Airborne electromagnetic sensing of shallow seawater using a helicopter time-domain system — Applications for bathymetric mapping and characterizing the seafloor

A helicopter time-domain airborne electromagnetic (AEM) system is under development for investigating the use of AEM for bathymetric mapping. Bathymetry and sediment thickness is computed from 1D inversion of the EM response based on a crude two-layer model (seawater/sediment) overlying resistive basement. The primary focus of this study is to test the accuracy of AEM for bathymetric mapping. A secondary objective is to map sediment thickness by determining the depth to bedrock. The AEM method senses the upper geo-electrical layers of the marine environment and is not sensitive to water turbidity and surf zone conditions because the optical opacity and presence of bubbles does not significantly affect the bulk electrical conductivity of seawater. The survey areas contain shallow waters (<; 25 m) overlying paleovalleys infilled with unconsolidated sediment, and reef areas. Water depth accuracy of 1-2 m was achieved in water shallower than 25 m. This study shows that the AEM method is suited as a reconnaissance technique for rapid bathymetric mapping in turbid and surf-zone waters.