Multi-layer underwater moving target combined measurement equipment and method

Abstract

The invention belongs to the technical field of marine surveying and mapping and engineering application, and relates to a multi-layer underwater moving target combined measurement device and method. Through the combined measurement equipment and method based on the ultra-short base line and the long base line and a distributed measurement framework under a geodetic coordinate system, high-precision fusion calculation of motion parameters such as the position and the speed of the underwater moving target is realized, a multi-target situation analysis scene under a unified space-time reference condition can be established, and the accuracy of the situation analysis is improved. According to the method, multi-target integrated situation acquisition under multiple working condition dimensions such as horizontal movement, vertical movement, low-speed movement, high-speed movement, a moving target and an underwater environment in an underwater application environment can be realized, and data support and reference basis can be provided for motion state analysis and safety state judgment of the underwater target under an engineering condition; important information foundation support can be provided for digital space mapping underwater operation environment; and practical application support can be provided for a measurement method of multivariate fusion solution.

Description

Technical Field

[0001] The invention belongs to the technical field of ocean surveying and engineering application, and relates to a multi-layer deep-water moving target combined measurement device and method. Background Art

[0002] Underwater moving targets have random movement direction and movement posture. The range of moving targets covers the entire depth range from the water surface to the bottom of the water, involving random movement processes of multiple depths and multiple targets. All of them need to realize the full process positioning of the corresponding targets. Most of the target positioning accuracy is required to reach the sub-meter level. Some targets involve vertical or up and down reciprocating movement processes across multiple depths, which have strong temporal and spatial variation characteristics. It is necessary to realize the trajectory acquisition and situation monitoring of the target movement process. In the past 20 years, the positioning and navigation technology based on hydroacoustic signals has gradually developed. Based on different measurement methods such as ultra-short baselines, short baselines, and long baselines, full sea depth and full precision coverage have been basically achieved. However, the measurement of relevant parameters of underwater moving targets, especially fast-changing targets and targets across multiple depths, has always been a difficult problem in engineering implementation. The corresponding measurement methods are required to be feasible and easy to operate under engineering practice conditions.

[0003] At present, the positioning measurement of underwater moving targets in the marine environment mainly includes two technical methods: one is based on sonar echo measurement technology, which performs real-time reception and processing of directional beam transmitter echo images during the underwater movement of the target to be measured. The echo image contains target information, and then the positioning measurement elements such as target ranging and direction finding are extracted from the acoustic echo image and the solution is completed; the other is the underwater acoustic positioning measurement method based on acoustic beacons, which mainly installs acoustic beacons on the outer surface of the target to be measured, and the beacon sends out a standard sound signal, which is received by long baseline array elements or ultra-short baseline multi-array elements to complete the extraction of positioning measurement elements and positioning parameter solution. Among them, the measurement method based on active sonar technology that uses fixed continuous multi-frame sonar images to identify target motion curves and key motion parameters has an application basis in engineering practice. However, this system is limited by the physical mechanism of sonar imaging and has certain application limitations, which are mainly reflected in the insufficient ability to suppress distance ambiguity, the impact of seawater media on image quality, and the impact of flow field and refraction absorption effects on measurement accuracy. At the same time, due to the influence of image quality, it is difficult to accurately identify and determine the precise position of acoustic reflection points on the target surface, and there are limitations on the high-precision measurement requirements of the target. With the continuous development and application of underwater acoustic positioning technology, the positioning measurement methods based on the acoustic beacon system, that is, the long baseline, ultra-short baseline and other measurement systems, have gradually expanded their application scope and improved their positioning accuracy. Long baseline measurement requires that the receiving array elements be reasonably arranged and have the slant range and arrival delay information of at least 3 array elements. Ultra-short baseline measurement requires the slant range, pitch angle and azimuth information of a single station, which can be analyzed to obtain a unique positioning result, and then the motion trajectory and motion parameters such as speed and attitude are calculated. The above-mentioned measurement equipment and methods require certain redundant measuring station information in engineering applications, and the target position parameters are calculated and estimated through the centroid method, iteration method, least squares method, etc.

[0004] For underwater motion parameter measurement of fast-changing targets and targets across multiple layers of depth, high frame rate transmission and reception mode of acoustic signals, full horizontal and vertical coverage of stereoscopic stations, and overcoming the attenuation effect of acoustic signals affected by cavitation flow fields are required. In order to meet the measurement requirements under the above special working conditions, in recent years, autonomous high-performance positioning acoustic beacons, high-precision benchmark transmission of ocean stations, high-precision measurement station design, and constrained vertical measurement compensation technologies have been developed to support the acquisition of high frame rate and high-precision related parameters of engineering-level underwater sections. With the cross-disciplinary integration and cooperation driven by demand, the complexity of underwater operation scenes continues to increase, and new-quality and new-domain underwater vehicles and moving targets present a development trend and operation requirements of multiple working conditions, high coordination, multiple scenes, and multiple uses. Therefore, it is necessary to combine the currently developed mature and reliable high-precision positioning technology means of underwater targets with sufficient stability in engineering practice to obtain the precise trajectory, position, speed, attitude and other motion parameters of single or multiple vertical high-speed moving targets underwater, so as to provide real-time or quasi-real-time refined motion status of the target. Summary of the invention

[0005] The present invention is to solve the problem of motion parameter measurement of underwater moving targets in multi-layer deep environment and high-precision motion parameter solution based on combined measurement equipment and methods. From the three levels of measurement equipment, measurement method and accuracy evaluation, a combined measurement equipment and corresponding measurement method for motion parameters of underwater moving targets are provided. The present invention is a target cooperative signal receiving solution measurement method suitable for underwater acoustic performance and hydrological environment based on ultra-short baseline and long baseline fusion measurement system, which can ensure that the standard acoustic signal is effectively detected by the receiving array while being able to overcome the harsh mechanical environment conditions. By fusing and solving the measurement results of ultra-short baseline and long baseline, the key motion parameters such as position, speed, trajectory and so on of underwater high-speed moving targets with sub-meter accuracy are obtained. The combined measurement equipment and method can achieve multi-layer deep coverage from the surface of the operating sea area to underwater, and the equipment and method can traverse and be applicable to low-speed or high-speed moving targets. In addition, it can provide equipment foundation and key technical methods for multi-target positioning and situation monitoring in deep-water environment.

[0006] The combined measurement equipment and method require the installation of a cooperative device on the target to emit a standard acoustic signal that can be accurately and synchronously identified by the measurement equipment, and adopt an ultra-short baseline or long baseline measurement system to collect the acoustic signal of the moving target for signal identification and parameter solution. Considering the error caused by the Doppler effect due to the directional randomness of the target's motion trajectory, a three-dimensional spatial stereo measurement formation covering the entire process of the target's underwater motion is constructed. At the same time, in order to overcome the influence of error sources such as ranging error, site error, sound speed error, timing error, array element spacing error, calibration error, and target motion introduction error in the ultra-short baseline and long baseline measurement systems on the accuracy results, it is necessary to identify the error sources under the two measurement systems, form the measurement results under the two measurement systems, compare the measurements and analyze the fusion results, and achieve high-precision measurement of underwater motion parameters.

[0007] The technical solution of the present invention is as follows:

[0008] A combined measurement device for multi-layer deep-water moving targets, comprising an acoustic beacon, an ultra-short baseline array and a long baseline array; the acoustic beacon is installed on the multi-layer deep-water moving target to be measured, the ultra-short baseline array is arranged on a surface operating ship or a surface measurement platform, the ultra-short baseline array is located under the water surface, and the long baseline array is arranged on a bottom-mounted measurement platform located on the seabed; the ultra-short baseline array and the long baseline array jointly receive the acoustic signal emitted by the acoustic beacon, jointly fuse and solve the acoustic signal, and obtain the position of the multi-layer deep-water moving target.

[0009] The acoustic beacons are at least one group of omnidirectional acoustic beacons or two groups of acoustic beacons with an opening angle of 180°.

[0010] A multi-layer deep-water moving target combined measurement method, using the above-mentioned equipment, has the following specific steps:

[0011] Step 1: Under the sea conditions required for the measurement operation, the surface operation vessel or surface measurement platform remains anchored or moving at a constant speed. A GNSS positioning device is installed above the water surface and without obstructions to obtain the position reference data of the ultra-short baseline array. The inertial navigation equipment is installed and ensured to maintain a rigid connection with the surface operation vessel or surface measurement platform. At the same time, the attitude data of the ultra-short baseline array is obtained through satellite navigation. A position with a depth of more than 2 meters below the water surface is selected and rigidly connected to the surface operation vessel or surface measurement platform, and the ultra-short baseline array is installed.

[0012] Step 2: Install a long baseline array at the bottom of the horizontal area where the underwater target moves through a bottom-mounted measurement platform to realize the reception, collection, and real-time processing of acoustic signals; install a timekeeping device on the bottom-mounted measurement platform to achieve time unification at the receiving signal end, and install a position calibration device to eliminate the site errors of each element of the long baseline array and thus realize the calibration of the deployment position.

[0013] Step 3: After the installation and deployment of the ultra-short baseline array and the long baseline array are completed, during the operation, the sound velocity profiler carried by the operation vessel will obtain the sound velocity profile data of the operation sea area at regular intervals to measure the vertical propagation delay error of the sound velocity in the operation sea area.

[0014] Step 4: Use the timing signal provided by the satellite-based high-precision timing module to provide a unified time reference for the acoustic beacons, ultra-short baseline arrays, long baseline arrays, and long baseline arrays of the deep underwater targets to be measured.

[0015] Step 5: The acoustic beacon continuously emits a standard acoustic signal, and the ultra-short baseline array and the long baseline array receive, collect, and store the signals respectively. The ultra-short baseline array calculates in real time and displays the target's geodetic coordinate position, speed and other motion parameters on the operating vessel console in real time. Each element of the long baseline array stores the original acoustic signal received in its own capacity, and obtains the target's motion parameters after subsequent retrieval and calculation.

[0016] Step 6: Before performing multivariate fusion solution using combined measurement, error propagation, identification methods, and error correction analysis are performed. The positioning, velocity measurement, and element measurement results of the ultra-short baseline array and the long baseline array are temporally and spatially aligned. An interactive multi-model adaptive filter is used for fusion solution to obtain the position, velocity, and other motion parameter results of the multivariate fusion solution.

[0017] The beneficial effects of the present invention are as follows: the present invention realizes high-precision fusion solution of motion parameters such as position and speed of underwater moving targets through a combined measurement device and method based on ultra-short baseline and long baseline, and a distributed measurement framework under a geodetic coordinate system, and can establish a multi-target situation analysis scenario under unified time and space reference conditions, and can realize multi-target integrated situation acquisition under multiple working conditions such as horizontal and vertical motion, low-speed motion and high-speed motion, moving targets and underwater environments in underwater application environments, and can provide data support and reference basis for underwater target motion state analysis and safety state judgment under engineering conditions, and can also provide important information basic support for digital space mapping of underwater operating environments; the measurement method and corresponding measurement equipment have a foundation under offshore operation engineering application conditions, and have mature equipment development plans and offshore operation implementation plans from subsystem to full system level, and can provide practical application support for the measurement method of multi-element fusion solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the operation of the measuring device of the present invention.

[0019] Figure 2 It is a working flow chart of the measuring method of the present invention.

[0020] Figure 3 It is the multivariate fusion solution flow chart of the present invention.

[0021] Figure 4 It is a schematic diagram of the installation layout and coordinate conversion of the ultra-short baseline array of the present invention. DETAILED DESCRIPTION

[0022] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but they are not intended to be limiting of the present invention.

[0023] 1. Multi-layer deep underwater moving target combined measurement equipment

[0024] The equipment includes an acoustic beacon, an ultra-short baseline array and a long baseline array; the acoustic beacon is installed on the deep underwater moving target to be measured, the ultra-short baseline array is arranged on a surface operation ship or a surface measurement platform, the ultra-short baseline array is located under the water surface, and the long baseline array is arranged on a bottom measurement platform located on the seabed; the ultra-short baseline array and the long baseline array jointly receive the acoustic signal emitted by the acoustic beacon, jointly solve the acoustic signal, and obtain the position of the deep underwater moving target. The specific introduction is as follows:

[0025] 1. Acoustic beacons

[0026] Acoustic beacons are installed on deep underwater targets. Their design should conform to the target's installation structure, have the acoustic performance required by the measurement accuracy indicators, and be able to emit acoustic signals that can be effectively detected under real working conditions and environmental conditions.

[0027] Acoustic performance design: In terms of working frequency band selection, the requirements of measurement accuracy and reliable propagation in underwater measurement environments should be taken into account, and the appropriate frequency band should be selected with reference to the current mainstream ultra-short baseline positioning equipment; in terms of transmitting sound source level design, consideration should be given to achieving a high signal-to-noise ratio within the effective receiving range of the ultra-short baseline array and the long baseline array, while considering the energy attenuation factor of the acoustic signal in water, which can be calculated based on the sonar equation; in terms of directivity design, the acoustic signal receiving coverage range of the ultra-short baseline array and the long baseline array should be considered, and at least one set of omnidirectional or two sets of 180° opening angle acoustic beacons can be installed on the target surface according to the external dimensions of the beacon to ensure omnidirectional coverage of underwater acoustic signal reception.

[0028] Signal coding design: It is necessary to balance the reliability of signal transmission and reception with the available data frame rate. For targets, the underwater movement section is generally short in duration, requiring the equipment to transmit acoustic signal coding with the characteristics of high frame rate, low pulse width, short period, high reliability and low bit error. At the same time, in order to ensure that adjacent signals can be distinguished, the acoustic beacon pulse signal adopts adjacent signal orthogonalization design.

[0029] Environmental adaptability design: The movement of underwater moving targets is accompanied by a large impact inertia. To ensure that the transmitting transducer can work normally under complex mechanical environmental conditions, the transmitting transducer should be designed to be impact-resistant, with a rigid structure installed externally and a vibration reduction device installed internally. The radiating surface should be sealed with special materials.

[0030] 2. Ultra-short baseline array

[0031] The surface measurement platform is the installation carrier and measurement coordinate system benchmark of the ultra-short baseline acoustic array. In order to obtain high-precision measurement data, it is necessary to accurately measure the motion parameters of the surface measurement platform, reliably detect the cooperative acoustic signals, and reliably identify and effectively control the error sources.

[0032] Surface measurement platform positioning: High-precision satellite navigation positioning equipment can be installed on the surface measurement platform, and the installation position error between the array center and the satellite antenna center can be calibrated. The ultra-short array measurement equipment needs to be rigidly connected to the measurement platform to obtain the accurate origin of the measurement coordinate system.

[0033] Attitude measurement of water surface measurement platform: The attitude change of the measurement platform has a great influence on the ultra-short baseline measurement. High-precision attitude sensors can be installed on the water surface measurement platform, and high-precision attitude angle parameters can be obtained through GPS or DVL assistance to achieve effective correction of attitude measurement parameters.

[0034] Time synchronization control: In order to achieve reliable detection of cooperative acoustic signals by the ultra-short array, and the motion parameter measurement results are solved by delay parameters, the signal transmitter and the signal receiver need to perform time synchronization control. Time signal synchronization and calibration can be performed at the acoustic beacon transmitter and the ultra-short array receiver. The synchronization calibration error should be in the millisecond level.

[0035] 3. Long baseline array

[0036] Unlike the ultra-short baseline array, the long baseline array elements do not have the conditions for cable control. They are arranged in a certain formation on the bottom measurement platform and adopt a self-contained design. They receive the standard acoustic signals emitted by the acoustic beacon and store them in the storage module of the acquisition control unit. After the equipment is recovered, the signal preprocessing and parameter solution are performed. Accurate calibration of its own position and identification and control of error sources are the key to achieving high-precision measurement.

[0037] Self-contained bottom-mounted measurement platform: The long baseline measurement array element is mounted on the bottom-mounted platform and pre-deployed on the seabed of the target activity sea area according to the measurement formation. It adopts anti-trawling, anti-corrosion, and anti-biological attachment designs, and has built-in power supply modules, synchronous timing modules, data acquisition modules, recovery control modules and other equipment.

[0038] Precise calibration of deployment position: After the bottom-mounted measurement platform is deployed on the seabed, the actual bottom-mounted position will be horizontally displaced from the surface deployment point due to the shear of the underwater vertical profile current. At the same time, the uncertainty of the deployment position on the seabed will cause site errors. It is necessary to carry out precise calibration of the bottom-mounted platform position in coordination with the surface measurement platform.

[0039] Timing error control: In order to achieve reliable detection of cooperative acoustic signals by each array element of the long baseline, and the motion parameter measurement results are solved through delay parameter solution and consistent with the ultra-short baseline, the signal transmitting end and the signal receiving end need to perform time synchronization control. Since the long baseline array elements are pre-deployed at the seabed measurement points for self-contained operation, a high-precision timing module can be built in. Before the operation, the array element timing module is timed by the precise timing unit. During the operation, the timing error is controlled by the timing module, and the time offset during the operation is read afterwards for time error correction to ensure that the time drift error is within an acceptable range.

[0040] In this embodiment, the combined measuring device is as follows: Figure 1 As shown, by installing an acoustic beacon outside the target to be measured to emit a standard acoustic signal, the ultra-short array equipment and the long baseline array element measurement equipment receive the standard acoustic signal of the target to be measured, and the key parameters such as the underwater motion position, speed, trajectory, etc. of the target to be measured can be solved respectively by the ultra-short baseline and long baseline positioning methods. At the same time, the multivariate data based on the above two methods are fused and solved to obtain the high-precision motion parameter measurement results under this measurement system method.

[0041] An acoustic beacon is installed outside the body of the target to be measured. The target to be measured can be described as a vertical or horizontal, low-speed or high-speed moving object of different sizes underwater. At least one group of omnidirectional or two groups of acoustic beacons with an opening angle of 180° are installed on its surface according to the external dimensions of the beacon, so as to meet the condition that the target to be measured emits a prefabricated fixed-coding format acoustic signal in a horizontal omnidirectional manner. At the same time, the signal is set to trigger a response working mode for periodic transmission, so that the ultra-short base array or long baseline array element can obtain the ranging delay information of the target.

[0042] The ultra-short baseline array and the long baseline array are designed with acoustic signal receiving and data processing measurement modules based on corresponding measurement systems. The ultra-short baseline array equipment includes an acoustic receiving array, GNSS positioning, Doppler speed measurement equipment, attitude measurement equipment, a time control module, etc. The long baseline array element measurement equipment can be described as a bottom-seated self-contained working mode. Multiple seabed working array elements form a long baseline formation through the bottom-seated structure of the bottom-seated measurement platform. Each formation includes a receiving array, a power supply module, a sound velocity profiler, a time control module, etc.

[0043] Through the time calibration and synchronization control of the transmitting and receiving ends, the ultra-short baseline array is integrated with the attitude sensor, Doppler speed measuring equipment, and GNSS positioning equipment. The acquired high-precision positioning, speed, and attitude data are used to participate in the underwater acoustic positioning signal solution, and the high-precision positioning results and time synchronization signals on the water surface are transmitted to the underwater to obtain the precise position, speed and other motion parameter results of the underwater moving target.

[0044] 2. Multi-layer deep underwater moving target combined measurement method

[0045] The method described is mainly based on the measurement system of cooperative acoustic equipment. The measurement system has two key elements: one is the signal transmitting end, that is, the acoustic beacon. The key to the design is to ensure that it reliably emits a detectable standard acoustic signal; the other is the signal receiving end, that is, the receiving array. The key to the design is to reasonably construct an optimized measurement array in the area where the standard acoustic signal can be effectively detected to support high-precision measurement results.

[0046] Considering that the acoustic beacon is installed on the head of the target, there are two options for the deployment of the receiving array: one is to deploy it on the carrier platform, and always maintain a relatively stable relative distance with the target before the launch. Such platforms should adopt an ultra-short baseline measurement system to achieve accurate positioning of the target and the carrier platform; the other is to deploy it on the seabed of the test sea area, and form a long baseline measurement system composed of multiple array elements to obtain multiple sets of slant range and radial velocity information, and then realize the calculation of position and velocity parameters. These two systems are both independent and redundant and complementary to each other, which can provide a basis for post-fusion processing.

[0047] 1. Ultra-short baseline system

[0048] The ultra-short baseline system uses the time delay and phase difference of the standard acoustic signal reaching each array element to solve the target position parameters. The installation position of the receiving array can be selected from the underwater measurement platform or the surface measurement platform. From the perspective of the array position, the former is an "upward-looking" measurement, and the latter is a "downward-looking" measurement. The movement process of the underwater moving target is a high-speed vertical movement. The acoustic signal emitted by the target is received by the receiving array element and needs to cover multiple depths from the bottom of the water to the surface. Since the long baseline array elements are arranged in the horizontal operating range of the seabed, the ultra-short receiving array is installed on the surface measurement platform, which is more conducive to the reception of standard acoustic signals. The surface measurement platform can obtain the precise position and elevation information of the measurement coordinate system by installing a high-precision GPS; in addition, the attitude change of the surface measurement platform during navigation is random, and a high-precision attitude sensor needs to be installed and relevant data needs to be recorded in real time to realize its attitude correction during the measurement process. Under the existing technical conditions, the measurement accuracy of the mainstream ultra-short baseline hydroacoustic positioning equipment can reach 3‰ slant distance, so the distance between the target to be measured and the center position of the ultra-short array can achieve a distance measurement accuracy better than the meter level within the range of 100 meters.

[0049] 2. Long baseline system

[0050] The long baseline system mainly calculates the position of the acoustic beacon by measuring the time delay information of more than three groups of received signals. At the same time, each measuring element can measure the radial velocity using the Doppler velocity measurement principle, and then obtain the velocity parameters through intersection calculation. During the measurement operation, each array element is independently distributed and pre-deployed on the seabed of the measurement operation area with a submerged buoy or a bottom-mounted platform as a carrier according to a certain geometric configuration. Each bottom-mounted measurement platform is pre-installed with a high-precision timing module to achieve the consistency of the timing information between the receiving end and the transmitting end. After the deployment is completed, all array elements need to be calibrated one by one with high precision to obtain sub-meter position information. Similarly, the long baseline ranging within the 100-meter measurement range can achieve a measurement accuracy of 3‰ slant range. Through the formation optimization design of the array element combination, the measurement accuracy capability of the target to be measured can be better than the meter level.

[0051] 3. Measurement element error control

[0052] For underwater moving targets, the accuracy index of their motion parameter measurement is an important reference index for verifying the capability of the measurement equipment. The equipment and methods based on the ultra-short baseline and long baseline combined measurement system are quite different from the conventional horizontal low-speed moving target measurement method, and it is necessary to make adaptive improvements to the ultra-short baseline and long baseline methods. Therefore, it is necessary to propose reasonable measurement accuracy index requirements based on the characteristics of the two measurement methods and equipment, and use system modeling and simulation methods to systematically analyze the measurement model, parameter solution and error transmission process of the measurement elements to obtain a comprehensive measurement element error impact effect. At the same time, the various error sources of the measurement elements are effectively controlled to achieve the high-precision measurement requirements under the combined measurement equipment and methods.

[0053] For the ultra-short baseline measurement method, the main measurement elements are delay error and delay difference error. The key to this error control is to obtain a high signal-to-noise ratio. In addition, the ultra-short array coordinate system is called the array coordinate system. In the process of converting from this coordinate system to the geodetic coordinate system, high-precision auxiliary measurement of the position and attitude parameters of the surface measurement platform is required to realize the correction and control of coordinate conversion errors. For the long baseline measurement method, the main measurement element of positioning measurement is the delay error. The key to error control is to ensure that more than three measuring elements reach the set signal-to-noise ratio, and there is a high-precision timekeeping module to ensure time synchronization. When the delay information is converted into the measured slant distance, the sound velocity profile of the sea area needs to be measured to correct the sound velocity error. In addition, the underwater station location of each measuring element must be calibrated to control the station error. The main measurement element of velocity measurement is Doppler frequency shift. The radial velocity of the target relative to each measuring element is calculated, and the target velocity parameters are obtained through intersection solution. The key to error control is to ensure that more than three measuring elements reach the set signal-to-noise ratio and effectively control time synchronization error, sound velocity error, station error, etc.

[0054] The measurement method of this embodiment is as follows Figure 2 and Figure 3 As shown, the following steps are included:

[0055] The multi-layer deep underwater moving target combined measurement device and method specifically comprises the following steps:

[0056] Step 1: Under the sea conditions required for the measurement operation, the surface operation ship or surface measurement platform remains anchored or moving at a constant speed. A GNSS positioning device is installed at a suitable position above the water surface and without obstructions to obtain high-precision position reference data. The inertial navigation device is installed and ensures that it is rigidly connected to the surface operation ship or surface measurement platform. At the same time, high-precision satellite navigation data is used to obtain high-precision attitude data. A position with a depth of more than 2 meters below the water surface is selected and rigidly connected to the surface operation ship or surface measurement platform. A fixed formation ultra-short array unit with a five-element plane or three-dimensional formation is installed to form an ultra-short baseline array measurement equipment deployment plan;

[0057] Step 2: Construct a long baseline array at the bottom of the horizontal area where the underwater target moves. There are no cable control conditions. The matrix is ​​composed of multiple array elements designed by calculation. Each array element works self-contained. The measurement and working loads can be carried by a bottom-mounted, anti-off-grid, split-structure bottom-mounted measurement platform. A high-precision timekeeping device is installed to achieve unified time at the receiving signal end. A long baseline array is installed to realize the reception, collection, and real-time processing of acoustic signals. A position calibration device is installed to eliminate the site error of each array element and thus achieve high-precision calibration of the deployment position.

[0058] Step 3: After the installation and deployment of the ultra-short baseline equipment and the submarine long baseline equipment on the surface operation vessel or surface measurement platform, during the operation, the sound velocity profiler carried by the operation vessel will obtain the sound velocity profile data of the operation sea area at intervals of 6 hours to realize the measurement of the vertical propagation delay error of the sound velocity in the operation sea area.

[0059] Step 4: Use the timing signal provided by the satellite-based high-precision timing module to provide a unified time reference for the target acoustic signal transmitter (acoustic beacon), ultra-short baseline array and long baseline array.

[0060] Step 5: The acoustic signal transmitting device of the target to be measured continuously emits a standard acoustic signal, and the ultra-short baseline array and the long baseline array respectively receive, collect and store the signals. Among them, the ultra-short baseline array can solve and display the target's geodetic coordinate position, speed and other motion parameters in real time on the operating vessel console in real time. Each array element of the long baseline array stores the received original acoustic signal in its own capacity, and obtains the target's motion parameters after subsequent retrieval and solution.

[0061] Step 6: Before the fusion solution is performed by combined measurement, error propagation, identification method and error correction analysis are performed, and the ultra-short baseline and long baseline positioning, velocity measurement and element results are temporally and spatially registered. The interactive multi-model adaptive filter is used for fusion solution to obtain the fused solution results of position, velocity and other motion parameters.

[0062] The specific method of fusion solution is as follows:

[0063] The fusion solution method extracts and solves the measurement elements of the measurement data to perform multi-measurement element parameter fusion solution, which is suitable for solving the motion parameters of the target to be measured by the acoustic beacon sounding, ultra-short baseline and long baseline combined measurement method in the present invention.

[0064] (1) Fusion solution model

[0065] The multi-measurement fusion position solution can be expressed as X=X0+ΔX, where X0 represents the initial value of the target position, and ΔX represents the relative position error between the measured value and the initial value of the target position. For this model, the slant range vector value can be solved using the time delay information of multiple groups of sound arrivals, and then the Gauss-Newton method is used for iterative solution. The solution process can be described as obtaining the target position based on the updated target position initial value and random error through an iterative calculation, and using it as the target position initial value for the next iteration. After multiple iterative solutions, the exit criterion for the end of the iteration can be determined according to the accuracy requirements, which is generally that the difference between the position results of the current iteration step and the previous iteration step is not greater than the required accuracy.

[0066] The matrix expression of relative position error is:

[0067] ΔX=(J T J)-1 J T ΔR

[0068] in:

[0069]

[0070] Where J represents the Jacobian matrix or direction cosine matrix, J1 represents the long baseline Jacobian matrix, J2 represents the ultra-short baseline Jacobian matrix, ΔR represents the measurement function deviation of the slant distance measurement elements of N long baseline measurement points and the RAE measurement elements of M ultra-short baseline measurement points, ΔR1~ΔR N Indicates the deviation of the slope distance measurement element of N long baseline measurement points, (ΔR N+1 , ΔA N+1 , ΔE N+1 )~(ΔR N+M , ΔA N+M , ΔE N+M ) represents the measurement function deviation of the RAE measurement elements of M ultra-short baseline measurement points.

[0071] in:

[0072]

[0073] Among them, l, m, and n represent the ratio of the difference components of each measuring point of the long baseline and ultra-short baseline in the three directions of x, y, and z to the slant distance R0 of the initial position measurement, and A and E represent the azimuth and elevation angle of each direction of the ultra-short baseline measuring point, respectively. The difference expression between the target position point and the measured value in each direction of the i-th measuring point of the long baseline is: The difference between the target position point and the measured value in the jth direction of the ultra-short baseline is expressed as follows:

[0074]

[0075] (2) Error analysis

[0076] For ultra-short baseline and long baseline measurement systems, the main error sources include ranging error and site error, which can be specifically divided into sound velocity error, timing error, array element spacing error, attitude error, calibration error, error introduced by target motion, etc.

[0077] ① Equipment installation error: Installation error is a random error. For acoustic beacons, an appropriate location is selected for installation according to the external structure of the target to be measured. Generally, a fixed position rigid connection is selected. Assuming that the acoustic beacon is accurately installed at a fixed position of the target to be measured and the coordinates are known, this error can be ignored. For ultra-short arrays, the transmitting and receiving array element structures are integrated into one. The wet-end and dry-end equipment are installed on the surface operating vessel or operating platform through a rigid fixed connection. Each receiving array element needs to be calibrated and adjusted after installation. The calibration angle error is relatively small, about 0.02°, and the mechanical installation error can be ignored. For submarine long-baseline array elements, the array elements are placed at a fixed position on the seabed through the bottom-sitting self-contained working mode. It is necessary to use high-precision surface equipment to calibrate the underwater points. The error source is mainly the array element calibration error. The array element's load equipment is rigidly connected to the deployment and recovery bracket equipment, and its installation error can also be ignored.

[0078] ②Sound velocity error: This error source will cause the ranging error between the array element and the target. The mathematical expression is the integral of the sound velocity error in the entire sound propagation process. Among them, Δc(t) represents the sound speed error value at time t. It can be seen that the effect of the sound speed error on the ranging error is related to the sound propagation time. The sound speed error can be regarded as a function of the distance change, or simply as a linear function. The farther the target is from the beacon, the greater the effect of the sound speed error. In addition, the sound speed error will affect the wavelength of the signal, thereby causing an error in the angle measurement between the line connecting the transponder and the interrogator and the coordinate axis. The effect on the wavelength can be written as Where Δc max It is the maximum difference between the true value and the measured value during the signal propagation process, and f0 is the frequency of the signal. The empirical data estimate of the sound velocity error is about 1‰. In order to reduce the influence of the sound velocity error, high-precision SVP can be used for on-site measurement.

[0079] ③ Delay error: The delay error is a Gaussian distribution noise error term that is only related to the signal-to-noise ratio of the signal. It mainly includes the fixed error and random error of the system platform. The fixed error refers to the filtering delay caused by the transducer and various levels of circuits. Generally, the system fixed error can be accurately corrected under laboratory conditions; the random error refers to the measurement error caused by random noise in the process of signal detection and delay estimation.

[0080] ④ Site error: The site error is mainly the site error term of each element of the ultra-short baseline array and the long baseline. For the ultra-short baseline positioning measurement system, the ultra-short array is rigidly connected to the surface platform, and it is necessary to obtain the precise point information and attitude data of the ultra-short array. The implementation method of the present invention is to achieve a positioning accuracy better than 10cm by installing a high-precision differential GNSS receiving device on the surface platform, and to achieve an attitude measurement accuracy of 0.01° by installing a high-precision, high-sensitivity, and high-resolution attitude sensor. During the measurement process, in order to obtain the geodetic coordinate system position information of the ultra-short array, it is necessary to first convert it into the position coordinates under the surface platform coordinate system, and then combine the GNSS and attitude data to achieve the transmission of high-precision surface position;

[0081] ⑤ Error introduced by target motion: For the long baseline measurement system, under the actual measurement environment, due to the slow propagation speed of sound, the time difference between the target sound signal and different underwater array elements is as much as several seconds. During this time difference, the position of the target has changed. Therefore, even if there is no ranging error, the intersection equation is unsolvable, and the positioning result obtained is only an approximate solution of the least squares. At this time, the error model is still regarded as the ranging information obtained by the target at the same position with an error, but under the actual sea trial conditions, the target's movement speed is much different from the speed of sound, and the time difference caused by the speed of sound causes a small change in the target position, so this error can be ignored.

[0082] (3) Accuracy evaluation

[0083] ① Distance measurement accuracy

[0084] The ultra-short baseline positioning measurement adopts the synchronous working mode, and the ranging error ΔR can be estimated according to the following formula:

[0085] ΔR=Δc·t+c·Δt (1)

[0086] For the sound speed environment in a certain offshore area, the sound speed value can be assumed to be a constant value, and the sound speed c = 1500m / s. The maximum slant distance between the target to be measured and the receiving array is R, and the corresponding propagation time can be calculated as R / c. Through high-precision SVP measurement and correction processing, the equivalent calculation value of the sound speed error, the target direct delay estimation error value, and the acoustic signal synchronization delay error value can be obtained. Substituting the above values ​​into the ranging error calculation formula, the ranging error value under the corresponding working conditions can be estimated.

[0087] ②Direction finding accuracy

[0088] Under the plane wave approximation condition, the time delay τ of the acoustic signal reaching different elements on the receiving array can be expressed as:

[0089]

[0090] Where c is the speed of sound, d is the length of the baseline, and α is the baseline angle, i.e., the angle between the line connecting the acoustic signal to the primitive and the baseline. For ultra-short baselines, since the baseline length is usually less than 1 meter, the sound speed error calculated by using the acoustic path difference during the propagation delay of the acoustic signal can be ignored. For long baselines, the baseline length is usually in the order of hundreds of meters to several kilometers, and the sound speed error needs to be considered. The direction finding error Δα can be estimated according to the following formula:

[0091]

[0092] For a typical acoustic field environment, the sound speed c = 1500m / s, the horizontal and vertical baseline lengths of the base array can be measured according to the relative position relationship of the array, the baseline level can be determined according to the heading deviation angle of the surface platform, and the vertical deviation angle of the baseline is generally about 90°; under high signal-to-noise ratio conditions, the estimated error value of the delay difference is usually in the order of microseconds. Substituting the above values ​​into the above formula, the direction finding errors obtained using the horizontal baseline and vertical baseline under this working condition can be estimated.

Claims

1. A multi-layer deep underwater moving target combined measurement device, characterized in that: The multi-layer deep-water moving target combined measurement equipment comprises an acoustic beacon, an ultra-short baseline array and a long baseline array; the acoustic beacon is installed on the multi-layer deep-water moving target to be measured, the ultra-short baseline array is arranged on a surface operating vessel or a surface measurement platform, the ultra-short baseline array is located under the water surface, and the long baseline array is arranged on a bottom measurement platform located on the seabed; the ultra-short baseline array and the long baseline array jointly receive the acoustic signal emitted by the acoustic beacon, jointly fuse and solve the acoustic signal, and obtain the position of the multi-layer deep-water moving target.

2. A multi-layer deep underwater moving target combined measurement device according to claim 1, characterized in that: The acoustic beacons are at least one group of omnidirectional acoustic beacons or two groups of acoustic beacons with an opening angle of 180°.

3. A multi-layer deep underwater moving target combined measurement method, using the device described in claim 1 or 2, characterized in that: The specific steps are as follows: Step 1: Under the sea conditions required for the measurement operation, the surface operation vessel or surface measurement platform remains anchored or moving at a constant speed. A GNSS positioning device is installed above the water surface and without obstructions to obtain the position reference data of the ultra-short baseline array. The inertial navigation equipment is installed and ensured to maintain a rigid connection with the surface operation vessel or surface measurement platform. At the same time, the attitude data of the ultra-short baseline array is obtained through satellite navigation. A position with a depth of more than 2 meters below the water surface is selected and rigidly connected to the surface operation vessel or surface measurement platform, and the ultra-short baseline array is installed. Step 2: Install a long baseline array at the bottom of the horizontal area where the underwater target moves through a bottom-mounted measurement platform to receive, collect, and process acoustic signals in real time; install a timekeeping device on the bottom-mounted measurement platform to unify the time of the receiving signal end, and install a position calibration device to eliminate the station error of each element of the long baseline array and thus realize the calibration of the deployment position; Step 3: After the installation and deployment of the ultra-short baseline array and the long baseline array are completed, during the operation, the sound velocity profiler carried by the operation ship obtains the sound velocity profile data of the operation sea area at regular intervals to achieve the measurement of the vertical propagation delay error of the sound velocity in the operation sea area; Step 4: Use the time signal provided by the satellite-based high-precision timing module to provide a unified time reference for the acoustic beacon, ultra-short baseline array, long baseline array, and long baseline array of the deep underwater target to be measured; Step 5: The acoustic beacon continuously emits a standard acoustic signal, and the ultra-short baseline array and the long baseline array receive, collect, and store the signal respectively. The ultra-short baseline array calculates in real time and displays the target's geodetic coordinate position, speed and other motion parameters on the operating vessel console in real time. Each element of the long baseline array stores the original acoustic signal received in its own capacity, and obtains the target's motion parameters after subsequent retrieval and calculation. Step 6: Before performing multivariate fusion solution using combined measurement, error propagation, identification methods, and error correction analysis are performed. The positioning, velocity measurement results of the ultra-short baseline array and the long baseline array are temporally and spatially aligned. An interactive multi-model adaptive filter is used for fusion solution to obtain the position and velocity motion parameter results of the multivariate fusion solution.

4. A multi-layer deep underwater moving target combined measurement method according to claim 3, characterized in that: In step six, the specific method of fusion solution is as follows: The multi-measurement fusion position solution model is expressed as X=X0+ΔX, where X0 represents the initial value of the target position, and ΔX represents the relative position error between the measured value and the initial value of the target position. For this model, the slant range vector value is solved using the time delay information of multiple groups of sound arrivals, and then the Gauss-Newton method is used for iterative solution. The solution process is described as obtaining the target position based on the updated target position initial value and random error through one iterative calculation, and using it as the target position initial value for the next iteration. After multiple iterative solutions, the exit criterion for the end of the iteration can be determined according to the accuracy requirements. The matrix expression of relative position error is: ΔX=(J T J) -1 J T ΔR in: Where J represents the Jacobian matrix or direction cosine matrix, J1 represents the long baseline Jacobian matrix, J2 represents the ultra-short baseline Jacobian matrix, ΔR represents the measurement function deviation of the slant distance measurement elements of N long baseline measurement points and the RAE measurement elements of M ultra-short baseline measurement points, ΔR1~ΔR N Indicates the deviation of the slope distance measurement element of N long baseline measurement points, (ΔR N+1 , ΔA N+1 , ΔE N+1 )~(ΔR N+M , ΔA N+M , ΔE N+M ) represents the measurement function deviation of the RAE measurement elements of M ultra-short baseline measurement points; in: Among them, l, m, and n represent the ratio of the difference components of each measuring point of the long baseline and ultra-short baseline in the three directions of x, y, and z to the slant distance R0 of the initial position measurement, and A and E represent the azimuth and elevation angle of each direction of the ultra-short baseline measuring point, respectively. The difference expression between the target position point and the measured value in each direction of the i-th measuring point of the long baseline is: The difference between the target position point and the measured value in the jth direction of the ultra-short baseline is expressed as follows:

5. A multi-layer deep underwater moving target combined measurement method according to claim 3, characterized in that: In step six, the error analysis includes sound velocity error, timing error, array element spacing error, attitude error, calibration error and error introduced by target motion.

6. A multi-layer deep underwater moving target combined measurement method according to claim 3, characterized in that: In step six, the accuracy assessment includes ranging accuracy and direction finding accuracy.

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