On the Determination of Marine Geoid Models by Least-Squares Collocation and Spectral Methods Using Heterogeneous Data

In the frame of the EU-sponsored GAVDOS project the need of a new high-resolution and high-accuracy geoid model for the calibration of altimeters onboard satellites like JASON-1, ENVISAT and EURO-GLOSS and for sea level monitoring purposes has become apparent. That was mainly due to the fact that the already available models have been estimated using outdated datasets and fail to meet the wanted, cm-level, accuracy requirements. To determine the new geoid models multi-satellite (ERS1 and GEOSAT) altimetry and land and marine gravity data have been used. The EGM96 global geopotential model has been employed, while the effect of the bathymetry has been taken into account using recently developed local Digital Depth Models (DDMs). Several solutions have been estimated based on the different datasets used and the two main methodologies followed, i.e., the Fast Fourier Transform (FFT) based Input Output System Theory (IOST) and Least Squares Collocation (LSC). The accuracy of the new models was assessed through comparisons with TOPEX/POSEIDON (T/P) data and the GEOMED geoid solution for the area under study. Finally, the consistency between the estimated solutions has been determined by comparing the geoid height value they provide at the Gavdos Tide Gauge (TG) station on the isle of Gavdos. From the results it was found that the precision of the new geoid models is between ±0.9 and ±3.3 cm, their accuracy ranges between ±5 and ±10 cm and their consistency is at the ±0.5 − 6 cm level.