A new land – based gravity data set for the Alps and adjacent regions – the AAGRG at work

A pan-Alpine gravity data map, homogeneous regarding input data sets, applied methods and corrections as well ascommon reference frames, is not available yet. Therefore, all countries around the Alps have agreed to contributewith gravity data and/or gravity data processing techniques to a recompilation of the alpine gravity field in theframe of the AlpArray Gravity Research Group (AAGRG). Also to collaborate with other groups in AlpArray.In the last year group members met two times to set up guidelines for joint processing and homogenizationof existing gravity data sets. Following the results and appointments of the last technical AAGRG meeting inBratislava October 2018, the members of the 9 participating countries decided to present a first data set of theBouguer gravity field in September 2019 on a 2km x 2km or 4km x 4km grid for the public. Other compilationswill follow: maps of Free Air Gravity, regional field and the corresponding residual gravity field. These new datasets will be available to all AlpArray partners for interdisciplinary work and modelling.This new Bouguer anomaly will be station completed with at least 1 point/4 km2 resolution and compiledaccording to the most modern criteria. In general, even though global models like SRTM1 perform well, thepreference was given to local DEMs - if available. Two software packages for topographic corrections on thebase of ellipsoidal heights are available: “TOPOSK”, developed by Slovak colleagues, and the “adaptive masscorrection” from the Kiel group. The results of both methods are being tested and compared. The geophysicalindirect effect and its determination are also taken into account. Special emphasis is put on the lakes in the studyarea. They have a considerable effect on the gravity of stations that lie at their edges (for example, the partiallyvery deep reservoirs in the Alps). In the Ligurian and the Adriatic seas ship data of the Bureau GravimétriqueIinternational will be used. Although not unproblematic, these data got the preference over satellite data.In the AAGRG, long discussions were centered on the calculation of long-distance effects of topogra-phy/bathymetry and its compensating masses (root). The first compilation of the AA Bouguer anomaly mapwill, however, be prepared WITHOUT taking long-distance effects in account. The group agreed to extendthe correction radius to the Hayford zone O2(167 km). All topographic corrections will be calculated as masscorrections between the physical surface and the ellipsoidal reference. The group further discussed the necessityof a 3D interpolation of the gravity grid values. Although a 3D interpolation would be required from themethodological-theoretical point of view (the problem is the non-identical gravity and height grids), it was decidedto perform a 2D interpolation in the first compilation - the method of Kriging shall be applied. The poster will visualize the mentioned correction effects and illuminate the necessity of a complete revision of the existing land based Alpine gravity data.