||In this thesis, an interpretation technique is developed and presented for two new airborne geophysical methods which are used for measuring natural magnetic fields: ZTEM and AirMt. The z-axis tipper electromagnetic (ZTEM) system measures the fields of natural audio-frequency sources using an airborne vertical magnetic field receiver and a pair of horizontal, magnetic field ground receivers at a base station. The AirMt method employs three orthogonal airborne magnetic field receivers and three horizontal orthogonal magnetic-field ground receivers at a base station. The magnetic field components acquired during the AirMt survey are converted into an amplification parameter, which is invariant to receiver reference systems. The airborne deployment makes it possible to acquire ZTEM and AirMt data over large areas for a relatively low cost compared to equivalent ground surveys. This makes it a practical method for mapping large-scale geological structures. This thesis develops the methods of three-dimensional (3D) forward modeling and inversion of ZTEM and AirMt data. For the forward modeling, I apply the integral equation method, while the inversion is based on Tikhonov regularization method. The model study in this thesis is conducted under different conditions which can affect accurate modeling and inversion of the data. In the final chapter of the thesis, I present the results of inversion of the field ZTEM data from the Cochrane test site in Ontario, Canada.