Airborne Gravimetric Survey of Switzerland

Abstract

The Institute of Geodesy and Photogrammetry (IGP) of the ETH Zurich has acquired airborne gravity data in a joint project with LaCoste and Romberg Gravity Meters, Inc. The survey covering the entire country of Switzerland was flown in a Twin-Otter aircraft owned by the Swiss Federal Office of Cadastral Measwements. The aircraft was outfitted with three GPS receivers, one for navigational purpose and two for positioning and monitoring of aircraft accelerations. A modified LaCoste and Romberg marine gravimeter recorded data at a sampling rate of one second. Modifications included anti-alias filters and an absolute encoder for the measuring screw. Flights were performed during November and December 1992 at barometric altitude of 5200 m above sea level. A preliminary airborne Bouguer anomaly map. computed at flight altitude with topographic corrections up to 167kmwith density of 2670 kg/m3 is presented and qualitatively compared to the existing ground Bouguer anomaly map. Computation of the g values at crossing points between lines flown at comparable altitudes shows differences of the order of 25 mgal (10-5 m/s2). Computation of the RMS difference between upward continued ground data (extracted from the Bouguer gravity map of Switzerland) and the airborne Bouguer anomaly data gives differences of the order of 6.3 mgal.