GPM Documents

  • Download File:
    C3VP 2007 IOP3 Case Summary
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    n all, 9 snowfall events were observed during IOP-3. All of these events were observed by the King City radars, 8 of the events were observed by the University of Massachusetts 3-frequency (W-, Ka, and Ku-band) Advanced Multi-Frequency Radar (AMFR), and 3 of the events were also observed with Convar-580 overflights.

    This document is a case summary of the dates, times, snowfall types, and instruments used during these 9 IOP-3 snowfall events.

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    Snowflake Video Imager at C3VP
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    The NASA Snowflake Video Imager obtained nearly continuous data from 1 Dec 06 thru 7 Mar 07.

    This presentation contains a summary for the entire data set, which is sorted into (a) priority days selected by GSFC investigators, and (b) non-priority days.

    The results are displayed in images of DSD(t), which reveal (a) the large variability of snowflakes sizes during events and (b) the intermittency of snowfall – even during intense storms.

    Additionally, results from a preliminary study of snowflake orientation reveals that there is a higher occurrence of snowflakes that are ‘horizontally’ orientated than ‘vertically’ orientated.

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    NASA GPM/PMM Participation in the Canadian Cloudsat / Calipso Validation Project (C3VP): Physical Process Studies in Snow
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    A complete understanding of the Earth’s hydrologic cycle necessarily dictates an ability to accurately quantify the global range of precipitation rates and types (rain, snow etc.). In turn, global observations of precipitation are most efficiently made from space. Great strides in the measurement of global tropical rainfall have occurred recently as a result of the NASA Tropical Rainfall Measurement Mission (TRMM). However, future international endeavors such as the Global Precipitation Mission (GPM) will require an expanded precipitation measurement capability due to the extension of the measurement to higher latitudes. Specifically, the NASA Precipitation Measurement Mission (PMM) and GPM algorithm development and Ground Validation (GV) teams are in great need of GPM pre-launch data sets for developing space-based snowfall detection and estimation algorithms. These data sets are needed to (1) develop and validate physical models that convert the physical characteristics of single snowflakes (shape, size distribution, density, ice-air-water ratio) to their radiative properties (asymmetry factor, absorption, scattering, and backscattering coefficients); and (2) relate the bulk layer radiative properties to calculated and observed passive microwave radiances and radar reflectivities.

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    A Global Precipitation Mission (GPM) Validation Network Prototype
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    A Validation Network (VN) prototype is currently underway that compares data from the Tropical Rainfall Measuring Mission (TRMM) satellite Precipitation Radar (PR) to similar measurements from the U.S. national network of operational weather radars. This prototype is being conducted as part of the ground validation activities of the Global Precipitation Measurement (GPM) mission. The purpose of the VN is to provide a means for the precipitation community to identify and resolve significant discrepancies between the U.S. national network of ground radar observations and satellite observations. The ultimate goal of such comparisons is to understand and resolve the first order variability and bias of precipitation retrievals in different meteorological/hydrological regimes at large scales. The VN prototype is based on research results and computer code described by Anagnostou et al. (2001), Bolen and Chandrasekar (2000), and Liao et al. (2001).

  • The Vertical Cross Section Display Program for GPM Validation Network Geometry-Matched PR and GV Data Sets
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    The IDL procedure pr_and_geo_match_x_sections.pro provides the capability to interactively select locations for, and display, vertical cross sections of PR and GV reflectivity from geometry-matched data produced by the GPM Validation Network prototype. These data are contained in a set of netCDF data files, one per “rainy” site overpass (a TRMM PR overpass of a GV radar site, with precipitation echoes present). By default, the procedure also displays a vertical cross section of the difference (PR-GV) between the PR and GV reflectivity from the geo-matched data. By default, the cross sections are along the PR cross-track scan line through the point selected by the user (i.e., perpendicular to the orbit track). Random cross section alignments are not supported.


    The procedure has a feature allowing a calibration offset to be applied to the GV reflectivity data. If a GV site or GV data for a particular event is known to have an error in calibration relative to the PR, the calibration of the GV reflectivity data may be adjusted up or down in 1 dBZ increments on the currently displayed cross sections, so that the relative vertical structures of the PR and GV reflectivity fields can be evaluated with the calibration bias removed.

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    GPM Ground Validation System Level 3 Operations Concept
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    This specification defines the Level 3 functional and performance requirements for NASA’s Global Precipitation Measurement (GPM) mission Ground Validation System (GVS). Overall, the GPM mission has defined a series of scientific objectives which include improvement in predicting terrestrial weather, climate, and hydrometeorology through a better observational understanding of the global water cycle. The purpose of the GPM GVS is rooted in the need for independent and objective evaluation of the precipitation products generated by the GPM mission. For its part, the GVS provides an independent means of evaluation, diagnosis, and ultimately improvement of the GPM spaceborne measurements and precipitation retrievals. These goals are more completely defined as follows:

    • Evaluation—Quantify the uncertainties in GPM standard precipitation retrieval algorithms
    • Diagnosis—Understand the time and space error characteristics of GPM precipitation products generated by these algorithms, and
    • Improvement—Contribute to the improvement of GPM precipitation retrieval algorithms throughout the mission.

    Achieving these goals is seen as a necessary step for improved GPM data products and for increased utilization of these products in Global Climate Models (GCMs), Numerical Weather Prediction (NWP) models, and hydrometeorological models for climate and weather forecasting.

  • The Statistical Analysis and Display Program for GPM Validation Network Geometry-Matched PR and GV Data Sets
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    The IDL procedure geo_match_z_pdf_profile_ppi_bb_prox_sca_ps.pro provides the capability to compute statistics and generate displays of PR and GV reflectivity from geometry-matched data produced by the GPM Validation Network prototype. These data are contained in a set of netCDF data files, one per “rainy” site overpass: a TRMM PR overpass of a ground radar (GV) site, with precipitation echoes present, referred to below as an “event”. The procedure computes and displays tables of mean differences (PR-GV) between the PR and GV reflectivity from the geo-matched data for a selected event, with the data stratified into vertical layers in two manners: (1) by height above the surface, in 1.5-km-deep layers, for 15 levels centered from 1.5 to 19.5 km, and (2) into three layers defined by proximity to the bright band (freezing level): above, within, and below the bright band. For purposes of the latter, match-up samples are categorized as above (below) the bright band if their base (top) is 500 m or more above (750 m or more below) the mean bright band height. The remaining points are assigned as within the bright band. The mean bright band height is computed from the bright band analysis in the TRMM PR 2A-25 product. Only the attenuation-corrected PR reflectivity is used in the program, even though the “raw” PR reflectivity also is present in the netCDF data files.

  • GPM Ground Validation System Level 3 Operations Concept
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    This specification defines the Level 3 functional and performance requirements for NASA’s Global Precipitation Measurement (GPM) mission Ground Validation System (GVS). Overall, the GPM mission has defined a series of scientific objectives which include improvement in predicting terrestrial weather, climate, and hydrometeorology through a better observational understanding of the global water cycle. The purpose of the GPM GVS is rooted in the need for independent and objective evaluation of the precipitation products generated by the GPM mission. For its part, the GVS provides an independent means of evaluation, diagnosis, and ultimately improvement of the GPM spaceborne measurements and precipitation retrievals. These goals are more completely defined as follows:

    • Evaluation—Quantify the uncertainties in GPM standard precipitation retrieval algorithms
    • Diagnosis—Understand the time and space error characteristics of GPM precipitation products generated by these algorithms, and
    • Improvement—Contribute to the improvement of GPM precipitation retrieval algorithms throughout the mission.

    Achieving these goals is seen as a necessary step for improved GPM data products and for increased utilization of these products in Global Climate Models (GCMs), Numerical Weather Prediction (NWP) models, and hydrometeorological models for climate and weather forecasting.

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    Annex K: Canadian CloudSat/CALIPSO Validation Project (C3VP) Data Protocol
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    Protocol for C3VP data.

  • Prototype of NASA’s Global Precipitation Measurement Mission Ground Validation System
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    NASA is developing a Ground Validation System (GVS) as one of its contributions to the Global Precipitation Mission (GPM). The GPM GVS provides an independent means for evaluation, diagnosis, and ultimately improvement of GPM spaceborne measurements and precipitation products. NASA’s GPM GVS consists of three elements: field campaigns/physical validation, direct network validation, and modeling and simulation. The GVS prototype of direct network validation compares Tropical Rainfall Measuring Mission (TRMM) satellite-borne radar data to similar measurements from the U.S. national network of operational weather radars. A prototype field campaign has also been conducted; modeling and simulation prototypes are under consideration.

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