EXPLORATION OF THE RESIDUAL TOPOGRAPHY EFFECT ON SOME FUNCTIONALS OF THE GRAVITY FIELD

As massas topograficas, tendo em vista suas distribuicoes e variacoes de densidade, exercem influencias nas grandezas vinculadas ao campo de gravidade. Neste trabalho, o efeito gerado pela Modelagem Residual do Terreno (Residual Terrain Model – RTM) sobre a anomalia de altura, anomalia da gravidade e as componentes do desvio da vertical foi explorado. Os modelos digitais de elevacao SRTM30 PLUS e o DTM2006.0, com base em uma filtragem de passa alta, foram usados no contextoda tecnica RTM. O Chile tem-se constituido um laboratorio natural para estudos em geodinâmica em vista das caracteristicas de sua topografia e de sua estrutura crustal. Diversos projetos sao desenvolvidos com base na analise de grandezas descritas no espaco do geopotencial. No entanto, nao sao reportadas investigacoes que vinculemos efeitos residuais do terreno sobre estas grandezas. Desta forma, busca-se a inclusao desta analise considerando-se duas regioes distintas do Chile: as regioes I e VIII, as quais tem caracteristicas crustais bastante diversas. Os resultados revelam a importância da contribuicao do RTM na modelagem da alta frequencia do campo de gravidade. Na anomalia de altura os valores alcancados situaram-se entre 1 e –1 m, ao passo que as anomalias de gravidade situam-se entre 100 e –100 mGal, enquanto que as componentes do desvio da vertical apresentaram valores entre 18 e –20 segundos de arco nas diferentes situacoes topograficas. O estudo mostra a possibilidade de recuperacao de grande parte do erro de omissao dos Modelos Globais do Geopotencial por intermedio da tecnica RTM. Alem disso, a estabilidade das diferentes grandezas em relacao a variacao do raio de integracao, no contexto da formulacao de Stokes-Pizzetti, foi explorada. ABSTRACT: The topographical masses, considering its distribution and variations in density, have a measurable influence on functionals of the gravity field. In thispaper, the effect modeled by the Residual Terrain Model (RTM) exerted on the height anomaly, on the gravity anomaly, and on the deflections of the vertical components was explored. The SRTM30 PLUS and DTM2006.0 Digital Elevation Models (DEM), based on a high-pass filter were used in the context of RTM technique. Chile is a natural laboratory for studies in geodynamics considering the characteristics of its topography and crustal structure. Several studies consider the analysis of functionals described in the geopotential space. However, investigations linking the residual effects of topography on these functionals have not yet been reported. Thus, this paper seeks to include this analysis considering two different regions of Chile: the 1st and 8th regions, which have very different crustal characteristics. The results reveal the importance of the contribution of RTM in modeling the high-frequencies of the Earth’s gravity field. The values of height anomaly obtained were between 1 and –1 m, while the gravity anomalies were between 100 and –100 mGal, whereas the deflections of the vertical components reach values between –20 and 18 arc seconds indifferent topographic settings. The study shows the possibility of retrieving large part of the omission errors in Global Geopotential Models (GGM) by using the RTM technique. Furthermore, the stability of different functionals in relation to the variation of the radius of integration, in the context of the Stokes-Pizzetti formulation wasexplored. Keywords : residual terrain model, digital elevation models, global geopotential model, gravity field functional.