Determination of global mean sea level variations using multi-satellite altimetry

In this study, multiple satellite altimeter measurements (four years of TOPEX/POSEIDON data, two years of ERS-1 data, and two years of Geosat data) are used to determine global mean sea level variations from 1986-1996 with a data gap of approximately four years. In addition to the highly accurate TOPEX/POSEIDON data set, the Geosat and ERS-1 data sets have been updated with the latest orbit and tide models, and where possible, improved media corrections.; The first part of the analysis involves a separate treatment of the three satellite altimetry systems. Global mean sea level variations are computed using a procedure aimed at calculating very precise sea level anomalies from a collinear database, or stackfile, formed by compiling measurements taken along the repeating groundtrack of each satellite. A detailed error analysis for the individual mission results is provided, whereby uncertainties in the orbits, internal instrument calibrations, and media and geophysical corrections are evaluated. The global mean sea level secular trends are determined to be {dollar}{lcub}+{rcub}1.2pm 3.2{dollar} mm/yr for Geosat (1986 to 1988), {dollar}{lcub}-{rcub}0.9pm 2.6{dollar} mm/yr for ERS-1 (1992 to 1994), and {dollar}{lcub}+{rcub}0.2pm 1.7{dollar} mm/yr for TOPEX (1992 to 1996). An assessment of the results shows agreement to within the determined uncertainties when comparisons are made between altimeter and tide gauge measurements, and between simultaneously operating missions.; The second part of the investigation involves combining the results from each mission to obtain a decadal (1986 to 1996) trend estimate of global mean sea level change. This is the first such determination performed with global satellite altimeter data over a decadal time span; previous studies using satellite altimetry have been limited to spans of under 4 years. ERS-1 is linked to TOPEX through the overlapping portion of their missions. Geosat, which lacked an external calibration of its altimeter bias and is separated from the other missions by four years, is linked to TOPEX using a determination of the relative altimeter instrument bias between the two systems, computed with independent tide gauge measurements at 35 island tide gauge locations. The combined Geosat/ERS-1/TOPEX decadal global mean sea level trend is determined to be {dollar}{lcub}+{rcub}1.0pm 2.1{dollar} mm/yr.