CN114252022B - Optical fiber multi-dimensional monitoring method and device based on GNSS signals - Google Patents

Abstract

The invention discloses an optical fiber multi-dimensional monitoring method based on GNSS signals. At the far end, GNSS signals are received by at least two GNSS antennas arranged at the monitoring point and the received GNSS signals are respectively modulated into the optical domain, and then the light-borne GNSS signals are transmitted to the near-end receiver through the transmission fiber; at the near end, By sending a broadband optical detection signal to the transmission fiber and processing the scattered signal along the fiber and the reflected light signal of the fiber end face to obtain the distributed monitoring results along the transmission fiber and the length information of the transmission fiber, and then based on the obtained fiber length information to obtain The hardware delay information, and finally the three-dimensional monitoring information of the monitoring point is obtained by using the hardware delay information and the carrier phase single-difference model. The invention also discloses an optical fiber multi-dimensional monitoring device based on GNSS signals. Compared with the prior art, the present invention can realize high-precision three-dimensional monitoring of key monitoring parts and large-scale distributed monitoring of strain, vibration, temperature and other information at the same time.

Description

Optical fiber multi-dimensional monitoring method and device based on GNSS signals

technical field

The invention relates to an optical fiber monitoring method, in particular to an optical fiber multi-dimensional monitoring method based on GNSS (Global Navigation Satellite System, Global Navigation Satellite System) signals.

Background technique

As an important branch of optical fiber sensing technology, distributed optical fiber sensing technology integrates optical signal transmission and parameter sensing. Optical fiber is both a transmission medium and a sensing medium, which can realize continuous measurement of parameters of the entire optical fiber link. The measurement range great. In the civil field, the structural safety of bridges, tunnels, airplanes, dams, etc. needs to be monitored, and distributed sensing technology is an effective means to detect the health of these building structures. The flammable, explosive and high-voltage fields in the petrochemical industry lack reliable safety monitoring technology means. Important and large-scale equipment such as aero-engines and port handling equipment also lack effective monitoring methods due to their complex structure and harsh working environment. Distributed sensing can effectively address these needs. In the military field, optical fiber systems, sensor equipment, and electronic systems are organically integrated, and physical parameters need to be detected at designated locations. For example, temperature data, pressure data, and strain data can be detected to build fault monitoring systems and flight control systems. Damage assessment of military equipment through advanced technology.

Traditional distributed optical fiber sensing technology mostly uses optical time domain reflection or optical frequency domain reflection method, which can monitor the loss and breakpoint in the optical fiber, and then based on Rayleigh scattering, it can monitor the strain, vibration, temperature, etc. of the optical fiber , but it can only achieve two-dimensional monitoring, and it cannot achieve high-precision three-dimensional monitoring for some key monitoring parts, and there are some limitations in the monitoring range. For example, in the monitoring of iron towers in the power grid, it is necessary to monitor the three-dimensional deformation of the iron towers and the distributed stress of cables; Accuracy monitoring. Under such circumstances, the traditional measurement method cannot meet the demand, and a new optical fiber multi-dimensional monitoring method is needed.

Contents of the invention

The technical problem to be solved by the present invention is to overcome the deficiencies of the existing technologies, provide a GNSS signal-based optical fiber multi-dimensional monitoring method, organically combine distributed optical fiber sensing technology with GNSS positioning technology, and realize high-precision monitoring of key monitoring parts at the same time Three-dimensional monitoring and large-scale distributed monitoring of strain, vibration, temperature and other information.

The present invention specifically adopts the following technical solutions to solve the above technical problems:

An optical fiber multi-dimensional monitoring method based on GNSS signals, at the remote end, receives GNSS signals through at least two GNSS antennas arranged at the monitoring point and modulates the received GNSS signals into the optical domain respectively, and then transmits the generated light-borne GNSS The signal is transmitted to the receiver at the near end through the transmission fiber; at the same time, at the near end, by transmitting a broadband optical detection signal to the transmission fiber and processing the scattered signal along the fiber and the reflected light signal at the end face of the fiber to obtain the signal along the transmission fiber Distributed monitoring results and the length information of the transmission fiber, and then based on the obtained fiber length information to obtain the hardware delay information between the GNSS antenna and the near-end receiver, and finally use the hardware delay between the GNSS antenna and the receiver Information and carrier phase single-difference model to obtain three-dimensional monitoring information of monitoring points.

Preferably, the broadband light detection signal is a chirp signal.

The following technical solutions can also be obtained based on the same inventive concept:

An optical fiber multi-dimensional monitoring device based on GNSS signals, comprising:

A three-dimensional baseline measurement unit, which is arranged at the far end, is used to receive GNSS signals through at least two GNSS antennas arranged at the monitoring point and modulate the received GNSS signals into the optical domain respectively;

A transmission fiber for transmitting the generated light-borne GNSS signal to a near-end receiver;

Distributed signal and hardware delay signal transmission and processing module, which is arranged at the near end, is used to transmit broadband optical detection signal to the transmission optical fiber and process the scattered signal along the optical fiber and the reflected optical signal on the end face of the optical fiber to obtain the Distributed monitoring results along the transmission optical fiber and the length information of the transmission optical fiber, and then obtain hardware delay information between the GNSS antenna and the near-end receiver based on the obtained optical fiber length information;

The three-dimensional baseline signal processing module uses the hardware delay information between the GNSS antenna and the receiver and the carrier phase single-difference model to obtain the three-dimensional monitoring information of the monitoring point.

Preferably, the broadband light detection signal is a chirp signal.

Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

The technical scheme of the present invention organically combines the distributed optical fiber sensing technology with the GNSS positioning technology, and can realize two-dimensional distributed monitoring and three-dimensional monitoring of key parts at the same time, and more importantly, can improve the three-dimensional The monitoring accuracy and monitoring range not only expand the functions of the optical fiber monitoring method but also improve the monitoring accuracy and other performances, thereby greatly broadening the application scenarios of the sensing system.

Description of drawings

Fig. 1 is the schematic diagram of the structural principle of the optical fiber multi-dimensional monitoring device of the present invention;

Fig. 2 is a structural schematic diagram of a specific embodiment of the optical fiber multi-dimensional monitoring device of the present invention.

Detailed ways

Aiming at the deficiencies of the prior art, the solution idea of the present invention is based on GNSS signals and optical fiber transmission and sensing principles, and obtains the three-dimensional vector between GNSS antennas by using the difference of multi-channel carrier observation values, so as to realize the three-dimensional omnidirectional monitoring of key parts, and at the same time The broadband optical detection signal is used to obtain hardware delay information and distributed sensing information, and the hardware delay information is further used to improve the measurement accuracy of the three-dimensional vector.

The optical fiber multi-dimensional monitoring method based on GNSS signal proposed by the present invention is as follows:

At the far end, the GNSS signals are received by at least two GNSS antennas arranged at the monitoring point and the received GNSS signals are respectively modulated into the optical domain, and then the generated light-borne GNSS signals are transmitted to the near-end receiver through the transmission fiber; at the same time , at the near end, the distributed monitoring results along the transmission fiber and the length of the transmission fiber are obtained by transmitting a broadband optical detection signal to the transmission fiber and processing the scattered signal along the fiber and the reflected light signal from the end face of the fiber information, and then obtain the hardware delay information between the GNSS antenna and the near-end receiver based on the obtained fiber length information, and finally use the hardware delay information between the GNSS antenna and the receiver and the carrier phase single-difference model to obtain the 3D monitoring information.

The optical fiber multi-dimensional monitoring device based on GNSS signals proposed by the present invention, as shown in Figure 1, includes: a three-dimensional baseline measurement unit, which is arranged at the far end, for receiving GNSS signals by at least two GNSS antennas arranged at monitoring points and modulate the received GNSS signals into the optical domain respectively;

A transmission fiber for transmitting the generated light-borne GNSS signal to a near-end receiver;

Distributed signal and hardware delay signal transmission and processing module, which is arranged at the near end, is used to transmit broadband optical detection signal to the transmission optical fiber and process the scattered signal along the optical fiber and the reflected optical signal on the end face of the optical fiber to obtain the Distributed monitoring results along the transmission optical fiber and the length information of the transmission optical fiber, and then obtain hardware delay information between the GNSS antenna and the near-end receiver based on the obtained optical fiber length information;

The three-dimensional baseline signal processing module uses the hardware delay information between the GNSS antenna and the receiver and the carrier phase single-difference model to obtain the three-dimensional monitoring information of the monitoring point.

Preferably, the broadband light detection signal is a chirp signal.

The technical scheme of the invention can be widely applied to structural health monitoring of dams, bridges, buildings, power supply towers, mines, etc., and can simultaneously realize high-precision three-dimensional monitoring of key monitoring parts and large-scale distribution of strain, vibration, temperature and other information monitor. In order to facilitate the public's understanding, the technical solution of the present invention will be described in detail below through a specific embodiment in conjunction with the accompanying drawings:

Fig. 2 shows the specific structure of the optical fiber monitoring device of the present invention applied to bridge structure health monitoring. The hardware laying method is shown in Figure 2. The GNSS antenna and the electro-optical modulator are respectively placed at the bridge head and the bridge tail to form a three-dimensional baseline measurement unit; The GNSS signal is transmitted to the near end; since the transmission fiber is also used as the sensing fiber of the distributed optical fiber sensing system, it is represented as a transmission/sensing fiber in the figure. After receiving the GNSS signal through the antenna, the three-dimensional baseline measurement unit at the far end modulates the GNSS signal onto the optical carrier through electro-optic modulation, and then transmits it to the near end through the transmission fiber, and recovers the GNSS signal by the photodetector. After the two GNSS signals are solved, the two carrier phase observations can be obtained, so as to calculate the three-dimensional baseline vector between the two antennas, and realize the key three-dimensional omnidirectional monitoring of the laying site. Multiple nodes can be set on the transmission fiber through couplers, and the antenna can be placed at any node on one fiber, so as to realize flexible monitoring of large-scale key parts. In this embodiment, the node 1 on the optical fiber 1 and the node 10 on the optical fiber 2 are selected to monitor the changes of the baseline vectors at the bridge head and the bridge tail. On the other hand, at the near end, through the hardware delay and the distributed signal transmitting and receiving module to transmit the broadband optical detection signal, the hardware delay monitoring between the GNSS antenna and the receiving module is realized to improve the accuracy of the three-dimensional monitoring; at the same time, using the broadband Optical detection signal, through Rayleigh scattering in the optical fiber, can obtain distributed sensing information on the sensing optical fiber, thereby realizing high-precision three-dimensional monitoring between GNSS antennas and optical fiber multi-dimensional monitoring of distributed monitoring along the optical fiber.

In this embodiment, by multiplexing the photoelectric detection module and the data acquisition unit, the signal returned in the optical fiber is collected once, and the scattering signal along the optical fiber and the reflection signal of the end face of the optical fiber are obtained at the same time; Cross-correlation processing is performed on the signals to obtain distributed monitoring information; high-precision hardware delay information is obtained by performing pulse compression processing on the reflected signals of the fiber end faces, thereby completing distributed calculations and three-dimensional baseline calculations.

The acquisition and calculation of optical fiber distributed sensing information involved in the present invention, the single-difference model of carrier phase, and the calculation of optical fiber length are all existing technologies. For the convenience of the public, the basic principles are briefly explained below:

The calculation of the 3D baseline is based on the optical GNSS single-difference model, which can realize 3D high-precision measurement. This model needs to measure the hardware delay information between the antenna and the receiver, that is, the measurement accuracy of the optical fiber length, and its accuracy is required to reach mm level.

By making differences for different antennas and using the receiver designed with a common clock board to eliminate the clock difference, the carrier phase single-difference model can be obtained:

为载波相位差、P^k为卫星与天线间的矢量关系,

为卫星的整周模糊度，ΔL_ij表示硬件延时。将测量值与待求值分开，单差模型可以表示为：where i and j represent different antennas, k represent different satellites,

is the carrier phase difference, P ^k is the vector relationship between the satellite and the antenna,

ΔL _ij represents the hardware delay. Separate the measured value from the value to be evaluated, the single-difference model can be expressed as:

The above model can be simplified as:

和

则三维基线的测量精度可表示为：Let the carrier phase measurement accuracy and the hardware delay measurement accuracy be respectively

and

Then the measurement accuracy of the 3D baseline can be expressed as:

It can be seen that the hardware delay measurement accuracy needs to reach the same level as the carrier phase measurement accuracy, and the accuracy of the carrier phase measurement method can reach the mm level, so the hardware delay measurement also needs to reach the mm level.

其理论的空间分辨率可表示为：In order to meet this requirement, the broadband optical detection signal used for measurement must have a sufficiently high spatial resolution. For this reason, in this embodiment, a linear frequency modulated signal (LFM) is used as the detection signal, so that the required accuracy can be achieved. Assuming linear The frequency sweep rate of FM signal is γ, then

Its theoretical spatial resolution can be expressed as:

where T is the duration. It can be seen that by choosing an appropriate sweep rate and duration, a spatial resolution that can meet the requirements can be obtained.

The principle of solving distributed information is as follows:

The solution of distributed sensing information comes from Rayleigh scattering in the optical fiber. When the light wave is transmitted in the optical fiber, it will generate scattered light in all directions. However, due to the constraints of the optical fiber, the scattered light will only appear in the forward direction. and back in both directions. At the same time, because the external environment of the optical fiber will affect the light waves in the optical fiber, when the external environment changes, such as temperature changes, optical fiber stress, optical fiber vibration, etc., the scattered light frequency domain signal detected from the detection end contains After demodulating the external environment information along the optical fiber, a signal that can reflect the external conditions along the optical fiber can be obtained, so as to realize the monitoring of the external environment.

If the reflection point of the test fiber is located at Z, τ _Z is the time delay difference between the test light returning to the detection end and the local oscillator light at the reflection point at Z, then:

τ _Z =2Zn/c (6)

Among them, n is the refractive index of the fiber, and c is the propagation speed of light in vacuum. So at this time, the frequency difference between the local oscillator light and the test light is the beat frequency, and the beat frequency signal between each scattering point on the optical fiber and the local oscillator light has a different fixed frequency difference, so different beat frequency frequency differences correspond to Scattering points at different positions are finally located on the optical fiber by detecting the frequency of the beat frequency signal between the local oscillator light and the scattered light, so Fourier transform is used to transform the beat frequency time domain signal collected by the photodetector into the frequency domain , the information of different positions along the optical fiber can be obtained.

The distributed information demodulation method is as follows: collect reference signals and measurement signals, and convert them to the distance domain by Fourier transform; use a sliding window to scan the signals on the distance domain and divide them into various local distance domain signals; use inverse Fourier transform to convert Each local distance domain signal is converted to the wavelength domain to obtain a local Rayleigh scattering spectrum signal; the local Rayleigh scattering spectrum signal of the reference signal and the test signal is cross-correlated to obtain a cross-correlation peak offset, and then the distributed transmission spectrum is obtained. emotional information.

The principle of calculating the 3D baseline is as follows:

For different nodes on the optical fiber, the coupler will make it appear as an obvious peak on the spectrum, and the corresponding hardware delay information can be calculated through the corresponding beat frequency of different nodes, which can be expressed as:

Where f _b is the frequency difference between the local oscillator light and the test light.

By making the difference for different antennas, the carrier phase single-difference model can be obtained:

做出合理近似得到其与基线矢量b的关系：where Δ is a single-difference operator, through which most common errors can be eliminated, such as ionosphere, tropospheric delay and satellite clock error. Since the baseline length is much smaller than the distance between the satellite and the antenna, the

Make a reasonable approximation to get its relationship to the baseline vector b:

Using the hardware design of the common clock board, after eliminating the clock error of the receiver, the carrier phase single-difference model is obtained as:

卫星与天线间的矢量关系P^k和卫星整周模糊度

均可得到，故通过上述硬件延时信息即可得到硬件延时差ΔL_ij，从而解算出基线向量b^T。In this equation, the carrier phase difference of the satellite

Vector relationship P ^k between satellite and antenna and satellite ambiguity

Both can be obtained, so the hardware delay difference ΔL _ij can be obtained through the above hardware delay information, and then the baseline vector b ^T can be calculated.

In summary, the present invention can realize two-dimensional distributed monitoring and three-dimensional monitoring of key parts at the same time, and can improve the accuracy and monitoring range of three-dimensional monitoring through the information fusion of the two, and broaden the application scenarios of the sensing system.

Claims (4)

1. A kind of optical fiber multi-dimensional monitoring method based on GNSS signal, it is characterized in that, at far-end, receive GNSS signal by being arranged at least two GNSS antennas of monitoring point and the received GNSS signal is modulated to optical domain respectively, and then The generated light-borne GNSS signal is transmitted to the near-end receiver through the transmission fiber; at the same time, at the near-end, by transmitting a broadband optical detection signal to the transmission fiber and processing the scattered signal along the fiber and the reflected light signal at the end face of the fiber respectively Obtain the distributed monitoring results along the transmission optical fiber and the length information of the transmission optical fiber, then obtain the hardware delay information between the GNSS antenna and the near-end receiver based on the obtained optical fiber length information, and finally use the GNSS antenna to receive The hardware delay information and the carrier phase single-difference model between the machines obtain the three-dimensional monitoring information of the monitoring point; the distributed information demodulation method in the process of obtaining the distributed monitoring results is as follows: collect reference signals and measurement signals, and perform Fu Convert the Fourier change to the distance domain; use the sliding window to scan the signal on the distance domain, and divide it into each local distance domain signal; use the inverse Fourier transform to convert each local distance domain signal to the wavelength domain to obtain the local Rayleigh scattering spectrum signal ; Cross-correlate the local Rayleigh scattering spectrum signals of the reference signal and the test signal to obtain the cross-correlation peak offset, and then obtain the distributed sensing information. 2. The optical fiber multi-dimensional monitoring method based on GNSS signals as claimed in claim 1, wherein the broadband optical detection signal is a chirp signal. 3. An optical fiber multi-dimensional monitoring device based on GNSS signals, characterized in that, comprising: A three-dimensional baseline measurement unit, which is arranged at the far end, is used to receive GNSS signals through at least two GNSS antennas arranged at the monitoring point and modulate the received GNSS signals into the optical domain respectively; A transmission fiber for transmitting the generated light-borne GNSS signal to a near-end receiver; A distributed signal and hardware delay signal transmitting and processing module, which is arranged at the near end, is used to transmit a broadband optical detection signal to the transmission optical fiber and process the scattered signal along the optical fiber and the reflected optical signal on the end face of the optical fiber to obtain The distributed monitoring results along the transmission optical fiber and the length information of the transmission optical fiber, and then obtain the hardware delay information between the GNSS antenna and the near-end receiver based on the obtained optical fiber length information; in the distributed monitoring results The distributed information demodulation method in the acquisition process is as follows: collect reference signals and measurement signals, and transform them into the distance domain by Fourier transformation; use sliding windows to scan the signals on the distance domain, and divide them into local distance domain signals; use Fourier The leaf inverse transform converts each local distance domain signal to the wavelength domain to obtain the local Rayleigh scattering spectrum signal; do cross-correlation on the local Rayleigh scattering spectrum signal of the reference signal and the test signal to obtain the cross-correlation peak offset, and then obtain the distribution type sensor information; The three-dimensional baseline signal processing module uses the hardware delay information between the GNSS antenna and the receiver and the carrier phase single-difference model to obtain the three-dimensional monitoring information of the monitoring point. 4. The optical fiber multi-dimensional monitoring device based on GNSS signals according to claim 3, wherein the broadband optical detection signal is a chirp signal.

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