A conversion of the geoid to the quasigeoid at the Hong Kong territories

IF 2.3 Q2 REMOTE SENSING
Albertini Nsiah Ababio, Ismael Foroughi, Robert Tenzer, Mohammad Bagherbandi
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引用次数: 0

Abstract

A levelling network was readjusted and a new geoid model compiled within the framework of geodetic vertical datum modernization at the Hong Kong territories. To accomplish all project objectives, the quasigeoid model has to be determined too. A quasigeoid model can be obtained from existing geoid model by applying the geoid-to-quasigeoid separation. The geoid-to-quasigeoid separation was traditionally computed as a function of the simple planar Bouguer gravity anomaly, while disregarding terrain geometry, topographic density variations, and vertical gravity changes due to mass density heterogeneities below the geoid surface. We applied this approximate method because orthometric heights of levelling benchmarks in Hong Kong were determined only approximately according to Helmert’s theory of orthometric heights. Considering a further improvement of the accuracy of orthometric heights by applying advanced numerical procedures, we determined the geoid-to-quasigeoid separation by applying an accurate method. The comparison of the accurately and approximately computed values of the geoid-to-quasigeoid separation revealed significant differences between them. The approximate values are all negative and reach -2.8 cm, whereas values from the accurate method vary between -4.1 and + 0.2 cm. In addition, we assessed the effect of anomalous topographic density on the geoid-to-quasigeoid separation by employing a newly developed digital rock density model. According to our estimates the effect of anomalous topographic density reaches a maximum value of 1.6 cm, reflecting a predominant presence of light volcanic rocks and sedimentary deposits at the Hong Kong territories. Our numerical findings indicate that the conversion between geoid and quasigeoid models should be done accurately, even in regions with a moderately elevated topography.

香港领土大地水准面到准大地水准面的转换
在香港地区大地测量垂直基准现代化的框架内,重新调整了一个水准测量网络,并编制了一个新的大地水准面模型。为实现所有项目目标,还必须确定准大地水准面模型。通过应用大地水准面-准大地水准面分离,可以从现有的大地水准面模型中获得准大地水准面模型。传统上,大地水准面与类大地水准面的分离是作为简单平面布格重力异常的函数来计算的,而不考虑地形几何、地形密度变化以及大地水准面以下质量密度异质性引起的垂直重力变化。我们之所以采用这种近似方法,是因为香港水准测量基准的正测高度只是根据海尔默特的正测高度理论近似确定的。考虑到通过应用先进的数值程序进一步提高正测高的精度,我们采用精确的方法确定了大地水准面与类大地水准面之间的距离。通过比较大地水准面与类大地水准面分离的精确计算值和近似计算值,发现两者之间存在显著差异。近似值均为负值,达到-2.8厘米,而精确方法计算出的值在-4.1到+0.2厘米之间。此外,我们还利用新开发的数字岩石密度模型评估了异常地形密度对大地水准面与类大地水准面分离的影响。根据我们的估算,异常地形密度的最大影响值为1.6厘米,反映了香港地区主要存在轻质火山岩和沉积沉淀物。我们的数值研究结果表明,即使在地形高度适中的地区,大地水准面与类大地水准面模型之间的转换也应准确无误。
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来源期刊
Applied Geomatics
Applied Geomatics REMOTE SENSING-
CiteScore
5.40
自引率
3.70%
发文量
61
期刊介绍: Applied Geomatics (AGMJ) is the official journal of SIFET the Italian Society of Photogrammetry and Topography and covers all aspects and information on scientific and technical advances in the geomatics sciences. The Journal publishes innovative contributions in geomatics applications ranging from the integration of instruments, methodologies and technologies and their use in the environmental sciences, engineering and other natural sciences. The areas of interest include many research fields such as: remote sensing, close range and videometric photogrammetry, image analysis, digital mapping, land and geographic information systems, geographic information science, integrated geodesy, spatial data analysis, heritage recording; network adjustment and numerical processes. Furthermore, Applied Geomatics is open to articles from all areas of deformation measurements and analysis, structural engineering, mechanical engineering and all trends in earth and planetary survey science and space technology. The Journal also contains notices of conferences and international workshops, industry news, and information on new products. It provides a useful forum for professional and academic scientists involved in geomatics science and technology. Information on Open Research Funding and Support may be found here: https://www.springernature.com/gp/open-research/institutional-agreements
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