Global Precipitation Measurement (GPM) Ground Validation will provide a quantitative check to the rainfall estimates generated from GPM satellite data. In support of this activity, designs for the GPM Ground Validation Segment (GVS) anticipate a combination of ground-based instruments and analysis tools that will:

	Quantify the accuracy and errors of GPM rainfall products
	Define the uncertainties in the GPM standard rainfall retrieval algorithms
	Contribute to the improvement of GPM rainfall algorithms throughout the mission

Achieving these goals should improve GPM data products and increase their utilization in Global Climate Models (GCMs), Numerical Weather Prediction (NWP) models, and hydrometeorological models for climate and weather forecasting.

The framework for the GPM GVS is based on the notion of a Multidimensional Observing Volume (MOV) and Satellite Simulator Model (SSM)as illustrated in Figure 1 and as described below.

Figure 1: The GPM Ground Validation Segment Concept

Multidimensional Observing Volume (MOV): The MOV consists of ground-based instruments that measure local surface and atmospheric properties required for GPM validation. The design of the MOV is still in progress, but its instruments will likely include surface precipitation gauges, ground-based radars and radiometers, and other meteorological sensors.

Satellite Simulator Model (SSM): The SSM utilizes MOV measurements in numerical models, the goal of which is to calculate (1) microwave quantities identical to within sensor noise of those measured by the GPM Core Satellite or other targeted satellites, (2) precipitation quantities identical to those generated by the standard GPM algorithms, and (3) quantitative/objective error estimates of both sets of quantities. The SSM thus supports the main objectives of the GPM GVS: error characterization of the standard GPM precipitation products, and continuous improvement of the GPM standard algorithms via reporting of product bias and uncertainty.

At present, the GPM GVS is in formulation. A peer-reviewed team has been established to study the feasibility of the MOV and SSM concepts identified above, and to contribute to the final design of the GVS. The members selected for this team include:

	V. Chandrasekar, Colorado State University
	Robert Meneghini, NASA/GSFC
	William Olson, NASA/GSFC
	Steven Rutledge, Colorado State University (team leader for a consortium that includes additional members from other institutions)
	Sandra Yuter, University of Washington

Reports from the GPM Ground Validation feasibility studies are expected in August 2005. These results, along with a planned prototype activity, will contribute to the GVS design, which is expected to be complete by July 2007. Following completion of the design, instrumentation will be fielded, analysis capabilities established, and the GVS will be ready for operations some time during the year prior to the launch of the GPM Core Spacecraft.

For more information on GPM Ground Validation, please contact

Mathew Schwaller
GPM Ground Validation Development Manager
mathew.r.schwaller@nasa.gov
+1-301-614-5382

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