CN106980141B

CN106980141B - Natural surface wave geological exploration system

Info

Publication number: CN106980141B
Application number: CN201710266904.2A
Authority: CN
Inventors: 郭澎; 尚佳彬; 张福海; 任立儒
Original assignee: Nankai University
Current assignee: Nankai University
Priority date: 2017-04-21
Filing date: 2017-04-21
Publication date: 2023-06-20
Anticipated expiration: 2037-04-21
Also published as: CN106980141A

Abstract

The invention discloses a natural surface wave geological exploration system, wherein a single longitudinal mode laser is connected with a first-stage coupler, the output of the first-stage coupler is connected with two second-stage couplers, and the output of the two second-stage couplers is respectively connected with 1 st, 3 rd, 5 th and 7 th three-stage couplers. The system comprises a 1 st single-mode fiber coil, a 2 nd three-level coupler, a 1 st double-mode fiber coil, a 3 rd three-level coupler, a 4 th three-level coupler, a 2 nd double-mode fiber coil, a 5 th three-level coupler, a 6 th three-level coupler, a 3 rd double-mode fiber coil, a 7 th three-level coupler, a 8 th double-mode fiber coil and a 4 th double-mode fiber coil respectively form a 1-4 Mach-Zehnder interference vibration sensing module, the generated signals are respectively transmitted to a 1-4 th photoelectric converter through the 2 nd three-level coupler, the 4 th three-level coupler, the 6 th three-level coupler and the 8 th three-level coupler, the 1-4 th photoelectric converter is respectively connected with a 1-4 th signal conditioning module, a 1-4 th analog-to-digital conversion module and an extraction filter module, and the extraction filter module and the GPS clock are respectively connected with an industrial control computer. The system is suitable for passive investigation of urban geological engineering, convenient in array arrangement and high in sensitivity.

Description

Natural surface wave geological exploration system

Technical Field

The invention relates to the field of geophysical prospecting instruments and photoelectric sensors, in particular to a natural surface wave geological prospecting system.

Background

The geological exploration by using the surface waves is a new physical exploration technology developed at home and abroad in recent years, so that the earth surface wave exploration equipment is a hot spot for research in the field of geophysical exploration equipment development in recent years.

The direct utilization of geothermal resources (stratum depth reaches 1000-3000 m) is obviously restricted by territory, and particularly, the geothermal resource is widely applied to urban groups with developed economy, but the geothermal investigation is difficult to carry out in urban group areas. Many urban geothermal fields belong to basin-type geothermal fields, are positioned in the fourth-line coverage area of plain areas, have no outcrop of bedrock, in urban groups, various interference factors are caused by human industrial activities, so that the conventional geophysical prospecting method cannot be normally performed; in addition, the dense buildings, limited traffic conditions and environmental protection requirements also make some important geophysical prospecting methods (such as artificial earthquakes) difficult to develop. Non-seismic geophysical methods such as gravity, electromagnetic methods, and the like (e.g. canada V8, U.S. GDP32 II) are not only expensive, manual excitation electric field is also needed, and exploration precision is still low by adopting special measures.

Early physical investigation work to drill in urban mass is necessary and difficult. The amplitude of the earth surface wave is very small (micron order), the earth surface tiny vibration wave (the components of which are complex and comprise various components such as surface wave and body wave, wherein the surface wave-micro Rayleigh wave method is the main component) which is not present on the earth surface is utilized as an observation object, the method does not need heavy artificial energy (artificial excitation electric field and seismic source) and does not cause harm to human living environment (such as noise or high voltage electricity, etc.), in addition, the measuring points are flexibly distributed, and the method is not limited by hard road surfaces and underground pipe networks.

However, the traditional steady or instantaneous surface wave instrument is used for acquiring the multipath micro-motion Rayleigh waves, and the unavoidable large error exists, the source of the error is that the sensitivity of each link of the earthquake pickup electronic sensor and the wave pickup is low and the phase synchronization error exists, chinese patent publication No. 102721983A discloses a fiber array submarine shallow geological structure detection system, and although a photoelectric sensor is adopted, problems of a sensor structure, a signal processing circuit and the like limit the detection range of a micro Rayleigh wave method, and only physical detection of a shallow layer of a stratum by 200-500 meters can be performed.

Disclosure of Invention

The invention aims to provide a natural surface wave geological exploration system which uses ground tiny vibration surface waves which are not on the earth surface at any time as an observation object and performs deep (1000-3000 m) physical detection on stratum.

For this purpose, the technical scheme of the invention is as follows:

a natural surface wave geological exploration system comprises a single longitudinal mode laser, a first-stage coupler, a 1 st and a 2 nd second-stage couplers, a 1 st to 8 th third-stage couplers, a 1 st to 4 th double single-mode fiber wire coil, a 1 st to 4 th optical phase-locked loop, a 1 st to 4 th photoelectric converter, a 1 st to 4 th signal conditioning module, a 1 st to 4 th extraction and filtering module, an industrial control computer and a GPS clock.

The single longitudinal mode laser is connected with a first-stage coupler, the output of the first-stage coupler is connected with two second-stage couplers, the output of the two second-stage couplers is respectively connected with 1 st, 3 rd, 5 th and 7 th three-stage couplers, the 1 st and 2 nd three-stage couplers are connected with a 1 st double single-mode fiber wire coil, the 3 rd and 4 th three-stage couplers are connected with a 2 nd double-mode fiber wire coil, the 5 th and 6 th three-stage couplers are respectively connected with a 3 rd double-mode fiber wire coil, the 7 th and 8 th three-stage couplers are connected with a 4 th double-mode fiber wire coil to form a 1 st-4 th Mach-Zehnder interference vibration sensing module, the generated interference vibration sensing signals are respectively output to the 1 st-4 photoelectric converter through the 2 nd, 4 th, 6 th and 8 th three-stage couplers, the 1 st-4 photoelectric converter is respectively connected with a 1 st-4 signal conditioning module, a 1 st-4 analog-digital conversion module and an extraction filter module in sequence, and the extraction filter module is connected with an industrial control computer. The GPS clock is connected with the industrial control computer and used for precisely synchronizing time.

Preferably, the system further comprises 1 st to 4 th optical phase-locked loops, and the 1 st to 4 th optical phase-locked loops are respectively connected in series in one arm of the 1 st to 4 th double single-mode optical fiber coil, so that the interference signals are stabilized in the orthogonal position.

Preferably, the single longitudinal mode laser is a narrow linewidth single longitudinal mode semiconductor laser; preferably, the 1 st to 4 th photoelectric converters are photoelectric converters of which dark current reaches pA level; the first-stage, second-stage and third-stage couplers are all 2 x 2 optical fiber couplers.

The single longitudinal mode laser 1 preferably employs a narrow linewidth single longitudinal mode semiconductor laser.

The beneficial effects of the invention are as follows:

the exploration system has light weight, convenient array and extremely high sensitivity

Magnitude of 0.01g, amplitude of 1550 um/2), low noise, light weight and strong anti-interference performance, extremely high sensitivity and sensing signals can be synchronously transmitted in a photon mode in a multipath manner, phase errors are avoided, reliability and rapidness are realized, deep (1000-3000 m) physical detection can be carried out on stratum in a passive mode in a city, and incomparable advantages of other types of vibration pickup wave sensors are provided for processing and geological analysis of micro-motion Rayleigh wave signals.

Drawings

FIG. 1 is a schematic diagram of a natural surface wave geological exploration system of the present invention;

FIG. 2 is a layout of a natural surface wave geological exploration system of the present invention;

fig. 3 is a phase velocity-dispersion curve.

Wherein:

1. single longitudinal mode semiconductor laser 2, first-order coupler 3-1, 3-2: a second-stage coupler;

4-1 to 4-8, three-stage coupler; 5-1 to 5-4, an optical phase-locked loop; 6-1 to 6-4, double single mode fiber wire coil

7-1 to 7-4: a photoelectric converter; 8-1 to 8-4: a signal conditioning module;

9-1 ultra-high 9-4: a sigma delta conversion analog-to-digital module; 10. filtering decimation Module

11. The panel industrial control computer; 12. GPS clock.

Detailed Description

The composition of the exploration system of the present invention is described in detail below with reference to the attached drawings and specific examples.

See one embodiment of the invention shown in fig. 1. In the figure, a narrow linewidth single longitudinal mode semiconductor laser 1 is connected with a primary coupler 2, laser is divided into two paths of outputs through the coupler 2, and the outputs of the primary coupler 2 are connected with secondary couplers 3-1 and 3-2. The laser is divided into four paths through the secondary couplers 3-1 and 3-2 and is respectively and simultaneously output to one ends of the tertiary couplers 4-1, 4-3, 4-5 and 4-7. The three-level couplers 4-1, 4-2 and the double single mode fiber wire coil 6-1 form a first Mach-Zehnder (M-Z) interference vibration sensing module; the three-level couplers 4-3, 4-4 and the double single mode fiber wire coil 6-2 form a second Mach-Zehnder (M-Z) interference vibration sensing module; the three-level coupler 4-5, 4-6 and the double single mode fiber coil 6-3 form a third Mach-Zehnder (M-Z) interference vibration sensing module; the third-level coupler 4-7, 4-8 and the double single mode fiber coil 6-4 form a fourth Mach-Zehnder (M-Z) interference vibration sensing module. The interference type vibration sensing signals are output to photoelectric converters 7-1, 7-2, 7-3 and 7-4 with dark current reaching pA level through three-level couplers 4-2, 4-4, 4-6 and 4-8 respectively in the form of optical phase change. The photoelectric converters 7-1, 7-2, 7-3 and 7-4 of dark current reaching pA level are respectively connected with the signal conditioning modules 8-1, 8-2, 8-3, 8-4 and the sigma-delta analog-digital conversion modules 9-1, 9-2, 9-3 and 9-4. The sigma delta analog-digital conversion modules 9-1, 9-2, 9-3 and 9-4 are connected with the filtering extraction module 10, the filtering extraction module 10 is connected with the tablet personal computer 11, and the GPS clock 12 is also connected with the personal computer 11.

Wherein, the optical phase-locked loops 5-1, 5-2, 5-3, 5-4 are respectively connected in series in one arm of the double single mode fiber coil 6-1, 6-2, 6-3, 6-4, which resists polarization and phase fading, so that the interference signals are stabilized in the orthogonal position, thereby improving the sensitivity and stability of the four interference type optical fiber vibration sensors.

The working process of the exploration system of the invention is as follows:

1. according to Mach-Zehnder optical fiber interference vibration sensor principle, two paths of synchronous interference laser modulation signals are relatively transmitted on an interferometer and a light path structure is picked up at two ends of the interferometer, common communication optical fibers are used as an interference arm and a reference arm of the interferometer, vibration signals are used as detected quantities, so that a high-sensitivity vibration detection sensor is formed, vibration signals are picked up in real time, and the high-sensitivity vibration detection sensor has extremely high sensitivity

Magnitude, 0.01g, amplitude 1550 um/2). The four Mach-Zehnder interference vibration sensing modules are arranged as follows: one is arranged in the center of an equilateral triangle, the other three are arranged at the three vertex positions of the equilateral triangle, the Mach-Zehnder interference vibration sensing module array radius r is determined according to the stratum layering depth, the relation between the stratum depth h to be measured and the sensing module array radius r is h=10r, and if the stratum layering depth is measured to be 1200 meters, r=120meters are connected through optical fibers.

2. According to FIG. 2, four Mach-Zehnder interferometric vibration sensing modules are sequentially arranged and work according to the following method, wherein the arrangement points are respectively 0, 1, 2 and 3 in the figure; 0. 4, 5 and 6; 0. 7, 8 and 9, wherein the distance from the 0 point to the 7, 8 and 9 points is 120 meters.

3. The device is started, the sensing system continuously picks up the natural surface wave signals, the four paths of signals are respectively input into the signal conditioning modules 8-1, 2, 3 and 4, and then 4 paths of 512kSPS code streams which are output after sigma-delta A/D conversion is finished through the analog-digital conversion modules 9-1, 2, 3 and 4 are respectively and independently sent to the extraction filter module 10, and the module arranges the 4 paths of 24-bit code stream signals into serial codes and outputs the serial codes to the industrial personal computer 11.

The invention can achieve the complete synchronization of 4 signals, the A/D analog-to-digital conversion module 9 and the extraction filter 10, the synchronous clock is generated by the extraction filter module 10, and the sampling clock signal of the extraction filter 10 is a half-duty square wave of 2 048 KHz in a normal state. It is input to the a/D analog-to-digital conversion module 9 in parallel by the decimation filter 100, in order to control the multiple pieces of a/D analog-to-digital conversion module 9, and send to the sigma-delta one bit stream interface of the decimation filter 10, where the four channels of data are at the same time. The data of the same time after being filtered by the decimation filter 10 are put in the corresponding position at the same time. The sampling clock of the a/D analog-to-digital conversion block 9 and the filtering clock of the decimation filter 10 are the same clock source as the GPS 12.

The optical phase-locked loops 5-1, 5-2, 5-3 and 5-4 are respectively connected in series in one arm of the double single-mode fiber coils 6-1, 6-2, 6-3 and 6-4, so that polarization resistance and phase fading resistance are realized, interference signals are stabilized at orthogonal positions, and the sensitivity and the stability of the four interference type optical fiber vibration sensors are improved.

4. The three and four sets of data measured above are subjected to signal conditioning and processing, and the digital values are formed into an on-site database in the industrial control computer 11.

5. The industrial control computer 11 performs spatial autocorrelation processing on the signals

The spatial autocorrelation method mainly performs surface wave extraction in a time domain to obtain spatial autocorrelation systems ρ of different frequencies, and the spatial autocorrelation coefficients are actually functions of the frequency component f of the surface wave and the spatial coordinates, that is, the spatial autocorrelation coefficients are related to not only the frequency but also the position of the vibration pickup. From the aspect of morphology, the actually measured spatial autocorrelation curve is an approximate zero-order Bessel function curve, the correction value is obtained through the curve, the phase velocity of each frequency point can be extracted by adding the spatial coordinate parameter, and the phase velocity-frequency dispersion curve is drawn according to the phase velocity-frequency dispersion curve, as shown in fig. 3.

6. From the above steps, it can be seen that the surface wave phase velocity obtained from the jogging has a dispersion phenomenon, which means that the wave velocity of each layer of rock in the underground is uneven, then the wave velocity distribution conditions of different depths can be obtained through inversion calculation, and the underground distribution layering of various rock layers can be estimated through the wave velocity differences (physical database) of different lithologic strata, so as to further judge the resources such as heat sources, minerals and the like in the underground distribution layering.

Claims

1. A natural surface wave geological exploration system is characterized in that: comprises a single longitudinal mode laser, a first-stage coupler, a 1 st and a 2 nd second-stage couplers, a 1 st to 8 th third-stage couplers, a 1 st to 4 th double single-mode fiber wire coil, a 1 st to 4 th optical phase-locked loop, a 1 st to 4 th photoelectric converter, a 1 st to 4 th signal conditioning module, a 1 st to 4 th extraction filter module, an industrial control computer and a GPS clock,

the single longitudinal mode laser is connected with a first-stage coupler, the output of the first-stage coupler is connected with two second-stage couplers, the output of the two second-stage couplers is respectively connected with 1 st, 3 rd, 5 th and 7 th three-stage couplers, the 1 st and 2 nd three-stage couplers are respectively connected with a 1 st double single-mode fiber wire coil, the 3 rd and 4 th three-stage couplers are respectively connected with a 2 nd double-mode fiber wire coil, the 5 th and 6 th three-stage couplers are respectively connected with a 3 rd double-mode fiber wire coil, the 7 th and 8 th three-stage couplers are respectively connected with a 4 th double-mode fiber wire coil, the generated interference type vibration sensing signals are respectively output to the 1 st to 4 th photoelectric converters through the 2 nd, 4 th, 6 th and 8 th three-stage couplers, the 1 st to 4 th photoelectric converters are respectively connected with a 1 st to 4 signal conditioning module, a 1 st to 4 th analog to digital conversion module and an extraction filter module in sequence, the extraction filter module is connected with an industrial control computer, and the GPS clock is connected with the industrial control computer.

2. The natural surface wave geological exploration system of claim 1, wherein: the optical phase-locked loop also comprises 1 st to 4 th optical phase-locked loops, wherein the 1 st to 4 th optical phase-locked loops are respectively connected in series in one arm of the 1 st to 4 th double single-mode optical fiber wire coil so as to enable interference signals to be stabilized in an orthogonal position.

3. The natural surface wave geological exploration system of claim 1, wherein: the single longitudinal mode laser is a narrow linewidth single longitudinal mode semiconductor laser.

4. The natural surface wave geological exploration system of claim 1, wherein: the 1 st to 4 th photoelectric converters are photoelectric converters with dark current reaching pA level.

5. The natural surface wave geological exploration system according to any of claims 1-4, wherein: the first-stage coupler, the second-stage coupler and the third-stage coupler are all 2 x 2 couplers.