Tehran Province (IRLG2020_Tehran)
Authors: S. Ramouz, A. Safari

Created: 2020

Resp: S. Ramouz

Description:
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 RemoteComputeRestore procedure, the EIGEN6C4 global gravity model up to degree and order 360 and the SRTM 1arcmin 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 TscherningRapp covariance model was fitted to the empirical one and its three parameters were estimated to calculate the auto and crosscovariance 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 TscherningRapp 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.
References:
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. 517535. 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. 6575. DOI: 10.5194/adgeo50652020

