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Regional Models

Iran (IRG2018)


  Authors: S. Ramouz, et al.     Created: 2018    Resp: S. Ramouz  
      Status: PUBLIC    
Description:
IRG2018 is a hybrid geoid model for Iran, covering the region between 25°E and 40°E in latitude and 44°N and 63°N in longitude with a grid spacing of 5'. It was computed by using about 21,450 terrestrial gravity observations from zeroth, first, second, and third order gravity networks, and also by using 1,286 GNSS/leveling points (GNSS-derived coordinates in ITRF2008). Therefore, the IRG2018 model represents the height of the IRGD2010 reference surface above the GRS80 ellipsoid. The geoid computation was based on least squares collocation in the framework of a remove-restore approach. The used global gravity model was EIGEN-6C4 up to degree and order 360, while the residual terrain correction was computed from SRTM-1". The region was divided into four quadrants, modelling a different covariance function for each of them. GNSS/leveling observations were directly used as input for the least squares collocation procedure together with the gravity data. This combination led to a hybrid geoid model with an estimated accuracy of about 20 cm in terms of RMS. Whereas all the available GNSS/leveling points were used for the IRG2018 computation, for the purpose of its accuracy assessment only a subset of these GNSS/leveling data was used as observations and the resulting geoid was evaluated on the remaining GNSS/leveling data. A purely gravimetric solution, called IRG2018g, was also computed by providing gravity data only as input for the least squares collocation procedure. When compared with the GNSS/leveling data, the IRG2018g model shows differences with a standard deviation of 24 cm and a mean bias of 44 cm.

References:
S. Ramouz, Y. Afrasteh, M. Reguzzoni, A. Safari, A. Saadat (2019). IRG2018: A regional geoid model in Iran using Least Squares Collocation. Studia Geophysica et Geodaetica, 63(2), pp. 191-214. DOI: 10.1007/s11200-018-0116-4


Iran