Phi-OTDR (Optical Time Domain Reflectometer) data real-time processing system and method based on unscented Kalman filtering

Abstract

The invention discloses a phi-OTDR (Optical Time Domain Reflectometer) data real-time processing system and a phi-OTDR data real-time processing method based on unscented Kalman filtering. The system comprises a modulation signal generation module, a data acquisition module, a data combination reading module, a phase calculation module, a data transmission module, a phase unpacking module and a communication module. The method comprises the following steps: after Rayleigh return light generated by three adjacent pulse light enters an unbalanced Michelson interferometer, applying modulation voltage to PZT piezoelectric ceramics, so that three paths of interfered RBSs respectively have additional phases; the signal acquisition module acquires three paths of light intensity signals, stores the light intensity signals into the data combination reading module, and reads the light intensity signals of the corresponding detection sequences; the phase calculation module calculates a corresponding wrapped phase and inputs the data into the unscented Kalman filtering module for phase unpacking; and the communication module sends the unpacked phase information to an upper computer. According to the method, the data real-time processing of the phi-OTDR system is realized, and the phase unpacking accuracy and the anti-noise capability are improved.

Description

Technical Field

[0001] The invention relates to the fields of optical sensing technology and FPGA signal processing technology, in particular to a Φ-OTDR data real-time processing system and method based on unscented Kalman filtering. Background Art

[0002] Distributed Acoustic Sensor (DAS) is a sensing system based on Rayleigh scattering that achieves acoustic wave perception by measuring the optical phase change caused by the change in the axial strain of the optical fiber. In recent years, the performance of DAS has developed rapidly. It is widely used because it can reconstruct information such as frequency and phase at any position of the optical fiber. Phase-sensitive optical time domain reflectometer (Φ-OTDR) is an important field in DAS systems. It achieves distributed sensing by detecting backscattered Rayleigh light (RBS). Compared with traditional optical time domain reflectometer systems, Φ-OTDR uses a high-coherence laser as a light source and has higher sensitivity and responsiveness. This technology has been widely used in perimeter security detection, structural health monitoring, and underwater sound source positioning.

[0003] However, fiber optic sensing focuses on real-time and accuracy. With the increase of sensing distance and sampling rate, the requirements for data processing speed and unpacking accuracy also increase accordingly. The correctness, real-time and noise resistance of phase unpacking have always been a difficult problem to solve. Kalman filtering is widely used in signal processing, robot control, unmanned vehicles and drones due to its strong filtering effect and strong noise resistance. However, the matrix multiplication involved can only be applied to linear systems. In the process of phase unpacking, complex trigonometric function calculations are involved, and standard Kalman filtering cannot be applied. Summary of the invention

[0004] The object of the present invention is to provide a Φ-OTDR data real-time processing system and method with fast processing rate, high phase unpacking accuracy and low hardware cost.

[0005] The technical solution to achieve the purpose of the present invention is: a Φ-OTDR data real-time processing system based on unscented Kalman filtering, including a modulation signal generation module, a data acquisition module, a data combination reading module, a phase calculation module, a data transmission module, a phase unpacking module and a communication module;

[0006] The modulation signal generating module applies a signal to the PZT piezoelectric ceramic through the FPGA, so that the backscattered Rayleigh scattered light RBS after three-way interference has additional phases of 2π / 3, -2π / 3, and 0 respectively;

[0007] The data acquisition module uses an analog-to-digital converter ADC to collect Rayleigh backscattering light intensity information;

[0008] The data combination reading module stores the light intensity data according to the number of channels and reads the corresponding detection sequence data;

[0009] The phase calculation module calculates the corresponding package phase using the three-way light intensity data;

[0010] The data transfer module uses a high-speed FIFO to realize data transfer between modules;

[0011] The phase unpacking module performs one-dimensional phase unpacking on the obtained wrapped phase data;

[0012] The communication module transmits the unpacked data to the host computer.

[0013] Furthermore, the data combination reading module includes a plurality of storage units for storing data; the storage units adopt dual-port RAM to support parallel reading and writing operations.

[0014] Furthermore, the data combination reading module uses a control program written based on Verilog to control the storage and reading of data.

[0015] Furthermore, the phase calculation module includes a plurality of logic units for performing data operations; the logic units adopt pipeline technology.

[0016] A method for real-time processing of Φ-OTDR data based on unscented Kalman filtering, the method adopts the real-time processing system for Φ-OTDR data, and specifically comprises the following steps:

[0017] Step 1: The modulation signal generation module converts the continuous light from the narrow linewidth laser into pulse light through the acousto-optic modulator AOM, and at the same time applies a modulation voltage to the PZT piezoelectric ceramic on the optical fiber through the FPGA to obtain a light intensity signal after interference with phase modulation;

[0018] Step 2: The data acquisition module uses an analog-to-digital converter (ADC) to collect the light intensity signal obtained in step 1, and the sampling rate corresponds to the sensing distance;

[0019] Step 3, the data combination reading module uses three dual-port RAMs to store the multi-channel light intensity data obtained in step 2, corresponding to the three-way light intensity information, and uses the control program to control the reading of the corresponding light intensity sequence, and after reading, replaces the light intensity data in the dual-port RAM with the light intensity data of the channel at the next moment;

[0020] Step 4: pass the light intensity data of step 3 to the phase calculation module, and use the arc tangent algorithm based on phase shifting to solve the wrapped phase;

[0021] Step 5: The wrapped phase data obtained in step 4 is transferred to the phase unpacking module through the data transfer module;

[0022] Step 6: The phase unpacking module performs one-dimensional phase unpacking on the wrapped phase through UKF;

[0023] Step 7: The communication module transmits the unpacked phase information to the host computer.

[0024] Furthermore, the step 1 is specifically as follows:

[0025] PZT piezoelectric ceramics are added to one arm of the unbalanced Michelson interferometer. By applying voltage to the PZT piezoelectric ceramics, the three-path Rayleigh return light after interference has an additional modulation phase.

[0026] Furthermore, the step 2 is specifically as follows:

[0027] The Rayleigh backscattered light RBS of the two arms of the balanced Michelson interferometer is received by the data acquisition module after interference by the coupler. The data acquisition module consists of a photodetector PD, an analog-to-digital converter ADC and an FPGA.

[0028] Furthermore, the step 3 is specifically as follows:

[0029] Step 3.1, store the data corresponding to all channels of the first light intensity channel into RAM1 by channel, store the second light intensity data into RAM2, and store the third light intensity data into RAM3;

[0030] Step 3.2, using the control program to control the reading of three-way light intensity data;

[0031] Step 3.3, replace the light intensity data in the dual-port RAM with the light intensity data of the channel at the next moment, and overwrite the data in RAM1 one by one according to the address. At this time, RAM2 and RAM3 still keep the original data. At this time, read the three-way light intensity, which is another detection sequence, and repeat the above operation to realize continuous storage and reading.

[0032] Furthermore, the step 4 is specifically as follows:

[0033] The three light intensity signals are added and subtracted and used as the numerator and denominator to be input into the phase calculation module for arc tangent operation to obtain the corresponding wrapped phase. The first 1000 data are taken and exported to a text document through Vivado, and the image is drawn through Python.

[0034] Furthermore, the step 6 is specifically as follows:

[0035] The initial parameters of the unscented Kalman filter are stored in the corresponding parameter storage RAM, and the corresponding initial detection sequence calls the initial parameters. The corresponding channel filter parameters are stored in the corresponding address through the control module and called when a group of detection sequences arrives in the same channel. The filter module adopts pipeline design, and the input signal is the sine and cosine information of the wrapped phase plus the initial filter parameters or the updated filter parameters. The output value of the unpacking module is also exported through vivado, and the curve is drawn using python.

[0036] Compared with the prior art, the present invention has the following significant advantages: (1) the overall data processing flow is completed through FPGA, and the pipeline is designed to improve the data processing speed; (2) one-dimensional phase unpacking is performed through unscented Kalman filtering, which improves the phase unpacking accuracy; (3) module reuse is designed to save hardware resources and reduce hardware costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 The present invention is a schematic structural diagram of a Φ-OTDR data real-time processing system based on unscented Kalman filtering.

[0038] Figure 2 The present invention is a flowchart of a method for real-time processing of Φ-OTDR data based on unscented Kalman filtering.

[0039] Figure 3 It is a schematic diagram of the wrapped phase result obtained by taking the first 1000 points after applying sinusoidal modulation to the sensing distance 278m corresponding to channel 139 in an embodiment of the present invention.

[0040] Figure 4 In the embodiment of the present invention, Figure 3 Wrapped Phase Results A plot of the results of further one-dimensional phase unwrapping. DETAILED DESCRIPTION

[0041] In order to make the above-mentioned purposes, features and advantages of the present invention more obvious and easy to understand, the specific implementation methods of the present invention are described in detail below in conjunction with the drawings of the specification. Obviously, the described embodiments are part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary persons in the art without creative work should fall within the scope of protection of the present invention.

[0042] In the following description, many specific details are set forth to facilitate a full understanding of the present invention, but the present invention may also be implemented in other ways different from those described herein, and those skilled in the art may make similar generalizations without violating the connotation of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0043] Combination Figure 1 , the present invention provides a Φ-OTDR data real-time processing system based on unscented Kalman filtering, comprising a modulation signal generating module, a data acquisition module, a data combination reading module, a phase calculation module, a data transmission module, a phase unpacking module and a communication module;

[0044] The modulation signal generating module applies a signal to the PZT piezoelectric ceramic through the FPGA, so that the backscattered Rayleigh scattered light RBS after three-way interference has additional phases of 2π / 3, -2π / 3, and 0 respectively;

[0045] The data acquisition module uses an analog-to-digital converter ADC to collect Rayleigh backscattering light intensity information;

[0046] The data combination reading module stores the light intensity data according to the number of channels and reads the corresponding detection sequence data;

[0047] The phase calculation module calculates the corresponding package phase using the three-way light intensity data;

[0048] The data transfer module uses a high-speed FIFO to realize data transfer between modules;

[0049] The phase unpacking module performs one-dimensional phase unpacking on the obtained wrapped phase data;

[0050] The communication module transmits the unpacked data to the host computer.

[0051] As a specific example, the data combination reading module includes a plurality of storage units for storing data; the storage units use dual-port RAM to support parallel reading and writing operations.

[0052] As a specific example, the data combination reading module uses a control program written based on Verilog to control the storage and reading of data.

[0053] As a specific example, the phase calculation module includes multiple logic units for performing data operations; the logic units use pipeline technology to improve data processing speed.

[0054] Combination Figure 2 , a real-time processing method of Φ-OTDR data based on unscented Kalman filtering, comprising the following steps:

[0055] Step 1: The modulation signal generation module converts the continuous light from the narrow linewidth laser into pulse light through the acousto-optic modulator AOM, and at the same time applies a modulation voltage to the PZT piezoelectric ceramic on the optical fiber through the FPGA to obtain a light intensity signal after interference with phase modulation;

[0056] Step 2: The data acquisition module uses an analog-to-digital converter (ADC) to collect the light intensity signal obtained in step 1, and the sampling rate corresponds to the sensing distance;

[0057] Step 3, the data combination reading module uses three dual-port RAMs to store the multi-channel light intensity data obtained in step 2, corresponding to the three-way light intensity information, and uses the control program to control the reading of the corresponding light intensity sequence, and after reading, replaces the light intensity data in the dual-port RAM with the light intensity data of the channel at the next moment;

[0058] Step 4: pass the light intensity data of step 3 to the phase calculation module, and use the arc tangent algorithm based on phase shifting to solve the wrapped phase;

[0059] Step 5: The wrapped phase data obtained in step 4 is transferred to the phase unpacking module through the data transfer module;

[0060] Step 6: The phase unpacking module performs one-dimensional phase unpacking on the wrapped phase through UKF;

[0061] Step 7: The communication module transmits the unpacked phase information to the host computer.

[0062] As a specific example, the modulation voltage is applied to the PZT piezoelectric ceramic on the optical fiber in step 1 to obtain a light intensity signal after interference with phase modulation, as follows:

[0063] PZT piezoelectric ceramics are added to one arm of the unbalanced Michelson interferometer. By applying voltage to the PZT piezoelectric ceramics, the three-path Rayleigh return light after interference has an additional modulation phase.

[0064] As a specific example, the data acquisition module described in step 2 uses an analog-to-digital converter ADC to collect the light intensity signal obtained in step 1, and the sampling rate corresponds to the sensing distance, as follows:

[0065] The Rayleigh backscattered light RBS of the two arms of the balanced Michelson interferometer is received by the data acquisition module after interference by the coupler. The data acquisition module consists of a photodetector PD, an analog-to-digital converter ADC and an FPGA.

[0066] As a specific example, the data combination reading module described in step 3 uses three dual-port RAMs to store the multi-channel light intensity data obtained in step 2, corresponding to three-way light intensity information, and uses a control program to control the reading of the corresponding light intensity sequence. After reading, the light intensity data in the dual-port RAM is replaced with the light intensity data of the channel at the next moment, as follows:

[0067] Step 3.1, store the data corresponding to all channels of the first light intensity channel into RAM1 by channel, store the second light intensity data into RAM2, and store the third light intensity data into RAM3;

[0068] Step 3.2, using the control program to control the reading of three-way light intensity data;

[0069] Step 3.3, replace the light intensity data in the dual-port RAM with the light intensity data of the channel at the next moment, and overwrite the data in RAM1 one by one according to the address. At this time, RAM2 and RAM3 still keep the original data. At this time, read the three-way light intensity, which is another detection sequence, and repeat the above operation to realize continuous storage and reading.

[0070] As a specific example, the method described in step 4 for solving the wrapped phase using the phase-shifted inverse tangent algorithm is as follows:

[0071] The three light intensity signals are added and subtracted and used as the numerator and denominator to be input into the phase calculation module for arc tangent operation to obtain the corresponding wrapped phase. The first 1000 data are taken and exported to a text document through Vivado, and the image is drawn through Python.

[0072] As a specific example, the phase unwrapping module in step 6 performs one-dimensional phase unwrapping on the wrapped phase through UKF, as follows:

[0073] The initial parameters of the unscented Kalman filter are stored in the corresponding parameter storage RAM, and the corresponding initial detection sequence calls the initial parameters. The corresponding channel filter parameters are stored in the corresponding address through the control module and called when a group of detection sequences arrives in the same channel. The filter module adopts pipeline design, and the input signal is the sine and cosine information of the wrapped phase plus the initial filter parameters or the updated filter parameters. The output value of the unpacking module is also exported through vivado, and the curve is drawn using python.

[0074] Example

[0075] Combination Figure 1 , a Φ-OTDR data real-time processing system based on unscented Kalman filtering provided in this embodiment includes a modulation signal generating module, a data acquisition module, a data combination reading module, a phase calculation module, a data transmission module, a phase unpacking module and a communication module;

[0076] The modulation signal generating module applies a signal to the PZT piezoelectric ceramic through the FPGA, so that the backscattered Rayleigh scattered light RBS after three-way interference has additional phases of 2π / 3, -2π / 3, and 0 respectively;

[0077] The data acquisition module uses an analog-to-digital converter ADC to collect Rayleigh backscattering light intensity information;

[0078] The data combination reading module stores the light intensity data according to the number of channels and reads the corresponding detection sequence data;

[0079] The phase calculation module calculates the corresponding package phase using the three-way light intensity data;

[0080] The data transfer module uses a high-speed FIFO to realize data transfer between modules;

[0081] The phase unpacking module performs one-dimensional phase unpacking on the obtained wrapped phase data;

[0082] The communication module transmits the unpacked data to the host computer.

[0083] As a specific example, the data combination reading module includes a plurality of storage units for storing data; the storage units use dual-port RAM to support parallel reading and writing operations.

[0084] As a specific example, the data combination reading module uses a control program written based on Verilog to control the storage and reading of data.

[0085] As a specific example, the phase calculation module includes multiple logic units for performing data operations; the logic units use pipeline technology to improve data processing speed.

[0086] Combination Figure 2 The present embodiment provides a method for real-time processing of Φ-OTDR data based on unscented Kalman filtering, comprising the following steps:

[0087] Step 1, the modulation signal generating module converts the continuous light from the narrow linewidth laser into pulse light through the acousto-optic modulator AOM. The system pulse light frequency is 20kHz. A sinusoidal voltage signal is applied to the piezoelectric ceramic at the corresponding sensing distance of 278m in channel 139 of the optical fiber. The three-way light intensity has modulation phases of 2π / 3, 0, and -2π / 3 respectively.

[0088] Step 2: The data acquisition module uses an analog-to-digital converter (ADC) to acquire the light intensity signal obtained in step 1, with a sampling rate of 50 Mb / s, corresponding to collecting a data point every 2 m along the length of the optical fiber;

[0089] Step 3, the data combination reading module uses three dual-port RAMs to store the multi-channel light intensity data obtained in step 2, corresponding to the three-way light intensity information, and uses the control program to control the reading of the corresponding light intensity sequence, and after reading, replaces the light intensity data in the dual-port RAM with the light intensity data of the channel at the next moment;

[0090] Step 4: pass the light intensity data I1, I2, and I3 of step 3 to the phase calculation modules RAM1, RAM2, and RAM3, and read the three-way data of the corresponding detection sequence at the same time, perform fixed-point processing on the data, calculate the wrapped phase through the phase calculation module, take the first 1000 of the obtained data and export it to a text document through vivado, and draw the image through python, such as Figure 3 As shown;

[0091] Depend on Figure 3 It can be seen that the wrapped phase process performed by the present invention results in a wrapped phase interval of [-π, π];

[0092] Step 5, calculating the sine value and cosine value of the wrapped phase obtained in step 5, and transmitting them to the unscented Kalman filter one-dimensional phase unpacking module through the high-speed FIFO;

[0093] Step 6: The phase unpacking module performs one-dimensional phase unpacking on the wrapped phase through UKF;

[0094] The initial parameters of the unscented Kalman filter are stored in the corresponding parameter storage RAM. The corresponding initial detection sequence calls the initial parameters. The corresponding channel filter parameters are stored in the corresponding address through the control module. When a group of detection sequences arrives in the same channel, it is called. The filter module adopts pipeline design. The input signal is the sine and cosine information of the wrapped phase plus the initial filter parameters or the updated filter parameters. The output value of the unpacking module is also exported through vivado, and the curve is drawn using python. The result is as follows Figure 4 shown.

[0095] Depend on Figure 4 It can be seen that the sinusoidal signal applied to the corresponding point of the optical fiber is well restored. The Φ-OTDR data real-time processing system and method based on unscented Kalman filtering provided by the present invention can perform high-precision phase unpacking when processing multi-channel data simultaneously.

[0096] Step 7: The communication module transmits the unpacked phase information to the host computer.

[0097] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A Φ-OTDR data real-time processing system based on unscented Kalman filtering, characterized in that: It includes a modulation signal generation module, a data acquisition module, a data combination reading module, a phase calculation module, a data transmission module, a phase unpacking module and a communication module; The modulation signal generating module applies a signal to the PZT piezoelectric ceramic through the FPGA, so that the backscattered Rayleigh scattered light RBS after three-way interference has additional phases of 2π / 3, -2π / 3, and 0 respectively; The data acquisition module uses an analog-to-digital converter ADC to collect Rayleigh backscattering light intensity information; The data combination reading module stores the light intensity data according to the number of channels and reads the corresponding detection sequence data; The phase calculation module calculates the corresponding package phase using the three-way light intensity data; The data transfer module uses a high-speed FIFO to realize data transfer between modules; The phase unpacking module performs one-dimensional phase unpacking on the obtained wrapped phase data; The communication module transmits the unpacked data to the host computer.

2. The Φ-OTDR data real-time processing system based on unscented Kalman filtering according to claim 1 is characterized in that: The data combination reading module includes a plurality of storage units for storing data; the storage units adopt dual-port RAM to support parallel reading and writing operations.

3. The Φ-OTDR data real-time processing system based on unscented Kalman filtering according to claim 1 is characterized in that: The data combination reading module adopts a control program written based on Verilog to control the storage and reading of data.

4. The Φ-OTDR data real-time processing system based on unscented Kalman filtering according to claim 1 is characterized in that: The phase calculation module includes a plurality of logic units for performing data operations; the logic units adopt pipeline technology.

5. A real-time processing method for Φ-OTDR data based on unscented Kalman filtering, characterized in that: The method adopts the Φ-OTDR data real-time processing system according to any one of claims 1 to 4, and specifically comprises the following steps: Step 1: The modulation signal generation module converts the continuous light from the narrow linewidth laser into pulse light through the acousto-optic modulator AOM, and at the same time applies a modulation voltage to the PZT piezoelectric ceramic on the optical fiber through the FPGA to obtain a light intensity signal after interference with phase modulation; Step 2: The data acquisition module uses an analog-to-digital converter (ADC) to collect the light intensity signal obtained in step 1, and the sampling rate corresponds to the sensing distance; Step 3, the data combination reading module uses three dual-port RAMs to store the multi-channel light intensity data obtained in step 2, corresponding to the three-way light intensity information, and uses the control program to control the reading of the corresponding light intensity sequence, and after reading, replaces the light intensity data in the dual-port RAM with the light intensity data of the channel at the next moment; Step 4: pass the light intensity data of step 3 to the phase calculation module, and use the arc tangent algorithm based on phase shifting to solve the wrapped phase; Step 5: The wrapped phase data obtained in step 4 is transferred to the phase unpacking module through the data transfer module; Step 6: The phase unpacking module performs one-dimensional phase unpacking on the wrapped phase through UKF; Step 7: The communication module transmits the unpacked phase information to the host computer.

6. The method for real-time processing of Φ-OTDR data based on unscented Kalman filtering according to claim 5, characterized in that: The step 1 is specifically as follows: PZT piezoelectric ceramics are added to one arm of the unbalanced Michelson interferometer. By applying voltage to the PZT piezoelectric ceramics, the three-path Rayleigh return light after interference has an additional modulation phase.

7. The method for real-time processing of Φ-OTDR data based on unscented Kalman filtering according to claim 5, characterized in that: The step 2 is specifically as follows: The Rayleigh backscattered light RBS of the two arms of the balanced Michelson interferometer is received by the data acquisition module after interference by the coupler. The data acquisition module consists of a photodetector PD, an analog-to-digital converter ADC and an FPGA.

8. The method for real-time processing of Φ-OTDR data based on unscented Kalman filtering according to claim 5, characterized in that: The step 3 is as follows: Step 3.1, store the data corresponding to all channels of the first light intensity channel into RAM1 by channel, store the second light intensity data into RAM2, and store the third light intensity data into RAM3; Step 3.2, using the control program to control the reading of three-way light intensity data; Step 3.3, replace the light intensity data in the dual-port RAM with the light intensity data of the channel at the next moment, and overwrite the data in RAM1 one by one according to the address. At this time, RAM2 and RAM3 still keep the original data. At this time, read the three-way light intensity, which is another detection sequence, and repeat the above operation to realize continuous storage and reading.

9. The method for real-time processing of Φ-OTDR data based on unscented Kalman filtering according to claim 5, characterized in that: The step 4 is specifically as follows: The three light intensity signals are added and subtracted and used as the numerator and denominator to be input into the phase calculation module for arc tangent operation to obtain the corresponding wrapped phase. The first 1000 data are taken and exported to a text document through Vivado, and the image is drawn through Python.

10. The method for real-time processing of Φ-OTDR data based on unscented Kalman filtering according to claim 5, characterized in that: The step 6 is specifically as follows: The initial parameters of the unscented Kalman filter are stored in the corresponding parameter storage RAM, and the initial parameters are called by the corresponding initial detection sequence. The corresponding channel filter parameters are stored in the corresponding address through the control module, and are called when a group of detection sequences arrives in the same channel; The filter module adopts pipeline design. The input signal is the sine and cosine information of the wrapped phase plus the initial filter parameters or updated filter parameters. The output value of the unpacking module is also exported through Vivado, and the curve is drawn using Python.

Images