1D Inversion of Large Loop Transient Electromagnetic Data Acquired Using Offset Loop Configuration Over Multi-layer Earth Models

Abstract

The present research describes a 1D inversion scheme for interpretation of large loop TEM data acquired using offset loop configuration due to a large loop source, over the layered earth models. The inversion is based on a non-linear least square method that generates a smooth layered earth model by minimizing the residual misfit function in an iterative process. It produces an inverted model from the data using the criteria of minimization of misfit function and/or convergence of residual in two successive iterations. The forward problem is formulated in frequency domain, and then it is transformed into the time domain using Fourier cosine and sine transform. The accuracy and robustness of algorithm is tested by inverting the large loop TEM data acquired using offset loop configurations over the homogeneous, two layer, three layer and four layer earth models, with or without the addition of random noises. Inverted results are in good accordance with the theoretical models and validate that different parameters are recovered with high accuracy. The program works satisfactorily with noisy data and produces inverted results with acceptable accuracy for synthetic data up to 5% random noises.