| Advanced magnetic signal detection technology is the basis of the lightning research.In recent years,high-precision magnetic signal detection technology developed at home and abroad,has greatly promoted the understanding of the lightning microphysical process and the mechanism of the lightning disasters,and has enormous theoretical value and economy benefit.This article overcomes the shortcomings of magnetic antennas,such as narrow operating bandwidth,short detection range,low time accuracy,and slow signal transmission.The two-dimensional positioning of low-gain magnetic antenna,three-dimensional positioning of high-gain magnetic antenna,andultra-long-distance positioning of ultra-long distance magnetic antenna,using three magnetic antenna integration innovations,improves the hardware sensitivity,broadens the working range of the magnetic antenna,and improves the acquisition system.Based on the principle of lightning detection,the high-temporal resolution of the ground-flash discharge process is analyzed by two-dimensional positioning,and on this basis,the combination of high precision GPS clock,NI high-speed acquisition card.Then the pre-breakdown process,the return stroke process and positioning error were studied and analyzed in detail,and the Narrow Bipolar pulse discharge events(Narrow Bipolar Event,NBE)are discussed.The main results are as follows:First of all,from the principleand design of the electromagnetic pulse sensor are introduced in detail from the aspects of the principle of the low-gain magnetic antenna,the selection of the magnetic core and the development of the detection coil,the composition and principle of the magnetic antenna signal processing circuit,and the frequency response curve.The principle and design of lightning electromagnetic field sensor are introduced in detail.The magnetic antenna independently developed in this article is compared with similar devices at home and abroad.Its features are:(1)In order to overcome the problem of air-core coil sensitivity low and miniaturization,the use of ferromagnetic materials so that induction coil miniaturization problem solved.(2)Magnetic antenna signal processing circuit adopt the differential amplifier circuit and the secondary amplifying circuit,which makes the original signal stable output.(3)The continuous waveform of the lightning discharge process can be recorded with a time resolution of 50ns.(4)The frequency response cure of the low-gain magnetic antenna is less than 10kHz,and the collected signal is dB/dt.Combining the calibration principle of the low-gain magnetic antenna,the magnetic antenna signal processing circuit was calibrated and corrected,and an 8/20?s lightning current impact platform was used to perform outdoor calibration experiments on the magnetic antenna.The result showed that the working bandwidth of the low-gain magnetic antenna was 10kHz to 500kHz.It is verified that waveform measured in the low gain linear part of the frequency response curve is dB/dt.On the other hand,the basic situation of the networking and joint testing in Nanjing region was introduced.The four-station synchronous waveforms recorded by the low-gain magnetic field were analyzed and it was found that the time synchronization of different stations was good.Using the low-gain lightning location system and magnetic field observation data obtained in Nanjing,Jiangsu in August 2016,the parameters of the 1004 return stroke waveforms during the lightning discharge process were statistically he analyzed,and 8 of them were analyzed and two dimensional orientation.Compared with the lightning location system in Jiangsu Province,we can see that the lightning strike point are mostly distributed in the strip zone between N32° to N32.3°in Nanjing,and except for the points where the individual positioning error is large.The location results of the two systems for the same ground flash are not much different.At the same time,TBB data is used to analyze thunderstorm process in the lightning,which shows that the low-gain magnetic antenna can record the lightning process in detail.Finally,according to the analysis of ultra-long distance magnetic antennas obtained from Nanjing area on August 29,2017,the average pulse width of 466 NBE is 19.6?s,the maximum is 30?s,and the standard deviation is 5.92?s.The average pulse width of the positive NBE is wider by about 1 to 2?s than of the negative NBE,and the maximum width is significantly greater than maximum width of the negative NBE.The development of the ultra-long distancemagnetic antenna measurement system based on single stand NBE three-dimensional positioning method,analyzed the NBE height and distance calculation method and the two NBE event inversion calculation,and comparison with data of WWLLN found that verify the time precision of the magnetic field measurement system and magnetic orientation precision is higher. |
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