Numerical investigation of downward continuation methods for airborne gravity data

Two airborne surveys were carried out in the Crete region of Greece. A first airborne gravity survey was done in February 2001 to cover the southern part of the Aegean sea and the island of Crete in the frame of the European Community CAATER (Coordinated Access to Aircraft for Transnational Environmental Research) project, primarily aiming at the establishment of the gravity information needed to connect the existing gravity data on the island of Crete to the altimetric gravity field in the open sea. A second airborne gravity survey was carried out in January 2003 over the island of Gavdos and the surrounding sea areas south of Crete, in the frame of the GAVDOS project, an ongoing European Community-funded project aiming at the development of a calibration site in the island of Gavdos for altimetric satellites. The main goal of this paper is the evaluation of the airborne measurements from the above mentioned campaigns through a comparison of the downward continuation methods in the space and frequency domain. Different downward continuation schemes are evaluated, with comparisons to satellite altimetry showing accuracies close to 4 mGal in terms of standard deviation of the differences between the downward continued gravity anomalies and the altimetry derived gravity anomalies. Finally, some remarks are presented with regards to the construction of a detailed gravity anomaly grid based on all the available satellite and surface gravity data sources.