Anomalous Long-Distance Propagation of ILS LOC Signals by the Es Layer and Its Impact on Aviation Receivers

IF 3.7 2区 地球科学 Space Weather Pub Date : 2023-11-15 DOI:10.1029/2023sw003577
S. Saito, K. Hosokawa, J. Sakai, I. Tomizawa
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Abstract

Anomalous long-distance propagation of Very High Frequency radio waves of aeronautical navigation systems was investigated by an airborne Instrument Landing System (ILS) localizer (ILS LOC) receiver installed on the ground at Kure, Japan (34.245°N, 132.528°E). Intense ILS LOC type signals were observed and the received power was strong enough for the aviation receiver to output course deviation. The radio source was identified by receiving the Morse Code for identification as the localizer-type directional aid (LDA) serving the Runway-21 of the Hualien Airport, Taiwan (24.0396°N, 121.6221°E) of which beam pointed close to the receiver. This result supports that the source of the signals often observed at the same frequency at the same location is most probably the LDA at the Hualien Airport. The maximum received power was −99 dBm for an omni-directional antenna. It was strong enough to cause co-channel interference. Considering stronger power (−70 dBm) found in previous observations at the same frequency at the same location, anomalous propagation of ILS LOC signals by the Es layer could be a cause of interference when a receiver was near the center of the ILS LOC beam. The course deviation output was consistent with the geometry between the beam of Runway-21 LDA at the Hualien Airport and the receiver. However, the observed course deviation fluctuated remarkably even when the received power was strong enough. The fluctuation of the course deviation may indicate the structure of the Es layer, and observation of the course deviation could be used to diagnose the Es layer structure.
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Es层对盲降LOC信号的异常长距离传播及其对航空接收机的影响
利用安装在日本Kure(34.245°N, 132.528°E)地面的机载仪表着陆系统(ILS)定位器(ILS LOC)接收机,研究了航空导航系统甚高频无线电波的异常长距离传播。观察到强烈的盲降LOC型信号,接收功率足以使航空接收机输出航向偏差。无线电源通过接收莫尔斯电码被识别为服务于台湾花莲机场21号跑道(24.0396°N, 121.6221°E)的定位器型定向辅助设备(LDA),其波束指向接收器附近。这一结果支持了在同一地点经常观测到的相同频率的信号源极有可能是花莲机场的LDA。全向天线最大接收功率为- 99 dBm。它的强度足以引起同信道干扰。考虑到先前在同一位置的相同频率观测到的更强功率(−70 dBm),当接收器靠近ILS LOC波束中心时,Es层对ILS LOC信号的异常传播可能是干扰的原因。航向偏差输出与花莲机场21跑道LDA波束与接收机之间的几何形状一致。然而,即使在接收功率足够强的情况下,观测到的航向偏差也有明显的波动。航向偏差的波动可以指示Es层的结构,对航向偏差的观测可以诊断Es层的结构。
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