The IndGG-LSMSA2021 is the Indian Gravimetric Geoid model developed using the Royal Institute of Technology (KTH) method of Least Squares Modification of the Stokes formula with Additive corrections (LSMSA). The method was used to calculate the quasigeoid model, which was converted to the geoid model by applying the geoid-quasigeoid separation term calculated using the method by Flury and Rummel (2009). Data used are terrestrial gravity anomalies from GETECH, satellite-altimeter derived marine gravity anomalies, MERIT digital elevation model, EGM2008 and GO_CONS_GCF_2_DIR_R5 global geopotential models. The LSMSA method was used with various combinations of modification degree and integration radius. This gravimetric geoid model was obtained with the modification degree of 300 and an integration radius of 1°. The IndGG-LSMSA2021 model extends from 7° N to 37° N latitude and 68° E to 98° E longitude with a grid spacing of 0.02°×0.02° and it is referred to the GRS80 ellipsoid. On validation with the available GNSS/levelling data, mean±STD (in m) for India is -0.14±0.43. However, on cluster-wise validation in the four regions of the country, Uttar Pradesh West, Uttar Pradesh East, Hyderabad, and Bangalore, mean±STD (in m) are -0.58±0.13, -0.49±0.10, 0.14±0.16, and 0.79±0.03, respectively.

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).