The spatial pattern of the daily magnetic variation over Australia, with application to the correction of magnetic survey data

Abstract

Time variations of the earth's geomagnetic field, with periods of a few seconds to the daily variation, can introduce errors of up to tens of nanoteslas into magnetic survey data (Lilley 1982; Riddihough 1971). These errors may be removed either by rapid looping methods similar to those used in gravity surveys, or, as is more usually the case, by subtracting from the survey data the record of a continuously monitored ground station. This latter method usually works well if the survey is undertaken relatively close to the base monitor, but when the distances involved become of the order of several hundred kilometres, as they may in aeromagnetic surveying in Australia, the assumption of uniform variations on this scale may not be valid. Since magnetic surveys are not usually undertaken on days of strong disturbance of the geomagnetic field, the main errors will arise from pulsation events (I. Hone & D. Pridmore, pers. comm.), and from the daily variation, which is further considered here.