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 th e 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 indicator s of electromagnetic induction in the Earth, and thus of electrical conduct ivity structure. The method derives estimates of a magnetic diurnal variati on function both for cells within the surveyed area and for a reference bas e station. Normalizing the former by the latter fives extra information fro m 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.