Scientific Computation Platform for Geophysical Geodesy

PAGravf4.5 program demo for various terrain effects on all-element gravity field in whole Earth space

Issuing time:2024-11-08 09:14Author:Chuanyin ZhangLink:http://www.zcyphygeodesy.com/en/
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Precise Approach of Earth Gravity Field and Geoid PAGravf4.5 includes the basic principles, main methods and all the formulas in physical geodesy and Earth gravity field have been realized completely   to imporve high education environment. Many long-term puzzles such as various terrain effects on various observations, all-element analytical modelling on gravity field, fine gravity prospecting modelling from heterogeneous observations, external accuracy index measurement and computational performance control have been effectively solved to strengthen the application capacity of Earth gravity field.

The group of programs construct the harmonic terrain influence field, and then develop the rigorous and unified analytical algorithm system for various modes of terrain effects on various types of gravity field elements in whole Earth space on or outside the geoid to synthesize effectively various complex geodetic observations for geophysical gravity prospecting modelling and gravity field data processing.

PAGravf4.5 developed the complete algorithm set of terrain effects to realize various modes of terrain effects on different types of gravity field elements on the geoid or in its outer space.

(1) The set of algorithms are rigorous in theory, the numerical integral has no computation error, and the accuracy of the FFT algorithms is controllable.

(2) There are various modes of terrain masses adjustment, the type of gravity field element affected by terrain can be arbitrary and the field element can be located on or outside the geoid.

(3) Strictly follows the analytical relationship of gravity field between the terrain effects on different types of field elements.

(4) Makes full use of the analytical compatibility between different modes of terrain effects, so that the algorithm codes can be short and concise.

From the terrain effect formulas in sections 7.5 to 7.8, it is easy to see that many algorithm formulas are very similar. Some terrain effect algorithms were realized only by adjusting some parameters with the same codes.

The normal gravity field is the agreed starting datum for the anomalous gravity field, and there is no terrain effect on the normal gravity field. Therefore, the terrain effects on the gravity, gravity disturbance and   gravity anomaly anywhere are exact equal, that on the geopotential and disturbing geopotential and that on the gravity gradient and disturbing gravity gradient are also equal, espectively.

From the terrain data of typical difficult mountainous areas with a mean altitude of 4000m and terrain undulation of more than 3000m, we verify and analyze the performance of various terrain effect algorithms in this group of programs to facilitate and quickly grasp the characteristics and usage of terrain effects.

The terrain effect has always been a very tricky trouble in physical geodesy and gravity prospecting modelling. According to the basic requirements of physical geodesy, PAGravf4.5 puts forward the convenient and practical quantitative criterion for terrain effects, which can give a reliable basis for effectively improving the performance and role of terrain effects in physical geodesy and gravity prospecting modelling.

The terrain effect optimization criterion proposed by PAGravf4.5 according to the basic principles of physical geodesy, can greatly reduce the complexity of terrain effect analysis, and provide a concrete and feasible technical route for effectively playing the key role of terrain effect in gravity prospecting modelling and gravity field approach.

The statistical properties of terrain effects vary significantly with the local terrain, gravity field nature and observations distribution in the computation area. PAGravf4.5 terrain effect computation subsystem presents some cases in a difficult mountain area, and the ratio of the maximum and minimum values to the standard deviation of various terrain effects on various field elements was statistically analyzed. The statistical analysis results of these cases show that, when ignoring the observation distribution and gravity field nature, the local terrain effect is favorable for the gravity data processing, the terrain Helmert condensation is favorable for the processing of gravity gradient data, and the residual terrain effect is more favorable for the refinement of geoid.

Before the computation, it is necessary to carefully test and analyze the technical route of terrain effects according to the local terrain, gravity field nature and available gravity resources in the target area according to the quantitative criterian of terrain effect, so as to ensure that the terrain effect algorithms and parameter settings can be based on some evidence. Only then can the applicability and technical level of the terrain effect processing scheme be significantly improved.





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