Reduction of inversion errors in helicopter EM data using auxiliary information

Abstract

A technique for minimising the calibration errors in helicopter electromagnetic data (HEM) is developed. The method is based on resistivity-depth information obtained from auxiliary geophysical data at locations scattered over the survey area. The technique compares measured HEM values with the calculated responses from resistivity-depth models at the auxiliary data sites. Correction factors which minimise the differences between the calculated and measured values are obtained by a least-squares method. The correction factor incorporates amplitude, phase and bias adjustments. The analysis shows that only the amplitude and phase corrections are stable enough to be of use. After the correction factors are applied to the data, resistivity-depth models for the entire survey area are determined by inversion. The correction procedure results in better agreement between measured and inverted bird elevation, as well as a smaller inversion misfit error.