The adjustment and combination of GEOS-3 and SEASAT altimeter data
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Date
1983-06
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Ohio State University. Division of Geodetic Science
Abstract
This report documents the processing of the revised NOAA-NGS 3.5 year GEOS-3 altimeter data at The Ohio State University. The goal of the processing is to put the GEOS-3 data set in the same system as the adjusted SEASAT data set and make them consistent with each other so that they can be used as a combined data set in related studies. Before this processing, sea surface heights had a root mean square (RMS) crossover discrepancies of 2.86 meters between SEASAT and GEOS-3 arcs and of 3.75 meters for GEOS-3 arcs at points where ground tracks cross (crossovers). A new procedure described in this report was used to edit GEOS-3 data and to compute crossovers. The new editing procedure is simpler than both the old GEOS-3 and the SEASAT editing procedure. The new crossover computing procedure has the following advantages: (1) It needs only 1/6 CPU time compared with the SEASAT crossover computing procedure used at OSU. (2) It has no limitation of revolution difference between GEOS-3 arcs. (3) It can compute crossovers between SEASAT and GEOS-3 arcs. Six regional crossover only adjustments were performed on the sea surface heights in order to diminish the effects of radial orbit error. The weight assigned to a crossover which is obtained by SEASAT and GEOS-3 arcs is twice as high as by two GEOS-3 arcs. After adjustments, the adjusted data have RMS crossover discrepancies of 0.40 meters between SEASAT and GEOS-3 arcs and of 0.41 meters for GEOS-3 arcs. From this processing, 3,739,905 adjusted GEOS-3 sea surface heights were obtained. Together with 2,282,645 adjusted SEASAT sea surface heights, the combined data set has 6,022,550 sea surface heights. The adjusted GEOS-3 sea surface heights were compared with the adjusted SEASAT data. For 1° x 1° average sea surface heights comparison, the mean difference (GEOS-3 - SEASAT) of 28,810 blocks is 5 cm with a standard deviation of ±52 cm. Considering point predictions of sea surface heights, the average mean difference (GEOS-3 - SEASAT) of 10 different areas is 7 cm with an average standard deviation of ±42 cm. The combined data were compared with both adjusted GEOS-3 and adjusted SEASAT data. Considering two different areas, the average mean difference (GEOS-3 - COMBINED) is 3 cm with an average standard deviation of ±32 cm, the average mean difference (SEASAT - COMBINED) is -1 cm with an average standard deviation of ±27 cm.
Description
Prepared for National Oceanic and Atmospheric Administration, Rockville, Maryland: Grant No. NA80AA-D-00070