Latest Documents

  • International Ground Validation Research Programme of GPM: Report of 1st International GPM GV Requirements Workshop
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    Report of the 1st International GPM GV Requirements Workshop.

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    2DVD at Egbert, CARE, Canada
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    Presentation of CSU's 2-Dimensional Video Disdrometer for the Canadian CloudSat/CALIPSO Validation Programme

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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.

  • 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.

  • Snowflake Size Distribution Measurements in South Central Ontario, Canada
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    Parsivel Distrometer Results presented at the American Geophysical Union, Spring 2007.

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    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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    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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