Spatial and Temporal Ionospheric Monitoring Using Broadband Sferic Measurements
Spatial and Temporal Ionospheric Monitoring Using Broadband Sferic Measurements
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DOI：
10.1002/2017ja024291
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发表时间：
2018-04
期刊：
影响因子：
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通讯作者：
J. McCormick;M. Cohen;N. Gross;R. Said
中科院分区：
文献类型：
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作者：
J. McCormick;M. Cohen;N. Gross;R. Said
电离层的 D 区（高度 60-90 公里）在时间尺度上变化很大，从几分之一秒到几个小时，在空间尺度上变化最大可达数百公里。甚低频 (VLF) 和低频 (LF)（3-30 kHz 和 30-300 kHz）无线电波通过地面和 D 区域的反射被引导至全球距离。因此，有关其当前状态的信息被编码在接收到的 VLF/LF 信号中。 VLF 发射机过去曾用于 D 区研究，电离层扰动表现为幅度和/或相位的扰动。闪电的回击是脉冲 VLF 辐射器，但与 VLF 发射机不同的是，闪电事件广泛分布在空间中，与基于 VLF 发射机的遥感相比，除了宽带频谱优势优于窄带发射机之外，D 区域的空间覆盖范围更大。挑战在于，除了 D 区电离层变化之外，单个闪电生成的波形（或“sferics”）还会因雷电电流参数和时间/位置信息的不确定性而变化。这些因素使得很难以直接的方式利用闪电的 VLF/LF 发射。我们描述了一种以高保真度恢复 B 和 Br 的时域和幅度/相位谱的技术，并考虑了我们的技术在环境和变化的电离层条件下的实用性。我们演示了一种模拟 sferics 并使用 Wait 和 Spies 参数（h ' 和 β）推断参数化电离层的技术，提供了全球测量所需的所有工具。
The D region of the ionosphere (60–90 km altitude) is highly variable on timescales from fractions of a second to many hours, and on spatial scales up to many hundreds of kilometers. Very low frequency (VLF) and low‐frequency (LF) (3–30 kHz and 30–300 kHz) radio waves are guided to global distances by reflections from the ground and the D region. Therefore, information about its current state is encoded in received VLF/LF signals. VLF transmitters have been used in the past for D region studies, with ionospheric disturbances manifesting as perturbations in amplitude and/or phase. The return stroke of lightning is an impulsive VLF radiator, but unlike VLF transmitters, lightning events are distributed broadly in space allowing for much greater spatial coverage of the D region compared to VLF transmitter‐based remote sensing in addition to the broadband spectral advantage over the narrowband transmitters. The challenge is that individual lightning‐generated waveforms, or “sferics,” vary due to the lightning current parameters and uncertainty in the time/location information, in addition to D region ionospheric variability. These factors make it difficult to utilize the VLF/LF emissions from lightning in a straightforward manner. We describe a technique to recover the time domain and amplitude/phase spectra for both Bϕ and Br with high fidelity and consider the utility of our technique with ambient and varied ionospheric conditions. We demonstrate a technique to simulate sferics and infer a parameterized ionosphere with the Wait and Spies parameters (h ′ and β) offering all of the tools needed for a global measurement.