Latest Documents

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    GPM Ground Validation: Strategy and Efforts
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    The validation of satellite products is classically defined as a ground-based observing strategy intended to assess whether satellite products meet their stated accuracy requirements and objectives. In the case of the Tropical Rainfall Measurement Mission (TRMM), this philosophy was translated to the quasi-continuous operation of four ground radar sites for which TRMM satellite sensor-based and ground-based rainfall products were compared. The findings from these four sites revealed that TRMM products generally met their stated objectives. In addition, a number of lessons have also been learned in the course of these efforts: (a) quality control and careful construction of ground validation datasets is very labor intensive, but methods that make calibration and quality control techniques more efficient continue to improve; (b) despite every effort, ground validation data has its own set of uncertainties, consisting of both biases (currently ~ 5%) and random errors that are difficult to quantify on short time/space scales such as a single satellite overpass; and (c) direct comparison between rainfall estimates from the TRMM Precipitation Radar (PR) and microwave imager (TMI) reveal that instrument differences have regional and seasonal components that require validation results to be interpreted in a similar fashion.

  • 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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    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.

  • 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.

  • 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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    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).

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