Abstract
SUMMARY It is well known that orthometric heights can be obtained without levelling by using ellipsoidal and geoidal heights. For engineering purposes, these orthometric heights must be determined with high accuracy. For this reason, the determination of a high-resolution geoid is necessary. In Iberia, since the publication of the most recent geoid (IBERGEO95), a new geopotential model has become available (EIGEN-CG01C, released on 2004 October 29) and a new high-resolution digital terrain model (SRTM 90M obtained from the Shuttle Radar Topography Mission) has been developed for the Earth. Logically, these new data represent improvements that must be included in a new geoid of Iberia. With this goal in mind, we have carried out a new gravimetric geoid determination in which these new data are included. The computation of the geoid uses the Stokes integral in convolution form, which has been shown as an efficient method to reach the proposed objective. The terrain correction has been applied to the gridded gravity anomalies to obtain the corresponding reduced anomalies. The indirect effect has also been taken into account. Thus, a new geoid is provided as grid data distributed for Iberia from 35° to 44° latitude and –10° to 4° longitude (extending to 9°× 14°) in a 361 × 561 regular grid with a mesh size of 1.5′× 1.5′ and 202 521 points in the GRS80 reference system. This calculated geoid and previous geoids that exist for this study area (IBERGEO95, EGM96, EGG97 and EIGEN-CG01C) are compared to the geoid undulations corresponding to 16 points of the European Vertical Reference Network (EUVN) on Iberia. The new geoid shows an improvement in precision and reliability, fitting the geoidal heights of these EUVN points with more accuracy than the other previous geoids.
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