Development of a novel approach for recovering SIP effects from 1-D inversion of HEM data: Case study from the Alut area, northwest of Iran

Abstract

We have developed a novel approach for recovering the induced polarization (IP) effects from one-dimensional (1-D) inversion of helicopter-borne electromagnetic data (HEM). To achieve this aim, we incorporate both electromagnetic and spectral induced polarization effects within the HEM data by taking the frequency dependence behaviour of resistivity/conductivity of polarizable formation into account. Furthermore, we have included the EM sensor altitude, magnetic permeability and dielectric permittivity of subsurface layers in order to conduct the full solution of forward operator. In this regard, we have calculated the magnetic permeability from the inversion of aeromagnetic data and incorporated the sensor altitude and dielectric permittivity as additional model parameters to be recovered using the inversion of the HEM data. We have carried out both forward and inverse modelling of the HEM data by implementing fast Hankel transform and hybrid algorithm including very fast simulated annealing (VFSA) and Marquardt-Levenberg (ML) strategies, respectively. This approach enables us to recover model parameters comprising of relaxation parameters of Cole-Cole model, dielectric permittivity and thickness of layered half space model and sensor altitude above the earth surface using 1-D inverse modelling of HEM data.We have tested our approach on both synthetic and field DIGHEM data. Implementing the forward solution indicates that incorporation of the IP effects may shift the frequency domain electromagnetic (FDEM) response so that it yields the sign reversal signature in the in-phase component at low frequencies. Moreover, the results of the inverse modelling of the HEM data show that the IP effect could be recovered using our approach effectively. It provides fast and cost-effective quantitative tool for recovering the IP effect from HEM data for the sake of more precise characterization of buried polarizable formations in the wide area. In addition, incorporation the IP effect along with magnetic permeability and sensor altitude provides a significant degree of improvement in the inversion and interpretation of negative responses occurred in the in-phase component at low frequencies.