RU2349939C1 - Earthquake and tsunami warning system - Google Patents

Abstract

FIELD: physics; mining engineering.

SUBSTANCE: system contains hermetic enclosure with attached seismic vibration receiver and distributed mass pendulum, optoelectronic sensor of preset limit pendulum deviation. Pendulum consists of optically matched coherent light source and photodetector connected through photocurrent amplifier and frequency meter to alarm initiating detector. Optoelectronic sensor is represented with signal and reference fibre coils, optically connected through coherent light source and photodetector to interferometer. Herewith signal and reference fibre coils are embedded in the enclosure mounted on sea-bed, while coherent light source and photodetector are arranged in above-water control and record centre. Alarm initiating detector is designed as a transmitter provided in above-water control and record centre, satellite transponder and terrestrial station. Transmitter represents modulation code generator, phase-shift modulator, high-frequency generator, power amplifier and transmitting antenna. Terrestrial station consists of receiving antenna, high-frequency amplifier, mixer, heterodyne, intermediate-frequency amplifier, phase-shift keying signal demodulator, registration unit, audible warning device. Phase-shift keying signal demodulator contains delay line, the first, second and third adders, the first and second amplitude detectors, phase inverter.

EFFECT: higher reliability of system.

3 dwg

Description

The proposed system relates to underwater geoacoustics and can be used to warn of earthquakes and tsunamis by turning on the appropriate alarm systems.

Known devices and systems for warning of earthquakes and tsunamis (ed. Certificate of the USSR No. 914702, 1070497, 1163287, 1198142, 1584585; RF patents No. 2034312, 2097792, 2124744, 2147060, 2156988, 2238574, 2290671; US patents No. 42859238, 458787238, 4587). , 4691661, 5124915, 5556229; UK patents No. 1163173, 2183038; Soloviev S.L., Burymskaya R.I. Evaluation of the effectiveness of new signs of earthquake tsunamigenicity. Izv. ANSSSR, Physics of the Earth series, 1981, No. 8 and others).

Of the known devices and systems closest to the proposed is the "System for warning of earthquakes and tsunamis" (RF patent No. 2290671, G01V 1/16, 2005), which is selected as a prototype.

The specified system contains an AES repeater, a seismic trigger, a transmitter, and a ground station, which includes an FMK signal demodulator consisting of multipliers, a narrow-band filter, and a low-pass filter. Serially connected multiplier and low-pass filter form a phase detector.

The disadvantage of this system is the presence of multipliers having a small dynamic range of input signals, limited bandwidth and low slope, which degrade the signal-to-noise ratio at signal levels comparable to the level of the receiver's own noise.

In addition, the presence of multiplication products (higher-order harmonics) reduces the efficiency of the receiver and requires the installation of filters that highlight useful information.

All this, ultimately, leads to a decrease in the reliability of the transmission of alarming information to warn about earthquakes and tsunamis and, as a result, to a decrease in the reliability of the radio channel.

An object of the invention is to increase the reliability of the radio channel by increasing the dynamic range of the input signals and improving the signal-to-noise ratio when receiving weak signals.

The problem is solved in that a system for warning of earthquakes and tsunamis, containing, in accordance with the closest analogue, a sealed enclosure with a seismic oscillation receiver attached to its lower part and a distributed pendulum to the upper part, as well as an optoelectronic sensor with a predetermined deviation limit value a pendulum that includes an optically matched coherent light source and a photodetector connected by an output through a series-connected photo current amplifier and the isomer to the alarm, while the optoelectronic sensor of the predetermined limit value of the pendulum deviation is made in the form of a signal and reference fiber coils optically coupled through a coherent light source and a photodetector to an interferometer, the signal and reference fiber coils are located in a housing mounted on the seabed, respectively on and off the trajectory of the pendulum deviation from the equilibrium position, and the coherent light source and photodetector are located on the surface control center and register The alarm indicator is made in the form of a transmitter installed on a surface control and registration center, an IS3 repeater and a ground station, the transmitter is made in the form of a modulator code generator, a phase manipulator connected in series to the output of the frequency meter, the second input of which is connected to the output of the high frequency generator, power amplifier and transmitting antenna, the ground station is made in the form of a series-connected receiving antenna, high-frequency amplifier, mixer, the second input of which it is single with the output of the local oscillator, the intermediate frequency amplifier, the FMN signal demodulator, to the output of which the recording unit and the sound signaling device are connected, differs from the closest analogue in that the FMN signal demodulator is made in the form of a delay line, the first adder connected in series to the output of the intermediate frequency amplifier , the second input of which is connected to the output of the intermediate frequency amplifier, the first amplitude detector and the third adder, to the output of which a recording unit and an audio signal are connected ator sequentially connected to the output of delay line phase inverter, a second adder, a second input coupled to an output of intermediate frequency amplifier, and the second amplitude detector, whose output is connected to a second input of the third adder.

The structural diagram of the seismic trigger and transmitter is presented in figure 1. The structural diagram of the ground station is presented in figure 2. Timing diagrams explaining the principle of the system are shown in Fig.3.

The seismic trigger contains a sealed housing 1 (Fig. 1) with a receiver 2 of seismic vibrations attached to its lower part, made in the form of a traditional pin stuck into the soil of the seabed 3. A pendulum 4 with a distributed mass is suspended from the upper part of the sealed housing 1. The trigger also includes an optoelectronic sensor at a predetermined limit value of the deviation of the pendulum 4, made in the form of signal and reference fiber coils 5 and 6, optically coupled to a coherent light source 7 and a photodetector 8 into an interferometer, for example, assembled according to the Mach-Zehnder scheme. The signal coil 5 of the interferometer is located on the trajectory of the deviation of the pendulum 4 from the equilibrium position, and the reference coil 6 is outside the trajectory of the deviation of the pendulum 4. The output of the photodetector 8 is connected through a series-connected amplifier 9 of the photocurrent and frequency counter 10 to the alarm signaling device.

The fiber coils 5 and 6 of the interferometer are mounted directly in the sealed enclosure 1, and the remaining trigger elements are located on the surface control and registration center. The connection of the underwater part of the seismic trigger with the surface is carried out by cable 11.

The transmitter 17 is made in the form of series-connected to the output of the frequency counter 10 of the shaper 12 of the modulating code, phase manipulator 14, the second input of which is connected to the output of the high-frequency generator 13, power amplifier 15 and transmitting antenna 16.

The ground station is made in the form of series-connected receiving antenna 19, high-frequency amplifier 20, mixer 22, the second input of which is connected to the output of the local oscillator 21, the intermediate frequency amplifier 23, the delay line 25, the first adder 27, the second input of which is connected to the output of the intermediate amplifier 23 frequency, the first amplitude detector 31 and the third adder 33, the output of which is connected to the recording unit 29 and an audible warning device 30, connected in series to the output of the delay line 25 of the bass reflex 26, of the second sum ator 28, the second input of which is connected to the output of the intermediate frequency amplifier 23, and the second amplitude detector 32, the output of which is connected to the second input of the third adder 33. Delay line 25, phase inverter 26, adders 27, 28 and 33 and amplitude detectors 31, 32 form demodulator 24 FMN signal.

The connection of the seismic trigger with the ground station is carried out using the radio channel through the IS3 relay 18.

The fiber spool 5 is biased into the housing 1 along the pendulum 4 with a distributed mass. To eliminate the influence of acoustic noise on the operation of the trigger, the fiber coils 5 and 6 are covered with a soundproof sheath.

The system for warning of earthquakes and tsunamis works as follows.

When 3 earthquakes or tsunamis occur near the seabed, seismic receiver 2, which is also the anchor of building 1, senses accelerations caused by the effects of tremors on the seismic trigger. A pendulum 4 with a distributed mass in response to an earthquake comes into oscillatory motion.

If the tremors reach a certain amplitude, the deviation of the pendulum 4 reaches a critical value at which it hits the signal coil 5. At the output of the photodetector 8, a signal appears in the form of a sequence of interference peaks. After amplifying the photocurrent in amplifier 9, the frequency counter 10 counts the frequency and number of interference peaks that enter the driver 12, where a modulating code M (f) is generated (Fig. 3, b) containing the frequency and number of interference peaks, as well as the number of the seismic trigger and its location. This code is fed to the first input of the phase manipulator 14, to the second input of which harmonic oscillation is output from the output of the high-frequency generator 13 (Fig. 3, a)

u _c (t) = U _c cos (ω _c t + φ _c ), 0≤t≤T _c ,

where U _c , ω _c , φ _c , T _c - amplitude, carrier frequency, initial phase and duration of harmonic oscillation.

At the output of the phase manipulator 14, a complex signal with phase shift keying (QPSK) is generated (Fig. 3, c)

u ₁ (t) = U _c · cos [ω _c t + φ _k (t) + φ _c ], 0≤t≤T _c

where φ _к = {0, π} is the manipulated phase component that displays the phase manipulation law in accordance with the modulating code M (t) (Fig. 3, b), and φ _к (t) = const for kτ _e <t <( k + 1) τ _e and can change stepwise at f = kτ _e , i.e. at the borders between elementary premises (k = 1,2, ..., N-1);

τ _e, N - duration and the number of chips of the composing signal of duration T _c (T _c = N · τ _e), which after amplification in the amplifier 15, the power radiated by the transmitting antenna 16 in ether is relayed HIS the relay 18 while maintaining phase ratios, is captured by the receiving antenna 19 of the ground station and through the high-frequency amplifier 20 is fed to the first input of the mixer 22, to the second input of which the local oscillator voltage 21

u _g (t) = U _g cos (ω _g t + φ _g ).

At the output of the mixer 22, voltages of combination frequencies are generated. The amplifier 23 is allocated an intermediate frequency voltage (figure 3, g)

u _pr (t) = U _pr · cos [ω _pr t + φ _k (t) + φ _pr ], 0≤t≤T _c

Where

To ₁ - gear ratio of the mixer;

ω _CR = ω _with -ω _g is the intermediate frequency;

φ _CR = φ _s -φ _g , which is fed to the input of the demodulator 24 FMN signal.

The delay time τ _{s of} the delay line 25 is chosen equal to the duration τ _{e of the} elementary premises (τ _s = τ _e ).

The composite QPSK signal of the intermediate frequency u _pr (t) (Fig. 3, d) from the output of the intermediate frequency amplifier 23 simultaneously arrives at the input of the delay line 25 and to the first inputs of the first 27 and second 28 adders, the second QPSK - an intermediate frequency signal from the output of the delay line 25, delayed by the time τ _s = τ _e . Moreover, to the second input of the second adder 28, the complex QPSK signal of the intermediate frequency arrives shifted in phase by π relative to the first adder 27.

Consequently, the first 27 and second 28 adders receive unstoppable and delayed for the duration τ _e elementary transmission PSK signals of intermediate frequency. In these adders, the sum of the delayed and delayed PSK signals is in phase and out of phase, i.e. On one of the adders, the PSK signals are added, and on the other, they are subtracted. If the amplitudes of the delayed and uncontrolled QPSK signals at the output of the adders 27 and 28 are equal, the voltage either doubles or becomes equal to zero, i.e. phase relations between amplitude code symbols are replaced. From the outputs of the adders 27 and 28, the signals are fed to amplitude detectors 31 and 32 of opposite polarity, respectively. The detected signals are fed to the adder 33.

Due to the fact that the signals are separated in time and have different polarity, then at the output of the adder 33 a bipolar video signal is generated (Fig. 3, e). A positive video signal corresponds to a phase difference of delayed and uncontrolled chips equal to zero, and a negative video signal corresponds to a phase difference of π.

A circuit consisting of amplitude detectors 31, 32 and an adder 33 operates as a maximum selection circuit. This does not degrade the signal-to-noise ratio at the output of the adder 33, since one of the amplitude detectors, for example 31, turns out to be a "locked" signal of the other amplitude detector 32.

The video signal (figure 3, d)

u _n (t) = U _Σ · cosφ _k (t), 0≤t≤T _c , proportional to the modulating code M (t) (Fig. 3, b), from the output of the adder 33 is fed to the inputs of the registration unit 29 and the sound signaling device 30. The latter plays an audible alarm about the occurrence of an earthquake and tsunami, and the recorded video signal judges the location and strength of the earthquake and tsunami.

The proposed demodulator of QPSK signals is also free from the phenomenon of “reverse operation” inherent in known devices for extracting the reference voltage directly from the received QPSK signal (Pistolkors A.A., Siforov V.I., Kostas D.F., Travina G. A. and others).

The system uses a radio channel and complex signals with phase shift keying.

These signals open up new possibilities in the technique of transmitting alarm information. They allow you to apply a new type of selection - structural selection. This means that there is a new opportunity to separate signals operating in the same frequency band and at the same time intervals. In principle, you can abandon the traditional method of dividing the operating frequencies of the used range between working seismic triggers and selecting them at a ground station using frequency filters. It can be replaced by a new method based on the simultaneous operation of each seismic trigger in the entire frequency range with phase-shift signals with the radio receiving device extracting the signal of the necessary seismic trigger through its structural selection.

Among other problems, the solution of which largely determines the further progress of the radio communications of seismic triggers with a ground station, should include the problem of establishing reliable communication between seismic triggers and a ground station via an IS3 repeater in the presence of a multipath nature of radio wave propagation. The presence of the multipath nature of the propagation of radio waves leads to a distortion of the received PSK signals, which complicates the reception and reduces the reliability of the transmission of alarm information to warn of earthquakes and tsunamis.

Attempts to overcome the harmful effects of multipath have been made for a long time. These include diversity reception, signal selection by time and angle of arrival, corrective coding, and some other methods. However, all of them do not provide a fundamental solution to the problem.

Due to its good correlation properties, a complex QPSK signal can be “folded” into a narrow pulse, the duration of which is inversely proportional to the used bandwidth. Choosing such a frequency band so that the duration of the “folded” pulse is less than the delay time, it is possible to separately receive pulses arriving at the receiving point in various ways, and by summing their energy, it is also possible to increase the noise immunity of complex QPSK signals. Thus, the indicated problem gets a fundamental solution.

From the point of view of detection, complex QPSK signals have high energy and structural secrecy.

The energy secrecy of these signals is due to their high compressibility in time and spectrum with optimal processing, which reduces the instantaneous radiated power. As a result, a complex QPSK signal at the receiving point may be masked by noise and interference. Moreover, the energy of a complex QPSK signal is by no means small; it is simply distributed over the time-frequency domain so that at each point of this region the signal power is less than the power of noise and interference.

The structural secrecy of complex QPSK signals is due to the wide variety of their shapes and significant ranges of parameter changes, which makes it difficult to optimize or at least quasi-optimal processing of complex QPSK signals of an a priori unknown structure in order to increase the sensitivity of the receiver.

To extract an analog of the modulating code from the received QPSK signal, a demodulator is used, free from the phenomenon of “reverse” operation.

Thus, the proposed system in comparison with the prototype provides increased reliability of the radio channel. This is achieved by increasing the dynamic range of the input signals and improving the signal-to-noise ratio when receiving weak signals.

Adders made, for example, on resistors, are practically inertia-free, and the time constant of amplitude detectors can be made very small.

In addition, the absence of higher-order combinational components that arise during multiplication and loss in the signal-to-noise ratio with weak signals makes it possible to increase the technical characteristics of the proposed system.

Claims (1)

An earthquake and tsunami warning system, comprising a sealed enclosure with a seismic oscillation receiver attached to its lower part and a distributed mass pendulum to the upper one, as well as an optoelectronic sensor with a predetermined limit value of the pendulum deviation, which includes an optically matched coherent light source and a photodetector connected by an output through a series-connected photo-current amplifier and frequency counter to an alarm, while the optoelectronic sensor of this limit value, the pendulum deviation is made in the form of a signal and reference fiber coils optically coupled through a coherent light source and a photodetector to an interferometer, the signal and reference fiber coils are located in a housing mounted on the seabed, respectively, on and outside the trajectory of the pendulum deviation from the equilibrium position, and the coherent light source and photodetector are located on the surface control and registration center, the alarm signal device is made in the form of a transmitter mounted on a surface control and registration center, a satellite repeater and a ground station, the transmitter is made in the form of a modulator code generator, a phase manipulator connected in series to the output of the frequency meter, the second input of which is connected to the output of a high frequency generator, power amplifier and transmitting antenna, the ground station is made in the form series-connected receiving antenna, high-frequency amplifier, mixer, the second input of which is connected to the output of the local oscillator, the intermediate frequency amplifier and demodulate ora of the QPSK signal, the output of which is connected to a recording unit and an audio signaling device, characterized in that the QPSK demodulator is made in the form of a delay line, a first adder, the second input of which is connected to the output of the intermediate frequency amplifier, to the output of the intermediate frequency amplifier an amplitude detector and a third adder, to the output of which a recording unit and an audible alarm are connected, connected in series to the output of the delay line of the phase inverter, the second adder , A second input coupled to an output of intermediate frequency amplifier, and the second amplitude detector, whose output is connected to a second input of the third adder.

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