Hilbert Transform Method of Determining the Period of Rayleigh-Acoustic Wave Generated Ionospheric Doppler Records

Abstract

An ionospheric Doppler record is a faithful representation of the well-dispersed earthquake generated long-period Rayleigh waves. This record displays oscillations with varying periods. In this paper, a method of determining the period of these oscillations is presented. The method consists essentially of determining the analytic signal representation of a Doppler record using Hilbert transform. From the analytic signal representation, the period of an oscillation is obtained by taking the time derivative of the instanteous phase plot of the analytic signal. This method is illustrated by applying it to a Doppler record obtained shortly after the Hachinohe, Japan earthquake of 1968. The results are compared with those obtained by using the traditional "peak and trough" method.