Laterally Constrained Inversion of Fixed-Wing Frequency-Domain AEM Data

New high-resolution airborne geophysical surveys of the UK, undertaken with the system developed under the Joint Airborne-geoscience Capability programme, established between the Geological Survey of Finland and the British Geological Survey, will provide large 4-frequency airborne electromagnetic data sets. These data sets will be used to characterise the conductivity distribution of the subsurface for environmental and exploration purposes. To invert these large data sets in a fast and robust manner we have developed “LC1DINV”, a laterally constrained one-dimensional inversion algorithm. This algorithm inverts simultaneously for all observation points along a profile and regularises the inverse problem by requiring that differences between model parameters at adjacent points be small. We use the conjugate gradient method for minimising the data misfit subject to the lateral constraints and a priori model terms. We have inverted 4-frequency data obtained over Suurpelto, a test area in southern Finland, characterised by conductive clays overlying a highly resistive granitic shield. The results show that LC1DINV can successfully locate the depth extent and variations of the clays. Comparison of these results with those obtained with two other types of inversion shows that LC1DINV produces well-defined layer boundaries and laterally smooth cross-sections.