5:15 PM - 7:15 PM
[PEM12-P08] Visualization of dynamical characteristics of sporadic E using maritime radio waves from automatic identification system
Keywords:sporadic-E, automatic identification system
The sporadic-E (Es) layer, which appears at altitudes of 95—120 km in the ionospheric E region, is a thin layer with increased electron density. It is known that Es generally occurs during the daytime in summer, and that Es causes anomalous long-distance propagation of very high-frequency (VHF) radio waves through reflection. Recent researches showed that anomalous long-distance propagation of aeronautical VHF radio waves occurs during Es. Furthermore, Chartier et al. (2022) demonstrated a correlation between Es and 1000—2500 km long-distance propagation of 162 MHz maritime radio waves used for the automatic identification system (AIS). However, the feasibility of observing Es from a commercial dense AIS receiver network has not yet been evaluated. In this study, we validate the feasibility of visualizing the structure and motion of Es using commercial AIS data from a network operated by TST Corporation.
We investigated anomalous long-distance propagation in the commercial AIS data during an Es event on July 7, 2024. It was found that the mid-points between the receiving (Rx) stations and transmitting (Tx) stations (i.e, ships) were distributed in a relatively narrow area on the Japan Sea, which confirms the feasibility of detecting Es with the AIS data. This mapping of the mid-points also allowed us to visualizing the shape and movement of Es in 2D, where the cluster of reflection points elongated northeast, and sometimes showed a curved structure. Furthermore, by analyzing the temporal variations in the positions of the reflection points, it was shown that Es was moving westward at approximately 84.2±24.9 m/s, and northward at approximately 27.3±8.2 m/s.
We also performed a statistical analysis on the commercial AIS data during four months from May to August 2024. The result showed a reasonable correlation between the occurrences of Es, long-distance propagation, and medium-distance propagation. In addition, there is a weak positive correlation between the occurrences of long-distance propagation and medium-distance propagation. From this correlation, we infer that the cause of medium-distance propagation is a localized high electron density structure within Es or radio scattering by Es, although Chartier et al. (2022) showed that medium-distance propagation is related to tropospheric ducting. In the poster presentation, we will discuss this point by mapping the reflection points of medium-distance propagation. In addition, we plan to introduce the results of analyses of events other than July 7, 2024.
We investigated anomalous long-distance propagation in the commercial AIS data during an Es event on July 7, 2024. It was found that the mid-points between the receiving (Rx) stations and transmitting (Tx) stations (i.e, ships) were distributed in a relatively narrow area on the Japan Sea, which confirms the feasibility of detecting Es with the AIS data. This mapping of the mid-points also allowed us to visualizing the shape and movement of Es in 2D, where the cluster of reflection points elongated northeast, and sometimes showed a curved structure. Furthermore, by analyzing the temporal variations in the positions of the reflection points, it was shown that Es was moving westward at approximately 84.2±24.9 m/s, and northward at approximately 27.3±8.2 m/s.
We also performed a statistical analysis on the commercial AIS data during four months from May to August 2024. The result showed a reasonable correlation between the occurrences of Es, long-distance propagation, and medium-distance propagation. In addition, there is a weak positive correlation between the occurrences of long-distance propagation and medium-distance propagation. From this correlation, we infer that the cause of medium-distance propagation is a localized high electron density structure within Es or radio scattering by Es, although Chartier et al. (2022) showed that medium-distance propagation is related to tropospheric ducting. In the poster presentation, we will discuss this point by mapping the reflection points of medium-distance propagation. In addition, we plan to introduce the results of analyses of events other than July 7, 2024.