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，然后根据与振动相关的电场变化来估计空间电荷密度。由于空间电荷分布可以实时测量，该系统有望在各个领域得到应用。例如，该系统将明确避雷针产生的空间电荷与输电钢塔周长之间的关系以及雷击的发展特征，为建立新的雷击理论提供了可能。该系统在已知雷云中电荷分布的情况下，能够对雷电的发生进行预报。结果表明，当声波频率为1 kHz，发射功率为900W，地面电场灵敏度为1μv/m时，空间电荷密度可测量到约8000m高，分辨率为1nC/m~3，并进行了室内实验验证。在直流高压下，对针面电极之间产生的空间电荷施加声波，同时测量电场的变化。我们可以探测到几个μC/m^3的空间电荷密度。此外，我们还在福井三滨市进行了冬季雷暴条件下的观测。结果表明，雷云下树梢的空间电荷密度约为10nC/m^3，且电荷密度随高度的升高而减小。如果电场天线具有更高的检测灵敏度，则可以检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.