Modelagem numérica e validação de dados tensoriais de aerogradiometria gravimétrica 3D-FTG

Abstract

ABSTRACT.Iron oxide mineralization style is usually controlled by both crustal and local scale structures such as major shear, fault zones and lithological contacts.Air-FTG (Airborne Full Tensor Gravity Gradiometry) is nowadays the only existing airborne full tensor gradiometer technology can be used for both detailed and regional surveys. The system takes real time measurements of gravity gradient field in three orthogonal directions and at same time compensates for bias in the orientation and accelerations of the aircraft. Each one of these measurements is related to either the density contrast or the geometry of discrete bodies. The aim of this work was to implement a numerical algorithm to compute the five gxx, gxy, gxz, gyy and gyz independent tensor components and use the knowledge acquired with them to help in real data interpretation and Air-FTG validation. To go over this subject, Air-FTG survey was flown over the Quadrilátero Ferrífero region, in Minas Gerais state, Brazil, to delineate and to map structures associated with iron oxide mineralizations. A complete procedure for data processing, together with joint interpretation of the geological models, ground gravity and air gravity gradiometry tensor components, indicates the high precision capability of the Air-FTG system in mapping and detecting iron oxide bodies with high accuracy. Results show that gradiometer depict a more observable advantage for identification of those near surface targets, revealing structures such as lineament, edges, corners and as a consequence, body shapes and their thickness. We have concluded that the best images of the subsurface rocks acquired by the Air-FTG platform can provide more realistic targets information than the conventional ground gravity field instruments.Keywords: full tensor gravity gradiometry, iron ore. RESUMO.Mineralizações deóxido de ferro são geralmente controladas por estruturas crustais e locais, como zonas de cisalhamento, zonas de falha e contatos litológicos. O sistema Air-FTG (Airborne Full Tensor Gravity Gradiometry )é atualmente aúnica tecnologia aérea existente capaz de medir o tensor total gradiente de gravidade associado a estas mineralizações. Ele faz medidas em tempo real do gradiente do campo gravitacional em três direções ortogonais e ao mesmo tempo corrige a orientação e as acelerações da aeronave. Cada uma destas medidasé relacionada a contrastes de densidade ou a geometria de corpos superficiais discretos.O objetivo deste artigoé implementar um algoritmo numérico capaz de calcular as cinco componentes independentes do tensor e utilizar o conhecimento adquirido com ele para auxiliar na interpretação dos dados reais e na validação do método. A aquisição de dados com o sistema Air-FTG foi realizada no Quadrilátero Ferrífero, no estado de Minas Gerais, Brasil, tendo como objetivo mapear os corpos de hematita compacta. Foi aplicado um procedimento completo para processamento dos dados de gravimetria terrestre com o intuito de compará-los com os dados reais de FTG. Os resultados indicam, ...

O uso dos dados da missão GOCE para a caracterização e a investigação das implicações na estrutura de densidade das Bacias Sedimentares do Amazonas e Solimões, Brasil

“…The T zz component is the one that closely resembles the standard gravity (Braga, 2006). But this is not always true.…”

“…The bandwidth allows an increased retention of the signal with short wavelength (high frequency) generated by shallow and intermediate geological features that are not retained in conventional ground gravity data. This increased sensitivity allows a significant increase in the resolution of the anomalous bodies (Braga, 2006). Each tensor component of the gravity gradient corresponds exclusively to the size, shape, depth and density of the mass anomaly providing a constraint during the process of interpretation.…”