A new whistler direction finder

Abstract

A new whistler direction finder is developed and described and it has the following essential features; 1. (1) The wave incidence situation is distinguished among the three cases, 1.1. (i) vertical incidence with nearly circular polarization, 1.2. (ii) oblique incidence with elliptical polarization, or 1.3. (iii) horizontal incidence with nearly linear polarization. 2. (2) The direction of arrival and polarization are deduced by the equation suitable for each wave incidence situation and yielding reduced polarization error. 3. (3) The directional measurement is done at two frequencies for each whistler signal. 4. (4) A method of recording and displaying the directional data is highly simplified so that it enables the measurement for a long period. 5. (5) A real time whistler analyzer providing the occurrence rate and dispersion in real time is used, as an auxiliary equipment, to choose the times when to start and end the measurement. The classification of the wave incidence situation is based on the outputs from eight detectors; six combinations of correlation among two horizontal magnetic field components at a point frequency, the corresponding phase-lagged (90°) components and the vertical electric field components, and two other signals yielding the nature of the polarization ellipse projected onto the ground. The overall system is described in detail in the present paper, which includes the principle of the direction finding measurement, antenna-receiver system, signal analyzer, data recording system, switching circuit of the filter frequency, sonagraphic display of the directional data and finally a real-time-whistler analyzer. Some results on the direction finding for whistlers observed at Moshiri (geomag. lat. 34.5°N) are presented to demonstrate the effectiveness of the present direction finder.