Frequency-Domain Controlled-Source Electromagnetic Sensitivity and Inverse Modelings Using Rotational Invariants

The electromagnetic (EM)-field components are commonly used in marine controlled-source EM (CSEM) inversion in which accurate orientations, i.e., the heading, tilt, and roll of the sources and receivers, are required for reliable data processing and inversion. However, potential uncertainties may be introduced in inversion and interpretation, especially when the orientation is lost during the field data collection when the compass and tilt recordings are unavailable. This study presents a new marine CSEM inversion algorithm using orientation-independent rotational invariants instead of EM fields, which permits not considering the source or receiver orientations in inversion. The application of the rotational invariants for the frequency-domain marine CSEM data inversion is presented. The Gauss-Newton optimization is carried out in the frequency domain for inverting the CSEM data, which iteratively searches for the seafloor resistivity compatible with the data. The sensitivity related to the rotational invariants is also computed. Numerical tests for both 1-D and 2-D cases using the rotational invariants and conventional EM-field components are validated and compared.