Automatic Whistler Detector and Analyzer system: Automatic Whistler Detector

Abstract

A new, unique system has been developed for the automatic detection and analysis of whistlers. The Automatic Whistler Detector and Analyzer (AWDA) system has two purposes: (1) to automatically provide plasmaspheric electron densities extracted from whistlers and (2) to collect statistical data for the investigation of whistler generation and propagation. This paper presents the details of and the first results obtained by the automatic detector segment. The detector algorithm is based on image correlation where the target image is a preprocessed spectrogram of raw VLF signals and the pattern is a model whistler. The first AWDA system has been working in Tihany, Hungary (L = 1.8), and has collected 100,000 whistler traces per year. The overall detection efficiency using a parameter set optimized for purpose 2 is 90% for misdetection and 50–80% for false detection. The statistical analysis over the period February 2002 to February 2008 including 600,000 whistler traces shows high diurnal variations; whistler were mainly, but not only, detected when both the source and receiver regions were unlit. The seasonal occurrence is high during austral summer and low during austral winter. Comparison with Tarcsai et al.'s (1988) statistical study on Tihany whistlers shows differences in both diurnal and seasonal variations, but the latter study was made on 1388 manually identified whistlers only. The L value distributions of both data sets are similar. A global network of AWDA systems (AWDAnet) has been set up to overcome the time and space limitations of a single station; the network consists of 13 nodes, and another 6 are envisaged for the near future.