Evaluation and combination of multi-sensor shipborne gravity surveys in the German exclusive economic zone of the North Sea

Between 2015 and 2024, a series of five shipborne gravimetry campaigns was conducted within the German exclusive economic zone of the North Sea and adjacent waters. The goal was to obtain an accurate, consistent and properly 3D geo-referenced gravity dataset in the area. This shall serve to compute the marine geoid as the official height reference surface in the German territorial waters, and to validate and calibrate less accurate and reliable historical shipborne gravity data available in the area. The measurement conditions were challenging with cruises lasting up to 78 h and varying sea state conditions. Thus, to ensure the required quality of the measurements in terms of fail-safety and external accuracy, a redundant set of up to four gravimeters of three different types were installed: gyro-stabilized platform spring gravimeter Chekan-AM and strapdown gravimeters iMAR iNAV-RQH-1003 and iMAR iCORUS-02. The gravimeter results are combined to obtain gravity disturbances with optimized accuracy along the trajectories of the nineteen cruises. Furthermore, a novel vehicle oscillation correction is introduced for the iNAV gravimeter that improves its accuracy by 67 to 82%. Following the implementation of a line-wise crossover leveling, an RMSE of 0.21 mGal is obtained for the combined results.