ELF/VLF direction‐finding taking account of earth‐ionosphere waveguide effect

Abstract

SUMMARYEstimation of the transmission point in the ionosphere for ELF/VLF waves arriving at the ground after propagation in the magnetosphere is performed by MUSIC, an estimation method having high resolution. This paper not only constructs an estimation method based on the observation data model common to various direction-finding methods, but also proposes a method of estimating the direction and polarization of the direct wave by using a model that expresses the propagation effects between the ground and the ionosphere in terms of superposition of multiply reflected waves. In the simulation assuming observation of three electromagnetic field components on the ground, the results of estimation by both methods are compared. It is confirmed that the estimated values are superior to those obtained by the conventional methods if more than 10 reflections are taken into account for estimation of a transmission point that is far away with a large angle of incidence at the observation point. Even when the wave is transmitted through the spread-out region in the lower ionosphere, the direction of the center of the transmission region can be estimated by MUSIC taking account of multiply reflected waves.