The earth's gravity field

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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.