Total dynamic sea surface topography can be recovered from radar altimeter data given an accurate estimate of the local level surface or geoid. A new technique, the “synthetic geoid,” has emerged from research using data from the GEOSAT 17-day exact repeat orbit (Eos, July 11, 1989, p. 698). The geoid estimate, useful for mesoscale topography, is constructed by subtracting an independent estimate of the mean mesoscale oceanography from the main sea surface as measured by the altimeter.
The GEOSAT Data Validation effort—a Navy-sponsored collaboration between the Johns Hopkins University Applied Physics Laboratory, Harvard University, and Rutgers University—has completed the construction and validation of a synthetic geoid that allows the total dynamic topography of the Gulf Stream front and eddy system to be determined from GEOSAT, the future GEOSAT Follow-On, or any future system in the SEASAT/GEOSAT ground track. The synthetic geoid covers the region between Cape Hatteras and the Grand Banks. The independent estimate of the mean oceanographic dynamic topography was obtained from the Harvard University Gulfcast data base which includes 1 year of daily realizations of the region's velocity field. The synthetic geoid was validated by comparing absolute dynamic topography derived from individual GEOSAT passes with concurrent topography from Gulfcast and AXBT underflights.
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