Up-to-date Terrain Correction Evaluation within the Gravity Database of the Slovak Republic

Abstract:

In our contribution we present a new method for the evaluation of terrain corrections (TC) and/or topographical effects (TE) for the Gravity Database of the Slovak Republic - using a new software solution (program Toposk) and up to date high-quality digital terrain models. The program was successfully tested on several synthetic models. In our algorithm we have used the well established approach, developed by the gravimetrical school in former Czechoslovakia i.e. dividing the surrounding area into so called inner zone T1 (0 - 250 m), intermediate zone T2 (250 - 5240 m) and outer zone (5.24 - 166.7 km). When calculating the T1 zone contribution we have used interpolated station elevations instead the measured ones, which yield in our opinion better solution to the problem of small-scale inaccuracies of the detailed terrain model. Newly recalculated TC values for the Gravity Database of the Slovak Republic (total number of gravity stations equals 212478, with an average of 3-6 points/km2) are in the range from 0.20 to 79.84 mGal (for the correction density 2.67 gcm-3). Thanks to the new TC values, the final version of the obtained Bouguer anomaly field is more independent from non-geological influences and determines in a better way the information content on the lithospheric density distributions.
In the frame of the presented recalculation of regional gravity database we have worked with the concept of terrain corrections, but for other types of gravity method applications, the evaluation of topographical effects is much more straightforward - e.g. elimination of the effect of topography in the vertical gravity (tower) gradients approximation or during processing of absolute gravity measurements (with FG-5 and/or A-10 gravity meters). Another very important property of our proposed approach is that we can evaluate TC and TE in calculating points below the Earth’s surface (applicable also in borehole gravity method, BHGM). This work was supported by the Slovak Research and Development Agency under the contracts APVV-0194-10 and APVV-0827-12.