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Regional Models

Tanzania (TZG08)

  Author: P.E. Ulotu     Created: 2008    Resp: P.E. Ulotu 
      Status: PUBLIC   
The TZG08 model is a gravimetric geoid for Tanzania at epoch 2008. It is referred to the GRS80 ellipsoid and it extents from 12° S to 1° N in latitude and from 29° E to 41° E in longitude, with a grid resolution of 1'x1'. The input gravity data consists in a 1'x1' surface gravity grid, which was computed through a remove-restore approach starting from 39677 point gravity observations in land and 57723 observations in the ocean. In this gridding procedure, the reference global gravity model was a combination between ITG-GRACE03S up to degree 120 and EIGEN-CG03C up to degree 360, while the residual terrain effect (RTE) was computed from the 3"x3" SRTM (CGIAR-CSI) digital elevation model. The TZG08 geoid determination is performed by the KTH method of a least-squares modification of the Stokes formula (LSMS) with additive corrections (AC). In particular, the satellite-only ITG-GRACE03S global gravity model up to degree 120 was used to compute the modification parameters and the long-wavelength component of the TZG08 model, while the short wavelength component of the geoid was computed from the 1'x1' residual surface gravity grid. The TGZ08 assessment was based on 21 GPS/levelling points, showing an overall accuracy of 22.7 cm; after approximately removing GPS and orthometric systematic effects by a 5-parameter model, the TGZ08 accuracy is finally estimated as 20.3 cm.

P.E. Ulotu (2009). Geoid Model of Tanzania from Sparse and Varying Gravity Data Density by the KTH Method. PhD thesis at the Royal Institute of Technology (KTH), Stockholm, Sweden.