Gravity terrain corrections in improvement of (quasi)geoid computation over test area in Bulgaria
20/09/2016 | 17:00 | Session 3: Local/regional geoid determination methods and models
Author(s): Lyubka Pashova and Stanislava Valcheva
Lyubka Pashova and Stanislava Valcheva
Nowadays, the computation of terrain corrections(TCs)on geoid/quasi-geoid heights is routinely performed by commonly used in geodesy conventional methods – classical integration of prism contribution and the 2-D Fast Fourier Transform (FFT)technique.The topography plays a key role for accurate gravimetric determination of the geoid heights; therefore a digital elevation model (DEM) with high spatial resolution is needed for the evaluation of TCs of the gravity-field related quantities.
The topography of Bulgaria is characterized by elevations varied from 0 to 2925m above the mean sea level; with hills and mountains as dominating land forms. The rough terrain gives good opportunity to explore the computed TCs through the classical integration and FFT methods. This paper deals with the numerical evaluation of TCs by two modeling methods using a high-resolution DEM model on a 1"" × 1"" grid of the Shuttle Radar Topography Mission for a test area in South West Bulgaria. The area bounded between 41.5° ≤ φ ≤ 43°and 23°≤ λ ≤ 24° comprise of flat areas and high-mountain massifs with large vertical segmentation and steep slopes. The density value used for the TCs determination was 2.67 g/cm3. The results obtained by both approaches are discussed considering their advantages and disadvantages in accounting the gravitational effect on TCs using grid resolution levels 1”, 3”, 30”, 1’ and 2’ of the terrain model. The classical integration has a better performance than FFT methods, especially in the highest mountain regions, where TCs can be overestimated more than several dozens of mGals in the gravity anomalies using FFT. The effect that the error of TCs computation has on (quasi-)geoid heights is discussed and numerically tested. Some comparisons with previously determined TCs values for the studied area are also done. Further improvement of the gravity field modeling and geoid determination could be expected based on the actual bedrock density information on the Bulgarian territory, which was recently compiled from different sources.