Avaliação de dados de altimetria do satélite Geosat a partir de comparação com dados do levantamento gravimétrico marinho Equant

Abstract

The principal objective of this thesis is to evaluate the use of satellite altimetry data to map the potential surface of the earth's gravity field at sea. This evaluation is done by comparing the resolution and accuracy of the altimeter data over an equipotential surface (the sea) with that computed from conventional sea survey data. From the potential surface, quantities such as the free air anomaly or the vertical deflection can be calculated. The altimetry data utilized in this thesis were collected by the Geosat satellite and each data point was averaged over a two year (44 orbital cycles) period. This averaging was done to improve the accuracy and resolution of the sea height over ocean areas. These data are available from NOAA and were supplied to UFPa for use in this thesis. The ship survey data from EQUANT 1 and EQUANT 2 were generated from a joint research project among several institutions whose scientific objective was to study the behavior of the Brazilian Equatorial Continental Margin. In order to integrate and compare the data between these two different sources (satellite and ship measurements), either the satellite data must be reduced to a vertical acceleration on the equipotential surface or alternately the ship survey data must be transformed into an equivalent potential surface. Taking into account the wide separation of the satellite tracks relative to the ship survey track, it was decided to transform the ship survey data into a potential surface, and the correlation and comparisons were carried out along satellite tracks. In this type of transformation, various factors must be considered such as the effects of aliasing, ship survey noise levels, reduction to the geoid, computational errors in the transformation, etc. In spite of these effects (particularly the aliasing problem) the results reflect a strong correlation between the two sets of data verifying that a satisfactory level of coherence exists for wavelengths greater than 11 km. The resolution for the 2 year cycle average of the satellite is, in fact, almost as good as the ship survey data.