Gravity Data Base Generation and Geoid Model Estimation Using Heterogeneous Data

Abstract

The computation of high-resolution and high-precision geoid models in the Eastern part of the Mediterranean Sea usually suffers from the few gravity observations available. In the frame of the EU-sponsored GAVDOS project, a systematic attempt has been made to collect all available gravity data for an area located in the Southern part of Greece and determine new and high-resolution geoid models. Thus, all available gravity data have been collected for both land and marine regions and an editing/blunder-removal processing scheme has been followed to generate an optimal gravity dataset for use in geoid determination. The basic analysis and validation of the gravity data-bank was based on a gross-error detection visualization and collocation scheme. The Least Squares Collocation (LSC) method was employed to predict gravity at known stations and then validate the observations and detect blunders. The finally generated gravity database presents a resolution of 1 arcmin in both latitude and longitude while its external and internal accuracies were estimated to about ±5 mGal and ±0.2 – ±0.4 mGal, respectively. Based on the derived gravity database a gravimetric geoid model was developed using the well-known remove-compute-restore method with an application of a 1D Fast Fourier Transform (FFT) to evaluate Stokes’ integral. Altimetric geoid solutions have been also determined from the GEOSAT and ERS1 geodetic mission altimetry data. Finally, combined geoid models have been computed using the FFT-based Input Output System Theory (IOST) and the LSC methods. The consistency of the geoid models estimated was assessed by comparing the geoid height value at the Gavdos Tide Gauge (TG) station on the isle of Gavdos. Their accuracy was determined through comparisons with stacked T/P sea surface heights. From the comparisons performed it was found that the accuracy of the gravimetric, altimetric and combined models was at the ±14.5 cm, ±8.6 cm and ±12.5 cm level, and their consistency at about ±2 cm.