Time domain airborne electromagnetic reconnaissance for seadepth measurement and shipwreck localisation

Abstract

An AEM bathymetric survey of a portion of Geographe Bay, WA, was carried out using the QUESTEM 450 system. The area covered includes the decommissioned HMAS Swan divewreck. The survey also included two tie lines skirting Cape Naturaliste, reaching out to the 200 m depth contour in the Indian Ocean. TEM data was interpreted using both layered earth inversion and conductivity-depth imaging methods. The maximum depth of investigation for bathymetric mapping to within 10% of chart soundings was estimated to be 60 m with the QUESTEM system. The EM interpretation methods gave similar results in Geographe Bay. The divewreck was readily detected and appears as an anomaly in the estimated water depth derived from inverted in-line component data. Preliminary numerical modelling results are presented for the EM response of a ``+' cross-section thin sheet high conductivity-contrast conductor, representing a hull, buried 60 m in a 5 S/m host.