Improving Gravity Field Modelling in the German-Danish Border Region by Combining Airborne, Satellite and Terrestrial Gr
In order to improve the gravity field and geoid modelling in the border area between Germany and Denmark including the Baltic Sea and North Sea, three airborne gravity surveys have been undertaken since 2006: BalGRACE-06, NorthGRACE-07, NorthGRACE-08 (Bal
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Improving Gravity Field Modelling in the German-Danish Border Region by Combining Airborne, Satellite and Terrestrial Gravity Data U. Schäfer, G. Liebsch, U. Schirmer, J. Ihde, A.V. Olesen, H. Skourup, R. Forsberg, and H. Pflug
Abstract In order to improve the gravity field and geoid modelling in the border area between Germany and Denmark including the Baltic Sea and North Sea, three airborne gravity surveys have been undertaken since 2006: BalGRACE-06, NorthGRACE-07, NorthGRACE-08 (Baltic resp. North Sea GRavity Airborne Campaign and Examine). These endeavours were aiming to give a substantial contribution towards comparison, verification and improvement of the vertical reference in this area. During these campaigns more than 25,000 km of track data were gathered with three different models of LaCoste&Romberg gravimeters mounted in two different aircrafts. Owing to the recent airborne gravity efforts we were able to cover most of the mentioned area yielding gravity anomalies with an accuracy better than 2 mgal according (i) to cross-over estimates and (ii) to comparison with non-airborne gravity data. Due to considerable turbulences on some flights not all of the airborne measurements could be successfully used. Data from turbulent flights were partly too noisy and did not meet the quality criteria. Attaining highquality airborne gravity anomalies is still a demanding business. In this study we present the data handling of the airborne gravity data from three campaigns carried out under quite different conditions. It is described how the airborne data have been checked, homogenized and used to fill-up various existing data gaps. A first result of improved regional gravity field and geoid modelling is presented, using the newly obtained U. Schäfer () Federal Agency for Cartography and Geodesy (BKG), Frankfurt am Main D-60598, Germany e-mail: [email protected]
airborne gravity data in connection with existing terrestrial data and satellite observations.
59.1 Motivation Before the BalGRACE and NorthGRACE campaigns the border region between Germany and Denmark and the adjacent Baltic and North Sea areas were characterized by a quite inhomogeneous spatial distribution of gravity points and of their measurement epochs. Compared to the land regions, the sea areas contain less observations with poorer data quality. In some areas, e.g. in the mud flats, lagoons, along coastlines, and around the numerous islands there were no observations at all (cf. to the previous existing gravity measurements, i.e. grey points in the background of Fig. 59.1). By their inherent nature the different existing data (land gravity, marine gravity, and reliable satellite altimetry data) have practically no over-lapping zones in the near-coastal areas. Neither by terrestrial observations nor by ship-borne measurements only, is it possible to obtain an appropriate, homogeneous data coverage along and across the coastlines. In the last years airborne gravimetry has become a major tool for gravity data acquisition in such areas. Acknowledging t
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