A high-resolution gravimetric quasigeoid model for Vietnam

Dinh Toan Vu,Sean Bruinsma,Sylvain Bonvalot

doi:10.1186/s40623-019-1045-3

Abstract

A high-resolution gravimetric quasigeoid model for Vietnam and its surrounding areas was determined based on new gravity data. A set of 29,121 land gravity measurements was used in combination with fill-in data where no gravity data existed. Global Gravity field Models plus Residual Terrain Model effects and gravity field derived from altimetry satellites were used to provide the fill-in information over land and marine areas. A mixed model up to degree/order 719 was used for the removal of the long and medium wavelengths and the calculation of the quasigeoid restore effects. The residual height anomalies have been determined employing the Stokes integral using the Fast Fourier Transform approach and deterministic kernel modification proposed by Wong–Gore, as well as by means of Least-Squares Collocation. The accuracy of the resulting quasigeoid models was evaluated by comparing with height anomalies derived from 812 co-located GNSS/levelling points. Results are very similar; both local quasigeoid models have a standard deviation of 9.7 cm and 50 cm in mean bias when compared to the GNSS/levelling points. This new local quasigeoid model for Vietnam represents a significant improvement over the global models EIGEN-6C4 and EGM2008, which have standard deviations of 19.2 and 29.1 cm, respectively, for this region.

Highlights

The quasigeoid is defined as a surface that is the closest to mean sea level (Hofmann-Wellenhof and Moritz 2006)
The results of GEOID_LSC show a standard deviations (STD) of 8.7 cm for the first- and secondorder points and 10.8 cm for the third-order points, while GEOID_FFT has a STD of 9.1 cm for the first- and second-order points and 10.4 cm for the third-order points (Table 7). These results show that the Least-Squares Collocation (LSC) method is a little more precise than the 1D Fast Fourier Transform (FFT) where gravity data are available. To further clarify this issue, we have evaluated the quasigeoid in two areas where there is sufficient terrestrial gravity as well as Global Navigation Satellite System (GNSS)/levelling data (136 GNSS/levelling points in a northern area defined by 20° ≤ φ ≤ 22° in latitude and 105° ≤ λ ≤ 108° in longitude and 120 GNSS/levelling points in a southern area defined by 8° ≤ φ ≤ 11° in latitude and 104° ≤ λ ≤ 108° in longitude)
Two gravimetric quasigeoid solutions, called GEOID_FFT and GEOID_LSC, were computed with the Stokes’ integral using the FFT-1D approach and deterministic kernel modification as proposed by Wong–Gore and the LSC method, respectively. These quasigeoid models were validated through a comparison with 812 GNSS/levelling points

Summary

Introduction

The quasigeoid is defined as a surface that is the closest to mean sea level (Hofmann-Wellenhof and Moritz 2006). It serves as a reference surface for the vertical system (Torge and Müller 2012). There is a strong need for a high-accuracy and highresolution gravimetric quasigeoid model of Vietnam and its vicinity for the purpose of modernizing the height system using GNSS instead of spirit levelling, as well as for other applications such as geology, geophysics, and oceanography. The resulting standard deviations (STD) obtained for the most recent geoids models range from a few cm up to 30 cm, depending on the quality of the available

Objectives

Findings

Conclusion