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FOR RELEASE DECEMBER 5 OR THEREAFTER

       A NASA Jet Propulsion Laboratory scientist has proposed monitoring the sea level in relation to the Earth's crust as potential way of observing greenhouse effect.

       Edward J. Christensen said change in global sea levels would be probable indirect response of global warming, and has proposed using altimetry transponders to measure changes.

       He is presenting paper entitled, "Monitoring Change in Global Sea Level with Altimeter Transponders," before the 1989 Fall Meeting of the American Geophysical Union at San Francisco, Dec. 5. co-author is Peter F. MacDoran of the University of Colorado at Boulder.

       In order to isolate the effects of change in the volume of the world's oceans, it is critical that tectonic, volcanic and other adjustments be considered, Christensen said.

       Monitoring global sea level is one of the goals of the proposed joint U.S.-French satellite project Topex/Poseidon, he said, but current plans do not include monitoring changes in sea level relative to the Earth's crust using altimetry alone.

       "We propose that this be accomplished using an array of altimeter transponders, equipped with Global Positioning System (GPS) receivers on open ocean and on land," Christensen said.

       The dual frequency transponders would be deployed along the satellite groundtrack and would serve as control points for the network.

       Data from the altimeters, which accurately measures the levels of the sea, when combined with the position of the orbit and transponder data, can provide continuous record of sea level relative to the land-based sites at five or 10 day intervals.

       The study was performed at JPL under contract with the National Aeronautics and Space Administration.

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