Abstract
Site specific geoid model is prerequisite for accurate determination of orthometric heights. No geoid model has been developed so far for India or any of its part. So, development of a geoid model for India or its part is of utmost need to make use of GNSS data towards determination of orthometric heights. In this research work, an attempt has been made to develop geoid undulation models by gravimetric method using Molodensky’s concept. Component parameters in line with the Remove – Compute – Restore (RCR) technique have been used recursively. Models have been developed for two study areas: one of these lies in and around Dehradun (30° 19′ N, 75° 04′E) in Uttarakhand state, India in lower Himalayan region having highly undulating topography and the other near Hyderabad (17° 30′N, 78°30′E) in Telengana state of India having gentle topography. The model has been tested for 7 stations in the first study area and accuracy has been found to be 17.5 cm; whereas, for the second area accuracy has been found to be 7.0 cm for 24 test stations. Further, the performances of the developed models have been evaluated with those from three global geoid models namely EIGEN6C4, EIGEN6C3stat and EGM2008; and have been found to be similar or better in case of first study and for second study area far more superior. Thus, local/regional geoid undulation model requiring accuracy better than 20 cm for any study area may be developed adopting the method. However, the optimality in the number and density of gravity stations may be considered as a future scope of work.
Highlights
Development of a local, regional or global geoid model is one of the forefront research works conducted by geodesists for decades
As the physiography of the area is much undulating and area belong to lower Himalayas i.e., the area is under the influence of huge mass accumulation around, there is much variations in gravity anomalies at different stations and its empirical covariance function
The empirical covariance function of the study area 2 has been found to be fitted with its analytical model, This is commensurate with the physiography of the Hyderabad area which is quite flat and associated with no accumulated mass around
Summary
Development of a local, regional or global geoid model is one of the forefront research works conducted by geodesists for decades. One of the primary uses of geoid model is to compute geoid undulation or geoid height (Seeber 2003), N which gets subsequently used to determine orthometric height. In the pursuit for accurate determination of orthometric heights, researchers work towards development of more and more accurate geoid models. The geoid undulation at any station or point is defined as the difference in elevation between its ellipsoidal height (h) and orthometric height (H) and is given by: h = H ± N, (1). Where N is called geoid undulation or geoid height (Seeber 2003) It depends on anomalous gravity potential (T) at the considered point and may be computed from gravity anomaly (Δg) (Heiskanen, Moritz 1987). T is the disturbing potential at ground level, γ is the normal gravity at telluroid (Heiskanen, Moritz 1987).
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