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Regional Models

Auvergne - France (AuvGeoid2017)


  Authors: J. Janák, et al.     Created: 2017    Resp: J. Janák  
      Status: PUBLIC    
Description:
This is a gravimetric geoid model computed for the Auvergne test area by using the UNB Stokes-Helmert's technique. Among the 244,009 values of the free-air gravity anomalies, 118 couples of duplicate points and 2 outliers were detected and eliminated. The reference field was taken from the GOCE-DIR-R5 global gravity model. Three digital terrain models were used: the SRTM3 version 4 for the computation of free-air anomalies on a regular gridand for the direct topographical effect; the ACE2 model for the computations where the mean elevations were needed; the JGP95 global terrain model for the “Helmerization” of the reference field. Lateral topographical density variations in the Auvergne area were estimated from surface geology on a 5'×5' grid from publicly available geological map. The effect of these approximate density variations on the geoid were computed in two terms of direct density effect and primary indirect density effect. The total effect of lateral topographical density varies between –5.8 and 2.4 cm. Two geoid models were computed, with and without the inclusion of the effect due to density variations. The accuracy of these geoid models was evaluated on 75 GNSS/levelling points supplied with normal Molodenskij heights, which for this investigation are transformed to rigorous orthometric heights. The standard deviation of the differences is equal to 3.4 cm if the density effect is not included, and decreases to 3.3 cm after adding it.

Reference:
J. Janák, P. Vanícek, I. Foroughi, R. Kingdon, M.B. Sheng, M.C. Santos (2017). Computation of precise geoid model of Auvergne using current UNB Stokes-Helmert’s approach. Contributions to Geophysics and Geodesy, 47(3), pp. 201-229. DOI: 10.1515/congeo-2017-0011


France