Ground-based geophysical measurements in salinity-affected areas prior to AEM surveys

Abstract

Ground-based electromagnetic and electrical surveys were conducted in areas of southeast Queensland in March 2001 to establish representative ground conductivity values down to depths of greater than 50 m for use in designing suitable airborne electromagnetic (AEM) surveys to be flown in those areas later that year. Once AEM data were available, a comparison between the results of the ground-based and AEM surveys was made. High resolution definition of near-surface conductive structures was achieved with the combined use of DC resistivity and frequency-domain EM31 measurements, while transient electromagnetic (TEM) soundings provided reliable values of deeper conductivity. A comparison of the results of ground-based and corresponding AEM data shows that there is broad agreement between the behaviour of the conductivity of the conductive layer detected by AEM and corresponding conductivity values derived from ground-based data. However, the models obtained from the two sets of data do not agree in detail, probably because the AEM inversions were constrained to have a resistive basement, whereas ground-based and down-hole results show that the basement is generally relatively conductive.