Nested anisotropic geostatistical gridding of airborne geophysical data

Airborne geophysical surveys routinely collect data along traverse lines at sample spacing distances that are two or more orders of magnitude less than between line separations. Grids and maps interpolated from such surveys can produce aliasing; features that cross flight lines can exhibit boudinage or string-of-beads artefacts. Boudinage effects can be addressed by novel gridding methods. Following developments in geostatistics, a nonstationary nested anisotropic gridding scheme is proposed that accommodates both sampling and data anisotropy in geophysical surveys. Computation is reduced by including anchor points throughout the interpolation region that contain localised anisotropy information that is propagated throughout the survey area with a smoothing kernel. Additional anisotropy can be required at certain locations in the region to be gridded. A model selection scheme is proposed that employs Laplace approximations for determining whether increased model complexity is supported by the surrounding data. The efficacy of the method is shown using a synthetic data set obtained from satellite imagery. A pseudo geophysical survey is created from the image and reconstructed with the method above. Two case histories are selected for further elucidation from airborne geophysical surveys conducted in Western Australia (WA). The first example illustrates improvement in gridding the depth of palaeochannels interpreted from along-line conductivity-depth models of a regional airborne electromagnetic survey in the Mid-West WA region. The second example shows how improvements can be made in producing grids of aeromagnetic data and inverted electrical conductivity from an airborne electromagnetic survey conducted in the Pilbara region. In both case histories, nested anisotropic kriging reduces the expression of boudinage patterns and sharpens cross-line features in the final gridded products permitting increased confidence in interpretations based on such products. © 2021 Society of Exploration Geophysicists.