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1 Reports on Geodesy

1 2003

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Accurate determination of the geoidal undulation N

Lambrou E., Pantazis G., Balodimos D.

Reports on Geodesy

2003

z. 1/64

165-172

This work, re!ated to the activities of the CERGOP Study Group Geodynamics or the Ba!kan Peninsula, presents a method for the determination or the variations AN and, indirectly, of the geoida! undulation N with an accuracy of a few millimetres. It is based on the determination of the components of the deviation of the vertical using modern geodetic instruments (digital total station and GPS receiver). An analysis of the method is given. Accuracy of the order of O.Olarcsec in the estimated values of the astronomical coordinates and lambda is achieved. The result of applying the proposed method in an area around Athens is presented. In this test application, a system is used which takes advantage of the capabilities of modern geodetic instruments. The GPS receiver permits the determination of the geodetic coordinates in a chosen reference system and, in addition, provides accurate time information. The astronomical observations are performed through a digital total station with electronic registering of angles and time. The required accuracy of the values of the coordinates is achieved in about four hours of fieldwork. In addition, the instrumentation is lightweight, easily transportable and can be setup in the field very quickly. Combined with a stream-lined data reduction procedure and the use of up-to-date astronomic data, the values of the components of the deviation of the vertical and, eventually, the changes deltaN of he geoidal undulations are determined easily and accurately. In conclusion, this work demonstrates that it is quite feasible to create an accurate map of the geoid undulation, especially in areas that present large geoid variations and other methods are not capable to give accurate and reliable results.