闪电直窜先导-回击过程MUSIC定位及其细节辐射特性研究

An important but fundamental question in lightning studies concerns how the process of dart leader-subsequent return stroke incept, propagate and radiate. There is insufficient understanding on some detailed characteristics during this process and their development mechanism due to a limit of observation techniques. Weak radiation and short duration are the main factors that constrain these details being detected. In this project, multiple signal classification (MUSIC) would be introduced and applied in the broadband VHF locations. A high-resolution broadband lightning VHF array MUSIC location technology is developed to conduct detailed observation for lightning breakdown discharge channels. Furthermore, comprehensive experiments are carried out to verify the robustness of the localization method; array error correction and beam focusing enhancement algorithms are designed to optimize the proposed technology and improve its detection capacity of the lightning fine structures; and parallel acceleration algorithm is developed to improve the localization efficiency. On the basis of these studies, field campaign focused on detailed characteristics of VHF radiation channels in the process of dart leader-subsequent return stroke, including channel formation process, connection process and breakdown process occurring in the return stroke channel. This study is not only benefit to the enriching of our knowledge about the establishment conditions, propagation process and radiation law of the breakdown discharging channels during the process of dart leader-subsequent return stroke, but also expected to enhance the understanding of the connection process in a natural cloud to ground flash. In addition, it is significance for improving the level of lightning detection.

闪电直窜先导-继后回击过程是雷电物理研究中非常重要的基础性问题，然而由于探测技术的限制，其中的一些细节特征及其发展机制尚不十分清楚，辐射弱、持续时间短是制约探测这些细节过程的主要因素。本项目拟将多重信号分类（MUSIC）技术引入宽带闪电VHF定位，建立高分辨宽带VHF阵列MUSIC定位方案，为实现闪电击穿放电通道的精细观测提供技术途径。进一步，开展综合性实验验证定位方法的鲁棒性；设计阵列误差校正方法和波束聚焦增强算法优化定位技术，提高其对闪电精细结构的探测能力；开发并行算法，提高定位效率。在此基础上，开展野外闪电观测试验，研究闪电直窜先导-继后回击过程中VHF辐射通道的细节特征，包括通道开辟过程、连接过程和回击通道中的击穿过程。这对于闪电直窜先导-继后回击过程击穿放电通道开辟条件、传输物理过程和辐射规律的理解具有重要的科学意义，有望增强对地闪连接过程的理解，对提升闪电探测技术具有指导意义。

面向闪电科学理论研究对闪电击穿放电过程高精度、高分辨的定位需求，提出了一种新的宽带闪电甚高频（VHF）探测技术，从理论和技术角度解决了一些现阶段闪电观测中存在的问题。项目的主要研究工作总结如下：.1. 创新提出了宽带闪电甚高频（VHF）阵列多重信号分类（MUSIC）定位方法，构建了多阵元宽带闪电VHF阵列定位系统。新方法充分利用了阵列接收信号的空域特性，具有较好的弱辐射源定位性能，并具备多源定位能力。通过大量的数据仿真、无人机实验、多源定位实验对定位方法和系统的探测性能进行了全面、系统地分析和评估。并利用人工引雷的观测数据对定位方法的有效性和实用性进行了验证，仿真、实验及观测结果表明提出的定位方法进一步提高了现阶段宽带闪电VHF探测系统定位弱辐射源的能力，并实现了宽带闪电VHF信号多源定位。.2. 系统分析了窄带干扰和宽带闪电VHF阵列误差对定位结果的影响，结果表明阵列误差的存在会导致阵列方向矢量的指向性出现偏差，严重时会定位失效，提出了直接测量法和有源估计法对多阵元阵列通道延时误差进行校正，并利用无人机高空实验验证了校正方法的可行性和有效性，同时提出了两步空间搜索策略和并行处理策略提升了闪电VHF-MUSIC定位技术的运算效率，这对于多阵元宽带VHF阵列探测走向实用化具有重要的应用价值和意义。.3. 利用提出的宽带闪电VHF阵列MUSIC定位技术综合分析了人工触发闪电和自然闪电典型放电通道发展过程、物理机制及其细节特征，以及相关频谱特征，主要包括上行正先导、下行正先导、K先导、反冲事件、直窜先导、回击、金属丝熔断等过程，并对有些闪电通道放电过程有了新的认识。.总的来说，提出的宽带闪电VHF阵列MUSIC定位技术及其应用与发现，对进一步认识闪电击穿放电通道特征，为闪电物理研究提供观测事实、验证已知结论、发现未知现象，进一步揭开闪电击穿放电物理机制的神秘面纱具有重要的应用价值和科学意义。