PIGEOID2021 is a purely gravimetric quasi-geoid model covering the whole Paracel Islands in the northwestern South China Sea. The quasi-geoid is referred to the GRS80 ellipsoid and extends from 15.27°N to 18.23°N and from 110.59°E to 113.30°E with a grid spacing of 30" in both the latitudinal and longitudinal directions. PIGEOID2021 is computed using localised airborne gravity anomalies (with an accuracy of 1.44 mGal at a resolution of 3 km) under the framework of the remove-compute-restore method, where XGM2019e_2159 (truncated to d/o 1080) is used as the reference model and the residual terrain model is applied for smoothing local gravity field at very short scales (< 3 km). The residual gravity field is parameterized using Poisson wavelets by assuming white noise of observations. Comparisons with altimeter-derived geometric quasi-geoid heights retrieved from Jason-2, CryoSat-2, and SARAL show the misfits of PIGEOID2021 are within 5 cm. Further analysis shows PIGEOID2021 reduces the bubble-like errors over island areas by a magnitude exceeding 6 cm compared to existing global geopotential models.

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.