Airborne gravimetry mapping of coastal and glacial regions in Norway with implications for the next Nordic geoid model

We present results from an airborne gravity campaign conducted in Norway during December 2024 by DTU Space on behalf of the Norwegian Mapping Authority (NMA). One part of the campaign covered the southwestern coast, mapping the marginal land-sea zone to support the realisation of one common future height system for land and sea areas. The second part covered Jostedalsbreen, a region experiencing large gravity variations due to rough topography including high mountains, glaciers and deep fjords. Root-mean-square-error estimates of crossover points show 1.63 mGal and 1.35 mGal, after modelling residual temperature errors in the iMAR system, in the coastal zone and Jostedalsbreen, respectively. Optimum full-width-half-maximum filtering length is found as 70 and 40 seconds for the two regions, respectively. Comparison with existing (DTU15 and DTU21) global altimetry-derived gravity in the sea area shows standard deviations in the order of 3.66 to 3.28 mGal. Comparison with a preliminary DTU26 altimetry model, including two years of data from the Surface Water and Ocean Topography (SWOT) mission, shows a standard deviation of 2.85 mGal. Outliers in marine gravity data are detected based on comparison with the airborne gravity data and DTU26. The long-wavelength pattern of the residuals between altimetry and marine gravity data coincides with existing questionable geostrophic currents based on geodetic mean dynamic topography models. This indicates erroneous long-wavelength signal in the underlying gravimetric geoids.