Forskning ved Københavns Universitet - Københavns Universitet


An estimation of the height system bias parameter N (0) using least squares collocation from observed gravity and GPS-levelling data

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  • Muhammad Sadiq
  • Carl C. Tscherning
  • Zulfiqar Ahmad
This paper deals with the analysis of gravity anomaly and precise levelling in conjunction with GPS-Levelling data for the computation of a gravimetric geoid and an estimate of the height system bias parameter N-o for the vertical datum in Pakistan by means of least squares collocation technique. The long term objective is to obtain a regional geoid (or quasi-geoid) modeling using a combination of local data with a high degree and order Earth gravity model (EGM) and to determine a bias (if there is one) with respect to a global mean sea surface. An application of collocation with the optimal covariance parameters has facilitated to achieve gravimetric height anomalies in a global geocentric datum. Residual terrain modeling (RTM) technique has been used in combination with the EGM96 for the reduction and smoothing of the gravity data. A value for the bias parameter N-o has been estimated with reference to the local GPS-Levelling datum that appears to be 0.705 m with 0.07 m mean square error. The gravimetric height anomalies were compared with height anomalies obtained from GPS-Levelling stations using least square collocation with and without bias adjustment. The bias adjustment minimizes the difference between the gravimetric height anomalies with respect to residual GPS-Levelling data and the standard deviation of the differences drops from 35 cm to 2.6 cm. The results of this study suggest that N-o adjustment may be a good alternative for the fitting of the final gravimetric geoid as is generally done when using FFT methods.
TidsskriftStudia Geophysica et Geodaetica
Udgave nummer3
Sider (fra-til)375-388
StatusUdgivet - 2009

ID: 16331390