An efficient 2D inversion scheme for airborne frequency-domain data

In many cases, inversion in 2D gives a better description of the subsurface compared to 1D inversion, but computationally 2D inversion is expensive, and it can be hard to employ for large-scale surveys. We present an efficient hybrid 2D airborne frequency-domain electromagnetic inversion algorithm. Our hybrid scheme combines 1D and 2D inversions in a three-stage process, where each step is progressively more accurate and computationally more expensive than the previous. This results in a ~2x – 6x speedup compared to full 2D inversions, and with only minor changes to the inversion results. Our inversion structure is based on a regular grid, where each sounding is discretized individually. The 1D modelling code uses layered models with derivatives derived through the finite difference method, while our 2D modelling code uses an adaptive finite element mesh, and the adjoint-state method to calculate the derivatives. By incorporating the inversion grid structure into the 2D finite element mesh, interpolation ...