amount of PR attenuation correction applied, with the PR–GR bias reaching −3.07 dBZ in cases where the attenuation correction applied is >6 dBZ. Additional analysis indicated that the version 6 TRMM PR retrieval algorithm underestimates rainfall in case of convective rain in the lower part of the atmosphere by 30%–40%.

  • GCPEX Science Plan
    Publication Date:
    09/02/2011
    Abstract / Summary:

    During the GPM pre-launch period physically-based snowfall retrieval algorithms are in an active phase of development. Further refinement and testing of these emerging algorithms requires the collection of targeted ground-validation datasets in snowing environments. This document describes a field campaign effort designed to provide both new datasets and physical insights related to the snowfall process- especially as they relate to the incorporation of appropriate physics into GPM snowfall retrieval algorithms. The referenced field campaign effort is the GPM Cold Season Precipitation Experiment (GCPEx), a collaboration between the NASA GPM Ground Validation (GV) program and its international partner Environment Canada (EC).

  • GPM/DPR Level 2 Algorithm Theoretical Basis Document (ATBD)
    Keywords:
    Publication Date:
    08/01/2017
    Abstract / Summary:

    The objective of the level 2 DPR algorithms is to generate from the level 1 DPR products radar-only 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.

  • Download File:
    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.

  • Download File:
    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.

  • Download File:
    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.

  • 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.

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