High-precision seabed in-situ testing method and system based on acoustic assistance

Abstract

The invention relates to the technical field of underwater acoustic detection, in particular to a high-precision seabed in-situ test method and system based on acoustic assistance, and the method comprises the steps: obtaining echo signals in all directions when a multi-beam depth finder scans the seabed in real time, and obtaining the time difference between the signal emission in all directions and the echo signal receiving in all directions; in a single scanning process, obtaining corrected sound velocities and sound velocity frequency offset values in all directions; acquiring goodness of fit for sine fitting of the echo signals in each direction, acquiring sound velocity correction coefficients in each direction through the goodness of fit in each direction and the deviation value of the goodness of fit in the symmetrical direction in combination with the sound velocity frequency offset value, and comparing the time difference between each direction and the adjacent direction to obtain a sound velocity correction coefficient in each direction. Correcting the time difference of each direction by combining the included angle between each direction and the vertical direction; and obtaining a seabed depth value of the scanning point in each direction, and constructing a seabed topographic map. The invention aims to improve the precision of seabed depth measurement.

Description

Technical Field

[0001] This application relates to the field of underwater acoustic detection technology, and particularly to a high-precision in-situ seabed testing method and system based on acoustic assistance. Background Art

[0002] In-situ seabed detection refers to a detection method that directly measures and analyzes the geological, physical, chemical and other characteristics of the seabed under the original position and environmental conditions of the seabed. Since there is no need to retrieve seabed substances to the laboratory and directly measure on the seabed site, it is possible to avoid the influence on samples during the sampling process, such as changes in pressure, temperature and chemical composition, so that the real seabed data can be obtained more accurately. Among them, seabed topography measurement is one of the important contents of in-situ seabed measurement.

[0003] At present, multi-beam detection technology based on acoustics is usually used for seabed topography measurement. The literature "Research on 3D Seabed Modeling Based on Multi-beam Bathymetry Outlier Detection" proposed a method based on seabed topography modeling, which uses trend surface filtering to test multi-beam bathymetry outliers, so as to realize seabed topography detection. However, in the actual measurement process, affected by the inhomogeneity of seawater, the actual sound speed of sound waves will change during seawater detection, resulting in the bending of sound rays and errors in the seabed topography measurement results. Summary of the Invention

[0004] In view of the above, it is necessary to provide a high-precision in-situ seabed testing method and system based on acoustic assistance, which improves the accuracy of seabed depth measurement compared with the traditional high-precision in-situ seabed testing method: In a first aspect, an embodiment of the present application provides a high-precision in-situ seabed testing method based on acoustic assistance, the method includes the following steps: Obtain in real time the echo signals in each direction when a multi-beam bathymeter scans the seabed, and the time difference between the transmitted signals and the received echo signals in each direction, wherein, including the direction perpendicular to the seabed; During a single scan, obtain the water depth in the vertical direction, and obtain the corrected sound speed in each direction through the water depth in the vertical direction and the time difference; Record the frequency with the maximum energy intensity in the frequency domain of the echo signals in each direction as the main frequency, and obtain the sound speed frequency deviation value in each direction through the difference between the transmission frequency of the transmitted signal in each direction and the main frequency, combined with the difference in the 3dB bandwidth of the main frequency between each direction and the vertical direction; Obtain the goodness of fit of the sine fitting of the echo signals in each direction, record the direction symmetric to each direction with respect to the vertical direction as the symmetric direction, and obtain the sound speed correction coefficient in each direction through the goodness of fit in each direction and the deviation amount between it and the goodness of fit in the symmetric direction, combined with the sound speed frequency deviation value; By comparing the time differences between each direction and its adjacent directions, and combining the angles between each direction and the vertical direction, the spatial deviation of each direction is obtained, and the time differences of each direction are corrected in combination with the sound speed correction coefficient; The intersection points of the emission signals in each direction with the seabed are denoted as scanning points. Through the correction result and the corrected sound speed, the seabed depth values of the scanning points in each direction are obtained, and a seabed topographic map is constructed.

[0005] In one embodiment, the calculation method of the corrected sound speed is as follows: Calculate the product of the time difference in the vertical direction and one-half; The corrected sound speed is the product of the water depth and the product.

[0006] In one embodiment, the process of obtaining the sound speed frequency deviation value is as follows: Calculate the difference between the emission frequency of the emission signal in each direction and the main frequency; Take the opposite number of the difference amount as the exponent of the exponential function with the natural constant as the base; The sound speed frequency deviation value is directly proportional to the difference value and inversely proportional to the calculation result of the exponential function.

[0007] In one embodiment, the sound speed frequency deviation value is the normalized value of the ratio of the difference value to the calculation result of the exponential function.

[0008] In one embodiment, the process of obtaining the sound speed correction coefficient is as follows: Calculate the absolute value of the sum of the goodness of fit and the deviation amount in each direction; the sound speed correction coefficient is the product of the sound speed frequency deviation value and the absolute value.

[0009] In one embodiment, the process of obtaining the spatial deviation is as follows: The serial numbers of each direction and the time difference are combined to form two-dimensional feature points of each direction. When the time difference of each direction is greater than the time differences of its two adjacent directions, the opposite number of the area enclosed by the two-dimensional feature points of each direction and its two adjacent directions is denoted as the enclosed area; otherwise, the area enclosed by the two-dimensional feature points of each direction and its two adjacent directions is denoted as the enclosed area; Calculate the mean value of the enclosed areas enclosed by the two-dimensional feature points of all continuously adjacent three directions; the ratio of the enclosed area to the mean value is denoted as the area ratio; The spatial deviation is the product of the area ratio and the cosine value of the angle.

[0010] In one embodiment, the method for correcting the time differences of each direction is as follows: Calculate the cumulative value of the sound speed correction coefficient and the spatial deviation; Denote the ratio of the cumulative value to a non-zero preset scaling factor as the correction ratio; Calculate the product value of the correction ratio and a preset correction step size; Correct the time differences in each direction by the product value.

[0011] In one embodiment, the correcting the time differences in each direction by the product value includes: taking the sum value of the product value and the time differences in each direction as the corrected time differences in each direction.

[0012] In one embodiment, the obtaining the seabed depth values of the scanning points in each direction includes: Taking half of the product of the corrected time differences in each direction and the correction sound speed as the distance from the multibeam echosounder to the scanning points in each direction; and obtaining the seabed depth values of the scanning points in each direction by using the trigonometric function relation according to the distance and the included angle.

[0013] In a second aspect, an embodiment of the present application further provides a high-precision seabed in-situ testing system based on acoustic assistance, including a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, the steps of the above-mentioned high-precision seabed in-situ testing method based on acoustic assistance are implemented.

[0014] The present application has at least the following beneficial effects: Compared with the prior art, in which the seabed depth values of each scanning point are obtained based on the propagation time of sound waves and the propagation speed of each sound wave in seawater, while ignoring the fact that in the actual measurement process, due to the limitation of the seabed water quality conditions, the propagation speed of sound waves varies at different seabed depths, resulting in errors in the seabed topography measurement results. By analyzing the echo signals in each direction, the sound speed frequency deviation value is obtained, which helps to quantify the propagation speed deviation of sound waves in different directions and provides a more accurate reference basis for subsequent time difference correction; Furthermore, by the difference in the goodness of fit of the sine fitting of the echo signals in different directions, combined with the sound speed frequency deviation value, the sound speed correction coefficient is obtained, which can comprehensively consider the frequency shift effect of sound waves during propagation and the fluctuation difference of echo signals, and can accurately reflect the propagation characteristics of sound waves in each direction, providing a more reasonable basis for the correction of time differences, thereby effectively reducing the measurement errors caused by the differences in seabed geological conditions and improving the accuracy and reliability of seabed topography measurement; Furthermore, based on the difference in the time differences between adjacent directions, a spatial deviation is obtained. By combining the sound velocity correction coefficient to correct the time differences in each direction, the time differences in each direction can be corrected more accurately, thereby balancing the influence caused by the sound velocity difference during the acoustic wave transmission process, improving the accuracy of the seabed depth measurement, and enabling the measurement result to more truly reflect the actual topography of the seabed. Description of the Drawings

[0015] To more clearly illustrate the technical solutions and advantages in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0016] Figure 1 It is a flowchart of the steps of a high-precision seabed in-situ testing method based on acoustic assistance provided by an embodiment of the present application; Figure 2 It is a schematic diagram of the time difference correction process; Figure 3 It is a schematic diagram of the calculation process of the seabed depth value. Detailed Embodiments

[0017] In the description of the embodiments of the present application, words such as "exemplary", "or", "for example", etc. are used to represent examples, illustrations, or explanations. Any embodiment or design solution described as "exemplary" or "for example" in the embodiments of the present application should not be construed as being more preferred or having more advantages than other embodiments or design solutions. Rather, the use of words such as "exemplary", "or", "for example" is intended to present relevant concepts in a specific manner.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which this application belongs. The terms used in this application are only for the purpose of describing specific embodiments and are not intended to limit this application. It should be understood that unless otherwise stated in this application, " / " means "or".

[0019] In addition, it should be noted that the terms "first" and "second" in this application are used to distinguish similar objects and are not used to describe a specific order or sequence.

[0020] The following specifically describes the specific solutions of the high-precision seabed in-situ testing method and system based on acoustic assistance provided by this application with reference to the drawings.

[0021] Please refer to Figure 1, which shows the step flow chart of the high-precision in-situ seabed testing method based on acoustic assistance provided by an embodiment of the present application. The method includes the following steps: Step 1, in real time, obtain the echo signals in each direction when the multibeam echosounder scans the seabed, as well as the time differences between the transmitted signals and the received echo signals in each direction, where the direction perpendicular to the seabed is included.

[0022] During the seabed detection process, sound waves are currently the only known energy form and information carrier that can propagate over long distances in water and can be utilized by humans. Specifically: for sound waves and electromagnetic waves with the same frequency of 10 KHz, the attenuation of sound waves in water is 1 decibel per kilometer, while the attenuation of electromagnetic waves is 3000 decibels per kilometer. Therefore, in this application, sound waves are used as acoustic assistance to achieve seabed topography measurement based on multibeam detection technology.

[0023] For the sea area where in-situ measurement is required, the multibeam echosounder is suspended at the bottom of the survey ship, and the survey ship accurately locates its own position by receiving Global Navigation Satellite System (GNSS) signals. The scanning direction of the multibeam echosounder is perpendicular to the sailing direction of the survey ship, and the survey ship is controlled to sail at a constant speed. During the scanning process of the multibeam echosounder, the survey ship conducts a scan every time it sails a distance equal to 10% of the average depth of the surveyed sea area.

[0024] During a single scan, the multibeam echosounder can cover an area with a width of 50 meters in the advancing direction of the survey ship, obtain the depth information of this area, uniformly set W scanning directions, where the angle of the vertical direction towards the seabed is set to 0°, and signals are transmitted in W directions. In real time, obtain the echo signals in each direction when the multibeam echosounder scans the seabed, as well as the time differences between the transmitted signals and the received echo signals in each direction; It should be noted that: the transmitting device during the measurement process of the multibeam echosounder is a low-frequency high-power transmitting transducer, with a transmitting frequency of 500 Hz and a transmitting duration of 50 ms of a sine wave. The receiving transducer of the multibeam echosounder can receive echo signals from all directions.

[0025] In this embodiment, the value of W is 101. The value of W is preset manually and can be set by the implementer himself / herself without special restrictions in this application.

[0026] In addition, since the survey ship is not horizontal during navigation, a horizontal measuring instrument needs to be deployed on the survey ship to obtain the tilt state of the survey ship itself in real time and achieve correction of the scanning direction.

[0027] Step 2, during a single scan, obtain the water depth in the vertical direction, and obtain the corrected sound speed in each direction through the water depth in the vertical direction and the time difference; obtain the sound speed frequency deviation value in each direction and obtain the sound speed correction coefficient in each direction.

[0028] In the process of using a multi-beam sounding instrument to measure the seabed topography, the basic principle of the measurement is as follows: By using the propagation time difference between the transmitted signal and the echo signal, and the propagation speed of sound waves in seawater, the true distance from the survey ship to the seabed in each scanning direction can be obtained. Denote the intersection point of the transmitted signal in each direction and the seabed as the scanning point, and according to the transmission angle, the seabed depth value of the scanning point in each scanning direction can be obtained using the trigonometric function relationship. Although the above measurement method is simple, the above measurement method assumes that the propagation speed of sound waves in seawater is constant. However, in the actual measurement process, affected by seawater quality conditions such as water pressure, water temperature, and salinity, etc., the propagation speed of sound waves in seawater may change, which may cause deviations in the measurement results of the seabed depth.

[0029] Step 2.1, during a single scan, obtain the water depth in the vertical direction, and through the water depth in the vertical direction and the time difference, obtain the corrected sound speed in each direction; Denote the frequency with the maximum energy intensity in the frequency domain of the echo signal in each direction as the main frequency, and through the difference between the transmission frequency of the transmitted signal in each direction and the main frequency, combined with the difference in the 3dB bandwidth of the main frequency between each direction and the vertical direction, obtain the sound speed frequency deviation value in each direction.

[0030] For a single scan process, analyze the echo signals in each azimuth. If the angle between a certain direction and the vertical direction is larger, then the actual sound speed deviation in the certain direction is larger, and the echo signal in the certain direction may show a smile curve or a crying face curve. Specifically: when the actual sound speed is less than the corrected sound speed, a smile curve appears, and when the actual sound speed is greater than the corrected sound speed, a crying face curve effect appears. Among them, the calculation method of the corrected sound speed is: extract the time difference in the vertical direction when the multi-beam sounding instrument scans the seabed, use a high-precision depth sounding device such as a single-beam sounding instrument to measure the water depth in the vertical direction, and calculate the product of the time difference in the vertical direction and one-half; take the product of the water depth and the product as the corrected sound speed in each direction.

[0031] For non-vertically incident directions, the propagation of the transmitted signal will be affected by various factors. The actual sound speed of the transmitted signal may change due to factors such as the temperature, salinity, and pressure of seawater, which may cause a frequency shift effect during the propagation of sound waves. At the same time, affected by the non-uniformity of the seawater medium, the echo signals in non-vertically incident directions show a frequency dispersion phenomenon. Therefore, convert the echo signals in each direction from the time domain to the frequency domain, and denote the frequency with the maximum energy intensity in the frequency domain of the echo signal in each direction as the main frequency.

[0032] In this embodiment, the fast Fourier transform is used to convert the acoustic wave signal from the time domain to the frequency domain. The fast Fourier transform is a well-known technology and will not be elaborated in this application. As other implementation manners, on the basis of being able to convert the acoustic wave signal from the time domain to the frequency domain, the implementer can adopt other existing technologies, such as the discrete Fourier transform, etc. This application does not make special restrictions.

[0033] Further, through the difference between the transmission frequency of the transmission signal in each direction and the main frequency, combined with the difference amount of the 3dB bandwidth of the main frequency between each direction and the vertical direction, the acoustic velocity frequency offset value in each direction is obtained, and the expression is: ; In the formula, represents the acoustic velocity frequency offset value in the i-th direction; ceil( ) represents the maximum absolute value normalization function; represents the transmission frequency of the transmission signal in the i-th direction. In this embodiment, is 500Hz; represents the main frequency in the i-th direction; exp( ) represents the exponential function with the natural constant as the base; represents the difference amount of the 3dB bandwidth of the main frequency between the i-th direction and the vertical direction. Among them, the 3dB bandwidth is a well-known technology and will not be elaborated in this application.

[0034] In this embodiment, the difference amount between the 3dB bandwidths is the absolute value of the difference. As other implementation manners, on the basis of being able to measure the difference between the 3dB bandwidths, the implementer can adopt other calculation methods, such as the square of the difference, the ratio, etc. This application does not make special restrictions.

[0035] It should be noted that: the calculated acoustic velocity frequency offset value has positive and negative properties. When the actual acoustic velocity is greater than the estimated corrected acoustic velocity, the transmission speed of the acoustic wave is faster, causing the frequency difference to shift to the negative value. On the contrary, when the actual acoustic velocity is less than the estimated corrected acoustic velocity, the transmission speed of the acoustic wave is slower, causing the frequency difference to shift to the positive value; at the same time, the greater the difference between the actual acoustic velocity and the estimated corrected acoustic velocity, the more serious the frequency dispersion of the echo signal. Since the interference degree of the acoustic wave in the vertical direction is the lowest, therefore, taking the 3dB bandwidth in the vertical direction as the reference benchmark, when the deviation of the 3dB bandwidth between the i-th direction and the vertical direction is greater, the acoustic velocity frequency offset value is greater.

[0036] Step 2.2, obtain the goodness of fit of the sine fitting for the echo signals in each direction. Denote the direction symmetric to each direction with respect to the vertical direction as the symmetric direction. Through the goodness of fit in each direction and the deviation amount between it and the goodness of fit in the symmetric direction, combined with the acoustic velocity frequency offset value, obtain the acoustic velocity correction coefficient in each direction.

[0037] In addition, the geological conditions of the seabed will also affect the reflection of sound waves. Generally, the geological conditions of the seabed are divided into two types. One is hard sediments such as submarine shale, which are formed by the extrusion of the seabed crust or volcanic eruptions. The other is soft sediments such as loose soil, which are formed by the decay of animals and plants and soil deposition. Hard sediments can often directly reflect sound waves, making the characteristics of the echo signal obvious. For soft sediments, due to the large degree of change in the medium during the propagation of sound waves, the echo signal is easily affected by large fluctuations, resulting in large waveform distortions in the echo signal and affecting the measurement results of the time difference.

[0038] Based on the above analysis, obtain the goodness of fit of the echo signals in each direction for sine fitting. Through the goodness of fit in each direction and the deviation amount between it and the goodness of fit in the vertical direction, combined with the sound speed frequency deviation value, obtain the sound speed correction coefficient in each direction. The expression is: ; represents the sound speed correction coefficient in the i-th direction; represents the sound speed frequency deviation value in the i-th direction; represents the goodness of fit of the echo signal in the i-th direction for sine fitting; Extract the directions symmetric about the vertical direction in each direction and record them as the symmetric directions in each direction. represents the deviation amount of the goodness of fit between the i-th direction and its symmetric direction.

[0039] In this embodiment, the goodness of fit is R-squared. The calculation of R-squared is a well-known technology and will not be elaborated in this application. As other implementation manners, on the basis of being able to measure the fitting effect of each echo signal for sine fitting, implementers can adopt other existing technologies, such as the reciprocal of the mean square error, etc. This application does not make special restrictions.

[0040] In this embodiment, the deviation amount between the goodness of fit is the absolute value of the difference between the goodness of fit. As other implementation manners, on the basis of being able to measure the difference between the goodness of fit, implementers can adopt other existing technologies, such as the square of the difference, the ratio, etc. This application does not make special restrictions.

[0041] It should be noted that: during the actual measurement process, the geological conditions of the seabed will also affect the propagation speed of sound waves and the measurement of the seabed topography. Especially when the sound wave passes through soft sediments, the boundary recognition of the sound wave will become difficult, resulting in the measured sound wave propagation time, that is, the time difference may be inaccurate. Therefore, it is necessary to correct the time difference; the greater the sound speed correction coefficient, the greater the correction intensity required for the time difference.

[0042] Step 3: By comparing the time differences between each direction and its adjacent directions, and combining the angles between each direction and the vertical direction, obtain the spatial deviations of each direction, and correct the time differences of each direction in combination with the sound speed correction coefficient.

[0043] Furthermore, since the seabed of the ocean floor has a certain degree of coherence, during a single scan, the sound speeds in different directions have a certain spatial continuity, and the scan points in adjacent directions generally do not change abruptly. Therefore, it is necessary to combine the spatial distribution of all directions to achieve further analysis of the data.

[0044] Since the seabed depth value in the vertical direction is measured by a high-precision depth sounding device, the sound speed and seabed depth value in the vertical direction are used as the standard sound speed and seabed depth value. Generally, as the angle between the scan direction and the vertical direction increases, the propagation distance of the sound wave in the scan direction becomes farther, and the time difference between the transmitted signal and the received echo signal in the scan direction becomes larger. Therefore, when the deviation of the time difference in a certain direction from the time differences in the adjacent two directions is larger, the correlation of the observed value in the certain direction with the adjacent two directions in space is weaker, indicating that the certain direction is more severely affected by the sound speed deviation, and thus the time difference needs to be corrected with a greater correction intensity to ensure the accuracy of the seabed depth value calculated from the sound speed and the time difference.

[0045] Based on the above analysis, by comparing the time differences between each direction and its adjacent directions, and combining the angles between each direction and the vertical direction, obtain the spatial deviations of each direction. The expression is: ; where represents the spatial deviation of the i-th direction; form the two-dimensional feature points of each direction by combining the serial numbers and the time differences of each direction. When the time difference of a certain direction is greater than the time differences of its adjacent two directions, the opposite number of the area enclosed by the two-dimensional feature points of the certain direction and its adjacent two directions is denoted as the enclosed area; otherwise, the area enclosed by the two-dimensional feature points of the certain direction and its adjacent two directions is denoted as the enclosed area; represents the enclosed area enclosed by the i-th direction and its adjacent two directions; cos( ) represents the cosine function; represents the angle between the i-th direction and the vertical direction; represents the mean value of the enclosed areas enclosed by the two-dimensional feature points of all continuously adjacent three directions. Denote as the area ratio.

[0046] It should be noted that when the time differences in all directions are greater than those in their adjacent directions, the time differences in all directions need to be shortened. Conversely, the time differences in all directions are extended. Among them, when the i-th direction has only one adjacent direction, the spatial deviation of the adjacent direction of the i-th direction is used as the spatial deviation of the i-th direction.

[0047] Furthermore, the time differences in all directions are corrected by the spatial deviations and sound speed correction coefficients in all directions. The correction formula is: ; represents the corrected time difference in the i-th direction; represents the time difference before correction in the i-th direction; represents the sound speed correction coefficient in the i-th direction; represents the spatial deviation in the i-th direction; represents a preset non-zero scaling factor used to control the correction strength of the time difference. The larger it is, the finer the scaling, the smaller the correction strength but the higher the fineness. The smaller it is, the greater the correction strength but the lower the fineness. To balance the correction strength and fineness, the value range of is (10, 30) to ensure the value range of is (-0.3, 0.3); represents a preset correction step size. To avoid excessive adjustment of the time difference, in this embodiment, the correction step size is set to 10% of the time difference in the vertical direction. Denote as the correction ratio.

[0048] It should be noted that during the in-situ measurement on the seabed, comprehensively analyzing the situation of the transmitted signals and received echo signals in all directions during a single scan, as well as the spatial coherence characteristics of the scan points in multiple directions. When the actual sound speed is greater than the corrected sound speed, there are soft sediments on the seabed, and the time differences in all directions are greater than those in adjacent directions, at this time, the observed acoustic wave transmission time is greater than the actual acoustic wave transmission time. Therefore, the observed acoustic wave transmission time is shortened, that is, the time differences in all directions are shortened to improve the accuracy of the measurement result of the time difference. Conversely, the time differences in all directions are extended to correct the sound speed deviation generated when the sound speed in the vertical direction is used as the corrected sound speed for all directions. The schematic diagram of the time difference correction process is as Figure 2 shown.

[0049] Step 4, obtain the seabed depth values of the scan points in all directions through the correction results and the corrected sound speed, and construct a seabed topographic map.

[0050] By calculating the corrected time differences in each direction, the problem of different sound wave propagation speeds caused by uneven seabed water quality conditions can be effectively solved, thereby improving the measurement accuracy of seabed depth values.

[0051] Take half of the product of the corrected time differences in each direction and the corrected sound speed as the distance from the multibeam echosounder to the scanning points in each direction; according to the distance and the angle between each direction and the vertical direction, use trigonometric function relations to obtain the seabed depth values of the scanning points in each direction, and use a 3D modeling tool, such as CARIS, to obtain the seabed topographic map during the current in-situ seabed measurement. The schematic diagram of the calculation process of the seabed depth value is as Figure 3 shown.

[0052] Based on the same inventive concept as the above method, the embodiment of the present application also provides a high-precision in-situ seabed testing system based on acoustic assistance, including a memory, a processor, and a computer program stored in the memory and running on the processor. When the processor executes the computer program, it implements the steps of any one of the above methods of the high-precision in-situ seabed testing method based on acoustic assistance.

[0053] In summary, compared with the prior art, which obtains the seabed depth values of each scanning point based on the transmission time of sound waves and the propagation speed of each sound wave in seawater, while ignoring the problem that the propagation speed of sound waves varies at different seabed depths due to the limitation of seabed water quality conditions during the actual measurement process, resulting in errors in the seabed topography measurement results. By analyzing the echo signals in each direction, the sound speed frequency deviation value is obtained, which helps to quantify the propagation speed deviation of sound waves in different directions and provides a more accurate reference basis for subsequent time difference correction; Furthermore, by the difference in the goodness of fit of the sine fitting of the echo signals in different directions, combined with the sound speed frequency deviation value, the sound speed correction coefficient is obtained, which can comprehensively consider the frequency shift effect of sound waves during the propagation process and the fluctuation difference of echo signals, and can accurately reflect the propagation characteristics of sound waves in each direction, providing a more reasonable basis for the correction of time differences, thereby effectively reducing the measurement errors caused by differences in seabed geological conditions and improving the accuracy and reliability of seabed topography measurement; Furthermore, based on the difference amount between the time differences in adjacent directions, the spatial deviation is obtained, and combined with the sound speed correction coefficient, the time differences in each direction are corrected, which can more accurately correct the time differences in each direction, thereby balancing the influence brought by the sound speed difference during the sound wave transmission process, improving the accuracy of seabed depth measurement, and enabling the measurement results to more truly reflect the actual topography of the seabed.

[0054] The flowcharts and block diagrams in the accompanying drawings illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to embodiments of the present disclosure. In this regard, each block in the flowchart or block diagram may represent a module, a segment of a program, or a portion of code, which contains one or more executable instructions for implementing a specified logical function. In some alternative implementations, the functions noted in the blocks may occur out of the order noted in the drawings. For example, two consecutive blocks may actually be executed substantially in parallel, or they may sometimes be executed in the reverse order, depending on the functions involved. In the description corresponding to the flowcharts and block diagrams in the accompanying drawings, the operations or steps corresponding to different blocks may also occur out of the order disclosed in the description. Sometimes, there is no specific order between different operations or steps. For example, two consecutive operations or steps may actually be executed substantially in parallel, or they may sometimes be executed in the reverse order, depending on the functions involved. Each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, can be implemented by a dedicated hardware-based system that performs the specified functions or actions, or can be implemented by a combination of dedicated hardware and computer instructions.

[0055] For those skilled in the art, it is obvious that the present application is not limited to the details of the above-described exemplary embodiments, and without departing from the basic characteristics of the present application, the present application can be implemented in other specific forms. Therefore, from any point of view, the above embodiments of the present application should be regarded as exemplary and non-limiting.

Claims

1. An acoustic-assisted high-precision in-situ seafloor testing method, characterized in that The method includes the following steps: Obtain the echo signals in each direction when the multi-beam echosounder scans the seabed in real time, as well as the time differences between the transmitted signals and the received echo signals in each direction, where the direction perpendicular to the seabed is included; During a single scan, obtain the water depth in the vertical direction, and obtain the corrected sound speed in each direction through the water depth in the vertical direction and the time difference; Denote the frequency with the maximum energy intensity in the frequency domain of the echo signals in each direction as the main frequency, and obtain the sound speed frequency deviation value in each direction through the difference between the transmission frequency of the transmitted signal in each direction and the main frequency, combined with the difference in the 3dB bandwidth of the main frequency between each direction and the vertical direction; Obtain the goodness of fit of the echo signals in each direction for sine fitting, denote the direction symmetric to each direction with respect to the vertical direction as the symmetric direction, and obtain the sound speed correction coefficient in each direction through the goodness of fit in each direction and the deviation amount from the goodness of fit in the symmetric direction, combined with the sound speed frequency deviation value; Obtain the spatial deviation in each direction by comparing the time differences between each direction and its adjacent directions, combined with the angle between each direction and the vertical direction, and correct the time differences in each direction in combination with the sound speed correction coefficient; Denote the intersection point of the transmitted signal in each direction and the seabed as the scan point, and obtain the seabed depth value of the scan point in each direction through the correction result and the corrected sound speed, and construct a seabed topographic map.

2. The high-precision in-situ seabed testing method based on acoustic assistance according to claim 1, characterized in that, The calculation method of the corrected sound speed is as follows: Calculate the product of the time difference in the vertical direction and one-half; The corrected sound speed is the product of the water depth and the product; 3. The high-precision in-situ seabed testing method based on acoustic assistance according to claim 1, characterized in that, The process of obtaining the sound speed frequency deviation value is as follows: Calculate the difference between the transmission frequency of the transmitted signal in each direction and the main frequency; Take the opposite number of the difference amount as the exponent of the exponential function with the natural constant as the base; The sound speed frequency deviation value is directly proportional to the difference and inversely proportional to the calculation result of the exponential function; 4. The high-precision in-situ seabed testing method based on acoustic assistance according to claim 3, wherein, The sound speed frequency deviation value is the normalized value of the ratio of the difference to the calculation result of the exponential function; 5. The high-precision in-situ seabed testing method based on acoustic assistance according to claim 1, wherein The process of obtaining the sound speed correction coefficient is as follows: Calculate the absolute value of the sum of the goodness of fit and the deviation amount in each direction; the sound speed correction coefficient is the product of the sound speed frequency deviation value and the absolute value; 6. The high-precision in-situ seabed testing method based on acoustic assistance according to claim 1, wherein, The process of obtaining the spatial deviation is as follows: Form two-dimensional feature points of each direction by combining the serial number of each direction and the time difference. When the time difference in each direction is greater than the time differences in its two adjacent directions, denote the opposite number of the area enclosed by the two-dimensional feature points of each direction and its two adjacent directions as the enclosed area; otherwise, denote the area enclosed by the two-dimensional feature points of each direction and its two adjacent directions as the enclosed area; Calculate the mean value of the enclosed areas formed by the two-dimensional feature points of all continuously adjacent three directions; Denote the ratio of the enclosed area to the mean value as the area ratio; The spatial deviation is the product of the area ratio and the cosine value of the angle; 7. The high-precision in-situ seabed testing method based on acoustic assistance according to claim 1, wherein, The method of correcting the time differences in each direction is as follows: Calculate the cumulative value of the sound speed correction coefficient and the spatial deviation; Denote the ratio of the cumulative value to a non-zero preset scaling factor as the correction ratio; Calculate the product value of the correction ratio and a preset correction step size; Correct the time differences in each direction by the product value.

8. The high-precision in-situ seabed testing method based on acoustic assistance according to claim 7, wherein The step of correcting the time differences in each direction by the product value includes: using the sum value of the product value and the time differences in each direction as the corrected time differences in each direction.

9. The high-precision in-situ seabed testing method based on acoustic assistance according to claim 1, characterized in that, The step of obtaining the seabed depth values of the scanning points in each direction includes: Taking half of the product of the corrected time differences in each direction and the corrected sound speed as the distance from the multibeam echosounder to the scanning points in each direction; and obtaining the seabed depth values of the scanning points in each direction according to the distance and the included angle by using trigonometric function relations.

10. A high-precision in-situ seabed testing system based on acoustic assistance, comprising a memory, a processor, and a computer program stored in the memory and running on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the high-precision seabed in-situ testing method based on acoustic assistance according to any one of claims 1-9.

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