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Weather Radar Technology: Beyond Nexrad
Spot beam and electronic scanning technology enable adaptive deployment. Although there are many advantages to satellite-borne systems, they still suffer a basic limitation of contamination by ground clutter at near-surface observations. In summary, space technologies may advance to a point where affordable space-borne weather surveillance radars can play an ancillary role in conjunction with ground-based radars.
Measurements of surface winds over the oceans by space-borne scatterometers and microwave radiometers have been made possible by satellite systems such as the NASA Scatterometer (NSCAT), by the scatterometers on the European Remote Sensing satellites (ERS-1 and 2), by QuickSat, and by the Special Sensor Microwave/Imager (SSM/I) on the Defense Meteorological Satellite Program (DMSP). The impact on global and regional forecast skill has been assessed by several organizations and is reviewed by Atlas et al. (2001). The key portions of their summary follow.
Scatterometer data over the oceans are able to delineate precise locations and structures of significant meteorological features, including cyclones, anticyclones, fronts, and cols. As such, their use by marine forecasters can result in improved analyses, forecasts, and warnings for ships at sea and other marine interests. The use of Scatterometer observations in data assimilation systems can extend their usefulness substantially and lead to improved sea level pressure analyses, improved upper air analyses of both wind and geopotential, and improved short and extended-range numerical weather forecasts. Typically, forecast improvements are skewed toward the Southern Hemisphere extratropics, with the length of a useful forecast extended by as much as 24 h in some Data Assimilation Systems. In the Northern Hemisphere extratropics forecast impact is close to neutral or slightly positive, but occasionally the depiction of an individual storm is improved substantially, leading to a more skillful forecast.
Finally, observations of the ocean surface by airborne and space-borne SAR have revealed heretofore unobservable atmospheric processes by virtue of the effects of the winds on the development of the short surface waves. The nature, intensity, and direction of storms have been deduced from the pattern of SAR echoes on the sea. SAR has also observed cyclonic circulations in the lower atmosphere prior to the development of hurricanes.
The capabilities of future space-based radar systems to supplement ground-based systems should be determined.