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Abstract
Some important oceanographic results have been obtained with Goddard Earth Models using satellite altimetry. GEM 9 and GEM 10 have been extended through the addition of worldwide GEOS‐3 altimetry to give new solutions, GEM 10B and IOC, fields that are complete in harmonics to degree 36 and 180, respectively. GEM 9 is a field derived solely from satellite tracking observations, whereas GEM 10 is a combination solution containing surface gravimetry. The accuracy of the oceanic geoid for these models has been estimated by using independent altimeter tracks of GEOS‐3. After empirically removing long wavelength orbital errors, residuals of 1.8 m (rms) were obtained for GEM 10, 0.94 m for GEM 10B, while GEM IOC gave 0.75 m.
Large discrepancies, as much as 60 mgals, were found when ocean gravimetry anomalies (5° blocks) were compared to altimetry‐derived values. Altimeter values were verified through comparison with anomalies from GEM‐9, yielding an rms difference of only 5 mgals.
An estimate of the long wavelength departures of the sea surface from the geoid has been made by comparing GEM‐9 to a geometrically derived altimetric surface. The value for the departure of the second degree zonal term was —43 ± 6 cm, an excess oblateness agreeing well with independent oceanographic data.
SEASAT orbital accuracies will be of concern for the most effective use of its 10‐cm altimetry. We demonstrate with the use of crossover arcs of GEOS‐3 altimetry that significant errors in satellite gravitational perturbations have been removed by improving the geopotential field (in GEM 10B) with the GEOS‐3 altimeter and laser tracking data.
