D. Solheim

Geoid of the Nordic and Baltic Region from Gravimetry and Satellite Altimetry

An updated high-resolution geoid model for the Scandinavian and Baltic region has been done by spherical FFT approaches, taking topography into account by a hybrid RTM/Helmert condensation approach. Significant new data sources have entered the geoid solution: a new spherical harmonic reference model, new gravity data over many regions, including the Baltic republics and the Russian border regions, and new high-resolution topographic sources. ERS-1 geodetic mission satellite altimetry has been included in the Baltic, using Fourier-based draping techniques, and taking sea surface topography from tide gauge levellings into account. Compared to more than 300 GPS-levelling points across the region the geoid shows a fit at the 10 cm level, thus being a major improvement over earlier models. In local regions with good gravity coverage, such as Denmark, the geoid fitted to the national GPS net yields accuracies at the 1 cm-level, thus allowing accurate operational levelling by GPS.

Combining altimetric/gravimetric and ocean model mean dynamic topography models in the GOCINA region

Initially, existing mean dynamic topography (MDT) models were collected and reviewed. The models were corrected for the differences in averaging period using the annual anomalies computed from satellite altimetry. Then a composite MDT was derived as the mean value in each grid node together with a standard deviation to represent its error. A new synthetic MDT was obtained from the new mean sea surface (MSS) KMS04 combined with a regional geoid updated using GRACE gravity and gravimetric data from a recent airborne survey. Compared with the composite MDT the synthetic MDT showed very similar results.

Updated OCTAS Geoid in the Northern North Atlantic - OCTAS07

A new gravimetric geoid (OCTAS07v2) is generated using Stokes’ formula with gravity data as input. As local gravity data, a combination of land gravity data, new and old airborne gravity data, and adjusted marine gravity data has been used. All marine gravity data has been error screened and quality assured by removing dubious data and adjusting the data when necessary. Voids in the gravity data distribution were patched with gravity data from satellite altimetry. The OCTAS07v2 geoid was estimated using the remove-compute-restore technique. The long-wavelength signal of the local gravity data was reduced using a Wong-Gore modified Stokes’ function. The long-wavelength part was represented by a global gravity field model based on GRACE data. The OCTAS07v2 geoid model was combined with the OCTAS07_MSS model to create a synthetic Mean Dynamic Topography (MDT) model. In comparison with the OCCAM MDT, our new synthetic MDT model gave a std. dev. of the residuals of 11 cm. A comparison to the main northern North Atlantic currents show many similar features