Fast and Effective Groundwater Mapping from 10 to 300 m Depth with Accurate Processing and Inversion of Skytem Data.

We present results from an airborne electromagnetic survey for groundwater mapping near Sidney, Nebraska, commissioned by the US Geological Survey in cooperation with the North Platte, South Platte, and Twin Platte Natural Resource Districts to SkyTEM Aps and Aarhus Geophysics who did processing and Inversion. An important innovation of this project is near real-time processing and Inversion performed daily in the field using a demo area, surveyed prior to collecting data in the actual project area, to illustrate the effectiveness of the system in resolving the target which contains a series of aquifers of varying thicknesses. Because SkyTEM data require no leveling and complex bias removal procedures, the data can be used immediately after each flight. A fast, first-pass processing (decoupling etc) can immediately start and, upon completion, the Inversion is carried out. with a quad-core desktop it is possible to process and invert overnight, with full non-linear Inversion, an average day’s worth of EM data acquisition. Although the results are not as accurate as obtained from more thorough processing and multiple Inversion runs, they are sufficient to evaluate the systems resolution and accuracy, and allow for informed decisions to move forward with production flights in the project areas. the data from these production areas were processed in the office to eliminate large and dense coupling effects due to power lines, pipelines, and irrigation infrastructure, and then inverted with a spatially-constrained Inversion, which incorporates prior Information to produce more robust results. from a hydrogeological standpoint, the results obtained greatly improved the understanding of the groundwater system, mapping aquifer thickness over ranges of 10 m to 300 meters. We present a comparisons with ancillary Information, including ground-based electromagnetic measurements, borehole lithologic and geophysical logs. using selected prior Information to constrain the Inversion can further improve the resolution of some model parameters.