Planning for the NASA GPM Ground Validation (GV) effort is currently focused on two key cost and schedule drivers: the location of the U.S. validation site(s), and the design of the precipitation radar(s) that will support them. To clarify the issues surrounding site selection and radar design, the GPM Project hosted 30 scientific and engineering experts for a two-day GV workshop at GSFC on June 8-9, 2005. The participants included GPM Project representatives, members of the Precipitation Measuring Mission Science Team, plus other NASA and university personnel. The primary goal of this GV workshop was to define a set of trade study criteria to be used in the selection of NASA's continental U.S. ground validation site and its associated precipitation radar.

The first day of the workshop was dedicated to explaining the goals and objectives of NASA’s GPM GV activities. Presenters provided information on the overall GPM status, and details about the GPM GV planned use scenarios, functions, schedule, and budget. Additional presentations explored possible GV instrumentation and output data products. Participants also examined how radar and radiometer simulators are expected to use GPM GV data for estimating top-of-the-atmosphere reflectivity and brightness temperatures. As elements of the GPM validation effort, these quantities will be compared to values measured by instruments flown on the GPM core and constellation satellites.

Day two of the workshop focused on the development of evaluation criteria that will be used in the GV site selection and ground radar trade studies. Four target locations were discussed as potential GPM GV sites:

	The Department of Energy Atmospheric Radiation Measurement site near Ponca City, Oklahoma
	The NASA Wallops Flight Facility sites located on Wallops Island, Virginia
	A site in Huntsville, Alabama managed by NASA’s Marshall Space Flight Center and the University of Alabama
	A site with an existing weather radar and an extensive ground rain gauge network in Melbourne, Florida.

Criteria established for site selection included facilities and logistics, existing instrumentation, installation and operations costs, institutional support, and the ability of each site to meet scientific requirements. Preliminary results of the site selection trade study are expected in September of this year.

Discussion at the workshop also yielded a well-defined trade space and trade study criteria for the GPM GV precipitation radar to be installed at the U.S. study site. It is expected that NASA will develop an X-band and/or S-band radar. Workshop participants defined options for radar deployment, as well as options for polarization, resolution, and other technical aspects of the radar. The radar trade study will progress in parallel with the site selection study to some degree, but results from the radar trade study are expected to follow those of the site selection study.

Access to all workshop presentations and results can be obtained by contacting Mathew Schwaller, the GPM Ground Validation Development Manager (email: mathew.r.schwaller@nasa.gov).

More information about GPM Ground Validation can be found at http://gpm.gsfc.nasa.gov/Newsletter/spring05/article4.htm.

By Mathew Schwaller/ GPM Ground Validation Development Manager

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