The ColFFTWG-Curtin2019 gravimetric quasi-geoid model has been computed by the Curtin University, Perth, Australia. It has 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 model is 250°E ≤ longitude ≤ 258°E, 35°N ≤ latitude ≤ 40°N with a grid spacing of 1' in both latitude and in longitude. Terrestrial and airborne free-air gravity anomalies were reduced by subtraction of gravity anomalies from the GO_CONS_GCF_2_DIR_R6 global gravity model (for pre-processing of the gravity data only) and a topographic correction based on the SRTM 3″ v4.1 model. These reduced data were simultaneously gridded by application of 3D least-squares collocation (LSC) with planar logarithmic covariance function, and then converted to Faye anomalies. The quasi-geoid computation was then computed with a remove-compute-restore technique, for which the xGEOID17RefB global gravity model was used. The 1D-FFT integration with Wong-Gore modified Stokes kernel was applied, where optimal modification parameters were determined from comparison to GPS-levelling data. The accuracy of the quasi-geoid model, when compared against GSVS17 GPS/leveling, is equal to 3.2 cm.

The geoid model is provided in ISG format 2.0 (ISG Format Specifications), while the file in its original data format is available at the model ISG webpage.

The International Service for the Geoid (ISG) was founded in 1992 (as International Geoid Service - IGeS) and it is now an official service of the International Association of Geodesy (IAG), under the umbrella of the International Gravity Field Service (IGFS). The main activities of ISG consist in collecting, analysing and redistributing local and regional geoid models, as well as organizing international schools on the geoid determination (Reguzzoni et al., 2021).