Description:
The QgeoidMEDE2026 gravimetric quasi-geoid model has been computed by the geoid computation team at the Instituto Geográfico Agustín Codazzi (IGAC),
the Colombian national mapping authority, using terrestrial and airborne gravity data provided by the same institution. The area covered by the model is
located between 281.5810838955° ≤ longitude ≤ 287.26441722883334° and 9.042739612399957°N ≤ latitude ≤ 3.359406279066625°N, with a grid spacing of 1' in both
latitude and longitude. The input data include terrestrial and airborne gravity observations, together with satellite altimetry-derived gravity data from the
DTU21Gra model, all used at their original observation locations. A bias estimation for the airborne gravity surveys was carried out using spherical radial
basis functions (SRBFs) by comparing the observations with GOCO06s and dv_ell_Earth2014, since the surveys were acquired at different times and by different
contractors. The computation method is based on spherical radial basis functions (SRBFs), using the Shannon function for the analysis of the terrestrial gravity
data, while the Cubic Polynomial (CuP) function is used for both the analysis of the airborne gravity data and the synthesis step. The computation is performed
following a remove-compute-restore procedure, using XGM2019 as the gravity background model and Earth2014, together with ERTM2160, for the topographic gravity
effects. The terrestrial, airborne, and satellite altimetry-derived gravity data observations were combined within a parameter estimation procedure, and the
relative weight among them was determined by the variance component estimation (VCE) method. The regularization parameter (lambda) was optimized using the
L-curve method. The accuracy of the quasi-geoid model compared against GPS/levelling is about 16 cm. In addition, a recent validation using a levelling line
of approximately 150 benchmarks, with gravity observations collected at each station, indicates that the model achieves a consistency of about 4 cm.
Reference:
C. A. Rico and H.S.Q. Olarte (2026). QgeoidMEDE2026 calculation, technical
report. Instituto Geográfico Agustín Codazzi (IGAC), Bogotá D.C., Colombia
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