Layered earth inversions of AEM bathymetry data incorporating aircraft attitude and bird offset – a case study of Torres Strait

Abstract

The potential of obtaining water depths derived from AEM data that are accurate to ~0.5 m cannot be fully realised if the variable geometry between transmitter and receiver is neglected. The rigorous approach of monitoring the bird offset in three dimensions is currently too costly. However, neglecting the bird offset variations from the assumed fixed nominal offset is problematic because the measured decay shape is sensitive to the transmitter–receiver geometry. An alternative procedure is to invert both layered earth parameters and geometric parameters using a non-linear least-squares method. This inversion procedure has been tested on 25 Hz GEOTEM data from a survey flown in the Torres Strait. The accuracy of the inverted water depths was appraised using data from laser airborne depth sounding surveys. Good agreement, to within ~1 m was obtained between the different methods.