The local geoid for Madeira was computed using strapdown airborne gravimetry measurements taken on 27 and 31 August 2010 as part of the GEOMAD campaign. The inertial measurements were acquired with an iXsea IMU. The observations made during the turns of the aircraft were disregarded and a decimation to a 50 second sampling was applied. The geoid determination was based on the standard remove-restore technique with EGM2008 as reference global geopotential model and SRTM for the computation of the residual terrain correction. The Least-Squares Collocation approach was used to convert the residual gravity disturbances at flight level into height anomalies at sea level. The subsequent conversion of height anomalies into geoid undulations was based on the corrections provided with the EGM2008 model. The datum of the local geoid model is WGS84, given in the tide-free system. According to the Least-Squares Collocation procedure the errors are around 5 cm, however a more realistic estimate of the uncertainty is of the order of 10 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).