Automatic Detection of Omega Signals Captured by the Poynting Flux Analyzer (PFX) on Board the Akebono Satellite

Abstract

Abstract-The Akebono satellite was launched in 1989 to observe the Earth's magnetosphere and plasmasphere. Omega was a navigation system with 8 ground stations transmitter and had transmission pattern that repeats every 10 s. From 1989 to 1997, the PFX on board the Akebono satellite received signals at 10.2 kHz from these stations. Huge amounts of PFX data became valuable for studying the propagation characteristics of VLF waves in the ionosphere and plasmasphere. In this study, we introduce a method for automatic detection of Omega signals from the PFX data in a systematic way, it involves identifying a transmission station, calculating the delay time, and estimating the signal intensity. We show the reliability of the automatic detection system where we able to detect the omega signal and confirmed its propagation to the opposite hemisphere along the Earth's magnetic field lines. For more than three years (39 months), we detected 43,734 and 111,049 signals in the magnetic and electric field, respectively, and demonstrated that the proposed method is powerful enough for the statistical analyses.

Statistical study on propagation characteristics of Omega signals (VLF) in magnetosphere detected by the Akebono satellite

“…The PFX data are stored as waveforms using the common data format (CDF) file format. We have already developed a method in the Java programming language to detect the presence of Omega signals measured by the PFX and then analyze them comprehensively (Suarjaya et al 2016). The flow of the data processing is described in the paper by Suarjaya et al (2016) in more detail, but we briefly outline the process as follows.…”

“…Next, we calculated the delay time of the signal by subtracting the raise time of the signal from the transmission time. The raise time is the arrival time of the Omega signal at 10.2 kHz, as determined by detecting the sudden increase in signal intensity at the center frequency (10.2 kHz), compared with those of surrounding frequencies (Suarjaya et al 2016). As a next step, the signal intensity was determined when the average intensity at the center frequency was large enough to compare with those of surrounding frequency and ambient noise.…”

“…Since the transmission pattern of frequency, transmission time, and location of each Omega station are known (described by Morris et al 1994 andSuarjaya et al 2016), it is easy to distinguish the signal source measured by the PFX. We can then determine many propagation properties such as attenuation ratio, propagation direction, delay time from the transmission station, and observation point along the satellite trajectories.…”

“…In the present paper, we investigate statistical features of the Omega signals detected by the PFX from 1989 to 1997. To achieve this purpose, we extracted Omega signals from the enormous amount of PFX data using an automatic detection program developed by Suarjaya et al (2016).…”

“…The outline of the present paper is as follows: In the next section, we briefly introduce our detection algorithm (Suarjaya et al 2016) and the datasets used for the statistical study, in which we investigated the Omega signals broadcast from the high-middle-latitude stations in Norway and North Dakota. Next, we show the results of propagation characteristics depending on the MLT, season, and solar activity.…”