Inverse modeling of HEM data using a new inversion algorithm

Helicopter-borne frequency-domain electromagnetic (HEM) surveys are used extensively for mineral and groundwater exploration and a number of environmental investigations. To have a meaningful interpretation of the measured multifrequency HEM data, in addition to the resistivity maps which are provided for each frequency or for some particular depth levels, it is a necessity to have a suitable modeling technique to produce resistivity cross-sections along some specific profiles. This paper aims to: (1) develop a new inversion method to handle HEM data; (2) compare its results with the well known Amplitude, Niblett-Bostick (NB), and Siemon inversion methods. The basic formulation of this new inversion routine was provided based on the Zonge spatial filtering procedure to cure static shift effect on the magnetotelluric (MT) apparent resistivity curves. When the relevant formulas and the required algorithm for the inverse modeling of HEM data were provided, they were then coded in Matlab software environment. This new inversion program, named as SUTHEM, was used to invert some sets of one and two dimensional (1D and 2D) model synthetic data which were contaminated by random noise. It was also applied to invert one set of real field data acquired in the NW part of Iran by the DIGHEM system. The obtained results of this method and their comparison with those of the aforementioned methods indicate that SUTHEM is able to produce the results like those produced by established Siemon routines. In addition, the new inversion method is superior to the Amplitude and the NB methods particularly in inversion of the noisy data.