Estimation of electric charge distribution in thundercloud by using the inverse approaches

地面电场强度的信息对闪电的预报很有帮助。为了验证所提出的方法从电场信息估计雷云中电荷分布的能力，进行了以下研究。首先，提出了一种新的边界元技术——半无限边界元，用于计算云中电荷引起的电场。结果表明，该方法可以很容易地计算出考虑地形影响的电场分布。其次，研究了牛顿格式、最小二乘法、采样模式匹配法、神经网络和卡尔曼滤波等算法，从地表电场中估计电荷分布；在电荷估计问题中，测量点的数量很少，必须引入一个特殊的装置来增加“虚拟测量点”。通过数值模拟发现，牛顿格式最适合于精确估计，并且电场强度数据必须以三位有效数字测量才能进行估计。在另一项研究中，研制了一种使用电位器测量地面电场的防风雨型设备。但是，在实际应用中，必须提高测量精度的质量。

The information of the electric field intensity on the ground is useful for forecasting the lightning. To investigate the capability of the proposed approaches for estimating the electric charge distribution in thundercloud from the electric field information, the following studies were carried out.First, a new boundary element technique named semi-infinit boundary element was proposed to calculate the electric field caused by the electric charge in cloud. It is found that the electric field distribution considering the effect of the topography can easily be evaluated by using the technique.Second, to estimate the electric charge distribution from the electric field measured on the ground surface, some algorithms such as Newton scheme, Least square's method, Sampled pattern matching method, Neural network and Kalman filter were investigated. In the electric charge estimation problem, the number of the measuring points may be so small that a special device must be introduced to increase the "virtual measuring point". It is found from the numerical simulation that Newton scheme would be most suitable for accurate estimation, and also the electric field intensity data must be measured with three significant digit figures for the estimation.As another study, a weather-proof type equipment using potentiometer was developed to measure the electric field on the ground. However, the quality of the measurement accuracy must be improved for practical use.