Study on the remote sensing of the space charge

我们开发了测量空间电荷密度的新系统。利用声波使空间电荷振动，然后根据振动引起的电场变化估计空间电荷密度。由于该系统可以实时测量空间电荷分布，因此有望在各个领域得到应用。例如，该系统将明确从避雷针和输电铁塔周长产生的空间电荷与雷击的发展特征之间的关系，从而有可能建立一种新的雷击理论。并且，如果该系统知道雷云中的电荷分布，就可以预测闪电的发生。首先，进行了理论预测，以确定该测量原理的有效性。结果表明，当声波的频率为1kHz，发射输出为900w，电场计在地面上的灵敏度为1 μ v/m时，可测量到8000m左右高的空间电荷密度，分辨率为1nC/m^3。为了证实这一结果，进行了室内实验。在针对面电极之间的空间电荷上施加声波，并施加直流高压，然后同时测量电场的变化。我们可以检测到空间电荷密度约为几μ C/m^3。此外，在福井的三滨进行了冬季雷暴条件下的观测。结果表明，雷雨云作用下树梢处的空间电荷密度约为10nC/m^3，且电荷密度随高度的增加而减小。如果电场天线具有较高的探测灵敏度，则可以探测雷云中的电荷密度。

We developed the new system which measures the space charge density. The space charge is made to vibrate by sound wave, and then the space charge density is estimated from the electric field change associated with the vibration. Scince the space charge distribution can be measured in real time, applications in the various fields is anticipated with this system. For example, this system will make clear the relation between the space charge which occurs from the lightning rod and the circumference of the power transmission steel tower and the progressing feature of lightning stroke, and it becomes possible that a new lightning striking theory is built. And, this system enables to predict the occurrence of lightning if it knows the charge distribution in the thundercloud.First, a theoretical prediction was done to ascertain the validity of this measurement principle. It was found out that space charge density to about 8000m high can be measured with the resolution of 1nC/m^3 when the frequency and the transmitting output of the sound wave is 1kHz and 900w respectively and the electric field meter has a sensitivity of 1 μ v/m on the ground.The indoor experiment was done to confirm this result. A sound wave was put on the space charge occurred between the needle-to-plane electrodes applied to a direct current high voltage, and then an electric field change was measured simultaneously. We could detect the space charge density of about a few μ C/m^3.Furthermore, the observations under winter thunderstorm were done at Mihama in Fukui. We got some results that the space charge densities which occurred at the tip of the tree under a thundercloud were about several 10nC/m^3, and the charge density decreases with increasing altitude. It becomes possible to detect the charge density in the thundercloud if the electric field antenna has a higher detection sensitivity.