3D airborne electromagnetic data inversion based on the block coordinate descent method

Abstract

Airborne electromagnetic (AEM) surveys usually cover a large area and create a large amount of data. This has limited the application of 3D AEM inversions. To make 3D AEM data inversion at a large scale possible, the local mesh method has been developed to avoid solving large matrix equations in 3D AEM modeling. However, the local mesh only saves the computational cost and memory during forward modeling and Jacobian calculations. When the survey area is very large, the cost for storing and solving the inversion equations can be very high. This brings significant challenges to practical 3D AEM inversions. To solve this problem, we develop a 3D scheme based on the block coordinate descent (BCD) method for inversions of large-scale AEM data. The BCD method divides the inversion for large models into series of small-local inversions, so that we can avoid solving the large matrix equations. Numerical experiments determine that the BCD method can obtain very similar results to those from the existing inversion methods but saves huge amounts of memory.