ISG

   International Service for the Geoid

   

Search in ISG Website



Links:










      

      

Services - Geoid Repository


Regional Models

Colorado - USA (ColFFTWG-DTU2019)


  Author: R. Forsberg   Created: 2019    Resp: R. Forsberg  
                       Status: PUBLIC   Licence: CC BY 4.0
Description:
The ColFFTWG-DTU2019 gravimetric quasi-geoid and geoid models have been computed by the Technical University of Denmark (DTU), Copenhagen. They have been worked out in the frame of the International Association of Geodesy Joint Working Group 2.2.2 "The 1 cm geoid experiment" and the so called "Colorado experiment". The area covered by the models is 250°E ≤ longitude ≤ 258°E, 35°N ≤ latitude ≤ 40°N with a grid spacing of 1' in both latitude and in longitude. The computation was performed by the GRAVSOFT package in the framework of a remove-compute-restore procedure. XGM2016 was used up to degree and order 360 as global gravity model, and SRTM v4.1 was used for the residual terrain reductions at 3″ resolution for both airborne and terrestrial data, computed from a 9″ mean model. The linear Prey term approximation was applied for the harmonic correction of surface gravity points below the mean elevation surface (Forsberg and Tscherning, 1981). The reduced airborne gravity data were downward continued and gridded, together with surface gravimetry, at the terrain surface using 3D Least-Squares Collocation with planar logarithmic covariance function (Forsberg, 1987). The resulting 1'x1' grid was converted to a residual quasi-geoid by spherical FFT, using a Wong-Gore modified Stokes kernel, with a low-wavelength cut-off transition band at harmonic degrees 180-190, to keep the GOCE information unchanged up to this degree. Residual terrain effects and the XGM2016 contribution were restored to obtain the final gravimetric quasi-geoid, and the geoid was obtained by adding the classical separation term (Heiskanen and Moritz, 1967). The accuracy of the quasi-geoid and geoid models, when compared against GSVS17 GPS/leveling, is equal to 3.1 cm and 2.7 cm, respectively.

References:
R. Forsberg, C.C. Tscherning (1981). The use of Height Data in Gravity Field Approximation by Collocation. Journal of Geophysical Research, 86(B9), pp. 7843-7854.
R. Forsberg (1987). A new covariance model for inertial gravimetry and gradiometry. Journal of Geophysical Research, 92(B2), pp. 1305- 1310.
R. Forsberg (2019). Colorado geoid computation - DTU Space. Report of the Joint Working Group 2.2.2 "The 1 cm geoid experiment", pp.1-4.



COLORADO