Electromagnetic induction information from differences at aeromagnetic crossover points

This paper describes an investigation of the use of aeromagnetic crossover misfits as a source of geological information. The misfits occur when, at a crossover point of an aeromagnetic survey, the separate measurements of the Earth's magnetic field are not the same. Misfits are mainly the result of time-dependent field changes and, in this paper, are analysed as indicators of electromagnetic induction in the Earth, and thus of electrical conductivity structure. The method derives estimates of a magnetic diurnal variation function both for cells within the surveyed area and for a reference base station. Normalizing the former by the latter gives extra information from the aeromagnetic data. A case history from Australia is presented of the method applied to an aeromagnetic survey conducted in a region containing a known electrical conductivity structure. The presence of the conductivity anomaly is evident in the aeromagnetic misfit results.