Contribuição do GPS para o aprimoramento do geóide no Estado de São Paulo

Abstract

Os resultados mostraram que a componente sistemática é semelhante à encontrada em muitos países. Na avaliação relativa do geóide gravimétrico, obtida a partir de pares das diferenças entre o geóide gravimétrico e o geóide GPS, observa-se que as diferenças encontradas estão dentro das exigências para a utilização destes modelos geoidais no nivelamento por satélite. Após a avaliação dos modelos geoidais, foi necessário compatibilizar modelo geoidal com o sistema altimétrico. O polinômio de segundo grau foi escolhido para representar a componente sistemática, e posteriormente, utilizado para compatibilizar o sistema altimétrico. A metodologia usada neste trabalho, para a detenninação e aprimoramento do geóide no Estado de São Paulo, constitui uma estratégia a ser aplicada em outras partes do Brasil e fornecer precisão para as alturas geoidais compatível com a do nivelamento.

The determination and the improvement of the gravimetric geoid in São Paulo State constitute the main objective o f this work. This idea became reality with the detennination o f two geoid models. The frrst one was calculated from an irregular distribution of gravity data (MDGI); the second one computed from a digital gravity model and topographic data (MDGR). These geoids were computed by least squares collocation method, which allows to combine terrestrial and oceanic gravity data, satellite altimetry derived data, topographic data, and coefficients of geopotencial model. In the evaluation of the geoids detennined in this work (MDGI and MDGR), and the two already existing ones (MDG95 and EGM96), was used a dense GPS network, established on benchmarks, and adjusted by flxing the RBMC stations net. These data have enabled the evaluation o f the geoid models in absolute and relative ways. In absolute evaluation, the geoid heights computed in the same points by different techniques, have been compared; in the relative evaluation, the differences of geoid heights among pairs of points have been compared. The results showed that the systematic component is similar to that one encountered in many countries. In relative evaluation of the gravimetric geoid, accomplished from pairs of differences between the gravimetric geoid and GPS geoid, was observed that the differences satis:fy the requirements for the use of these geoidal models in the satellite levelling. After the evaluation of geoidal models, it was necessary make them compatible geoidal model with the altimetric system geoid. The second degree polynomial was chosen to represent the systematic component, and later on to make these geoids compatible with the altimetric system geoid. The methodology used in this work for the detennination and improvement o f the geoid in the São Paulo State, constitutes a strategy to be applied in other parts of Brazil and to provide the precision the geoid heights compatible with that one of levelling.