Different topographic reduction methods in practical gravimetric geoid determination

Abstract

Three different topographic reduction methods in geoid determination were investigated. The first method is the classical Helmert second method of condensation yielding the geoid, the second is the Residual Terrain Model (RTM) method yielding the quasigeoid and the third is the Rudzki inversion method. The different types of indirect effects (indirect effect on gravity and indirect effect on geoid) in Helmert's method were also investigated. All three methods use the remove-restore technique and the EGM96 geopotential model as the reference gravity field. A mountainous area, ranging from 32°S to 42°S in latitude and 72°W to 68°W in longitude, was chosen as test area. The area was selected due to its high topography, with a maximum height of 6795 meters and a mean height of 1188 meters, and due to the existence of GPS/leveling points in three different networks. The topography in the test area is-represented by a digital terrain model (DTM) with a grid spacing of 1 km x 1 km. Another test was carried out in a flat area with denser data coverage. The external accuracy of the three gravimetric geoids was evaluated by comparing them to undulations derived from GPS/leveling.

En el siguiente trabajo se investigan tres métodos diferentes de reducciones gravimétricas para la determinación práctica del geoide gravimétrico: el clásico segundo método de condensación de Helmert, el modelo residual de terreno y el método de inversión de Rudzki. Los tres métodos utilizan la técnica remover-restaurar y el modelo de geopotencial EGM96. Fueron seleccionadas dos áreas, una en una zona montañosa de alta topografía con una altura máxima de 6795 metros y una altura promedio de 1188 metros y otra en una zona plana con cobertura más densa. La topografía está representada por un modelo digital de terreno con un espaciamiento de grillado de un kilómetro por un kilómetro. La evaluación externa del geoide gravimétrico se realiza comparándolo con ondulaciones obtenidas a partir de puntos GPS sobre nivelación.