Ground Validation Documents

  • Parsivel (Laser Optical) Disdrometer
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    Overview of the Parsivel instrument:

    • Measures size and fall velocity of hydrometeors
    • Present weather sensor
    • Sampling area: ~50 cm2, varies with drop diameter
    • Number of size and velocity bins: 32 x 32 matrix
    • Drop size range: 0.06-24.5 mm
    • Velocity range: 0.05-20.8 m/sec
    • Operation period at Wallops Island: Spring 2002 - present
    • Manufacturer: OTT in Germany www.ott-hydrometry.de
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    2-Dimensional Video Disdrometer (2DVD) from IOP-2
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    A series of measurements at the CARE site from the 2DVD instrument.

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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.

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

  • GPM Ground Validation System Level 3 Operations Concept
    Author(s):
    Keywords:
    Publication Date:
    Abstract / Summary:

    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.

  • 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.

  • 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.

  • 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.

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    C3VP Access Information
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    A summary of C3VP data access.

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    Disdrometer Derived Z-S Relations in South Central Ontario, Canada
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    During the winter of 2006-2007, a number of in-situ and remote sensing precipitation measuring devices were operated at the Center of Atmospheric Research Experiment (CARE) site located near Egbert, Ontario about 30 km to the NW of the King City C-band operational dual-polarized radar. While the experiment was originally designed to measure winter precipitation for the Canadian Cloudsat/CALIPSO validation program (C3VP), the NASA’s Global Precipitation Measurement (GPM) ground validation program joined the efforts (cf. Petersen et al., 2007; this conference) bringing optical disdrometers (2D-video and two Parsivel disdrometers) and a multi-frequency radar. The CARE is a well- instrumented facility including Vaisala FD12P visibility sensor, Precipitation Occurrence Sensor System (POSS), the McGill University’s vertically-pointing X- band Doppler, and Hydrometeor Velocity and Shape Detector (HVSD).

    In this paper we focus on two case studies, (a) the 6 December 2006 and (b) the 22 January 2007 snow events. Our objectives are six-fold, (a) to determine the characteriscs of snow size spectra, (b) to determine the bulk density of snow by comparing measurements of Parsivel and FD12P, (c) to estimate a density (ρ) versus ‘size’ relation for snow by comparing the 2D-video derived Zh measurements with the well-calibrated King City Zh data, (d) to compare the Zh between 2D-video, POSS and King City radars, (e) to estimate snowfall rate (SR) and equivalent melt water (MWR) rate, including comparison of melt water accumulations from 2D-video, POSS, and other ground-based instruments at the CARE site, and (f) to derive the Zh-SR and Zh-MWR power law relations from 2D-video and Parsivel data.

     

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