IMPROVEMENT OF THE GEOPOTENTIAL
AND DETECTION OF INTERANNUAL OCEANOGRAPHIC SIGNALS
FROM INVERSIOM OF SINGLE AND DUAL SATELLITE ALTIMETRY
Carl A. Wagner
,
Abstract
Extensive analyses of long-term averaged altimetrically determined sea height differences at crossovers for the satellites Geosat, Ers1, and Topex/Poseidon as well as between the pairs Geosat:T/P, Geosat:Ers1 and Ers1:T/P clearly show the effects of orbit errors arising from the geopotential model used in computing their paths. Upon inversion for an adjusted geopotential,
the residuals for the dual satellite crossovers with multi-year gaps reveal surprisingly strong and consistent signals which appear to be largely of interannual oceanographic origin. These cross-mission residuals always compare better with equivalent tide gauge interannual differences at tropical Pacific locations than the original altimetric data. Their consistency was verified with the use of independent collinear Ers2-Ers1 altimetry (1995-1992, without geopotential effect) to connect the 5 year gap of Geosat-Ers1 (1987-1992) with the 8 year Geosat-T/P (1987-1995). Current ocean model differences over these gaps yield only poor to fair correlation with these global residual signals. Their strength limits the precision of the geopotential recovery from both kinds of crossovers. We also show that the height differences are sensitive to a variety of other orbit, instrument, tide and even geodetic error, generally at a lower level of observability. The inversion itself was for a 50x50 harmonic geopotential coefficients, instrument biases, time tag errors, 1 cycle per revolution orbit errors in each satellite and geocenter shifts for each of the three dual satellite pairs.
complete paper is on web:
http://ibis.grdl.noaa.gov/SAT/pubs/papers/wagner_2000
or
http://panurgos.fsv.cvut.cz/~kost/eur00.html