Determining regional sea surface topography by GNSS surveys on ice

Sea surface topography (SST) - the difference between the geoid and sea surface height (SSH), is requested for many marine applications, e.g. for analyzing currents and variation of salinity. Globally, SST can be roughly determined by using satellite altimetry and oceanographic data. However, in coastal areas, the accuracy and spatial resolution of these methods are rather low. Accordingly, issues related to enhancing SST resolution and accuracy with GNSS (Global Navigation Satellite Systems) measurements are explored in this study. A practical case study that was carried out on the ice surface over a part of the Baltic Sea tackles profile- and point-wise GNSS measurements for determining SST. Profile-wise GNSS measurements were proceeded on official ice roads (altogether 50 km) between the mainland and the two major islands (Saaremaa and Hiiumaa). The GNSS profiles were complemented with GNSS point-wise measurements scattered (1 point per 25 km²) all over the study area. The GNSS-derived SSH, which is the difference between the ellipsoid and the sea surface, was corrected with ice freeboard and corrections due to offsets of instantaneous sea level height values from the mean sea level. For calculating SST from the GNSS-derived and corrected SSH, a recent high-resolution (1´ × 2´) gravimetric geoid model GRAV-GEOID2011 was used. The estimated SST was compared to the global SST model DTU10MDT and with an earlier regional SST model.