Comparison Between GPS Sea Surface Heights, MSS Models and Satellite Altimetry Data in the Aegean Sea. Implications for Local Geoid Improvement

Abstract

We have conducted various experiments of sea surface height (SSH) measurements in Greece’s Aegean Sea using on-board kinematic GPS recordings and the KMSS04 satellite altimetry-derived mean sea surface for comparison. This region is of particular interest because of strong crustal movements due to intense tectonic activity that create significant local geoid variations. In this paper, we report on the results of separate SSH surveys that were conducted in three test areas in the Aegean Sea. Ship borne GPS data were collected together with GPS data simultaneously collected at nearby mainland reference stations. These high rate data were processed in kinematic mode using scientific GPS software and related to SSH observations, thus allowing us to obtain maps of the instantaneous sea surface, which was estimated with a precision at the level of a few centimeters. Tidal recordings from nearby tidal stations provided us with the required tidal corrections for the reduction of the GPS-derived SSHs to mean sea level (MSL). Following a filtering process, a cross over adjustment and gridding of the pointwise SSH observations in each test area, local maps of the mean sea surface (MSS) were obtained, which can be compared with the available KMSS04 global solution for the MSS. To examine further the MSS-related results that we observed in these experiments, we compared both the GPS-derived and the KMSS04-related MSS with JASON-1 radar altimetry and ICEsat laser altimetry data over the same areas. We show that the SSHs derived from the GPS ship surveys, when carefully analyzed and applying suitable filtering techniques and necessary corrections for the Dynamic Ocean Topography (DOT) can provide enhanced shorter wavelength components of the local geoid. This is illustrated with additional comparisons with the EGM96 and EGM08 global geoid models, in order to reveal any significant differences, mainly in the short wavelength domain, when compared to the aforementioned local geoid models computed from purely GPS-derived SSH data.