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September 2001

The Mesa Lab becomes a test bed for GPS observations

Left to right: Sandy MacDonald (director of NOAA Forecast Systems Laboratory), GST director Randolph "Stick" Ware, and NCAR director Tim Killeen unveil the new GPS receiver. (Photo by Carlye Calvin.)

The receiver is now atop the Mesa Lab's B1 tower. (Photo by Carlye Calvin.)

The striking view toward the east that wows visitors to the Mesa Lab is now serving a scientific purpose. UNAVCO, part of UOP's GPS Science and Technology Program (GST), installed a Global Positioning System receiver this summer on a tripod atop the lab's B1 tower. The receiver measures slant-path signals, those arriving at low angles and thus passing through the lower atmosphere for long distances. Recently Sandy MacDonald, director of NOAA Forecast Systems Laboratory, demonstrated that the combination of slant GPS with wind radar and microwave profiler data can provide high- resolution three-dimensional moisture and wind fields. Such a three-dimensional picture may improve local-area models. According to GST director Randolph "Stick" Ware, "The moisture field has been very poorly sampled [to date], and yet it is fundamental to climate and weather. Slant GPS measurements can improve the definition of atmospheric moisture fields." In a forthcoming paper in the Journal of Geophysical Research, Aiguo Dai (CGD) and coauthors show that GPS measurements capture the diurnal ebb and flow of precipitable water, something that twice-daily radiosondes can't do. Francois Vandenberghe (RAP) is comparing the technique's results to model output. The ML tower site is part of SuomiNet, an NSF-sponsored UOP program that is establishing real-time GPS stations for atmospheric sensing at universities in the United States and abroad.

• Bob Henson

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Last revised: Mon Sep 17 15:38:00 MDT 2001