International Service for the Geoid


Search in ISG Website




Services - Geoid Repository

Regional Models

Tehran Province (IRLG2020_Tehran)

  Authors: S. Ramouz, A. Safari     Created: 2020    Resp: S. Ramouz  
      Status: ON-DEMAND   
IRLG2020_Tehran is a gravimetric geoid model for the Tehran Province (Iran), based on terrestrial gravimetric observations measured by the National Cartographic Center of Iran (NCC). In the framework of the Remote-Compute-Restore procedure, the EIGEN-6C4 global gravity model up to degree and order 360 and the SRTM 1-arc-min digital elevation model were also used as input data. The model was computed by Least Squares Collocation (LSC) using an improved covariance (I_COV) modelling (Ramouz et al. 2020). First, an empirical covariance was computed from the terrestrial observations. Then, the Tscherning-Rapp covariance model was fitted to the empirical one and its three parameters were estimated to calculate the auto and cross-covariance of the LSC formula. Finally, the systematic parts of the signal, namely the global and topographic effects, were restored. To implement the I_COV idea in gravity field localization, the Tscherning-Rapp covariance were refined by an iterative process where the available gravimetric dataset was split into observations and control points. The assessment of the computed local geoid model were performed by comparing it with the 141 GNSS/Leveling points (measured by NCC), showing differences with a standard deviation of about 8.9 cm. Furthermore, if the comparison is limited to 40 control points inside Tehran City, the standard deviation of the differences is about 6.1 cm. To draw a comparative picture, the accuracy of this local model is 49% and 51% higher than the EGM2008 model over the same control data sets.

S. Ramouz, A. Safari (2020). Assessment of the improved covariance in local geoid modeling using Least Squares Collocation - Case study: Tehran Province, Journal of the Earth and Space Physics, 46(3), pp. 517-535. DOI: 10.22059/jesphys.2020.303845.1007221
S. Ramouz, Y. Afrasteh, M. Reguzzoni, A. Safari (2020). Assessment of local covariance estimation through Least Squares Collocation over Iran. Advances in Geosciences, 50, pp. 65-75. DOI: 10.5194/adgeo-50-65-2020