Tuesday 23 August 2005

G2

PT0006
Ideal combination of deflection components and gravity anomalies for precise geoid computation
Abd-Elmotaal, Hussein¹, Kühtreiber, Norbert²
1 Minia University, Egypt
2 Graz University of Technology, Austria
Author email: abdelmotaal@lycos.com
Recently, a relatively high precision and efficient technique for astronomical deflection measurements has been available (Bürki et al., 2004). It depends on a modern digital zenith camera. The measurement precision is in the order of 3 -5 arc seconds. Using this efficient measurements technique, detailed deflection measurements can be done in mountainous and desert areas in a relatively short time with high precision. Such areas usually suffer from lack of gravity field information. These gaps can either be filled by the measured deflection components, which are combined with the gravity anomalies to predict the geoid, or by transforming deflection components into derived gravity anomalies. This paper investigates strategies for the best way of combination. Two sets of data within Austria are available. The first is a set of 716 deflection components, and the second is a set of 5796 gravity anomalies. Artificial gaps in the Austrian gravity data set are simulated. As for the first approach, the deflections data, restricted to these gaps only, are used with gravity data to compute a detailed geoid for Austria using least squares collocation technique. As for the second approach, deflection components will be used to estimate derived gravity anomalies (through least squares collocation), and then these derived gravity anomalies are used with the rest of the gravity data to compute a gravimetric geoid for Austria. A scaling of the derived gravity anomalies has been taken into account. A wide comparison among the obtained results is carried out. Reference Bürki, B., Müller, A. and Kahle, H.-G, 2004, DIADEM: The New Digital Astronomical Deflection Measuring System for High-Precision Measurements of Deflections of the Vertical at ETH Zurich. Presented at the IAG International Symposium on Gravity, Geoid and Space Missions - GGSM2004 Porto, Portugal, August 30 - September 3, 2004.

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