Complex hydrological multi-target laser polarization detection device

Abstract

The invention belongs to the technical field of underwater laser detection, and discloses a complex hydrological multi-target laser polarization detection device which is designed by adopting a transceiving heteroaxial design, effectively overcomes strong background interference of a water body, splits scattered light collected by a single telescope into four different polarization angles (0 degree, 45 degrees, 90 degrees and 135 degrees), and improves the detection accuracy. Signal amplitude detection is carried out through a PMT photoelectric detector, meanwhile, according to interval numerical values provided by a simulation time-varying model, adjustment can be carried out for different water qualities and detection threshold values of different target receivers, the system detection robustness can be effectively improved, and under the water quality with the attenuation coefficient larger than 0.385 m <-1 >, the system detection robustness can be effectively improved within the 8m range. Detection and material identification are carried out on a target with the diameter larger than 300 microns, meanwhile, data processing is concise and efficient, and the real-time performance is high. The working principle is advanced, the technical method is unique and novel, and the real-time requirement of multiple targets in a complex water area is met.

Description

Technical Field

[0001] The invention belongs to the technical field of underwater laser detection, and in particular relates to a complex hydrological multi-target laser polarization detection device. Background Art

[0002] The ocean is an important part of the earth's environment and human ecosystem. With the development and progress of science and technology, the exploration and development of unknown areas of the ocean has always been the focus of human activities, such as deep-sea exploration, seabed mapping, underwater archaeology, marine biological population monitoring, rescue operations, infrastructure maintenance, etc. The acquisition of information and monitoring and analysis of the marine environment are important means to carry out these tasks. Optical information is one of the most important sources of information in the process of human exploration of the ocean. It has the advantage of being able to directly reflect the underwater environment and targets. Underwater laser detection is one of the important means to obtain underwater information. Compared with the low resolution of intensity detection and the high complexity of frequency and phase detection, light scattering polarization detection has the advantages of good target extraction and recognition accuracy and relatively simple detection system composition. In the underwater weak light environment where scattering media exist, its information retention ability is far greater than that of intensity and frequency detection. The key to limiting scattering polarization detection is: first, how to extract and identify multiple mutually occluded and intertwined targets with high robustness in highly heterogeneous natural water bodies; second, how to overcome the depolarization phenomenon caused by multiple scattering of underwater particles and interference from obstacle targets, resulting in the loss of polarization information. Therefore, there is an urgent need for a polarization detection model that can not only realize the accurate polarization information extraction of multiple underwater targets, but also effectively combat particle multiple scattering and enhance the recognition of target polarization information, thereby realizing accurate feature extraction and separation of the detection target and the environment, and ultimately achieving refined target identification and efficient construction of the marine environment target field.

[0003] The existing underwater optical detection methods are mainly based on remote sensing detection and image detection methods. However, whether it is airborne or satellite remote sensing technology, due to the large detection area, the large amount of data required, and the high requirements on the capabilities of laser transmitting and receiving devices, it leads to complex structure, large size, and identification is restricted by the environment and is not precise. For example, in order to adapt to the needs of large-scale high-speed real-time detection, my country's first ocean color satellite (HY-1A) uses a scalar radiation theory approximation algorithm to process atmospheric correction, which limits its information extraction accuracy and application scope; while the image detection method pays more attention to the model optimization and image quality improvement of underwater polarization imaging, but pays less attention to the real-time and engineering application of underwater polarization imaging algorithms. As a result, its detection processing algorithm is complex and has poor real-time performance. It has high requirements on the structure of the detection device, large amount of detection data, and much interference, which is not conducive to the engineering practice of integrated sensing, storage and computing.

[0004] Through the above analysis, the problems and defects of the prior art are as follows:

[0005] The existing underwater optical detection methods are mainly based on remote sensing detection and image detection methods. However, whether it is airborne or satellite remote sensing technology, due to the large detection area, the large amount of data required, and the high capabilities of the laser transmitting and receiving devices, it leads to complex structure, large size, and the recognition is restricted by the environment and is not precise. Summary of the invention

[0006] In view of the problems existing in the prior art, the present invention provides a complex hydrological multi-target laser polarization detection device.

[0007] The present invention is implemented in this way: a complex hydrological multi-target laser polarization detection device comprises:

[0008] Laser emission system, laser polarization receiving system, signal control and processing system;

[0009] Laser emission system: It is composed of a laser generation subsystem, a collimated emission subsystem, and an adjustable optical attenuator. It is effectively strapped down with the power supply and control module. The laser head is controlled by the signal sent by the control system, and it emits a fixed 1KHZ optical signal. After passing through the beam splitter, one beam enters the acquisition storage module as a trigger signal as a reference to the 0 moment. After turning, focusing, and collimating, one beam is emitted through a beam expanding telescope, and finally the optical power is adjusted by a rotating attenuation plate and emitted to the external environment.

[0010] Laser polarization receiving system: It consists of a laser receiving mirror, a 532nm filter, a beam splitter, a light collecting mirror, and a PMT photodiode. The laser echo emitted by the object passes through a 532nm filter to filter out stray light, is divided into four beams by a beam splitter, and then is focused on the photosensitive surface of the PMT by a light collecting mirror.

[0011] Signal control and processing system: It is composed of FPGA drive control, AD data acquisition, storage and processing, and host computer program. It is connected to the transmitting and receiving systems to control various parameters of the device and process and output detection data results in real time.

[0012] Furthermore, the laser emission system consists of a laser, a power supply, a beam expansion and collimation device, and an integrated processing and display control module. The laser is connected to the power supply, the beam expansion and collimation system, and the integrated processing and display control module respectively, and the beam expansion and collimation system and the integrated processing and display control module are connected to a computer host computer.

[0013] Furthermore, the beam expansion and collimation device realizes the function of electric focusing through a computer host computer to control the change of the laser emission beam angle, and the comprehensive processing and display control module is used to adjust the laser switch and energy parameters by controlling the current of the driving module and the TEC temperature control module.

[0014] Furthermore, the laser polarization receiving system is composed of a beam expanding lens group, a beam splitter, a focusing lens, a rotating polarizer, and a PMT detector. The beam expanding ratio of the beam expanding lens group is 5:1; the beam splitting ratio of the beam splitter RP and PP is 0.5 / 0.5; the rotating polarizer L2 adjusts the polarization angle to 0 degrees, the rotating polarizer L3 adjusts the polarization angle to 45 degrees, the rotating polarizer L4 adjusts the polarization angle to 90 degrees, and the rotating polarizer L5 adjusts the polarization angle to 135 degrees; a horizontal light with a diameter of 75 mm is incident through the beam expanding lens group and becomes a diameter of 15 mm before being incident. On the beam splitter 1, the beam splitter reflects 50% of the energy and transmits 50% of the energy. The reflected and transmitted light rays are respectively received by the beam splitter PP and incident on the rotating polarizers L2, L3, L4, and L5. After being polarized by 0, 45, 90, and 135 degrees through the rotating polarizers, they are incident on the focusing lens, and after being focused, they are incident on the PMT photomultiplier tubes D1, D2, D3, and D4. BF is a narrowband filter with a central wavelength of ; L is the axial distance of the receiving system, which is , the diameter of the receiving telescope is 50 mm, the focal length is 20 mm, and the receiving field angle is 2.85°.

[0015] Furthermore, the signal control and processing system is composed of FPGA drive control, Ethernet communication, and AD sampling processing; sampling ARP protocol and UDP protocol dual protocol communication, and the pins on the GMII receiving side are simultaneously connected to the ARP top-level module and the UDP top-level module.

[0016] Furthermore, in the PMT detection circuit, the optical signal is converted into photoelectric signals by the PMT and TIA, and then processed by the weak voltage signal processing circuit and input into the signal processing platform FPGA.

[0017] Another object of the present invention is to provide a complex hydrological multi-target laser polarization detection method comprising:

[0018] Step 1: The computer host outputs a control instruction to control the laser to output a pulsed laser. The output pulsed laser is incident into the water environment after being collimated. A large number of photons are absorbed or scattered by the water. The scattered photons are received by the polarization receiving system and transmitted to the PMT gain control system through optical fiber. The system collects and processes the light scattering intensity of the natural water body. Through multiple cumulative measurements, and adjusting the laser emission energy, frequency and PMT receiving gain parameters, the optimal emission and receiving system parameters for the measured water area are obtained.

[0019] Step 2, when the detection equipment performs radial detection on multiple targets in the area, the laser beam composed of a large number of photons collides with the natural water body and the surface of each target, and a large number of photons are absorbed or scattered by the natural water body and bubbles. The scattered photons are received by the polarization receiving system and transmitted to the PMT gain control system through the optical fiber, and the output signal enters the AD data acquisition and processing system;

[0020] Step 3: After AD data acquisition completes the detection data, the data processing module optimizes the processed data, which is divided into two stages: preprocessing and output.

[0021] Another object of the present invention is to provide a computer device, which includes a memory and a processor, wherein the memory stores a computer program, and when the computer program is executed by the processor, the processor executes the steps of the complex hydrological multi-target laser polarization detection method.

[0022] Another object of the present invention is to provide a computer-readable storage medium storing a computer program, which, when executed by a processor, enables the processor to perform the steps of the complex hydrological multi-target laser polarization detection method.

[0023] Another object of the present invention is to provide an information data processing terminal, which is used to implement the complex hydrological multi-target laser polarization detection device.

[0024] In combination with the above technical solutions and the technical problems solved, the advantages and positive effects of the technical solutions to be protected by the present invention are as follows:

[0025] First, the underwater laser polarization detection and recognition capability is related to multiple parameters such as water quality, target composition, and target characteristics. The existing underwater polarization detection model cannot simultaneously meet the combination of theoretical accuracy and real-time and robustness in engineering applications. In response to the demand for high-robust extraction and recognition of polarization information of small targets under the background of multiple scattering of underwater particles and mutual occlusion and interlaced target interference, combined with the current status of underwater target recognition test technology, the present invention provides a multi-target laser polarization detection method in a complex underwater environment based on data optimization, and analyzes the system composition and key technical methods.

[0026] The multi-target laser polarization detection provided by the present invention has high real-time performance, and the test results can be obtained on-site in one go. During the detection process, the present invention performs polarization neighborhood preprocessing estimation on the object to be identified, outputs the approximate linear polarization threshold of the object, and splits the scattered light collected by a single telescope into 4 different polarization angles (0°, 45°, 90°, 135°), and uses a PMT photoelectric detector to detect the signal amplitude, and describes the calculation process of the DOLP of the echo light of different targets. The data output is fast and accurate. In short, the present invention has a leapfrog improvement in test speed, test accuracy, completeness of test parameters, and cheap operation, which is incomparable to previous methods. It has an advanced working principle and a unique and novel technical method, which meets the real-time requirements of underwater multiple target detection and identification.

[0027] The present invention establishes a small target time-varying detection model based on multiple scattering and polarization characteristics under different water quality conditions and a multi-target polarization detection method based on the polarization state of a priori neighborhood photons, and completes the hardware design, which can simulate the polarization optical characteristics of various small targets in real time and correct the data results. At the same time, combined with the above detection method, a multi-target polarization recognition and detection device under complex hydrological conditions is designed, which can detect polarization signals with an attenuation coefficient greater than 0.385m -1 Under water quality, it can detect and identify the material of targets with a diameter greater than 300um within a range of 8m. The system has a simple structure, high recognition efficiency, and a simple recognition method. It can realize real-time data output, which is convenient for operators to timely control the underwater situation. At the same time, it is less affected by changes in the underwater environment (temperature, salinity, turbulence), and can effectively detect multiple targets radially distributed in complex waters with a distance resolution of 20cm. Therefore, it can be widely used in offshore marine target identification, offshore marine disaster warning, underwater unmanned navigation, and underwater robot obstacle avoidance, providing a potential application technology for the fields of ocean profile lidar detection and ocean laser stereo remote sensing.

[0028] In order to achieve real-time detection and identification of multiple targets in complex waters and resist the loss of polarization information caused by natural interference such as different degrees of water turbulence, salinity values ​​and obstacles, the present invention provides a complex underwater environment multi-target laser polarization detection device based on data optimization, analyzes the composition of the system and key technical methods, and can provide support for underwater target identification. At the same time, the present invention has a unique PMT four-channel independent control, multi-step laser emission state adjustable, simple structure, convenient operation, wide range of engineering applications, and low cost.

[0029] Second, the expected benefits and commercial value of the technical solution of the present invention after transformation are as follows: the technical solution of the present invention can be applied to optical detection equipment after transformation, and can be widely used in offshore marine target identification, offshore marine disaster warning, underwater unmanned navigation and underwater robot obstacle avoidance.

[0030] The technical solution of the present invention fills the technical gaps in the industry at home and abroad: a. The test functions are complete, with high precision, high speed and high real-time performance. In the previous studies on underwater polarization detection, the environmental field construction was relatively monotonous, and the polarization transmission and detection models were relatively ideal. The actual situation that multiple material targets of different scales are mixed and randomly distributed in the underwater target field and multiple scattering phenomena are obvious was not considered. In this case, the target field has the characteristics of high degree of homogenization and non-uniformity, which makes it relatively difficult to extract and identify the target polarization information, and the detected target polarization state has low robustness. The instrument adopts a different-axis design for transmitting and receiving, which effectively overcomes the strong background interference of the water body, and splits the scattered light collected by a single telescope into 4 different polarization angles (0°, 45°, 90°, 135°), and uses a PMT photoelectric detector to detect the signal amplitude. At the same time, according to the interval value provided by the simulation time-varying model, the detection threshold of different water quality and different target receivers can be adjusted, which can effectively improve the detection robustness of the system, and can be used when the attenuation coefficient is greater than 0.385m -1 Under water quality, it can detect and identify the material of targets with a diameter greater than 300um within a range of 8m. At the same time, the data processing is simple and efficient with high real-time performance. b. The system has a compact structure and simple operation, and is suitable for field use. Since the field use problem is fully considered in the structural design of the tester, the device components used are all integrated and miniaturized. The overall structure consists of only one main box and one upper computer control software. The connections are all watertight and impact-resistant tested, and can be directly put into field use. By comparing the above methods, it can be seen that the test method of the present invention has a leapfrog improvement in test speed, test accuracy, completeness of test parameters, and cheapness of operation, which is incomparable to previous methods. It has an advanced working principle and unique and novel technical methods, which meet the requirements of underwater optical detection instruments.

[0031] Third, in the case of multi-target detection in complex hydrological environments, traditional technologies are limited by factors such as light attenuation, scattering, and multi-target interference in water bodies, and cannot accurately distinguish the nature and location of targets. Although existing laser detection technology can be used for underwater environment detection, the detection accuracy and reliability are seriously affected when facing different targets and complex water conditions. In addition, traditional detection methods often lack effective analysis of the target's polarization characteristics, resulting in large errors in the detection results, making it difficult to meet the actual needs of high-precision underwater detection.

[0032] The present invention solves the problems of insufficient detection accuracy, severe light attenuation and multi-target interference in traditional underwater detection technology through a complex hydrological multi-target detection method based on laser polarization technology. By introducing laser polarization detection technology, the polarization characteristics of underwater targets can be effectively utilized to achieve accurate positioning and identification of targets. In addition, by simulating the scattering process of photons through the vector Monte Carlo method, multiple scattered photons can be monitored and counted in real time, and echo signals can be accurately calculated, effectively improving the accuracy and precision of detection.

[0033] Compared with the prior art, the laser polarization detection system of the present invention has a number of significant technical advances. First, it can maintain a high detection accuracy in high turbidity water bodies, solving the problem that traditional technologies are difficult to detect in harsh environments. Second, by introducing Stokes vector analysis, the system can effectively capture the polarization information of the target and improve the ability to identify different types of targets. In addition, the combination of data preprocessing and multi-scattered photon statistics greatly improves the system's response speed and data processing capabilities, providing technical support for real-time underwater detection.

[0034] The present invention has significant industrial value in underwater detection applications. It can not only be applied to environmental monitoring, marine engineering, military detection and other fields, but also can realize accurate underwater target identification and positioning in complex multi-target environments. By improving detection accuracy and signal processing capabilities, the present invention can significantly reduce detection errors, improve the reliability and service life of equipment, and ultimately provide a set of efficient, accurate and intelligent solutions for underwater detection systems, which will help promote the development of related industries. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a structural block diagram of a complex hydrological multi-target laser polarization detection device provided by an embodiment of the present invention.

[0036] Figure 2 It is an optical design diagram of a detection system provided by an embodiment of the present invention.

[0037] Figure 3 It is a design diagram of a communication control circuit provided by an embodiment of the present invention.

[0038] Figure 4 It is a design diagram of a PMT receiving circuit provided by an embodiment of the present invention.

[0039] Figure 5 It is a preprocessing flow chart provided by an embodiment of the present invention.

[0040] Figure 6 This is a real machine display diagram provided by an embodiment of the present invention.

[0041] Figure 7This is an experimental detection scene diagram provided by an embodiment of the present invention.

[0042] Figure 8 Graphs of polarization characteristics of different paired target groups at different times provided by embodiments of the present invention: (a) polarization characteristics curve of fishing net + ceramic target group; (b) polarization characteristics curve of fishing net + plastic fishing line target group; (c) polarization characteristics curve of fishing net plus iron wire target group.

[0043] Fig. 9 It is a flow chart of the complex hydrological multi-target laser polarization detection method provided by an embodiment of the present invention.

[0044] Fig.10 There are four peaks in the four polarization directions in (a) and 10(b). The first peak is the sampling distance reference signal; the second peak is the echo signal of the bubble group in each polarization direction; the third peak is the echo signal of the fishing net in each polarization direction; the fourth peak is the echo signal of the ceramic sheet and the iron wire in each polarization direction. DETAILED DESCRIPTION

[0045] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0046] like Figure 1 As shown, a complex hydrological multi-target laser polarization detection device provided by an embodiment of the present invention is composed of a laser emission system (laser, optical shaping, etc.), a laser polarization receiving system (receiving mirror group, APD photoelectric conversion module) and a signal control and processing system (control trigger circuit, FPGA signal processing module), as follows Figure 1 shown.

[0047] Laser emission system: It is composed of laser generation subsystem, collimation emission subsystem and adjustable optical attenuator. At the same time, it is effectively strapped with the power supply and control module. The laser head is controlled by the signal sent by the control system, and it emits a fixed 1KHZ optical signal. After passing through the beam splitter, one beam enters the acquisition storage module as a trigger signal as the reference 0 moment, and one beam is sent out through the beam expansion telescope after turning, focusing and collimation. Finally, the light output power is adjusted by the rotating attenuation plate and emitted to the external environment.

[0048] Laser polarization receiving system: It is composed of laser receiving mirror, 532nm filter, beam splitter, light collecting mirror, and PMT photodiode. The laser echo emitted by the object is filtered out by the 532nm filter to remove stray light, and is divided into four beams by the beam splitter, and then converged on the photosensitive surface of the PMT by the light collecting mirror.

[0049] Signal control and processing system: It is composed of FPGA drive control, AD data acquisition, storage and processing, and host computer program. It is connected to the transmitting and receiving systems to control various parameters of the device and process and output detection data results in real time.

[0050] The laser emission system provided in the embodiment of the present invention is composed of a laser, a power supply, a beam expansion and collimation device, and a comprehensive processing and display control module. The laser is connected to the power supply, the beam expansion and collimation system, and the comprehensive processing and display control module respectively, and the beam expansion and collimation system and the comprehensive processing and display control module are connected to a computer host computer;

[0051] The beam expansion and collimation device realizes the electric focusing function through the computer host computer to control the change of the laser emission beam angle. The comprehensive processing and display control module is used to adjust the laser switch and energy parameters by controlling the current of the driving module and the TEC temperature control module.

[0052] The laser polarization receiving system provided by the embodiment of the present invention is composed of a beam expansion lens group, a beam splitter, a focusing lens, a rotating polarizer, and a PMT detector. The beam expansion ratio of the beam expansion lens group is 5:1; the beam splitter RP and PP splitting ratios are 0.5 / 0.5; the rotating polarizer L2 adjusts the polarization angle to 0 degrees, the rotating polarizer L3 adjusts the polarization angle to 45 degrees, the rotating polarizer L4 adjusts the polarization angle to 90 degrees, and the rotating polarizer L5 adjusts the polarization angle to 135 degrees. The horizontal light with a diameter of 75 mm is incident through the beam expansion lens group, becomes a diameter of 15 mm, and then enters the beam splitter 1. The beam splitter splits the light according to the ratio of 50% energy reflection and 50% energy transmission; the reflected and transmitted light rays are respectively taken into the beam splitter PP and incident on the rotating polarizers L2, L3, L4, and L5. After being polarized by 0, 45, 90, and 135 degrees through the rotating polarizer, they are incident on the focusing lens, and after focusing, they are incident on the PMT photomultiplier tubes D1, D2, D3, and D4. BF is a narrowband filter with a central wavelength of; L is the axial distance of the receiving system, which is, the receiving telescope diameter is 50mm, the focal length is 20mm, and the receiving field of view is 2.85°. The specific design is as follows Figure 2 shown.

[0053] The signal control and processing system provided by the embodiment of the present invention is composed of FPGA drive control, Ethernet communication, and AD sampling and processing. The dual-protocol communication of the sampling ARP protocol and the UDP protocol, the pins of the GMII receiving side are connected to the ARP top-level module and the UDP top-level module at the same time, and these two modules will parse the data according to the ARP protocol and the UDP protocol respectively. The GMII sending side pin can only be connected to one of the ARP top-level module and the UDP top-level module, so the Ethernet control module will choose to switch the GMII sending side pin and the ARP top-level module or the UDP top-level module connection according to the currently received protocol type. In addition, the Ethernet control module controls the ARP top-level module to return the ARP reply signal according to the type of input ARP reception. Ethernet will receive a large amount of data at a time, so this experiment requires a FIFO module to cache data. Since the GMII receiving clock and the GMII sending clock used in this experiment are actually the same clock, a synchronous FIFO is used here. The size of the FIFO is 2048 2-bit bytes. In order to meet the situation where the amount of data in a single packet is large (although usually, the effective data of an Ethernet frame does not exceed 1500 bytes), the depth of the FIFO is better set larger. Here, the depth is set to 2048 and the width is 32 bits. Figure 3 Shown

[0054] In the PMT detection circuit provided by the embodiment of the present invention, the optical signal is converted into photoelectric signals by PMT and TIA, and then processed by the weak voltage signal processing circuit and input into the signal processing platform FPGA. Figure 6-8 As shown, when the signal light propagates through the underwater channel to the receiver, it first passes through a filter to filter out the remaining clutter, and then converges to the photosensitive surface of the large-area PMT through an optical antenna, providing a reverse high bias voltage to the PMT to obtain a relatively high gain. The optical signal at the receiving end is converted into a photocurrent after passing through the PMT, and then the current signal is converted to a voltage signal through the TIA circuit. At this time, the voltage signal amplitude is usually very small, and a low-noise operational amplifier is used to amplify the low-amplitude voltage signal. In order to obtain a larger gain, the signal is limited and amplified by a limiting amplifier, and a PECL level that is easy to process is obtained at the same time. The limiting amplifier often has a differential signal input and a differential signal output, so it is necessary to add a single-ended to differential circuit, and finally convert the limited amplified signal into an easy-to-process LVTTL level input to the FPGA. As shown below Figure 4 shown.

[0055] like Fig. 9 As shown, the complex hydrological multi-target laser polarization detection method provided by the embodiment of the present invention includes the following steps:

[0056] S101, the computer host outputs control instructions to control the laser to output pulsed laser, and the output pulsed laser is incident into the water environment after being collimated. A large number of photons are absorbed or scattered by the water body, and the scattered photons are received by the polarization receiving system and transmitted to the PMT gain control system through optical fiber. The system collects and processes the light scattering intensity of the natural water body, and obtains the best transmission and receiving system parameters for the measured water area through multiple cumulative measurements and adjustment of parameters such as laser emission energy, frequency, and PMT receiving gain.

[0057] S102, when the detection equipment performs radial detection on multiple targets in the area, the laser beam composed of a large number of photons collides with the natural water body and the surface of each target, and a large number of photons are absorbed or scattered by the natural water body and bubbles. The scattered photons are received by the polarization receiving system and transmitted to the PMT gain control system through the optical fiber, and the output signal enters the AD data acquisition and processing system.

[0058] S103, when AD data acquisition completes the detection data, the data processing module optimizes the processed data, which is divided into two stages: preprocessing and output.

[0059] The complex hydrological multi-target laser polarization detection method of the present invention starts with laser control, and a computer host computer issues instructions to control the laser to output pulsed laser. After the pulsed laser is collimated, it enters the water environment. Since the water body has strong absorption and scattering characteristics, the incident laser will interact with water molecules and suspended particles, resulting in the scattering and absorption of photons. Part of the scattered photons are captured by the polarization receiving system and transmitted to the PMT (photomultiplier tube) gain control system through optical fiber. The system can measure the light scattering intensity in the water body, and ensure the best detection conditions by adjusting the laser emission energy, frequency and PMT gain parameters.

[0060] In the laser detection area, when multiple targets are within the detection range, the laser beam collides with the natural water body and the surface of each target. At this time, the laser will be absorbed or scattered by bubbles, suspended matter and target objects in the natural water body. The scattered photons are received by the polarization receiving system, and the optical fiber transmits the received light signal to the PMT gain control system to amplify and process these signals. This process ensures that the laser detection signals of multiple targets in the water body can be effectively received and transmitted, providing a basis for subsequent data collection and analysis.

[0061] After the PMT system processes the scattered photon signal received by polarization, the signal is sent to the AD data acquisition and processing system. The system converts the analog signal into a digital signal for subsequent data analysis. The AD acquisition process ensures that the scattered signal is digitized with high precision, and the system extracts effective detection information based on multiple accumulated detection results. Through multiple adjustments to the laser emission and photon reception, the detection accuracy and sensitivity of the detection equipment can be gradually optimized.

[0062] After the AD data collection is completed, the data processing module optimizes the collected detection data. First, in the preprocessing stage, the system denoises, smoothes and corrects the deviation of the collected data to ensure the accuracy of the data. Then, in the output stage, the system analyzes and calculates the processed detection data, and finally generates the hydrological information or target detection report of the detection area. The optimization processing of this step effectively improves the accuracy of the detection results and ensures the feasibility and reliability of the multi-target laser polarization detection method.

[0063] The preprocessing process is as follows Figure 5 .

[0064] The statistical photon preprocessing process is to determine the median value of the statistical neighborhood by extracting the linear polarization degree of scattered photons in the near field of the target, and at the same time extract some scattered photons in the far field to screen and determine the upper and lower limits of the neighborhood, and finally accumulate the number of photons in the neighborhood to approximate the target linear polarization degree. After preprocessing, it enters the data shaping and correction stage.

[0065] The main difference between the vector Monte Carlo method and the traditional scalar Monte Carlo method is that the former introduces the Stokes vector that can characterize the polarization state information of the photon. Therefore, the state parameter N of the photon at the mth collision point is m for:

[0066] N m =(P m ,U m ,S m ,ω m ,L m )

[0067] Where P m is the spatial coordinate of the mth collision point of the photon; U m is the motion direction vector of the photon at the mth collision; S m is the Stokes vector of the photon at the mth collision; ω m is the weight of the photon after the mth collision; L m is the total length of the free path that the photon has traveled after the mth collision.

[0068] The returned photons can be statistically analyzed to generate an echo signal waveform. During the simulation, the contribution of all scattering of photons in the receiving field of view to the echo signal is recorded. The recorded values ​​consist of two arrays: R dis (i pho ,j scat ) and R sig (i pho ,j scat ,k pol ).

[0069] R dis (i pho ,j scat ) represents the i-th pho Photon j scat The total length of the scattered light that travels back to the receiving lens. sig (i pho ,j scat ,k pol ) represents the i-th pho Photon j scat The kth scattered Stokes vector pol elements, there are k pol =1,2,3,4, representing the four Stokes components I, Q, U, and V respectively.

[0070] First, the total walking length data R of all scattering points dis Convert to time series T dis =R dis / c′, where c′ represents the speed of light in water. The two endpoints of the prior neighborhood interval are simultaneously converted into a time series T dis (i ref ,1),T dis (i ref ,j ref ). The time neighborhood integration interval ΔT can be expressed as:

[0071] ΔT=T dis (i ref ,j ref )-T dis (i ref ,1)

[0072] Where T dis (i ref ,1) represents the time series of single scattering of reference photons, T dis (i ref ,j ref ) represents the reference photon j ref (j ref >3) The time series of sub-scattering can be modulated according to the actual simulation design.

[0073] Let matrix To finally process the data to be displayed, j max represents the number of time integration intervals, The first column represents the jth, (j=1,2…j max ) start time of ΔT, The second column represents the jth, (j=1,2…j max ) number of photon scatterings within ΔT, The 3rd to 6th columns are represented as jth, (j=1, 2…j max ) is the sum of the contributions of the four Stokes components I, Q, U, and V of a ΔT photon.

[0074] When you need to get the jth scat When calculating the intensity of the I component of the secondary scattering, first calculate the photon i pho =1,2…nThe contribution of the I component intensity falls in which integral interval in time, the expression is:

[0075]

[0076] In the formula, the function Floor(a) represents the largest integer less than or equal to a. Then the jth photon scat The intensity information R of the secondary scattered I component sig (i pho ,j scat ,1)Write Right now

[0077] D(j,3)=D(j,3)+R sig (i pho ,j scat ,1)

[0078] The number of simultaneous photon scattering j scat Write Then, all photons i pho ,(i pho =1,2…n)According to the above method, we can get Similarly, we get 4-6 columns, and The first column of can be expressed as D(j,1)=j·ΔT. The above method calculates the values ​​of the four Stokes components of each time neighborhood interval ΔT and stores them in the matrix In preparation for processing.

[0079] For multiple target detection simulations, multiple neighborhood intervals can be set. Finally, the Stokes vector S of the mixed beam in any time neighborhood interval ΔT is jIt is equal to the weighted sum of the Stokes vectors of multiple scattered photons received, that is, the following formula holds:

[0080]

[0081] Where N i is the number of photons scattered for the i-th time in the neighborhood, S i is the sum of the Stokes vectors of the photons scattered for the i-th time in the neighborhood

[0082] Since the polarization effect after laser irradiation on underwater targets is related to many factors such as target type, target number, and relative spatial distribution of targets and laser detection systems, this example application carried out typical multi-target detection experiments under three different hydrological conditions. The first experimental scenario is a laboratory pool. Five targets, including fishing nets, plastic fishing lines, ceramic pieces, iron wires, and bubble groups, are placed at a distance of 4m under turbidity water quality of 0.6NTU and 3.2NTU, respectively. The measured light attenuation coefficients of the water bodies are 0.121m-1 and 0.386m-1, respectively. The second experimental scenario is a simulated sea pool. The target groups are fishing nets-ceramic pieces, fishing nets-plastic fishing lines, and fishing nets-iron wires. The front and rear targets in each target group are placed at a distance of 4m and 8m, respectively, under turbidity water quality of 3.2NTU. The measured light attenuation coefficient of the water body is 0.394m-1. The third experimental scenario is a nearshore lake water area with turbidity water quality of 10.89NTU. The target groups are bubble groups-fishing nets-ceramic pieces and bubble groups-fishing nets-iron wires. The targets of each target group are placed at a distance of 2m, 4m, and 8m, respectively, to simulate a typical scenario with multiple tiny mixed obstacles on the laser detection channel. The measured light attenuation coefficient of the water body is 1.348m-1.

[0083] The laser is partially reflected and scattered on the target surface, and partially transmitted through the target, so that each target can be illuminated by the laser. At the same time, according to the values ​​provided by the simulation time-varying model, the detection thresholds of different water qualities and different target receivers can be adjusted. Through indoor microscope lens photography and measurement, it can be seen that the use of microporous ceramic tube pumping can produce bubble groups with a diameter of 200-300μm. Therefore, the bubble scale is set to 200-300μm during the detection process. The test target size is shown in the following table. The experimental system design is as follows Figure 7 shown.

[0084]

[0085] The embodiments of the present invention have achieved some positive effects during the development or use process, and indeed have great advantages over the prior art. The following content is described in conjunction with data, charts, etc. of the experimental process.

[0086] The underwater laser polarization detection and recognition capability is related to multiple parameters such as water quality, target composition, and target characteristics. However, the existing underwater polarization detection model cannot simultaneously meet the combination of theoretical accuracy and real-time and robustness in engineering applications. Aiming at the high robustness extraction and recognition requirements of small target polarization information under the background of multiple scattering of underwater particles and mutual occlusion and interlaced target interference, combined with the current status of underwater target recognition test technology, this invention provides a multi-target laser polarization detection method in a complex underwater environment based on data optimization, and analyzes the system composition and key technical methods. This method can be used in an underwater environment with an attenuation coefficient greater than 0.385m -1 Under water quality, it can detect and identify the material of targets with a diameter greater than 300um within a range of 8m. The system has a simple structure, high recognition efficiency, and a simple recognition method. It can realize real-time data output, which is convenient for operators to timely control the underwater situation. At the same time, it is less affected by changes in the underwater environment (temperature, salinity, turbulence), and can effectively detect multiple targets radially distributed in complex waters with a distance resolution of 20cm. Therefore, it can be widely used in offshore marine target identification, offshore marine disaster warning, underwater unmanned navigation, and underwater robot obstacle avoidance, providing a potential application technology for the fields of ocean profile lidar detection and ocean laser stereo remote sensing.

[0087] In a simulated seawater pool with a water quality of 3.2NTU and the presence of sediment and phytoplankton, the water light attenuation coefficient is 0.394m-1. The fishing net is fixed at a distance of 4m from the detection system, and ceramic pieces, plastic fishing lines, and iron wires are placed in batches at a distance of 6m from the system to form three target groups: fishing net-ceramic pieces, fishing net-plastic fishing lines, and fishing net-iron wires. The polarization characteristics are tested, and the statistical signals are subjected to median filtering, peak extraction, and data normalization. The results are as follows Figure 8 As shown, Figure 8 There are three peaks in each of the four polarization directions in a, 8b, and 8c. The first peak is the sampling reference signal, the second peak is the echo signal of each polarization direction of the fishing net, and the third peak is the echo of each polarization direction of the ceramic piece, plastic fishing line, and iron wire.

[0088] Table 1 Polarization degree of dual target group

[0089]

[0090] Figure 8The results in Table 1 confirm that the linear polarization orientation angle of the scattered light of one of the paired targets still has similar results to the single target results reported in Table 5 (turbidity 3.2 NTU). The DOLP values ​​of the four typical targets used in the experiment are ~0.78 (ceramic), ~1 (iron wire), ~0.4 (plastic fishing line) and ~0.64 (fishing net), respectively. The scattered light emitted by the second target (6m) that is farther away in the paired targets does not interfere with the polarization state of the scattered light emitted by the target (4m) that is closer to the detection system. Therefore, using the proposed pre-processed neighborhood polarization state statistics method, one of the four typical underwater targets can be effectively identified and paired with another target in all three water environments.

[0091] The water quality is 10.86NTU, and the attenuation coefficient is 1.348m -1 In the nearshore lake waters after rain, the bubble generating device was placed at a water depth of 1.5m and 2m away from the detection system. The fishing net was placed at 4m, and the iron wire and ceramic sheet were placed at 6m respectively, forming two typical multi-target groups: bubble group-fishing net-ceramic tile and bubble group-fishing net-iron wire. The polarization characteristics were tested, the statistical signal was median filtered, the peak was extracted, and the data was normalized. The results are shown in the figure below. Fig.10 There are four peaks in each of the four polarization directions in (a) and 10(b). The first peak is the sampling distance reference signal; the second peak is the echo signal of each polarization direction of the bubble group; the third peak is the echo signal of each polarization direction of the fishing net; the fourth peak is the echo signal of each polarization direction of the ceramic sheet and the iron wire. The data are shown in the following table.

[0092] Table 2 Polarization degree of multi-target group

[0093]

[0094] Fig.10 The results in Table 2 confirm that the linear polarization orientation angle of the scattered light from one of the multiple targets still has a similar DOLP value to the single target result reported in Table 5 (turbidity 3.2 NTU) or the paired target result reported in Table 6 (turbidity 3.2 NTU). The DOLP values ​​of the four typical targets used in the experiment are 0.78 (ceramic), 1 (iron wire), 0.55 (bubble), 0.4 (plastic fishing line) and 0.65 (fishing net). Figure 8As shown in the figure, the signal amplitudes of the ceramic wire and the iron wire fluctuate greatly in all four different polarization directions. This is due to the random swinging of the fishing net in the water. The laser beam irradiating different parts of the wavy fishing net will produce different shielding attenuation effects, and further propagate to the ceramic plate and iron wire behind the fishing net. In addition, the scattered echo signals of these strong reflectivity targets will experience random attenuation effects before polarization state measurement. Therefore, when detecting the light scattered by the ceramic plate and the wire target, the linear polarization data deviation can reach 6%. Since the DOLP values ​​of the scattered echoes of a single target are ~0.78 (ceramic), ~1 (iron wire), ~0.55 (bubble), ~0.4 (plastic fishing line) and ~0.65 (fishing net), such a small deviation will not affect the identification of the target by polarization state measurement. Therefore, it is confirmed that the scattered light signals of the second and third targets at farther positions in the multi-target do not interfere much with the polarization state of the scattered light detected by the target at closer position. Therefore, using the proposed pre-processed neighborhood polarization state statistics method, one of the five typical underwater targets grouped with other two different targets in all three water environments can be effectively identified.

[0095] It should be noted that the embodiments of the present invention can be implemented by hardware, software, or a combination of software and hardware. The hardware part can be implemented using dedicated logic; the software part can be stored in a memory and executed by an appropriate instruction execution system, such as a microprocessor or dedicated design hardware. It can be understood by a person of ordinary skill in the art that the above-mentioned devices and methods can be implemented using computer executable instructions and / or contained in a processor control code, such as a carrier medium such as a disk, CD or DVD-ROM, a programmable memory such as a read-only memory (firmware), or a data carrier such as an optical or electronic signal carrier. Such code is provided on the carrier medium. The device and its modules of the present invention can be implemented by hardware circuits such as very large-scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, etc., or programmable hardware devices such as field programmable gate arrays, programmable logic devices, etc., can also be implemented by software executed by various types of processors, and can also be implemented by a combination of the above-mentioned hardware circuits and software, such as firmware.

[0096] The above description is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any modifications, equivalent substitutions and improvements made by any technician familiar with the technical field within the technical scope disclosed by the present invention and within the spirit and principle of the present invention should be covered by the protection scope of the present invention.

Claims

1. A complex hydrological multi-target laser polarization detection device, It is characterized in that The complex hydrological multi-target laser polarization detection device comprises: Laser emission system, laser polarization receiving system, signal control and processing system; Laser emission system: It is composed of a laser generation subsystem, a collimated emission subsystem, and an adjustable optical attenuator. It is effectively strapped down with the power supply and control module. The laser head is controlled by the signal sent by the control system, and it emits a fixed 1KHZ optical signal. After passing through the beam splitter, one beam enters the acquisition storage module as a trigger signal as a reference to the 0 moment. After turning, focusing, and collimating, one beam is emitted through a beam expanding telescope, and finally the optical power is adjusted by a rotating attenuation plate and emitted to the external environment. Laser polarization receiving system: It consists of a laser receiving mirror, a 532nm filter, a beam splitter, a light collecting mirror, and a PMT photodiode. The laser echo emitted by the object passes through a 532nm filter to filter out stray light, is divided into four beams by a beam splitter, and then is focused on the photosensitive surface of the PMT by a light collecting mirror. Signal control and processing system: It is composed of FPGA drive control, AD data acquisition, storage and processing, and host computer program. It is connected to the transmitting and receiving systems to control various parameters of the device and process and output detection data results in real time.

2. The complex hydrological multi-target laser polarization detection device as claimed in claim 1, It is characterized in that The laser emission system consists of a laser, a power supply, a beam expansion and collimation device, and a comprehensive processing and display control module. The laser is connected to the power supply, the beam expansion and collimation system, and the comprehensive processing and display control module respectively, and the beam expansion and collimation system and the comprehensive processing and display control module are connected to a computer host computer.

3. The complex hydrological multi-target laser polarization detection device as claimed in claim 2, It is characterized in that The beam expansion and collimation device realizes the electric focusing function through the computer host computer to control the change of the laser emission beam angle. The comprehensive processing and display control module is used to adjust the laser switch and energy parameters by controlling the current of the driving module and the TEC temperature control module.

4. The complex hydrological multi-target laser polarization detection device as claimed in claim 1, It is characterized in that The laser polarization receiving system is composed of a beam expanding lens group, a beam splitter, a focusing lens, a rotating polarizer, and a PMT detector. The beam expanding ratio of the beam expanding lens group is 5:1; the beam splitting ratio of the beam splitters RP and PP is 0.5 / 0.5; the rotating polarizer L2 adjusts the polarization angle to 0 degrees, the rotating polarizer L3 adjusts the polarization angle to 45 degrees, the rotating polarizer L4 adjusts the polarization angle to 90 degrees, and the rotating polarizer L5 adjusts the polarization angle to 135 degrees; a horizontal light with a diameter of 75 mm is incident through the beam expanding lens group, becomes a diameter of 15 mm, and is incident on the beam splitter. On sheet 1, the beam splitter reflects 50% of the energy and transmits 50% of the energy; the reflected and transmitted light rays are respectively received by the beam splitter PP and incident on the rotating polarizers L2, L3, L4, and L5, and after being polarized by 0, 45, 90, and 135 degrees by the rotating polarizers, they are incident on the focusing lens, and after being focused, they are incident on the PMT photomultiplier tubes D1, D2, D3, and D4; BF is a narrowband filter with a central wavelength of ; L is the axial distance of the receiving system, which is , the diameter of the receiving telescope is 50 mm, the focal length is 20 mm, and the receiving field angle is 2.85°.

5. The complex hydrological multi-target laser polarization detection device as claimed in claim 1, It is characterized in that The signal control and processing system is composed of FPGA drive control, Ethernet communication, and AD sampling processing; sampling ARP protocol and UDP protocol dual protocol communication, and the pins on the GMII receiving side are simultaneously connected to the ARP top-level module and the UDP top-level module.

6. The complex hydrological multi-target laser polarization detection device as claimed in claim 4, It is characterized in that In the PMT detection circuit, the optical signal is converted into photoelectric signals by PMT and TIA, and then processed by a weak voltage signal processing circuit and input into the signal processing platform FPGA.

7. The complex hydrological multi-target laser polarization detection device as claimed in claim 1, It is characterized in that The system further comprises: A laser emitting device, used for emitting pulsed laser to the water body; Polarization receiving system, used to receive polarized photon signals scattered back by water or target; An optical fiber transmission system, used for transmitting the scattered photon signal received by the polarization receiving system to a photomultiplier tube (PMT) gain control system; PMT gain control system, used to adjust laser emission energy, frequency and receiving gain, and obtain the best detection parameters through multiple cumulative measurements; The AD data acquisition and processing system is used to collect and process the signals transmitted by the PMT system. It calculates the echo signal waveform by counting the number of photon scattering times, Stokes vector and photon path information to achieve laser polarization detection of the target.

8. The complex hydrological multi-target laser polarization detection device as claimed in claim 7, It is characterized in that The system further comprises: The data preprocessing module is used to preprocess the data in the AD data acquisition and processing system, extract the linear polarization degree of scattered photons in the near field and far field of the target, determine the number of photons in the statistical neighborhood and calculate the linear polarization degree of the target; The data shaping and correction module is used to convert the time series of photon scattering into the Stokes vector contribution value of each time neighborhood interval based on the vector Monte Carlo method, and accumulate the scattered photon Stokes vector of each target according to the time integration interval to output the laser polarization detection results of multiple targets.

9. A complex hydrological multi-target laser polarization detection method implementing the complex hydrological multi-target laser polarization detection device as claimed in any one of claims 1 to 8, It is characterized in that The complex hydrological multi-target laser polarization detection method comprises: Step 1: The computer host outputs a control instruction to control the laser to output a pulsed laser. The output pulsed laser is incident into the water environment after being collimated. A large number of photons are absorbed or scattered by the water. The scattered photons are received by the polarization receiving system and transmitted to the PMT gain control system through optical fiber. The system collects and processes the light scattering intensity of the natural water body. Through multiple cumulative measurements, and adjusting the laser emission energy, frequency and PMT receiving gain parameters, the optimal emission and receiving system parameters for the measured water area are obtained. Step 2, when the detection equipment performs radial detection on multiple targets in the area, the laser beam composed of a large number of photons collides with the natural water body and the surface of each target, and a large number of photons are absorbed or scattered by the natural water body and bubbles. The scattered photons are received by the polarization receiving system and transmitted to the PMT gain control system through the optical fiber, and the output signal enters the AD data acquisition and processing system; Step 3: After AD data acquisition completes the detection data, the data processing module optimizes the processed data, which is divided into two stages: preprocessing and output.

10. An information data processing terminal, It is characterized in that The information data processing terminal is used to implement the complex hydrological multi-target laser polarization detection device as described in any one of claims 1-8.

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