We introduce a network observation of anomalous long-distance propagation of aeronautical navigation (NAV) very high-frequency (VHF) radio waves due to sporadic E layer (Es). The system has been operative since May 2019 at 6 stations in Japan. The receiver consists of a log-periodic antenna, air-band filter, software-defined radio and small computer which is capable of recording the strength of radio signals in the frequency band from 98 to 118 MHz with a temporal resolution of 2 s. The receiver covers not only the NAV band including VHF omnidirectional radio range (VOR), instrument landing system localizer (ILS LOC) and ground-based augmentation system VHF data broadcast (GBAS VDB) from 108 to 118 MHz, but also broadcasting channels from 98 to 108 MHz. Soon after the start of the full operation of the network observation, a strong Es event was detected by an ionosonde in Tokyo during the daytime on July 4, 2019, in which foEs (critical frequency of Es) was sometimes higher than 15 MHz. The VHF radio wave monitoring system detected multiple signatures of Es anomalous propagation (EsAP) at all the stations extending from Okinawa to Hokkaido. At some stations, the EsAP signatures continued for a few hours with some brief intervals of disappearance. The observed correspondence between the enhancement of foEs and the occurrence of anomalous propagation confirmed that an extreme electron density enhancement within Es caused the anomalous long-distance propagation of VHF NAV signals. The data from this network observation can be browsed at http://gwave.cei.uec.ac.jp/cgi-bin/vor/vhf.cgi in near real-time basis. This near real-time monitoring capability allows people in the aeronautical operation community such as air navigation service providers, pilots, and airline engineers to check the propagation environment of VHF NAV signals online, which contributes to a mitigation of ionospheric space weather impacts on the aeronautical navigation systems. Not only that the current method for detecting Es in a wide area can be used to visualize the spatial distribution of Es in two-dimensional fashion through a combination of other observation techniques such as ionosondes and total electron content (TEC) measurements using Global Navigation Satellite System (GNSS) signals.

中文翻译：

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日本零星辐射引起的航空甚高频无线电波异常传播监测网络

我们介绍了对航空导航 (NAV) 甚高频 (VHF) 无线电波由于零星 E 层 (Es) 的异常长距离传播的网络观察。该系统自 2019 年 5 月起在日本的 6 个车站运行。接收器由对数周期天线、空气带滤波器、软件定义无线电和小型计算机组成，能够记录 98 至 118 MHz 频带内无线电信号的强度，时间分辨率为 2 秒。接收器不仅覆盖 NAV 频段，包括 VHF 全向无线电范围 (VOR)、仪表着陆系统定位器 (ILS LOC) 和地基增强系统 VHF 数据广播 (GBAS VDB)，范围从 108 到 118 MHz，还覆盖了 98到 108 MHz。在网络观测全面运行开始后不久，2019 年 7 月 4 日白天，东京的一个离子探空仪检测到强 Es 事件，其中 foEs（Es 的临界频率）有时高于 15 MHz。VHF 无线电波监测系统在从冲绳延伸到北海道的所有电台都检测到 Es 异常传播 (EsAP) 的多个特征。在某些站点，EsAP 签名持续了几个小时，并有一些短暂的消失间隔。观察到的 foEs 增强与异常传播的发生之间的对应关系证实，Es 内的极端电子密度增强导致了 VHF NAV 信号的异常长距离传播。可以在 http://gwave.cei.uec.ac.jp/cgi-bin/vor/vhf.cgi 上近乎实时地浏览来自该网络观察的数据。这种近乎实时的监测能力使空中导航服务提供商、飞行员和航空公司工程师等航空运营界的人们可以在线检查 VHF NAV 信号的传播环境，这有助于减轻电离层空间天气对航空的影响。导航系统。不仅可以使用当前在大范围内检测 Es 的方法，通过结合使用全球导航卫星的电离探空仪和总电子含量 (TEC) 测量等其他观测技术，以二维方式可视化 Es 的空间分布系统 (GNSS) 信号。这有助于减轻电离层空间天气对航空导航系统的影响。不仅可以使用当前在大范围内检测 Es 的方法，通过结合使用全球导航卫星的电离探空仪和总电子含量 (TEC) 测量等其他观测技术，以二维方式可视化 Es 的空间分布系统 (GNSS) 信号。这有助于减轻电离层空间天气对航空导航系统的影响。不仅可以使用当前在大范围内检测 Es 的方法，通过结合使用全球导航卫星的电离探空仪和总电子含量 (TEC) 测量等其他观测技术，以二维方式可视化 Es 的空间分布系统 (GNSS) 信号。