Joint Inversion of Ground Based and Helicopter-borne Electromagnetic Data

Abstract

The use of ground-based electromagnetic methods (transient electromagnetics (TEM) and radiomagnetotellurics (RMT)) is increased in last decades for hydrogeological purposes. However, airborne electromagnetic methods were also proposed as a possible tool for near surface investigations due to the capability to cover large areas in short time. By jointly inverting different kinds of geophysical measurements at a site, the ambiguity inherent in different geophysical methods can be avoided. In order to couple spatial data from helicopter-borne electromagnetics (HEM) with ground-based electromagnetics, a common 1D joint inversion algorithm for HEM, TEM and RMT data is developed. The depth of investigation of HEM data is rather limited compared to time-domain EM sounding methods. In order to improve the accuracy of model parameters of shallow as well as of the deeper subsurface, the HEM, TEM, and RMT measurements are combined using joint inversion methodology. The 1D joint inversion algorithm is verified for the synthetic HEM, TEM and RMT data. The proposed concept of joint inversion takes advantage of each single method, which provides the capability to resolve near surface (RMT and HEM) and deeper electrical structures (TEM). Furthermore, the joint inversion is realized for the field data (HEM and TEM) from Cuxhaven area, Germany.