JP2001004731A - Broadband interferometer - Google Patents

Abstract

(57) [Summary] [Problem] Observation that can be widely applied to various electromagnetic pulse radiations such as a single pulse or a burst pulse of a lightning discharge and can accurately and precisely locate a radiation source two-dimensionally or three-dimensionally at a low cost. The realization of the means. [Constitution] Since an electromagnetic wave pulse contains many frequency components, an interferometer can be configured in a wide band and adapted to various characteristics of the electromagnetic wave pulse, thereby enabling high-accuracy orientation. . Therefore, a plurality of broadband antennas are installed to receive electromagnetic wave pulse signals in a wide band, interference analysis is performed in parallel for each of a plurality of frequency components included in the received signal of each antenna, and the radiation source position of the electromagnetic wave pulse is determined. Multiple orientations are displayed. Also, the signal from the antenna is fetched only for a certain period including valid information, so that the memory is not wasted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a broadband interferometer for locating a radiation source of an electromagnetic wave pulse generated in the air such as a lightning discharge from a distance, and particularly relates to a single pulse or a burst pulse. In response to input of various electromagnetic wave pulses, a two-dimensional or three-dimensional position of the radiation source can be accurately located at low cost.

[0002]

2. Description of the Related Art Overview of Lightning Discharge Phenomenon The earth is a planet surrounded by the atmosphere such as nitrogen and oxygen. This atmosphere is usually classified vertically by temperature,
It is called the troposphere, stratosphere, mesosphere, and thermosphere in order from the ground surface. It is a phenomenon in the troposphere that, on average, is about 10 km thick, which causes the weather changes that we come into contact with every day. When the atmosphere in the troposphere forms an unstable stratification due to heating from the surface, cumulonimbus or thundercloud develops to resolve the instability. Its structure and development differ depending on the weather conditions, and the rate of change in wind direction and wind speed with respect to altitude (this is called shear) greatly affects the form of thunderclouds.
Thunderclouds are broadly classified into three types: air mass thunderclouds generated when the shear is weak, multi-cell thunderclouds generated when the shear is strong, and supercell-type thunderclouds. However, in general, a thundercloud, except for a supercell-type thunderstorm, is composed of an aggregate of convection units including a violent updraft and a downdraft at about several meters per second, which are called convection cells or precipitation cells. Each convection cell has a unique life cycle of a developmental period, a maturation period, and an annihilation period. Charge separation progresses in the cloud as the precipitation mainly composed of the hail of the development period progresses, and charges are accumulated. Then, the charge in the cloud is neutralized in the form of discharge when the dielectric breakdown strength of the atmosphere is exceeded. This is called lightning discharge, and the above is collectively called lightning discharge phenomenon.

Lightning discharges are roughly classified into two types: ground discharges (lightning strikes) and cloud discharges. Ground discharge, which is a major cause of lightning damage, is the process of discharging the charge in the cloud to the ground.For example, when the negative charge in the cloud is neutralized, this is conventionally called a negative lightning strike I have. The precursor discharge prior to the lightning strike starts inside the cloud, and the precursor discharge path extending outside the cloud branches and emits light at intervals of several tens of microseconds while branching. This is called a step leader. When the lower end of the reader reaches the ground, a phenomenon called return stroke or return stroke occurs, and a strong light-emitting portion rises on the reader at a speed close to the speed of light, and the duration from the reader to the ground is 100
A pulse current of about microsecond flows. After several tens to several hundreds of milliseconds have elapsed, the leader again follows the previously formed discharge path and progresses to the ground. This is called a dirt leader, and its speed is about ten times faster than that of a step leader, and it often progresses continuously without stepping. When the dirt leader reaches the ground, a second return stroke occurs and the discharge continues through a similar process. This is called a subsequent lightning strike, and a lightning strike with a subsequent lightning strike is called a multiple lightning strike. Negative lightning strikes account for more than 90% of summer lightning strikes, while positive lightning strikes account for more than half of winter lightning strikes along the Sea of Japan.

[0004] The lightning discharge phenomenon is closely related to power engineering. Of the total number of accidents involving power supply and distribution interruptions, lightning accidents vary according to voltage and year, but transmission lines account for 25 to 64% and distribution lines for 11 to 45%. ing. In particular, measures to prevent nuclear power plants and large-capacity thermal power plants are important because once they occur, they affect a wide area. For these reasons, the observation of winter lightning has been energetically conducted mainly by electric power companies and universities since the early 1950s, and the nature of winter lightning has been clarified. For example, there are the following characteristics that are often mentioned as characteristics of winter lightning compared to summer lightning. (1) The ratio of positive lightning strikes is high. (2) The number of discharges per thundercloud cell is small. (3) An upward lightning discharge occurs. (4) Simultaneous lightning strikes at multiple points. (5) Super bolt is generated. (6) Long horizontal discharge path under thundercloud.

[0005] Superbolt is lightning that is one to two orders of magnitude higher than the light energy of normal lightning discharge discovered by optical observations from satellites in the United States, and is relatively frequently observed over Japan in winter. . Supervolts are thought to be positive lightning strikes with large neutralizing charge and lightning current values from ground-based observations, but their statistical treatment is not yet sufficient. Such peculiarities, especially the nature of the positive lightning strike, are considered to be one of the major factors of the accident due to winter lightning on the transmission and distribution line.

There are various methods for preventing such lightning damage. For example, shielding to prevent lightning strikes on towers, prevention of flashover when lightning strikes transmission lines, application of zinc oxide lightning arresters, short-term accident elimination by reopening,
Restoration In addition, there are wide-area lightning location systems and lightning prediction using weather radar.

Research on such lightning damage prevention techniques is as follows.
It can be broadly classified into three categories: lightning resistance after lightning strike, control of lightning, and understanding of lightning properties, which are the basic knowledge thereof. In research on lightning immunity, transmission was conducted mainly by power companies,
For the purpose of rationalization and elaboration of substations and distribution facilities, understanding of lightning strikes, application of zinc oxide surge arresters, rationalization of insulation of substation equipment based on analysis, and surge analysis are still being vigorously conducted. In the study on lightning control, in Japan, rocket-based lightning strikes have been conducted mainly for the rocket lightning strike group (now mainly the Nagoya Institute of Technology group) for winter lightning in the Hokuriku region. And many findings have been obtained. Recently, another group has been conducting research on laser-induced lightning and water-induced lightning, and field experiments have actually been conducted. On the other hand, research on lightning prediction and understanding of lightning properties has generally received little interest. In the first place, lightning phenomena are meteorological phenomena and are usually studied by meteorologists, but such cases are very rare in Japan.
However, it is considered that research on lightning phenomena itself is indispensable in considering lightning damage prevention, and based on the knowledge obtained as a result, it is possible to find clues for lightning suppression and lightning prediction. Can be

Conventional Lightning Discharge Observation Technique When observing a lightning discharge, its occurrence is difficult to specify the place and time, so that remote measurement and remote sensing are the main means. What is observed as a physical quantity is an electric field, a magnetic field, an electromagnetic wave including light, and the like. Originally, lightning discharge is a phenomenon that involves charge transfer, so that much information about lightning discharge can be obtained by electromagnetic field measurement. The electric field radiated or changed by the lightning discharge is very wide in the frequency domain and ranges from DC to the microwave band. Therefore, the measurement method differs depending on what kind of discharge process is to be observed.

A rotating sector type electric field meter called a field mill is used to measure an electric field associated with the approach of a thundercloud before electric discharge or a change in electric field before and after lightning electric discharge up to several hundred hertz. On the other hand, a capacitive antenna called a slow antenna or a fast antenna is generally used for measuring an electric field change up to several tens of megahertz having a higher frequency. In these, the time constant is determined by the input resistance and the capacitor of the amplifier, and those with a time constant of several seconds or more are called a slow antenna, and those with a time constant of about several milliseconds are called a first antenna for convenience. However, recently, large-capacity memories and high-speed and high-resolution A / D conversion systems have been relatively inexpensively available. In practice, a dynamic range having both characteristics of a fast antenna and a slow antenna has been developed. A measurement system which can be called a wideband wideband slow antenna has been used.

The measurement of this region has been carried out since the 1950's due to the ease of measurement and the fact that most of the spectrum of electromagnetic waves that change or radiate due to lightning discharge is in this region. Are mostly obtained from measurements in this region. However, most of these findings are related to summer lightning, especially negative lightning strikes and cloud discharges, and there are few reports about winter lightning strikes and positive lightning strikes that have recently become a problem. Therefore, in the first half of this paper, we describe the results of applying the electric field observation from the electrostatic field using a slow antenna or a fast antenna to a frequency around several MHz to the positive lightning strike in winter, especially the discharge initiation process.

On the other hand, in the high frequency band region of several tens of megahertz or more, the measurement technology has been developed with the recent progress of the high frequency technology. Electromagnetic waves in this frequency band are considered to be emitted from the minute discharge process of lightning discharge,
It has been applied to visualize discharge phenomena in clouds as a sign of lightning strike with high time and spatial resolution. as a result,
The evolution of the discharge in the cloud, which could not be seen directly until now, has been clarified.From now on, observations in this area will elucidate basic matters of lightning discharge phenomena, such as the discharge process and the electrical structure of the thundercloud, In addition, it is likely to find clues for lightning prediction.

Electromagnetic radiation source localization techniques using VHF / UHF radiation are broadly divided into two methods: the time-of-arrival method and the interferometry.
The time-of-arrival method is a method of measuring the time-of-arrival of waveforms observed simultaneously at multiple points and determining the source of the radio wave from it. The method of measuring the phase difference and obtaining the direction of arrival is called an interference method. Research on lightning discharge using these techniques has been actively conducted mainly in the United States and France, and some of them have been put to practical use, such as the LDAR system (reference documents 1 and 2) and the SAFIR system. However, the lightning discharge may be accompanied by a phenomenon that proceeds at a high speed, such as branching by a step leader, in a series of processes, and the time difference method or the interferometry cannot have sufficient time resolution for such a phenomenon.

On the other hand, as a result of recent advances in digital and high-frequency technologies, ultra-high-speed sampling technology has been developed, and high-speed sampling of electromagnetic waves in the VHF / UHF band has become possible. This technique is applied to the diagnosis of electric equipment and the like (Reference Document 3), but the sampling frequency is extremely high and the time resolution is good. Further, in this method, since the signal of the electromagnetic wave is directly recorded, various software processes can be applied. However, there is no example of applying this method to actual lightning discharge observations and locating the source of electromagnetic wave radiation. At present, the possibility is discussed only in one dimension (Reference Document 4). . <References> 1. Taylor, W., A VHF technique for space-time mappi
ng of lightning discharge processes, J.Geophys.Re
s., 83, 3575-3583, 1978 2. Rustan, PL, MAUman, DGChilders, and WHBeas
ley, Lightning sourcelocations from VHF radiation d
ata for a flash at Kennedy Space Center, J.Geophys.
Res., 85,4893-4903,1980 Kawasaki, Z.-I., J.-M.Li, K.Matsuura, M.Kawasaki, a
nd O. Sugimoto, Localization of partial discharges u
sing time difference of arrival of radiation field
s, Proc. 3rd International Conference on Properties
and Applications of Dielectric Materials, Tokyo, Jap
an, 1991 4. Shao, XM, DNHolden, and CTRhodes, Broad band
radio interferometry for lightning observations, G
eophys. Res. Lett., 23, 1917-1920, 1996 Principle of Interferometer The principle of a narrow band interferometer based on a conventional interferometer will be described with reference to FIGS.

The narrow-band interferometer is basically composed of two narrow-band antennas arranged at a predetermined interval D, as shown in FIG. 1 / 4λ for narrowband antennas
A monopole antenna is used. When an electromagnetic wave based on lightning discharge is incident at an angle of φ from a distance to a straight line connecting two antennas, a phase difference θ is generated between the electromagnetic waves received by each antenna based on a stroke difference. Therefore, conversely, 2
If a phase difference θ is detected between signals of the same frequency received by each of the two antennas, the discharge point is located on the circumference of the bottom surface of a cone having an apex angle of φ with a straight line connecting the two antennas as an axis. Will exist somewhere in Equation (1) shown in Equation 1 holds between φ and θ.

[0015]

(Equation 1)

[0016] Therefore, A ₀ as shown in FIG. 23 (b)
-A ₁ and A ₀ -A ₂ of by orthogonal two sets of antenna pairs 2
The azimuth and elevation direction of the discharge point are estimated in one direction by dimensional arrangement. FIG. 24 illustrates the estimation method.

In FIG. 24, assuming that the incident angles of the electromagnetic waves obtained by the two pairs of antennas are φ ₁ and φ ₂ , the direction of the discharge point is defined by using a straight line connecting the antennas in each pair of antennas as a rotation axis (FIG. The X and Y axes are shown in the figure), and the rotation angle is obtained as the intersection of _two cones C ₁ and C ₂ with φ ₁ and φ ₂ .

At this time, the coordinates (x, y) of the discharge point are represented by the distance r from the antenna to the discharge point, and the incident angles φ ₁ , φ ₂
Is obtained by using the following equations (2) and (3). x = r × cos φ ₁ (2) y = r × cos φ ₂ (3) On the other hand, when the coordinates (x, y) of the discharge point are represented by the azimuth angle α and the elevation angle β, the following expressions (4) and (5) are obtained.

X = r × cos β × cos α (4) y = r × cos β × sin α (5) By solving equations (2) to (5) simultaneously and solving for azimuth angle α and elevation angle β, equations (6), (7), and (8) shown in equation 2 are obtained.

[0020]

(Equation 2)

As described above, the direction of the electromagnetic wave radiation source such as the lightning discharge point can be specified by obtaining the received signal phase difference θ between the antennas. If the direction of the electromagnetic wave radiation source can be specified at each of the plurality of observation points, the three-dimensional position of the electromagnetic wave radiation source can be located. The method of three-dimensional orientation will be described with reference to FIG.

In FIG. 25, the coordinates of the observation point 1 are represented by (X _1,
Y ₁ ), the coordinates of observation point 2 are (X2 _, Y ₂ ), the azimuth and elevation angle when viewing the radiation source from observation point 1 are α ₁ and β ₁ , respectively, and the azimuth and elevation angle when viewing the radiation source from observation point 2 Are α ₂ and β ₂ , the coordinates of the radiation source obtained at observation point 1 are (x, y, z ₁ ), and the coordinates of the radiation source obtained at observation point 2 are (x, y, z ₂ ), and ₁ = tan α ₁ (9) a ₂ = tan α ₂ (10), the following equation (11) holds.

Y = a ₁ (x−X ₁ ) + Y ₁ = a ₂ (x−X ₂ ) + Y ₂ (11) When the equation (11) is solved for x and y, the following equation (12) is obtained.
(13) is obtained.

X = (a ₁ X ₁ −a ₂ X ₂ −Y ₁ + Y ₂ ) / (a ₁ −a ₂ ) (12) y = (a ₁ a ₂ (X ₁ −X ₂ ) + a ₁ Y ₂ ) −a ₂ Y ₁ ) / (a ₁ −a ₂ ) (13) Further, z ₁ and z ₂ are expressed by the following equations (14) and (3) using x, y and β ₁ and β _2. 15).

[0025]

(Equation 3)

[0026]

Conventionally, the time-of-arrival method or the interferometry has been used to locate the position of the radiation source of an electromagnetic wave pulse due to lightning discharge. However, in the case of the time-of-arrival method, an isolated single shot is used. Although effective in locating the source position of a pulse, it has been difficult to locate the source position of a burst-like persistent pulse in a three-dimensional image. On the other hand, in the case of interferometry, it is relatively easy to locate and visualize the source position of a burst-like persistent pulse, but it was difficult to locate the source position of an isolated single pulse. . As described above, conventionally, there has been a problem that one lightning observation method cannot cope with various lightning discharges.

The present invention provides an observation means which can be widely applied to various electromagnetic pulse radiations such as a single pulse or a burst pulse of a lightning discharge, and which can accurately and two-dimensionally locate a radiation source position at a low cost. It is intended to be realized.

[0028]

According to the present invention, since an electromagnetic wave pulse contains many frequency components, an interferometer can be constructed in a wide band and adapted to various characteristics of the electromagnetic wave pulse, thereby achieving high accuracy. This allows for orientation at Therefore, a plurality of broadband antennas are installed to receive electromagnetic wave pulse signals in a wide band, interference analysis is performed in parallel for each of a plurality of frequency components included in the received signal of each antenna, and the radiation source position of the electromagnetic wave pulse is determined. Multiple orientations are displayed. Also, the signal from the antenna is fetched only for a certain period including valid information, so that the memory is not wasted.

The broadband interferometer of the present invention is configured as follows. (1) A broadband antenna installed at a predetermined interval, and an observation processing device that processes signals of electromagnetic wave pulses received by the plurality of wideband antennas and locates a radiation source thereof, the observation processing device comprising: A signal input detection unit that detects the arrival of an electromagnetic wave pulse to generate a trigger signal, and, in response to the generation of the trigger signal, a signal capturing unit that captures and accumulates a reception signal from each of the wideband antennas only for a certain period of time, A Fourier transform unit that performs a Fourier transform on the accumulated received signals of each of the wideband antennas, and a phase difference between signals of the same frequency between the received signals of the respective Fourier-transformed antennas for a plurality of pairs of the wideband antennas. Orientation calculation for locating the source of the electromagnetic pulse for each frequency based on the phase difference detector to be found and the phase difference of each frequency found And a part. (2) In the above (1), the received signals of the plurality of wideband antennas captured by the signal capturing unit are GP
Time synchronization by S. (3) In the preceding paragraph (1), the position of the radiation source of the electromagnetic pulse shall be located in three dimensions and displayed as an image.

Referring to FIG. 1, the basic configuration of the present invention will be described. It should be noted that the configuration shown is exemplary.

In order to locate the electromagnetic pulse radiation source 1 appearing at an arbitrary place such as a lightning discharge, the broadband antennas 2a to 2e are respectively divided into two orthogonal directions such as an east-west direction and a north-south direction on the ground surface. It is installed on the ground surface at regular intervals. Broadband antennas 2a to 2e receive electromagnetic wave pulse signals in a wide band of, for example, VHF to HF, and are amplified and A / D converted by observers 3a to 3e, respectively.
The data is input to the observation processing device 4. Each broadband antenna 2a ~
If the distance between 2e and the observation processing device 4 is short, the observation processing device 4 may be provided with an amplifier or an A / D converter, and each antenna 2a to 2e may be directly connected to the observation processing device 4 by a coaxial cable. . The sampling frequency of the A / D conversion needs to be set to twice or more the upper limit frequency of the reception band. For example, if the upper limit frequency is 250 MHz, the sampling frequency is set to 500 MHz.

The signal take-in section 5 includes the antennas 2a to 2a
The received signal from e is fetched in a digital signal format for a certain period of time and stored in the data memory 6. This signal capture
The operation is started by the input of a trigger signal from the signal input detection unit 7 and is continued for a fixed time. The reason why the signal is fetched only for a certain period of time is to prevent the limited memory resources of the data memory 6 from being wasted by redundant data when there is no signal. The length may be determined in consideration of the effective length of the electromagnetic wave pulse, for example, the maximum duration of the discharge in the case of lightning discharge, and the capacity of the data memory 6.

The signal input detecting section 7 includes a wideband antenna 2f
Detects the head of the received electromagnetic wave pulse, and sends a trigger signal to the signal capturing unit 5. The signal input detection unit 7 includes an integral type time constant circuit (for example, C
R integration circuit) and a threshold circuit. The time constant circuit extracts a slow change from the signal received by the wideband antenna 2f and compares it with a preset threshold by a threshold circuit, so that it does not respond to weak noise and rises in a strong single-shot pulse or burst-like pulse. Only to detect and generate a trigger signal. Instead of providing the wideband antenna 2f dedicated to signal input detection, the trigger signal may be generated using any one of the received signals of the wideband antennas 2a to 2e or a signal obtained by ORing the received signals.

The received signal which the signal receiving section 5 captures from each of the observation devices 3a to 3e is the G signal received by the GPS receiver 8
Synchronization is achieved by the PS pulse, and each reception time can be identified with high accuracy.

The processing unit 9 takes out the reception data of each of the wideband antennas 2a to 2e from the data memory 6 and performs the process of locating the radiation source. First, in the Fourier transform unit 10,
Fourier transform is performed for each of the reception data of the wideband antennas 2a to 2e, and the amplitude and phase of each component frequency are obtained. The phase difference detection unit 11 detects a zero phase difference between signals having the same component frequency for each pair of antennas arranged in the same direction.
The locating operation unit 12 performs an operation of locating a two-dimensional or three-dimensional radiation source position by triangulation described later, based on the position of each antenna pair and the phase difference between the same component frequencies. The image output unit 13 performs image processing on the information on the orientation position of the calculation result, and displays the information on the display device 14.

Next, the analysis process of each part of the orientation processing will be described in order with reference to FIG.

In FIG. 2, an antenna pair of antenna 1 and antenna 2 is used. First, consider a waveform recorded by one antenna. For example, a signal detected by the antenna 1 is represented as f ₁ (t) using time as a parameter.

Since f ₁ (t) is actually a discrete signal, it can be expressed by the following equation (15) by applying the discrete Fourier transform.

[0039]

(Equation 4)

When the same signal reaches the antenna 2 at a distance d from the antenna 1 at the same angle of incidence, the detection signal f ₂ (t) at the antenna 2 becomes equal to f ₁ (t + kΔt). When this is represented by a discrete signal system, it is as shown in Expression (16) of Expression 5.

[0041]

(Equation 5)

Considering the relationship of equation (16), the antenna 2
Similarly, when the discrete Fourier transform is applied to the signal of, the following equation (17) is obtained.

[0043]

(Equation 6)

Here, if the number N of data points is made sufficiently large with respect to k so as to include the entire waveform of the pulse, the following equation (18) is obtained.

[0045]

(Equation 7)

Since the left side of equation (18) is a term included in the right side of equation (11) and the right side of equation (18) is a term included in the right side of equation (17), discrete Fourier transform is performed on the waveform of antenna 1. When the value obtained by applying the discrete Fourier transform to the waveform of the antenna 2 is divided by the applied value, 2πkΔ at each frequency is obtained.
The value of t can be calculated. kΔt is the arrival time difference to the antenna
Since it is equal to d cos θ / c, it is possible to obtain the angle of incidence of the arriving electromagnetic wave with respect to the antenna pair at each frequency by substituting the known values of the baseline length d and the light velocity c. The above is the analysis procedure of the Fourier transform unit 10 and the phase difference detection unit 11 shown in FIG.

When the angle of incidence for one set of antenna pairs is determined, the electromagnetic wave radiation source is located on the circumference of the bottom of a cone whose axis is the straight line connecting the two antennas and whose apex angle is the angle of incidence. Will do. Now, the two antenna pairs are arranged at right angles to the east, west, and north and south, respectively, so that the radio wave source uses each baseline as the axis of rotation, and the angle of rotation is the calculated incident angle for each antenna pair. Can be obtained as an intersection of two cones. This is the analysis procedure of the orientation calculation unit 12 shown in FIG. With the above procedure, the electromagnetic wave radiation source is located in two dimensions. The procedure of the orientation calculation unit 12 is as shown in FIG.
3. The procedure is the same as that of the procedure for locating the electromagnetic radiation source in the narrow band interferometer described with reference to FIG.

[0048]

Example diagram 3 of the embodiment CARRYING OUT THE INVENTION broadband interferometer shows a system configuration of a wideband interferometer according to the present invention embodiment. In the system shown in the figure, two sets of broadband interferometers, each centered on computer terminals 18a and 18b, are installed at two separate points, and the azimuth and elevation angle of the arrival direction of the electromagnetic pulse obtained by each broadband interferometer are determined. Are transmitted in real time to the host computer 23 via the line network 22, and the host computer 23 determines the intersection of the arrival direction of the electromagnetic wave pulse based on the azimuth and elevation data sent from each of the wideband interferometers. ,
Locate the three-dimensional location of the source.

The details will be described by taking a wide band interferometer shown in the upper left part of the figure as an example. The figure shows four broadband antennas 15-1.
Although a to 15-4a are shown, at least three antennas are required, and they are arranged at right angles to east, west, and north and south. Each antenna can receive a VHF wave band (20 to 250 MHz), and for example, a disc-shaped capacitive antenna can be used. However, in the case of a capacitive antenna, it becomes impossible to immediately respond as a sensor due to saturation of the electric charge accumulated by induction, and it is necessary to create a time constant circuit for slowly releasing the electric charge. For example, a resistor may be connected to the ground so as to obtain a discharge time constant of about 5 seconds. This makes it possible to easily recover the sensor function even when the sensor function is temporarily saturated.

The signals received by each antenna are logarithmically compressed and amplified by wide-band logarithmic amplifiers 16-1a to 16-4a, and amplified by high-speed A / D converters 17-1a to 17-4a having a sampling frequency of 500 MHz, respectively. It is converted into a digital signal and input to a computer terminal 18a having a 4-channel input interface.

In the computer terminal 18a, the signal input to the input interface of four channels is monitored by the signal input detection processing 19a, and when a signal input exceeding a predetermined threshold value is detected, the input interface of each channel is detected by the signal capture timer processing 20a. , For example, continuously for 2 microseconds and store it in the memory. The captured signal includes the GPS receiver 21
Label the time synchronization with an accuracy of 1 μs using the GPS pulse from b. The signal data stored in the memory is composed of 8 bits per word, and the memory length per channel is 50 kilobytes. Here, the signal input detection processing 19a and the signal capture timer processing 20a
Is executed on software using a program, but it is needless to say that it may be realized by a dedicated hardware circuit. The computer terminal 18a extracts the input signal data of each channel stored in the memory in real time, calculates the azimuth and the elevation angle by performing the Fourier transform and the phase difference detection, and transmits the calculation result data to the host computer via the network 22. 23. The wideband interferometer at the upper right of the figure also performs the same operation as the above-mentioned wideband interferometer at the upper left.

Next, an example of an observation experiment of a lightning discharge caused by a rocket-induced lightning using a VHF broadband interferometer will be described.

FIG. 4 shows an outline of the observation experiment system.
The observation point where the VHF broadband interferometer was installed is located 3.6 km away from the lightning test site where the rocket launch pad is located, and three disc-shaped capacitive antennas are arranged at 5 m intervals.

FIG. 5A shows an example of a recorded waveform. The waveforms of the respective antennas show similar waveforms although there is a difference in amplitude, and it is indicated that there is a time difference between the waveforms. For this waveform,
FIG. 5B shows the result of numerically performing Fourier transform by (Fast Fourier Transformation) to obtain a spectrum. It can be seen that the spectrum required for each antenna input shows a similar tendency. In any of the waveforms, the higher the frequency is, the lower the spectral intensity tends to be. In any of the waveforms around 30 MHz, there are low spectral intensity points,
This is considered to be due to the frequency characteristics of the antenna.

FIG. 6 shows each antenna pair (east-west, north-south direction).
5 shows the result of extracting the phase difference for. ± 2π phase difference
It can be seen that periodic characteristics are shown up to about 120 MHz in the range of. After 120MHz,
The phase difference becomes random, which corresponds to regions where the intensity of the spectrum is low.

In this embodiment, since the FFT is used, the extracted phase difference is limited to ± 2π. However, since the phase difference increases as the high frequency component increases, the actual phase difference is calculated by ± 2π even if it takes a value of ± 2π or more.
It will take a value within π. This is called fringe. To select a correct fringe, it is necessary to add ± 2π, ± 4π, ± 8π, etc. to the obtained phase difference. The result of this addition is shown in FIG.
It can be seen that by performing addition and subtraction by a factor of 2π, the phase difference changes continuously according to the frequency.

Since the arrival direction of the electromagnetic wave is limited to one, it is necessary to select a correct fringe from this pattern. In the case of the present embodiment, since the base line length is 5 meters, if an electromagnetic wave arrives so as to take an incident angle having the largest phase difference, the frequency in which these irregularities, that is, no fringes exist, is limited to 30 MHz. Therefore, by selecting the fringe based on the phase difference in this area, correct phase difference detection can be performed.
In fact, as shown in FIG. 7B, it can be confirmed that the phase difference is correctly selected.

FIG. 8 shows the result of calculating the incident angle after the fringe selection. As described above, the dependence on the frequency is not remarkable, and both the azimuth and the elevation show an almost constant tendency with respect to the frequency.

FIG. 9A shows that at 20:59 on November 15
An overall view of the electric field change of the ground lightning strike at 34 minutes is shown. This waveform shows a characteristic in which a large number of pulses are superimposed on a gradual change in the negative direction, and the pulse train is often seen at the beginning of the discharge and gradually decreases toward the end of recording. The polarity of the electric field change of the entire waveform suggests that the positive lightning in the sky was neutralized by the lightning strike. Also, no fast-rising changes, which are thought to be due to a positive polarity return stroke as seen in natural lightning, have been recorded. It can be confirmed that there is no return lightning strike in the positive rocket induced lightning regardless of summer or winter.

FIG. 9B is an enlarged view of the time axis of the discharge start portion of this lightning strike. The vertical bar in the figure indicates the time at which the broadband pulse was recorded. No change was observed before the discharge started, and the signal showed a nearly flat noise level.After that, the electric field change began to change gradually in the negative direction, and the amplitude of the pulse superimposed on the change also increased gradually. You can see that it is. Broadband pulses are emitted prior to this significant electric field change. On the other hand, the current waveform measured by the shunt resistor at the same time has a duration of about 13 milliseconds, which is almost the same as the duration of the electric field change, and its polarity is positive, that is, this lightning strike has a negative polarity upward discharge. And that the positive charges in the sky are neutralized. Therefore, it is considered that the pulse train seen in the electric field change and the broadband pulse radiated corresponding to the time are due to the negatively stepped leader continuously evolving from the ground toward the sky. Similarly, the pulse train recorded in the current waveform indicates several kiloamps to several tens of kiloamps, and the pulse train recorded in the electric field change is considered to be a large current pulse specific to winter positive triggered lightning. Can be

FIG. 10 shows a histogram of the time intervals of the broadband pulses. The average time interval is about 22 microseconds.

FIG. 11 shows a graph of the calculated azimuth and elevation angle versus frequency. As can be seen from the figure, the azimuth and elevation tend to be several degrees at the same time as the frequency increases.
This tendency seems to be related to the microscopic radiation process of the radiation source, but a detailed study is a topic for the future. At tens of megahertz or higher, the azimuth and elevation of the electromagnetic wave radiation source show an almost constant tendency. In this region, the average value is calculated and one discharge point is used for further analysis.

FIG. 1 shows the time change of the elevation angle of the broadband signal considered to be radiated from the negative step reader.
It is shown in FIG. From the figure, it can be seen that the electromagnetic wave radiation source evolves upward. Since the distance from the observation point to the rocket launch pad is known, the speed can be evaluated, and 6 × 1
0 is calculated as ⁵ m / s. This value is a two-dimensional velocity of 6 × 10 ⁵ m / determined by optical observation of a negative lightning strike.
s, similar to 5.7 × 10 ⁵ m / s by electric field observation. These values also suggest that the radiation source of the electromagnetic wave is the tip of the reader.

By the way, the radiation point located at the start of the leader coincides with the position of the rocket launcher within a few degrees, and the standard deviation of the variation of the radiation source in the azimuth direction is 1.6 degrees. Indicates that the orientation error is within several degrees. In addition, a communication radio tower having a frequency of around 58 MHz was present near the observation point, and when lightning discharge did not occur, this frequency was extracted for position location. As a result, the directions are almost the same, and the variation of the control points is calculated to be 2 to 3 degrees, and the standard deviation is calculated to be 1 degree or less. Accurate evaluation is difficult due to the inability to measure the exact location of the radio tower, but the radiation source from the tower lightning strike is within a few degrees of the position of the rocket launch pad, and its standard deviation Considering that the distance is within several degrees and the variation in the orientation of the communication wave is about several degrees, it can be understood that the observation system has the orientation accuracy of about several degrees.

FIG. 13 shows that the information is displayed on November 15, 20:54:22.
The whole figure of the electric field change of the tower lightning strike in seconds is shown. In the case of this experiment, this was a lightning strike to a 50-meter test tower, and the rocket and wires launched into the sky were insulated from the ground. In addition, the lightning strike of this method is Altitu in France.
Note that it is of the same kind as de lightning.
As can be seen from the figure, the process starts with a gradual change in the electric field, and after the change in the positive direction, several stepwise changes continue around 60 ms. This characteristic is similar to that of the electric field change in the rocket-induced lightning strike in Europe and the United States, and this stepwise change is probably due to the subsequent lightning strike of the negative polarity. On the other hand, the overall polarity of the electric field change indicates that the neutralization of the negative charge in the sky was performed by this lightning, and there is no contradiction. Since it is not possible to directly measure the lightning strike current of the tower lightning strike, no comparison with the current waveform is performed.

FIG. 14 is a schematic diagram in which the lightning induction process of the lightning tower is assumed to neutralize the negative charges in the sky, in the case of Europe and the United States and in the case of Japan. The upper part of the figure shows the rocket lightning strike in Europe and the United States, especially in Florida, and the lower part is the rocket lightning strike experiment in Japan in the winter Hokuriku region. The notable difference is its lightning altitude. In Europe and the United States, the height of the wire bottom of the tower lightning strike is nearly 400 meters, while in Japan the tower lightning strike in the Hokuriku region is up to 100 meters.
Furthermore, in the case of Japan, the height of the tower is about 50 meters, and the length of the leader that actually advances toward the tower is about 50 meters.

Next, a specific lightning triggering process of a tower lightning trigger will be described. In a tower lightning strike, nylon wire is insulated up to about 100 meters from the ground, and a steel wire (piano wire) is drawn out of a bobbin attached to a rocket. That is, the rocket and the wires following it are insulated from the tower and the ground. Therefore, for example, in the case of a negative polarity lightning strike in which the negative charge in the sky is neutralized, the positive polarity leader first advances toward the sky from the tip of the rocket, and from the lower end of the wire a few milliseconds later toward the ground Leaders evolve. In the case of rocket lightning strikes in Japan, the height of the lower end of the wire is 10 times higher than in Europe and the United States.
The process of this part is not well understood because it is about twice as low, and it is a mountainous area in winter and visibility near the experimental site is poor, but the process of simultaneous progression of leaders of opposite polarity is the same. And leaders starting from the lower end of the wire are usually associated with connecting leaders from towers or lightning rods, so that a partial return stroke or small retu
Through the process of neutralizing the negative charges stored in the discharge path of the downward leader called rnstroke, it becomes an upward positive leader and further ascends toward the cloud. After several tens of milliseconds, the dirt leader descends from the cloud and a subsequent lightning strike occurs, repeating this process several times. This is the process of lightning strike of the negative tower.

FIG. 15 is an enlarged view of the electric field change at the start of the lightning strike. The vertical bar with the number in the figure is the occurrence time of the broadband pulse. From this figure, it can be seen that this lightning starts with a bipolar pulse, and a broadband pulse is emitted prior to the pulse.

FIG. 16 shows the results of two-dimensional orientation of these pulses. As can be seen from the figure, these pulse numbers 1 to 6 are emitted from near the steel tower. The positive polarity reader has a higher VH than the negative polarity reader.
Since the F radiation intensity is weak, it is considered that these pulses are emitted from the negative polarity reader that continuously extends from the lower end of the wire toward the steel tower. In the case of Japanese rocket lightning strike, the lightning strike height is about 100 meters, which is much lower than 400 meters in Europe and America. In other words, the results of this analysis specified near the steel tower are in good agreement with the experimental facts. Also,
From this, the bipolar pulse recorded in the electric field change was small return str when the negative polarity reader struck the tower.
Probably radiated by oke.

After the first bipolar pulse, no VHF radiation has been recorded for about 46 milliseconds. During this time, it is considered that the positive polarity leader corresponds to the process of progressing toward the cloud,
The swing of the electric field change in the positive direction coincides with the swing direction when the positive polarity leader is ascending (see FIG. 17). At about 398 milliseconds thereafter, VHF pulses are recorded at short time intervals, as can be seen from FIG.

FIG. 18 shows the results of locating the radio-frequency radiation sources of these VHF pulses. As shown in this figure, the radiation source of these pulses is located within a few degrees at a point about 30 degrees from the lightning tower and about 2 km away from the tower. From this, the development speed of the positive polarity leader is calculated to be 4.4 × 10 ⁴ m / s. As for the origin of these pulses, a rapid change was recorded 130 microseconds after this burst emission, which is likely to be equivalent to a return stroke, so that these pulses were associated with the negative breakdown associated with the formation of the dirt leader. It is thought to be radiation from a positive polarity reader that is developing in the process or negative charge region in the cloud.
The average value of the pulse time interval is 77 microseconds. FIG. 19 shows the histogram.

FIG. 20 shows the change in the electric field after the pulse burst emitted prior to the first subsequent lightning stroke. As can be seen from the figure, several wide band signals are recorded in response to the rapid change of the electric field. These enlarged views are shown in FIGS. 21 (a), (b) and (c). FIG. 22 shows the two-dimensional orientation results of these pulses. Pulses 34 and 38 are emitted in synchronization with the rapid change of the electric field. And these pulse radiation sources are located near the tower. This indicates that the changes denoted by R1 and R3 are due to the return stroke. The reason why the waveform of this change is different from the waveform seen in a typical negative lightning strike in summer is considered to be the bending of the discharge path.

Approximately 130 microseconds prior to R1, a thirty-third pulse of the pulse emission train presumably due to the dirt reader has been emitted. If the dirt leader is moving towards the tower during this time, the speed will be 1.5 × 10
⁷ m / s.

After the change in R1, broadband pulses 35 and 36 are emitted, the positions of which are near the start of the dirt leader. This is considered to be a positive dielectric breakdown process in which the return stroke reaches the negative charge layer above and then the positive streamer continuously progresses in the negative charge layer. This tendency is R3
Can also be seen for the orientation of the pulse 39 in the change of.
Since the control points of R2 and the pulse 37 are not near the tower, this pulse is considered to be caused by discharge activity in the cloud. The localization result up to the pulse 39 and its interpretation have been described above. Similar localization results are shown for the remaining pulses.

The following conclusions were obtained from the above observation results. (1) The broadband interferometer is operating with an accuracy within several degrees. (2) Within the observed range, the time interval of the broadband pulse emitted from the negative-polarity upward reader is 22 microseconds on average, and the propagation speed is 6 × 10 ⁵ m / s. (3) There should be no rapid change equivalent to return stroke in the positive rocket lightning strike. (4) The broadband pulse preceding the bipolar pulse at the discharge start part of the negative rocket lightning strike is emitted by the negative reader extending from the lower end of the wire toward the tower, and the bipolar pulse is transmitted to the tower of the negative leader. To be radiated by the connecting process to (5) The broadband interferometer is capable of locating both pulse burst and single-shot pulse types. (6) From the observation of the lightning strike of the negative rocket, within the range of the analysis example, the speed of the positive upward reader was 4 × 10 ⁴ m /
s. (7) Within the range of observation, the time interval of the broadband pulse emission preceding the downward dartleader was 78 μs on average, and the speed of the dartleader was 1.5 × 10 ⁴ from the observation of the negative rocket-induced lightning strike. m / s.

[0076]

According to the wideband interferometer of the present invention, a wideband antenna is used as an antenna, and each component frequency signal within the band is extracted from a received signal by Fourier transform, and a signal having the same component frequency is output between a pair of antennas. Detects the phase difference between each other and performs locating calculations for each component frequency in a multiplexed manner, thereby minimizing the cost of observation equipment and locating electromagnetic pulse radiation sources such as lightning discharges more accurately than conventional methods. Can be observed. In particular, the reception of signals from each antenna is limited to a certain length of time after the signal input is detected, so it is necessary even if signals of the VHF band are captured for several microseconds for each channel. The capacity of the memory to be stored is only tens to hundreds of kilobytes, and only valid signal data is taken in.
U does not have to spend time on unnecessary processing, thereby saving hardware and speeding up observation processing.

[Brief description of the drawings]

FIG. 1 is a basic configuration diagram of the present invention.

FIG. 2 is an explanatory diagram of a location process.

FIG. 3 is a configuration diagram of a broadband interferometer according to an embodiment of the present invention.

FIG. 4 is a schematic diagram of an observation experiment system.

FIG. 5 is a waveform diagram of an example of a broadband signal and a spectrum.

FIG. 6 is a graph showing a phase difference between signals in each antenna pair.

FIG. 7 is a graph showing a signal phase difference between antennas.

FIG. 8 is a graph showing a calculated angle of incidence of a broadband signal incident on each antenna pair arranged in east, west, and north and south directions.

FIG. 9 is a waveform diagram of an electric field change of a ground dielectric.

FIG. 10 is a histogram of time intervals of broadband pulses emitted from a negative polarity upward reader.

FIG. 11 is a graph showing the frequency dependence of the calculated azimuth angle and suppression angle of the broadband pulse.

FIG. 12 is a graph showing a change over time of the elevation angle of a broadband pulse train emitted by a negative upward reader.

FIG. 13 is an overall view of an electric field change of a tower lightning strike.

FIG. 14 is a schematic diagram of a lightning strike process of a tower lightning strike.

FIG. 15 is an enlarged view of a discharge start portion of a tower lightning strike.

FIG. 16 is a graph showing a two-dimensional orientation result of a broadband pulse.

FIG. 17 is a graph showing the first half of the electric field change of the tower lightning strike.

FIG. 18 is a graph showing a two-dimensional orientation result of a broadband pulse.

FIG. 19 is a time interval histogram of a broadband pulse emitted with the formation of a dirt leader.

FIG. 20 is an enlarged view of a subsequent lightning strike portion of an electric field change accompanying a tower lightning strike.

FIG. 21 is an enlarged view of an electric field change of a tower lightning strike.

FIG. 22 is a graph showing a two-dimensional orientation result of a broadband pulse.

FIG. 23 is a diagram illustrating the principle of an interferometer.

FIG. 24 is an explanatory diagram of an estimation method of an arrival direction of an electromagnetic wave pulse.

FIG. 25 is an explanatory diagram of three-dimensional orientation.

[Explanation of symbols]

 1: Electromagnetic pulse radiation sources 2a to 2f: Broadband antennas 3a to 3e: Observer 4: Observation processing unit 5: Signal acquisition unit 6: Data memory 9: Processing unit 10: Fourier transform unit 11: Phase difference detection unit 12: Orientation Operation unit 13: Image output unit 14: Display device

Claims (3)

[Claims] 1. An observation processing apparatus comprising: a wide-band antenna installed at a predetermined interval; and an observation processing device that processes signals of electromagnetic wave pulses received by the plurality of wide-band antennas and locates a position of a radiation source. The apparatus includes: a signal input detection unit that detects the arrival of an electromagnetic wave pulse and generates a trigger signal; and a signal capture unit that captures and accumulates a reception signal from each of the wideband antennas only for a predetermined time according to the generation of the trigger signal. And a Fourier transform unit that Fourier-transforms the accumulated received signals of each of the wideband antennas. For a plurality of pairs of wideband antennas, the positions of signals of the same frequency between the received signals of the respective Fourier-transformed antennas are compared. Based on the phase difference detector that calculates the phase difference and the phase difference of each frequency, the position of the radiation source of the electromagnetic pulse is located for each frequency. A wideband interferometer, comprising: 2. The wideband interferometer according to claim 1, wherein the reception signals of the plurality of wideband antennas captured by the signal capturing unit are time-synchronized by GPS, respectively. 3. The broadband interferometer according to claim 1, wherein the position of the radiation source of the electromagnetic wave pulse is located three-dimensionally and displayed as an image.