Airborne electromagnetic bathymetry of Sydney Harbour

Abstract

An airborne electromagnetic survey using the helicopter-borne DIGHEMV system was carried out over lower Port Jackson, Sydney Harbour. The study served to review the capacity of this system to provide accurate bathymetry data in shallow seawater down to 30 m, which is the maximum depth of the survey area. The DIGHEM^V system operated at frequencies of 328 Hz, 7337 Hz and 55300 Hz in a horizontal coplanar transmitter/receiver coil configuration and 889 Hz and 5658 Hz in a vertical coaxial transmitter/receiver coil configuration. In order to obtain high-quality data with optimised signal to noise ratio, rigorous calibration procedures were carried out to ensure data accuracy. These included low-altitude profiles over deep seawater of known electrical conductivity, thorough calibration of phase and gain over very resistive background at a remote site, and high-altitude zero level calibrations throughout the survey flights. Two-layer inversion of the data yielded a thickness of the upper layer (bathymetry) which is generally consistent with depth-sounding data. This study verified the use of airborne electromagnetics as a promising low-resolution bathymetric reconnaissance tool that can be used to rapidly survey shallow coastal waters.