雷电热效应的微波遥感理论与实验观测研究

The lightning discharge currents, on the order of several thousands of amperes, may result in the temperature of the lightning discharge channel to rise to thousands of Kelvin in a very short time. The intensity, the influencing scope and lasting time of the lightning heating effect are important characteristic parameters of lightning itself and are significant in application fields such as lightning disaster monitoring, lightning protection, lightning chemistry and so on. Optical spectrometer is known to be the only way to obtain the temperature of lightning so far but the optical light in visible band lasts short as compared with infrared and microwave according to Planck’s law for thermal radiation. In the proposed project, we intend to study the V-band microwave features of the lightning heating effect and present the principle of microwave remote sensing for lightning heating effect (Temperature and time-space scope), radiometer technical performance parameters, observation technique requirement and data processing method to establish the relationship between brightness temperature of the microwave radiometer, thunder cloud parameters, lightning discharge channel, return strokes and the lightning heating effect. Moreover, based on the ground-based, V-band microwave radiometer, we will make in-situ observation experiment in an artificially triggered lightning field experiment site, and access the observed brightness temperature data with those measured from other instruments, such as high-speed video, weather radar, optical spectrometer and so on, to carry out the research of integrated data processing and mutual verification. It is hoped to explore a new technique based on ground-based microwave radiometer for lightning observation and provide data support for further understanding and making use of lightning.

雷电放电通道中电流峰值高达几十千安，使得温度在短时间内上升至数千上万度。雷电热效应强度及其影响范围和持续时间，既是雷电的重要特征参数，也是雷电致灾、雷电防护、雷电化学等应用领域的重要因子。一直以来，光谱技术被称为是获得温度的唯一途径。但闪电可见光持续时间短，不利于观测。红外和微波持续时间较长。本项目拟提出雷电热效应（温度及其时空尺度）的微波遥感理论、地基微波辐射计技术性能参数、观测方式需求以及数据处理方法，建立微波辐射亮温、雷暴云参数、雷电流、放电发光通道、回击次数与雷电热效应特征量之间的关系。本项目将开展针对“人工引雷”作业的地基微波辐射计观测实验，获得“人工引雷”放电热效应遥感观测和反演数据，结合“人工引雷”基地高速摄像、雷达、光谱仪等其他仪器的观测，开展数据综合处理与交互验证，为雷电观测探索一种基于地基微波辐射计的新技术，为雷电的探测、认识和利用提供科学依据和数据支持。

闪电通道温度及其持续时间是非常重要的闪电特征参数。目前，光谱测量技术是获得闪电通道温度的唯一途径，即，利用回击前期产生的可见光范围内特征光谱或者闪电通道演化后期的中性原子辐射产生的近红外光谱可获得通道温度。根据普朗克热辐射定律，闪电通道产生的热辐射在微波波段持续时间更长，更有利于观测。因此，本项目组创新性地提出利用雷电“热”效应产生的微波辐射信号来探测雷电特性。经过4年的观测和研究，项目组基于微波辐射传输理论，研究建立了雷电热效应的微波遥感理论，提出了地基微波辐射计观测雷电热效应的表达式；从 2016 年初夏开始利用地基微波辐射计在广东野外雷电试验基地开展了连续 4 年夏季的观测实验，根据雷电热效应的特征，制定了观测方案，并为地基微波辐射计设置了引雷观测模式；通过观测实验与数据分析不断调整观测方案，2017-2019年三年辐射计对人工引闪的平均观测效率可达71%，验证了地基微波辐射计具有对雷电热效应产生响应的能力；根据辐射计的人工引闪观测方式及其所得数据，估算出了雷电热效应的持续时间；结合闪电的雷电流等多元同步观测数据，给出了2017-2019年雷电流热效应特征量与闪电参数之间的统计关系式，脉冲幅度、持续时间与闪电参数的相关性分别达68%与73%。由亮温观测数据通过亮温响应表达式和大气辐射传输模式反演的闪电通道温度初步结果为大多在数千至4万K,平均11420 K。本项目所得成果有助于丰富雷电热效应的微波遥感理论和技术，可供雷电流热效应的微波遥感研究参考，同时有助于促进地基微波辐射计的技术发展与应用。