A Multilayer Combined Measuring Device and Method for Deep - underwater Moving Targets

Abstract

The present invention belongs to the technical field of marine surveying and mapping and engineering applications, and relates to a combined measurement device and method for multi-layer underwater moving targets. Through a combined measurement device and method based on ultra-short baseline and long baseline, as well as a distributed measurement framework in the geodetic coordinate system, the present invention realizes high-precision fusion solution of motion parameters such as the position and velocity of underwater moving targets, can establish a multi-target situation analysis scenario under unified spatio-temporal reference conditions, can realize the acquisition of multi-target integrated situation in multiple working condition dimensions such as horizontal and vertical movements, low-speed and high-speed movements, moving targets and underwater environments in the underwater application environment, can provide data support and reference basis for the analysis of the motion state and the discrimination of the safety state of underwater targets under engineering conditions, and can also provide important information basic support for mapping the underwater operation environment in the digital space; it can provide practical application support for the measurement method of multi-source fusion solution.

Description

Technical Field

[0001] The present invention belongs to the technical field of marine surveying and mapping and engineering applications, and relates to a multi-layer underwater moving target combined measurement device and method. Background Art

[0002] Underwater moving targets have randomness in motion direction and motion attitude. The activity range of moving targets covers the entire depth range from the water surface to the bottom, involving the random motion process of multiple layers of deep multi-targets. The whole process positioning of corresponding targets needs to be realized. The positioning accuracy of most targets is required to reach the sub-meter level. Some targets involve vertical or up-and-down reciprocating and other cross-multiple depth motion processes, with strong time and space variation characteristics, and the trajectory acquisition and situation monitoring of the target motion process need to be realized. In the past 20 years, the positioning and navigation technology based on underwater acoustic signals has gradually developed. Based on different measurement methods such as ultra-short baseline, short baseline, and long baseline, full-depth and full-precision coverage has been basically achieved. However, the measurement of relevant parameters of underwater moving targets, especially fast-changing targets and cross-multiple depth targets, has always been a difficult problem in engineering implementation. The corresponding measurement methods require practicability and easy operation under engineering practice conditions.

[0003] Currently, the positioning and measurement of underwater moving targets in the marine environment mainly include two technical methods: one is based on sonar echo measurement technology. During the underwater movement of the target to be measured, the echo image of the directional beam transmitter is received and processed in real time. 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 calculation is completed; the other is the underwater acoustic positioning measurement method based on acoustic beacons. It mainly installs acoustic beacons on the outer surface of the target to be measured. The beacons emit standard acoustic signals, and the signals are received by long baseline array elements or ultra-short baseline multi-array elements, and the extraction of positioning measurement elements and the calculation of positioning parameters are completed. Among them, the measurement method based on active sonar technology for identifying the target motion curve and key motion parameters using fixed continuous multi-frame sonar images has an application basis in engineering practice. However, this system has certain application limitations due to the physical mechanism of sonar imaging, mainly reflected in aspects such as insufficient ability to suppress range ambiguity, the influence of seawater medium on image quality, the influence of flow field and refraction absorption effects on measurement accuracy, etc. At the same time, it is difficult to accurately identify and determine the position of the precise acoustic reflection point on the target surface due to image quality, which has limitations for 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, such as long baseline and ultra-short baseline measurement systems, have gradually expanded their application scope and gradually improved their positioning accuracy. Long baseline measurement requires reasonable layout of receiving array elements and slant range and arrival time delay information of at least 3 or more array elements. Ultra-short baseline measurement requires slant range, elevation angle, and azimuth angle information of a single station, and then a unique positioning result can be obtained, and then the motion trajectory, speed, attitude and other motion parameter results can be calculated. The above measurement equipment and methods require certain redundant station information in engineering applications, and the target position parameters are calculated and estimated through methods such as the centroid method, iterative method, and least squares method.

[0004] For the measurement of underwater motion parameters of similar fast-changing targets and targets spanning multiple depths, it is required to have a high frame rate transmission and reception mode of acoustic signals, a horizontal and vertical full-coverage three-dimensional layout of stations, and to overcome the attenuation effect of acoustic signals affected by the cavitation flow field. To meet the measurement requirements under the above special working conditions, in recent years, technologies such as autonomous high-performance positioning acoustic beacons, high-precision reference transfer of ocean stations, high-precision measurement layout design, and constrained vertical measurement compensation have been developed, which can support the acquisition of high frame rate and high-precision related parameters in the underwater section at the engineering level. With the multi-disciplinary cross-integration cooperation driven by demand, the complexity of underwater operation scenarios is increasing continuously. New types of underwater vehicles and moving targets in new fields show a development trend and operation requirements of multi-working conditions, high coordination, multi-scenarios, and multi-uses. Therefore, it is necessary to combine the currently developed, mature, reliable, and fully stable underwater target high-precision positioning technology means in engineering practice to obtain the precise trajectory, position, speed, attitude and other motion parameters of single or multiple vertically moving underwater targets, so as to provide the real-time or quasi-real-time refined motion situation of the target. Summary of the Invention

[0005] The present invention aims to solve the problems of measuring the motion parameters of underwater moving targets in a multi-layer deep environment and calculating the high-precision motion parameters based on a combined measurement device and method. Considering from three levels: measurement device, measurement method, and accuracy evaluation, a combined measurement device for the motion parameters of underwater moving targets and the corresponding measurement method are provided. The present invention is a target cooperative signal receiving and calculating measurement method based on the fusion measurement system of ultra-short baseline and long baseline, which is applicable to underwater acoustic performance and hydrological environment. It can ensure that the standard acoustic signal is effectively detected by the receiving array while overcoming the harsh mechanical environment conditions. By fusing and calculating the measurement results of the ultra-short baseline and long baseline measurement elements, key motion parameters such as the position, velocity, and trajectory of underwater high-speed moving targets with sub-meter accuracy can be obtained. The combined measurement device and method can achieve multi-layer deep coverage from the water surface to underwater in the operation sea area, and the device and method can be applicable to low-speed or high-speed moving targets. In addition, it can provide the equipment basis and key technical methods for multi-target positioning and situation monitoring in deep water environments.

[0006] For the combined measurement device and method, a cooperative device needs to be installed on the target to emit a standard acoustic signal that can be accurately synchronized and identified by the measurement device, and the ultra-short baseline or long baseline measurement system is used to collect the acoustic signals of the moving target for signal identification and parameter calculation. Considering the errors caused by the Doppler effect due to the randomness of the target motion trajectory direction, a three-dimensional space stereo measurement array covering the entire underwater motion process of the target is constructed. At the same time, to overcome the influence of error sources such as ranging error, station location error, sound speed error, time measurement error, array element spacing error, calibration error, and error introduced by target motion on the accuracy result in the ultra-short baseline and long baseline measurement systems, it is necessary to identify the error sources in the two measurement systems, form the measurement results in the two measurement systems, conduct measurement comparison and fusion result analysis, 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 underwater moving targets includes an acoustic beacon, an ultra-short baseline array, and a long baseline array; the acoustic beacon is installed on the multi-layer deep underwater moving target to be measured, the ultra-short baseline array is arranged on a surface operation ship or a surface measurement platform, and the ultra-short baseline array is located underwater; 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 signals emitted by the acoustic beacon and jointly perform fusion calculation on the acoustic signals to obtain the position of the multi-layer deep underwater moving target.

[0009] The acoustic beacon is at least one group of acoustic beacons that can be omnidirectional or two groups with an opening angle of 180°.

[0010] A combined measurement method for multi-layer deep underwater moving targets uses the above device, and the specific steps are as follows:

[0011] Step 1: Under the sea state conditions required for the measurement operation, the surface operation vessel or surface measurement platform maintains an anchored or constant speed sailing state. Select an unobstructed position above the water surface to install a GNSS positioning device to obtain the position reference data of the ultra-short baseline array, install an inertial navigation device and ensure it is rigidly connected to the surface operation vessel or surface measurement platform. At the same time, obtain the attitude data of the ultra-short baseline array through satellite navigation. Select a position at a depth of more than 2 meters below the water surface and rigidly connected to the surface operation vessel or surface measurement platform, and install the ultra-short baseline array.

[0012] Step 2: At the bottom of the horizontal movement area of the underwater target, install a long baseline array through a bottom-mounted measurement platform to realize the reception, acquisition, and real-time processing of acoustic signals. On the bottom-mounted measurement platform, install a timing device to unify the time at the signal receiving 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 operation vessel is equipped with a sound velocity profiler to obtain the sound velocity profile data of the operation sea area at regular intervals, and realize the measurement of the vertical propagation time delay error of the sound velocity in the operation sea area.

[0014] Step 4: Use the time synchronization signal provided by the high-precision satellite navigation 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 underwater target 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 respectively receive, acquire, and store the signals. Among them, the ultra-short baseline array real-time calculates and displays the geodetic coordinate position, speed and other motion parameters of the target on the console of the operation vessel in real time. Each element of the long baseline array self-contains and stores the received original acoustic signals, and the motion parameters of the target are obtained through post-event retrieval and calculation.

[0016] Step 6: Before performing multi-source fusion calculation in the combined measurement mode, conduct error propagation, identification method, and error correction analysis. Perform time registration and space registration on the positioning and velocity measurement results of the ultra-short baseline array and the long baseline array, and use an interactive multi-model adaptive filter for fusion calculation to obtain the motion parameter results such as position and speed of the multi-source fusion calculation.

[0017] The beneficial effects of the present invention are as follows: Through the combined measurement device and method based on ultra-short baseline and long baseline, as well as the distributed measurement framework in the geodetic coordinate system, the present invention realizes high-precision fusion calculation of motion parameters such as the position and velocity of underwater moving targets, can establish a multi-target situation analysis scenario under unified spatio-temporal reference conditions, and can achieve multi-target integrated situation acquisition in multiple working condition dimensions such as horizontal and vertical motions, low-speed and high-speed motions, moving targets and underwater environments in the underwater application environment, which can provide data support and reference basis for the analysis of the motion state and the discrimination of the safety state of underwater targets under engineering conditions, and can also provide important information basis support for mapping the underwater operation environment in the digital space; The measurement method and the corresponding measurement device have the basis for engineering applications at sea, have a mature equipment development plan and a sea operation implementation plan from the subsystem level to the whole system level, and can provide practical application support for the measurement method of multi-source fusion calculation. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0019] Figure 2 is a flowchart of the working process of the measurement method of the present invention.

[0020] Figure 3 is a flowchart of the multi-source fusion calculation of the present invention.

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

[0022] The following is further described in conjunction with the drawings and specific embodiments, but it is not a limitation of the present invention.

[0023] I. Combined Measurement Device for Underwater Moving Targets at Multiple Depths

[0024] The described device includes an acoustic beacon, an ultra-short baseline array, and a long baseline array; the acoustic beacon is installed on the 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 below 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 signals emitted by the acoustic beacon and jointly perform calculations on the acoustic signals to obtain the position of the underwater moving target. The specific introduction is as follows:

[0025] 1. Acoustic Beacon

[0026] The acoustic beacon is installed on the underwater target. Its design should conform to the installation structure of the target, have the acoustic performance required by the measurement accuracy index, 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 the selection of the working frequency band, the requirements of measurement accuracy and reliable propagation in the underwater measurement environment should be taken into account. Referring to the current mainstream ultra-short baseline positioning equipment, a suitable frequency band should be selected; in terms of the design of the transmitting sound source level, it should be considered to achieve a high signal-to-noise ratio within the effective receiving range of the ultra-short baseline array and the long baseline array. At the same time, considering the factor of sound energy attenuation in water, it can be calculated according to the sonar equation; in terms of the directivity design, the sound signal receiving coverage range of the ultra-short baseline array and the long baseline array should be considered. At least one set of omnidirectional or two sets of acoustic beacons with an opening angle of 180° can be installed on the target surface according to the beacon shape size to ensure the omnidirectional coverage of underwater sound signal reception.

[0028] Signal coding design: It is necessary to balance the reliability of signal transmission-reception and the obtainable data frame rate. For the target, generally, the underwater movement section has a short process and time. It is required that the transmitted acoustic signal coding of the equipment has the characteristics of high frame rate, low pulse width, short period, high reliability, and low error rate; at the same time, to ensure the resolvability of adjacent signals, the acoustic beacon pulse signal adopts the design of orthogonalization of adjacent signals.

[0029] Environmental adaptability design: The movement process of underwater moving targets is accompanied by a large impact inertia. To ensure that the transmitting transducer can work normally under complex mechanical environment conditions, the transmitting transducer should be designed for shock resistance. A rigid structure should be installed externally, a shock absorption device should be installed internally, and the radiation 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 reference of the ultra-short baseline acoustic array. To obtain high-precision measurement data, it is necessary to achieve accurate measurement of the movement parameters of the surface measurement platform, reliable detection of cooperative sound signals, reliable identification and effective control of 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 navigation antenna center can be calibrated. The ultra-short baseline measurement equipment needs to be rigidly connected to the measurement platform to obtain the accurate origin of the measurement coordinate system.

[0033] Surface measurement platform attitude measurement: 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 surface measurement platform, and high-precision attitude angle parameters can be obtained through means such as GPS or DVL assistance to achieve effective correction of the attitude measurement parameters.

[0034] Time synchronization control: To achieve reliable detection of cooperative acoustic signals by the ultra-short baseline array and calculate the motion parameter measurement results through time-delay parameter resolution, time synchronization control is required for both the signal transmitter and the signal receiver. Time synchronization and calibration of the time synchronization signal can be carried out at the acoustic beacon transmitter and the ultra-short baseline array receiver, and the synchronization calibration error should be on the order of milliseconds.

[0035] 3. Long baseline array

[0036] Different from the ultra-short baseline array, the elements of the long baseline array do not have the condition of cable control. They are arranged in a certain formation on the bottom-mounted measurement platform and adopt a self-contained design. They receive the standard acoustic signals transmitted by the acoustic beacon and store them in the storage module of the acquisition control unit. After the equipment is recovered, signal preprocessing and parameter resolution are carried out. The accurate calibration of its own position and the identification and control of error sources are the keys to achieving high-precision measurement.

[0037] Self-contained bottom-mounted measurement platform: The long baseline measurement elements are carried on the bottom-mounted platform and are pre-laid on the seabed of the target activity sea area according to the measurement formation. Designs such as anti-trawl, anti-rust, and anti-biofouling are adopted, and equipment such as a power supply module, a synchronous timekeeping module, a data acquisition module, and a recovery control module are built-in.

[0038] Accurate calibration of the deployment position: After the bottom-mounted measurement platform is deployed on the seabed, due to the shear effect of the underwater vertical profile current, there is a horizontal displacement between the actual bottom-mounted position and the water surface deployment point position. At the same time, the uncertainty of the position deployed on the seabed will generate a station site error. It is necessary to carry out accurate calibration of the bottom-mounted platform position in cooperation with the water surface measurement platform.

[0039] Timekeeping error control: To achieve reliable detection of cooperative acoustic signals by each element of the long baseline and calculate the motion parameter measurement results through time-delay parameter resolution, similar to the ultra-short baseline, time synchronization control is required for both the signal transmitter and the signal receiver. Since the long baseline elements are pre-laid on the seabed measurement points for self-contained operation, a high-precision timekeeping module can be built-in. Before the operation, the timekeeping module of the element is timed by the precise timing unit. During the operation, the timekeeping module controls the timekeeping error, 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 measurement equipment is as Figure 1 shown. By installing an acoustic beacon outside the measured target to emit standard acoustic signals, the ultra-short baseline array equipment and the long baseline element measurement equipment receive the standard acoustic signals of the measured target. The key parameters such as the underwater motion position, speed, and trajectory of the measured target can be calculated respectively through the ultra-short baseline and long baseline positioning methods. At the same time, multi-source data based on the above two methods are fused and resolved to obtain the high-precision motion parameter measurement results under this measurement system method.

[0041] An acoustic beacon is installed outside the target to be measured. The target to be measured can be described as vertical or horizontal, low-speed or high-speed moving objects of different sizes underwater. At least one set of omnidirectional or two sets of acoustic beacons with an opening angle of 180° are installed on its surface according to the beacon's outer dimension, meeting the condition that the target to be measured emits acoustic signals with a prefabricated fixed coding format omnidirectionally horizontally. At the same time, it is set that the signal is periodically transmitted in a trigger response working mode for the ultra-short baseline or long baseline array elements to obtain the ranging delay information of the target.

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

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

[0044] II. Combined Measurement Method for Multi-layer Underwater Moving Targets

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

[0046] Considering that the acoustic beacon is installed at the head of the target, there are two options for the layout carrier of the receiving array: one is to be placed on the carrier platform, maintaining a relatively stable relative distance from it before the target is launched. Such a platform is preferably equipped with an ultra-short baseline measurement system to achieve precise positioning of the target and the carrier platform; the other is to be placed on the seabed of the test sea area, and a long baseline measurement system is formed by multiple array elements to obtain multiple sets of slant range and radial velocity information, and then the position and velocity parameter solutions are realized. These two systems are both independent of each other and redundant and complementary to each other, providing a basis for post-event 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 arriving at each array element to calculate the target position parameters. The installation position of the receiving array can be selected as an underwater measurement platform or a water surface measurement platform. From the perspective of the array layout, the former is an "upward-looking" measurement, and the latter is a "downward-looking" measurement. During the movement of an underwater moving target, it moves at a high speed vertically. The acoustic signal emitted by the target needs to be received by the receiving array elements covering multiple depths from the bottom to the water surface. Since the long baseline array elements are deployed in the horizontal operating range of the seabed, it is more beneficial to install the ultra-short receiving array on the water surface measurement platform for receiving the standard acoustic signal. The water surface measurement platform can obtain the accurate position and elevation information of the measurement coordinate system by installing a high-precision GPS; in addition, during the navigation of the water surface measurement platform, the attitude changes randomly. It is necessary to install a high-precision attitude sensor and record relevant data in real time to achieve attitude correction during the measurement process. Under the existing technical conditions, the measurement accuracy of mainstream ultra-short baseline underwater acoustic positioning equipment can reach 3‰ slant range. Therefore, within the range of hundreds of meters from the center position of the ultra-short array to the target to be measured, a distance measurement accuracy better than one meter can be achieved.

[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 through intersection, and at the same time, each measurement 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 is pre-deployed on the seabed of the measurement operation area in a certain geometric configuration with a submerged buoy or a bottom-mounted platform as the carrier. Each bottom-mounted measurement platform is pre-installed with a high-precision timekeeping module to achieve the consistency of the time synchronization information between the receiving end and the transmitting end. After the deployment, it is necessary to conduct high-precision position calibration operations on all array elements one by one to obtain sub-meter-level position information. Similarly, within the range of hundreds of meters of measurement, the long baseline ranging can achieve a measurement accuracy of 3‰ slant range, and through the optimized design of the array configuration of the array elements, a measurement accuracy better than one meter for the target to be measured can be achieved.

[0051] 3. Measurement element error control

[0052] For underwater moving targets, the accuracy index of their motion parameter measurement is an important reference basis for verifying the capabilities of measurement equipment. The equipment and methods relying on the combined measurement system of ultra-short baseline and long baseline are quite different from the measurement methods for conventional horizontal and low-speed moving targets, and need to be adaptively improved for the ultra-short baseline and long baseline methods. Therefore, reasonable measurement accuracy index requirements need to be proposed for the two measurement methods and equipment characteristics, and systematic modeling and simulation methods are used to systematically analyze the measurement model, parameter calculation, and the error transfer process of measurement elements, obtain the comprehensive influence effect of measurement element errors, and at the same time effectively control each error source of measurement elements to achieve the high-precision measurement requirements under this combined measurement equipment and method.

[0053] For the ultra-short baseline measurement method, the main measurement elements are time-delay error and time-delay difference error. The key to controlling this error is to obtain a high signal-to-noise ratio. In addition, the ultra-short array coordinate system is called the array coordinate system. During the conversion from this coordinate system to the geodetic coordinate system, high-precision auxiliary measurements of the position and attitude parameters of the water surface measurement platform are required to achieve coordinate conversion error correction and control. For the long baseline measurement method, the main measurement element for positioning measurement is time-delay error. The key to error control is to ensure that more than 3 measurement elements reach the set signal-to-noise ratio, and at the same time, there is a high-precision timekeeping module to ensure time synchronization. When converting time-delay information into measured slant range, it is necessary to measure the sound speed profile of the sea area to correct the sound speed error. In addition, the underwater site positions of each measurement element need to be calibrated to control the site error. The main measurement element for velocity measurement is Doppler frequency shift. The radial velocity of the target relative to each measurement element is calculated, and the target velocity parameters are obtained through intersection calculation. The key to error control is to ensure that more than 3 measurement elements reach the set signal-to-noise ratio and effectively control time synchronization error, sound speed error, site error, etc.

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

[0055] The specific steps of the described multi-layer deep underwater moving target combined measurement device and method include the following:

[0056] Step 1: Under the sea condition requirements of the measurement operation, the surface operation ship or the surface measurement platform maintains an anchored or uniform sailing state. Select a suitable position above the water surface without obstruction and install a GNSS positioning device to obtain high-precision position reference data. Install an inertial navigation device and ensure that it is rigidly connected to the surface operation ship or the surface measurement platform. At the same time, supplement it with high-precision satellite navigation data to obtain high-precision attitude data. Select a position at a depth of more than 2 meters below the water surface and at a position rigidly connected to the surface operation ship or the surface measurement platform, and install a fixed-array ultra-short base array unit with a five-element planar or three-dimensional array to form an ultra-short baseline base array measurement device layout plan;

[0057] Step 2: Build a long baseline array at the bottom of the horizontal area where the underwater target moves. Without the condition of cable control, the matrix consists of multiple array elements designed by calculation. Each array element works in a self-contained manner and can be carried by a bottom-mounted measurement platform with a bottom-mounted, anti-disconnection net, and split structure to carry measurement and working loads. Install a high-precision timekeeping device to achieve time unity at the signal receiving end. Install a long baseline array to achieve the reception, acquisition, and real-time processing of acoustic signals. Install a position calibration device 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 long baseline equipment on the seabed of the surface operation vessel or the surface measurement platform are completed, during the operation, the sound velocity profiler carried by the operation vessel obtains the sound velocity profile data of the operation sea area at intervals of 6 hours to measure the vertical propagation time delay error of the sound velocity in the operation sea area.

[0059] Step 4: Use the time synchronization signal provided by the high-precision time service module based on satellite navigation to provide a unified time reference for the target sound signal transmitting device (acoustic beacon), the ultra-short baseline array, and the long baseline array to be measured.

[0060] Step 5: The target sound signal transmitting device continuously emits a standard sound 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 perform real-time calculation and display the movement parameters such as the geodetic coordinate position and speed of the target on the console of the operation vessel in real time. Each element of the long baseline array self-contains and stores the original sound signals received, and the movement parameters of the target are obtained through post-event retrieval and calculation.

[0061] Step 6: Before performing the fusion calculation in the combined measurement mode, perform error propagation, identification method, and error correction analysis. Perform time registration and space registration on the positioning and velocity measurement results of the ultra-short baseline and the long baseline, and use an interactive multi-model adaptive filter to perform the fusion calculation to obtain the movement parameter results such as the position and speed of the fusion calculation.

[0062] Among them, the specific method of the fusion calculation is as follows:

[0063] The fusion calculation method extracts the calculation elements from the measurement data for multi-measurement element parameter fusion calculation, and is applicable to the solution of the movement parameters of the target to be measured by the combination measurement method of the acoustic beacon sounding, the ultra-short baseline, and the long baseline in the present invention.

[0064] (1) Fusion calculation model

[0065] The multi-measurement element fusion position calculation 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 measurement value and the initial value of the target position; for this model, the slant range vector value can be solved by using multiple sets of sound arrival time delay information, 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 initial value of the target position and the random error through one iteration calculation, and using it as the initial value of the target position for the next iteration. After multiple iterations of calculation, the iteration end criterion can be determined according to the accuracy requirement. Generally, the difference between the calculation position results of the current iteration step and the previous iteration step is not greater than the required accuracy.

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

[0067] ΔX = (J T J)-1 J T ΔR

[0068] Among them:

[0069]

[0070] In the formula, J represents the Jacobian matrix or the 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 N long baseline measurement point slant range measurement elements and M ultra-short baseline measurement point RAE measurement elements, and ΔR1 to ΔR N represents the deviation of N long baseline measurement point slant range measurement elements, (ΔR N+1 , ΔA N+1 , ΔE N+1 ) to (ΔR N+M , ΔA N+M , ΔE N+M ) represents the measurement function deviation of M ultra-short baseline measurement point RAE measurement elements.

[0071] Among them:

[0072]

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

[0074]

[0075] (2) Error analysis

[0076] For the ultra-short baseline and long baseline measurement systems, the main error sources include ranging error and station location error, which can be specifically divided into sound speed error, time measurement error, array element spacing error, attitude error, calibration error, target motion induced error, 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 mainly refers to the site error terms of the ultra-short baseline array and each element of the long baseline. For the ultra-short baseline positioning measurement system, the ultra-short baseline array is rigidly connected to the water surface platform, and accurate point position information and attitude data of the ultra-short baseline array need to be obtained. In the implementation of the present invention, the positioning accuracy better than 10 cm is achieved by installing a high-precision differential GNSS receiving device on the water surface platform, and the attitude measurement accuracy of 0.01° is achieved by installing a high-precision, high-sensitivity and high-resolution attitude sensor. During the measurement process, to obtain the position information of the ultra-short baseline array in the geodetic coordinate system, it is necessary to first convert it into the position coordinates in the water surface platform coordinate system, and then combine the GNSS and attitude data to achieve the transmission of high-precision positions on the water surface;

[0081] ⑤ Error introduced by target movement: For the long baseline measurement system, under actual measurement environmental conditions, due to the slow sound propagation speed, the time difference of the target sound signal reaching different bottom elements can be up to several seconds. During this time difference, the position of the target has changed. Therefore, even under the condition of no ranging error, the intersection equation has no solution, and the obtained positioning result 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 amount. However, under actual sea trial conditions, the movement speed of the target is much smaller than the sound speed, and the change in the target position caused by the time difference generated by the sound speed is very small. Therefore, this kind of error can be ignored.

[0082] (3) Accuracy evaluation

[0083] ① Ranging accuracy

[0084] The ultra-short baseline positioning measurement adopts a 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 sea area, it can be assumed that the sound speed value is a constant value. Taking the sound speed c = 1500 m / s and the maximum slant range between the target to be measured and the receiving array as R, the corresponding propagation time can be calculated as R / c. Through high-precision SVP measurement and correction processing, the equivalent calculated value of the sound speed error, the estimated error value of the target direct arrival time delay, and the synchronous time delay error value of the sound signal 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] ② Direction finding accuracy

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

[0089]

[0090] Among them, c is the speed of sound, d is the baseline length, and α is the baseline included angle, that is, the included angle between the line connecting the acoustic signal to the element and the baseline. For ultra-short baseline, since the baseline length is usually less than 1 meter, the sound speed error can be ignored when calculating the propagation time delay of the acoustic signal using the acoustic path difference. For long baseline, 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, take the speed of sound c = 1500 m / s. The horizontal and vertical baseline lengths of the array configuration can be measured according to the relative position relationship of the configuration. The horizontal baseline can be determined according to the course deviation angle of the surface platform navigation, and the vertical deviation angle of the baseline is generally about 90°; under the condition of high signal-to-noise ratio, the estimated error value of the time 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 the vertical baseline under this working condition can be estimated.

Claims

1. A method for combined measurement of multi-layer deep underwater moving targets, the equipment used includes acoustic beacons, ultra-short baseline arrays and long baseline arrays; the acoustic beacons are installed on the multi-layer deep underwater moving targets to be measured, the ultra-short baseline arrays are arranged on a surface operating ship or a surface measurement platform, the ultra-short baseline arrays are located under the water surface, and the long baseline arrays are arranged on a bottom measurement platform located on the seabed; the ultra-short baseline arrays and the long baseline arrays jointly receive the acoustic signals emitted by the acoustic beacons, and jointly fuse and solve the acoustic signals to obtain the positions of the multi-layer deep underwater moving targets; it is 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 multi-element fusion solution in a combined measurement mode, 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 registered. The interactive multi-model adaptive filter is used for fusion solution to obtain the position and velocity motion parameter results of the multi-element fusion solution. 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 N 、m N 、n N They 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 measured at the initial position. A and E represent the azimuth and elevation angle of the ultra-short baseline measuring point in each direction, 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:

2. A multi-layer deep underwater moving target combined measurement method according to claim 1, 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.

3. A multi-layer deep underwater moving target combined measurement method according to claim 1, characterized in that: In step six, the accuracy assessment includes ranging accuracy and direction finding accuracy.

4. A multi-layer deep underwater moving target combined measurement method 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°.

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