Radio science issues surrounding HF/VHF/UHF radar meteor studies
Radio science issues surrounding HF/VHF/UHF radar meteor studies
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围绕 HF/VHF/UHF 雷达流星研究的无线电科学问题
DOI：
10.1016/j.jastp.2003.11.001
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发表时间：
2004
影响因子：
1.9
通讯作者：
J. Mathews
中科院分区：
文献类型：
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作者：
J. Mathews
经典流星雷达依赖于流星轨迹的相干（菲涅耳）散射，该流星轨迹垂直于最接近雷达的雷达波矢量。以这种方式观察到的流星轨迹被描述为具有过密/过密轨迹的“经典”雷达流星。虽然流星“头部回声”很少在经典的低功率、宽波束高频流星雷达中看到，但基本上总是可以在大孔径（窄波束）、高功率 VHF/UHF 雷达中看到。我们讨论了头部回波与尾部回波的预期雷达散射截面（RCS），以及等离子频率等平衡概念在描述结果时的用途有限。特别关注 RCS 的频率依赖性，以及频率依赖性如何产生有关流星体周围“慧发”中等离子体分布的大量新信息。由于头部回波与流星体直接相关，因此可以进行瞬时（单脉冲）多普勒观测。在经典尾迹回波的情况下，RCS 作为频率函数的时间演化可以提供有关等离子体扩散速率的新信息，从而提供有关大气密度和温度的新信息。然而，必须根据新的结果来考虑来自尾迹随时间演变的信息，该结果表明，尾迹快速 B 场排列的方式显然是由尾迹沉积后 10-100 毫秒内出现的等离子体不稳定性驱动的。正是在不稳定驱动的 B 场轨迹排列的背景下，我们讨论了异常轨迹回波。异常尾迹回波是一种范围传播的混沌（非经典）尾迹回波，源自相对于雷达波矢量以任意角度行进的流星。我们提出理论模拟来说明这些概念。
Classical meteor radars depend on coherent (Fresnel) scattering from a meteor trail oriented perpendicular to the radar wave vector at closest approach to the radar. Meteor trails viewed in this manner are described as “classical” radar meteors with under/over-dense trails. While meteor “head-echoes” are rarely seen with classical low-power, wide-beam HF meteor radars, they are essentially always seen by large aperture (narrow-beam), high-power VHF/UHF radars. We discuss the expected radar scattering cross-sections (RCSs) of head-versus trail-echoes and how equilibrium concepts such as plasma frequency are of limited use in describing the results. Particular attention is given to the frequency dependence of the RCS and how the frequency dependence may yield considerable new information regarding the plasma distribution in the “coma” surrounding the meteoroid. As the head-echo is directly associated with the meteoroid, instantaneous (single-pulse) Doppler observations are possible. In the case of classical trail-echoes, the time evolution of the RCS as a function of frequency may provide new information on the plasma diffusion rate and thus on atmospheric density and temperature. Information from the time evolution of the trail must however be considered in light of new results showing that the trail rapidly B-field-aligns in a manner apparently driven by plasma instabilities that develop in 10–100 ms after trail deposition. It is in the context of instability-driven B-field alignment of the trails that we discuss anomalous trail-echoes. The anomalous trail-echo is a range-spread chaotic (non-classical) trail-echo derived from a meteor that travels at an arbitrary angle relative to the radar wave vector. We present theoretical simulations illustrating these concepts.