Simultaneous joint inversion of MT and CSEM data using a multiplicative cost function

Abstract

SUMMARY We present an inversion algorithm to jointly invert controlledsource electromagnetic (CSEM) data and magnetotelluric (MT) data. CSEM and MT data provide complementary information about the subsea conductivity distribution, hence it is useful to derive earth conductivity models that simultaneously fit both data sets. One of the issues of this simultaneous joint inversion approach is how to assign the relative weight between CSEM and MT cost functions. In this work we propose a multiplicative cost function of the CSEM and MT data instead of the additive one. This multiplicative cost function mismatches does not require a choice of the relative weights between these two data sets. This cost function will adaptively put CSEM and MT data on equal footing in the inversion process. The inversion is accomplished with a regularized GaussNewton technique where the model parameters are forced to lie within their upper and lower bounds by a non-linear transformation procedure. A line search method is employed to enforce a reduction of the cost function at each iteration. We demonstrate the pros and cons of this joint inversion approach by using some synthetic examples.