The earth's gravity field

拟议的研究包括两个相互交织的项目，它们建立在以前研究的基础上，第三个项目涉及新的调查路线。前两个项目涉及对澳大利亚境内合成(即人造)重力场的微调，以及同时改进用于大地水准面计算的UNB技术(在大地测量界称为Stokes-Helmert技术)。大地水准面是测绘中用作高程基准的水平面，它与重力有着非常密切而又错综复杂的关系。因此，合成重力场可用于大地水准面计算技术的客观和/或盲法测试。国际大地测量协会希望进行这种测试，以确定一种可推荐用于计算国家大地水准面的技术。我们在澳大利亚的合成场地上测试了UNB技术，这是有史以来第一次进行此类测试，我们发现结果中存在35 mm的偏差，加上山区120 mm峰值的一些较大的点差。虽然点值可以解释为离散化误差，但如果它与澳大利亚合成场有关，偏差太大，无法将该场作为无误差标准具接受。合成领域和UNB技术都需要进一步研究，以达到5毫米的精度水平，这将通过拟议的研究进行。

The proposed research comprises two intertwined projects that build on previous research, and a third project involving a new line of investigation. The first two projects concern the fine tuning of the synthetic (i.e., artificial) gravity field formulated for the territory of Australia and a simultaneous improvement of the UNB technique (known in geodetic circles as the Stokes-Helmert technique) for geoid computation. Geoid, being the horizontal surface used as a datum for heights in surveying and mapping, is very closely but intricately related to gravity. Thus, a synthetic gravity field can be used for objective and/or blind testing of geoid computation techniques. The International Association of geodesy wishes to conduct such testing to identify a technique to recommend for computing national geoids. Having tested the UNB technique on the Australian synthetic field, the first ever test of its kind, we discovered that there is a bias of 35mm in the results, plus some larger point discrepancies of the peak value of 120mm in the mountains. While the point values are explainable as discretization errors, the bias is too large, if it is associated with the Australian synthetic field, to make the field acceptable as an errorless etalon. Both the synthetic field and the UNB technique require further investigation to reach a level of accuracy of 5mm, and this will be pursued through the proposed research.