A comparison between sea-bottom gravity and satellite altimeter-derived gravity in coastal environments: A case study of the Gulf of Manfredonia (SW Adriatic Sea)

The marine gravity field derived from satellite altimetry is generally biased in coastal areas by signals back-scattered from the adjacent land. As a result, the derived gravity anomalies are generally unreliable for geophysical and geological interpretations of near-shore environments. We compared two different altimetry models with sea-bottom gravity measurements acquired along the Italian coast to quantify the errors generated by reflections from onshore areas and verify the quality of the geologic models inferred from gravity data. We focused on the Gulf of Manfredonia, in the SE sector of the Adriatic Sea, where (i) two different sea-bottom gravity surveys have been conducted over the years, (ii) the bathymetry is mainly flat, and (iii) seismic data has revealed a prominent carbonate ridge covered by hundreds of meters of Oligocene-Quaternary sediments. Gravity field derivatives have been used to enhance both deep geological contacts and coastal noise. The analyses point to a ringing noise that degrades the altimeter signals up to 17 km from the coast. Differences between observations and gravity calculated from a geological model and constrained by seismic data show that all the datasets investigated register approximately the same interference patterns associated with the Gondola Fault Zone. This study shows the potential for integrating gravity anomalies from satellite altimetry with high-resolution near-shore data, such as that provided by sea-bottom gravity network available around the Italian coasts. Future applications will use this technique to improve the analysis of the connections between marine and inland geology in transitional areas.