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

Abstract

The present application relates to the field of underwater acoustic detection technology, and specifically to a high-precision seabed in-situ testing method and system based on acoustic assistance. The method comprises: obtaining echo signals in all directions when a multi-beam echo sounder scans the seabed in real time, as well as the time difference between the transmitted signal and the received echo signal in each direction; obtaining the corrected sound velocity and sound velocity frequency deviation value in each direction during a single scan; obtaining the goodness of fit of the echo signals in each direction for sinusoidal fitting, obtaining the sound velocity correction coefficient in each direction by combining the goodness of fit in each direction and its deviation from the goodness of fit in the symmetrical direction, and correcting the time difference in each direction by comparing the time difference in each direction with its adjacent direction and combining the angle between each direction and the vertical direction; obtaining the seabed depth value at the scanning point in each direction and constructing a seabed topography map. The present application aims to improve the accuracy of seabed depth measurement.

Description

Technical Field

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

[0002] In-situ seafloor surveying involves directly measuring and analyzing the geological, physical, and chemical properties of the seafloor in its original location and environmental conditions. By eliminating the need to retrieve seafloor material for laboratory testing and conducting measurements directly on the seafloor, the effects of the sampling process, such as changes in pressure, temperature, and chemical composition, can be avoided, enabling more accurate acquisition of true seafloor data. Seafloor topography measurement is a key component of in-situ seafloor surveying.

[0003] Currently, acoustic multi-beam sounding technology is commonly used for seafloor topography measurement. The paper "Research on Three-Dimensional Seafloor Modeling Based on Multi-Beam Bathymetry Anomaly Detection" proposes a method based on seafloor topography modeling, which uses trend surface filtering to detect multi-beam bathymetry anomalies, thereby enabling seafloor topography detection. However, in actual measurements, the actual speed of the sound waves changes during seawater detection due to the heterogeneity of the seawater, causing the sound lines to bend and resulting in errors in the seafloor topography measurement results. Summary of the Invention

[0004] In view of the above, it is necessary to provide a high-precision seabed in-situ testing method and system based on acoustic assistance, which improves the accuracy of seabed depth measurement compared with traditional high-precision seabed in-situ testing methods:

[0005] In a first aspect, an embodiment of the present application provides a high-precision seabed in-situ testing method based on acoustic assistance, the method comprising the following steps:

[0006] Real-time acquisition of echo signals in all directions when the multi-beam echo sounder scans the seabed, as well as the time difference between the transmitted signal and the received echo signal in all directions, including the direction perpendicular to the seabed;

[0007] During a single scan, the water depth in the vertical direction is obtained, and the corrected sound speed in each direction is obtained by using the water depth in the vertical direction and the time difference;

[0008] The frequency with the maximum energy intensity of the echo signal in each direction in the frequency domain is recorded as the main frequency, and the sound velocity frequency deviation value in each direction is obtained by the difference between the transmission frequency of the transmission 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 perpendicular direction;

[0009] Obtaining the goodness of fit of the echo signal in each direction for sinusoidal fitting, recording the direction symmetrical about the vertical direction as the symmetric direction, and obtaining the sound velocity correction coefficient in each direction by combining the goodness of fit in each direction and its deviation from the goodness of fit in the symmetric direction with the sound velocity frequency deviation value;

[0010] By comparing the time difference between each direction and its adjacent direction, combining the angle between each direction and the vertical direction, obtaining the spatial deviation of each direction, and combining the sound speed correction coefficient, correcting the time difference in each direction;

[0011] The intersection of the transmitted signal in each direction and the seabed is recorded as a scanning point. The seabed depth value of the scanning point in each direction is obtained through the correction result and the corrected sound speed to construct a seabed topography map.

[0012] In one embodiment, the calculation method of the corrected sound velocity is:

[0013] Calculating the product of the time difference in the vertical direction and one half;

[0014] The corrected sound velocity is the product of the water depth and the product.

[0015] In one embodiment, the process of obtaining the sound velocity frequency deviation value is as follows:

[0016] Calculating the difference between the transmission frequency of the transmission signal in each direction and the main frequency;

[0017] Taking the opposite of the difference as the exponent of an exponential function with a natural constant as the base;

[0018] The sound velocity frequency deviation value is directly proportional to the difference value and inversely proportional to the calculation result of the exponential function.

[0019] In one embodiment, the sound velocity frequency deviation value is a normalized value of the ratio of the difference value to a calculation result of the exponential function.

[0020] In one embodiment, the process of obtaining the sound velocity correction coefficient is as follows:

[0021] The absolute value of the sum of the goodness of fit and the deviation in each direction is calculated; and the sound velocity correction coefficient is the product of the sound velocity frequency deviation value and the absolute value.

[0022] In one embodiment, the process of obtaining the spatial deviation is:

[0023] The sequence number of each direction and the time difference are combined to form a two-dimensional feature point in each direction. When the time difference in each direction is greater than the time difference in its two adjacent directions, the inverse of the area enclosed by the two-dimensional feature points in each direction and its two adjacent directions is recorded as the enclosed area; otherwise, the area enclosed by the two-dimensional feature points in each direction and its two adjacent directions is recorded as the enclosed area.

[0024] Calculating the average value of the enclosed area of ​​all consecutive adjacent two-dimensional feature points in three directions; recording the ratio of the enclosed area to the average value as the area ratio;

[0025] The spatial deviation is the product of the area ratio and the cosine value of the included angle.

[0026] In one embodiment, the method for correcting the time difference in each direction is:

[0027] Calculating a cumulative value of the sound velocity correction coefficient and the spatial deviation;

[0028] The ratio of the accumulated value to the preset non-zero scaling factor is recorded as a correction ratio;

[0029] Calculating the product of the correction ratio and a preset correction step length;

[0030] The time difference in each direction is corrected using the product value.

[0031] In one embodiment, correcting the time difference in each direction by using the product value includes: taking the sum of the product value and the time difference in each direction as the corrected time difference in each direction.

[0032] In one embodiment, obtaining the seabed depth value of the scanning point in each direction includes:

[0033] Half of the product of the corrected time difference and the corrected sound speed in each direction is used as the distance from the multi-beam echo sounder to the scanning point in each direction; based on the distance and the angle, the seabed depth value of the scanning point in each direction is obtained using a trigonometric function relationship.

[0034] In the second aspect, an embodiment of the present application also provides a high-precision seabed in-situ testing system based on acoustic assistance, comprising 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 any one of the above-mentioned high-precision seabed in-situ testing methods based on acoustic assistance are implemented.

[0035] This application has at least the following beneficial effects:

[0036] Compared with the prior art, the present application obtains the seabed depth value of each scanning point based on the propagation speed of each sound wave in seawater during the transmission time of the sound wave, while ignoring the problem that the propagation speed of the sound wave at different depths of the seabed is different due to the limitations of the seabed water quality conditions during the actual measurement process, which leads to 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 the sound wave in different directions and provide a more accurate reference basis for subsequent time difference correction;

[0037] Furthermore, by taking into account the difference in goodness of fit of sinusoidal fitting of echo signals in different directions and combining it with the sound velocity frequency deviation value, the sound velocity correction coefficient is obtained. This can comprehensively consider the frequency shift effect of the sound wave during propagation and the fluctuation difference of the echo signal, accurately reflect the propagation characteristics of the sound wave in various directions, and provide a more reasonable basis for the correction of the time difference, thereby effectively reducing the measurement error caused by differences in seabed geological conditions and improving the accuracy and reliability of seabed topography measurement.

[0038] Furthermore, based on the difference between the time differences in adjacent directions, the spatial deviation is obtained, and combined with the sound speed correction coefficient, the time difference in each direction is corrected. This can more accurately correct the time difference in each direction, thereby balancing the impact of the sound speed difference in the sound wave transmission process, improving the accuracy of seabed depth measurement, and making the measurement results more realistically reflect the actual topography of the seabed. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions and advantages of the embodiments of the present application or the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0040] Figure 1 A flowchart of the steps of a high-precision seabed in-situ testing method based on acoustic assistance provided in one embodiment of the present application;

[0041] Figure 2 Schematic diagram of the time difference correction process;

[0042] Figure 3 Schematic diagram of the calculation process of seabed depth value. DETAILED DESCRIPTION

[0043] In the description of the embodiments of this application, words such as "exemplary," "or," and "for example" are used to indicate examples, illustrations, or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of this application should not be construed as being preferred or advantageous over other embodiments or designs. Rather, the use of words such as "exemplary," "or," and "for example" is intended to present the relevant concepts in a concrete manner.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application relates. The terms used in this application are for the purpose of describing specific embodiments only and are not intended to limit this application. It should be understood that, unless otherwise indicated, " / " represents or.

[0045] It should also be noted that the terms "first" and "second" in this application are used to distinguish similar objects, rather than to describe a specific order or sequence.

[0046] The specific scheme of the acoustically assisted high-precision seabed in-situ testing method and system provided by this application is described in detail below with reference to the accompanying drawings.

[0047] See also Figure 1 , which shows a flowchart of a high-precision seabed in-situ testing method based on acoustic assistance provided by an embodiment of the present application, the method comprising the following steps:

[0048] Step 1: Acquire in real time the echo signals in all directions when the multi-beam echo sounder scans the seabed, as well as the time difference between the transmitted signal and the received echo signal in all directions, including the direction perpendicular to the seabed.

[0049] During seafloor exploration, sound waves are the only known energy form and information carrier that can propagate long distances underwater and be utilized by humans. Specifically, for both 10kHz sound waves and electromagnetic waves, the attenuation of sound waves in water is 1 decibel per kilometer, while the attenuation of electromagnetic waves is 3000 decibels per kilometer. Therefore, this application uses sound waves as an acoustic aid and implements seafloor topography measurement based on multi-beam detection technology.

[0050] For areas requiring in-situ measurements, a multibeam echosounder is suspended from the bottom of a survey vessel, which accurately determines its position by receiving Global Navigation Satellite System (GNSS) signals. The multibeam echosounder's scanning direction is perpendicular to the vessel's direction of travel, and the vessel is controlled to maintain a constant speed. During the multibeam echosounder's scanning process, the vessel conducts a scan every 10% of the average depth of the surveyed area.

[0051] During a single scan, the multibeam echo sounder can cover an area 50 meters wide in the direction of the survey vessel's travel, acquiring depth information for that area. W scanning directions are evenly set, with the angle perpendicular to the seabed set at 0°, and signals are transmitted in W directions. The echo signals from each direction as the multibeam echo sounder scans the seabed are acquired in real time, along with the time difference between the transmitted and received echo signals in each direction.

[0052] It should be noted that the transmitting device in the measurement process of the multi-beam echo sounder is a low-frequency, high-power transmitting transducer with a transmitting frequency of 500 Hz and a sine wave transmitting duration of 50 ms. The receiving transducer of the multi-beam echo sounder can receive echo signals in all directions.

[0053] In this embodiment, the value of W is 101. The value of W is preset manually and can be set by the implementer. This application does not impose any special restrictions.

[0054] In addition, since the survey ship is not level during navigation, a level meter needs to be deployed on the survey ship to obtain the tilt state of the survey ship itself in real time and correct the scanning direction.

[0055] 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.

[0056] When using a multi-beam echo sounder to measure seabed topography, the basic principle is to use the propagation time difference between the transmitted signal and the echo signal, as well as the propagation speed of sound waves in seawater, to determine the true distance from the survey vessel to the seabed in each scanning direction. The intersection of the transmitted signal in each direction and the seabed is recorded as the scanning point, and the seabed depth value at the scanning point in each scanning direction is obtained using trigonometric functions based on the transmission angle. Although this measurement method is simple, it assumes that the propagation speed of sound waves in seawater is constant. However, in actual measurements, the propagation speed of sound waves in seawater may vary due to the influence of seawater quality conditions such as water pressure, water temperature, and salinity, resulting in deviations in the seabed depth measurement results.

[0057] Step 2.1: During a single scan, obtain the water depth in the vertical direction, and obtain the corrected sound speed in each direction using the water depth in the vertical direction and the time difference. Record the frequency with the highest energy intensity of the echo signal in each direction in the frequency domain as the main frequency, and obtain the sound speed frequency deviation value in each direction by taking the difference between the transmission frequency of the transmission 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.

[0058] During a single scan, the echo signals in all directions are analyzed. The larger the angle between a certain direction and the vertical direction, the greater the deviation in the actual sound speed in that direction. The echo signal in that direction may exhibit a smile curve or a crying face curve. Specifically, when the actual sound speed is less than the corrected sound speed, a smile curve is exhibited, while when the actual sound speed is greater than the corrected sound speed, a crying face curve effect is exhibited. The corrected sound speed is calculated by extracting the vertical time difference when the multi-beam echo sounder scans the seabed, using a high-precision sounding device, such as a single-beam echo sounder, to measure the water depth in the vertical direction, and calculating the product of the vertical time difference and one-half. The product of the water depth and the product is used as the corrected sound speed in each direction.

[0059] For non-perpendicular incidence directions, the propagation of the transmitted signal is affected by a variety of factors. The actual speed of the transmitted signal may vary due to factors such as seawater temperature, salinity, and pressure, which in turn causes a frequency shift effect during the propagation of the sound wave. Furthermore, the non-uniformity of the seawater medium causes the echo signal from the non-perpendicular incidence direction to exhibit dispersion. Therefore, the echo signals from each direction are converted from the time domain to the frequency domain, and the frequency with the highest energy intensity in the frequency domain is recorded as the primary frequency.

[0060] In this embodiment, the fast Fourier transform is used to convert the sound wave signal from the time domain to the frequency domain. The fast Fourier transform is a well-known technology and will not be described in detail in this application. As other implementation methods, on the basis of being able to convert the sound wave signal from the time domain to the frequency domain, the implementer can adopt other existing technologies, such as discrete Fourier transform, etc., and this application does not impose any special restrictions.

[0061] Furthermore, the sound velocity frequency deviation value in each direction is obtained by taking the difference between the transmission frequency of the transmission signal in each direction and the main frequency and combining the difference in the 3dB bandwidth of the main frequency between each direction and the perpendicular direction. The expression is:

[0062] Where, represents the sound velocity frequency deviation value in the i-th direction; ceil() represents the maximum absolute value normalization function; Indicates the transmission frequency of the transmission signal in the i-th direction. In this embodiment, 500Hz; represents the main frequency in the i-th direction; exp( ) represents an exponential function with a natural constant as the base; represents the difference in 3dB bandwidth of the main frequency between the ith direction and the vertical direction. 3dB bandwidth is a well-known technology and will not be described in detail in this application.

[0063] In this embodiment, the difference between the 3dB bandwidths is the absolute value of the difference. As other implementation methods, on the basis of being able to measure the difference between the 3dB bandwidths, the implementer may adopt other calculation methods, such as the square of the difference, the ratio, etc., and this application does not impose any special restrictions.

[0064] It should be noted that the calculated sound velocity frequency deviation value has positive and negative properties. When the actual sound velocity is greater than the estimated corrected sound velocity, the sound wave propagates faster, causing the frequency difference to shift toward a negative value. Conversely, when the actual sound velocity is less than the estimated corrected sound velocity, the sound wave propagates slower, causing the frequency difference to shift toward a positive value. Furthermore, the greater the difference between the actual sound velocity and the estimated corrected sound velocity, the more severe the dispersion of the echo signal. Since sound waves in the vertical direction are least subject to interference, the 3dB bandwidth in the vertical direction is used as a reference. The greater the deviation of the 3dB bandwidth between the i-th direction and the vertical direction, the greater the sound velocity frequency deviation value.

[0065] Step 2.2, obtain the goodness of fit of the echo signal in each direction for sinusoidal fitting, record the direction that is symmetrical about the vertical direction as the symmetric direction, and obtain the sound velocity correction coefficient in each direction through the goodness of fit in each direction and its deviation from the goodness of fit in the symmetric direction, combined with the sound velocity frequency deviation value.

[0066] In addition, the geological conditions of the seabed will also affect the reflection of sound waves. Among them, the geological conditions of the seabed are generally divided into two types. One is hard sediments such as seabed shale, which are formed by the compression of the seabed crust or volcanic eruptions. The other is soft sediments such as loose mud, which are formed by the decomposition of plants and animals and soil deposition. Hard sediments can often directly reflect sound waves, making the characteristics of the echo signal obvious. For soft sediments, since the degree of change of the medium during the propagation of sound waves is large, the echo signal is easily affected by large fluctuations, which may cause large waveform distortion of the echo signal, affecting the measurement results of the time difference.

[0067] Based on the above analysis, the goodness of fit of the echo signal in each direction is obtained for sinusoidal fitting. The sound velocity correction coefficient in each direction is obtained by combining the goodness of fit in each direction and its deviation from the goodness of fit in the vertical direction with the sound velocity frequency deviation value. The expression is:

[0068] ; represents the sound velocity correction coefficient in the i-th direction; represents the sound velocity frequency deviation value in the i-th direction; Indicates the goodness of fit of the sine fitting of the echo signal in the i-th direction; extract the direction that is symmetrical about the vertical direction and record it as the symmetric direction of each direction, It represents the deviation of the goodness of fit between the i-th direction and its symmetric direction.

[0069] In this embodiment, the goodness of fit is R-squared. The calculation of R-squared is a well-known technology and will not be described in detail in this application. As other implementation methods, on the basis of being able to measure the fitting effect of sinusoidal fitting of each echo signal, the implementer may adopt other existing technologies, such as the inverse of the mean square error, etc., and this application does not impose any special restrictions.

[0070] In this embodiment, the deviation between the goodness of fit is the absolute value of the difference between the goodness of fit. As other implementation methods, on the basis of being able to measure the difference between the goodness of fit, the implementer can adopt other existing technologies, such as the square of the difference, the ratio, etc., and this application does not impose any special restrictions.

[0071] It should be noted that during the actual measurement process, the geological conditions of the seabed will also affect the propagation speed of the sound waves and the measurement of the seabed topography. In particular, when the sound waves pass through soft sediments, it will become difficult to identify the boundaries of the sound waves, resulting in the measured sound wave propagation time, that is, the time difference, may be inaccurate. Therefore, the time difference needs to be corrected; the larger the sound speed correction coefficient, the greater the correction force required for the time difference.

[0072] Step 3: By comparing the time difference between each direction and its adjacent direction and combining the angle between each direction and the vertical direction, the spatial deviation of each direction is obtained, and the time difference in each direction is corrected in combination with the sound speed correction coefficient.

[0073] Furthermore, since the seabed has a certain degree of continuity, the sound speed in different directions has a certain spatial continuity during a single scan, and the scanning points in adjacent directions generally do not change suddenly. Therefore, it is necessary to combine the spatial distribution in all directions to achieve further analysis of the data.

[0074] Since the vertical seabed depth value is measured by a high-precision sounding device, the sound velocity and seabed depth values ​​in the vertical direction are used as standard sound velocity and seabed depth values. Generally speaking, as the angle between the scanning direction and the vertical direction increases, the sound wave propagation distance in the scanning direction increases, and the time difference between the transmitted signal and the received echo signal in the scanning direction increases. Therefore, when the deviation between the time difference in a certain direction and the time difference in the two adjacent directions increases, the spatial correlation between the observation value in the certain direction and the two adjacent directions becomes weaker, indicating that the direction is more seriously affected by the sound velocity deviation, and the time difference needs to be corrected and the correction strength is greater to ensure the accuracy of the seabed depth value calculated by the sound velocity and time difference.

[0075] Based on the above analysis, by comparing the time difference between each direction and its adjacent direction and combining the angle between each direction and the vertical direction, the spatial deviation of each direction is obtained, and the expression is:

[0076] Where, Represents the spatial deviation of the i-th direction; the sequence number of each direction and the time difference constitute the two-dimensional feature point of each direction. When the time difference of each direction is greater than the time difference of its two adjacent directions, the inverse of the area enclosed by the two-dimensional feature points of each direction and its two adjacent directions is recorded as the enclosed area; otherwise, the area enclosed by the two-dimensional feature points of each direction and its two adjacent directions is recorded as the enclosed area; represents the area enclosed by the i-th direction and its two adjacent directions; cos() represents the cosine function; represents the angle between the i-th direction and the vertical direction; Represents the mean value of the area enclosed by all consecutive adjacent two-dimensional feature points in three directions. Recorded as area ratio.

[0077] It should be noted that when the time difference in each direction is greater than the time difference in its adjacent direction, the time difference in each direction needs to be shortened; otherwise, the time difference in each direction needs to be lengthened. 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.

[0078] Furthermore, the time difference in each direction is corrected by the spatial deviation and sound speed correction coefficient in each direction. The correction formula is:

[0079] ; represents the time difference after correction in the i-th direction; represents the time difference before correction in the i-th direction; represents the sound velocity correction coefficient in the i-th direction; represents the spatial deviation in the i-th direction; Indicates a non-zero scaling factor, used to control the correction strength of the time difference. The larger it is, the finer the zoom, the smaller the correction strength but the higher the precision. The smaller it is, the greater the correction strength but the lower the precision. To balance the correction strength and precision, The value range is (10,30), ensuring The value range is (-0.3, 0.3); Indicates the preset correction step size. To avoid over-adjustment of the time difference, the correction step size is set to 10% of the time difference in the vertical direction in this embodiment. Recorded as the correction ratio.

[0080] It should be noted that: during the in-situ measurement of the seabed, the transmitted signals and received echo signals in each direction, as well as the spatial coherence characteristics of the scanning points in multiple directions, are comprehensively analyzed during a single scan. When the actual sound speed is greater than the corrected sound speed, there are soft sediments on the seabed, and the time difference in each direction is greater than the time difference in the adjacent directions, then the observed sound wave transmission time is greater than the actual sound wave transmission time. Therefore, the observed sound wave transmission time is shortened, that is, the time difference in each direction is shortened to improve the accuracy of the time difference measurement results. Conversely, the time difference in each direction is extended to achieve the correction of the sound speed deviation generated when the sound speed in the vertical direction is used as the corrected sound speed in each direction. The schematic diagram of the time difference correction process is shown as follows. Figure 2 shown.

[0081] Step 4: Obtain the seabed depth values ​​of the scanning points in each direction using the correction results and the corrected sound velocity, and construct a seabed topography map.

[0082] By calculating the corrected time difference in each direction, the problem of differences in sound wave propagation speed due to uneven seabed water conditions can be effectively solved, thereby improving the measurement accuracy of the seabed depth value.

[0083] The half of the product of the corrected time difference and the corrected sound velocity in each direction is used as the distance from the multi-beam echo sounder to the scanning point in each direction; based on the distance and the angle between each direction and the vertical direction, the seabed depth value of the scanning point in each direction is obtained using trigonometric function relationships, and a three-dimensional modeling tool such as CARIS is used to obtain the seabed topography during the current seabed in-situ measurement process. The schematic diagram of the calculation process of the seabed depth value is shown in the figure below. Figure 3 shown.

[0084] Based on the same inventive concept as the above method, an embodiment of the present application also 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, it implements the steps of any one of the above-mentioned high-precision seabed in-situ testing methods based on acoustic assistance.

[0085] In summary, compared with the prior art, which obtains the seabed depth value of each scanning point based on the propagation speed of each sound wave in seawater during the transmission time of the sound wave, the present application ignores the problem that the propagation speed of the sound wave at different depths of the seabed is different due to the limitations of the 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 and obtaining the sound speed frequency deviation value, the present application helps to quantify the propagation speed deviation of the sound wave in different directions, providing a more accurate reference basis for subsequent time difference correction.

[0086] Furthermore, by taking into account the difference in goodness of fit of sinusoidal fitting of echo signals in different directions and combining it with the sound velocity frequency deviation value, the sound velocity correction coefficient is obtained. This can comprehensively consider the frequency shift effect of the sound wave during propagation and the fluctuation difference of the echo signal, accurately reflect the propagation characteristics of the sound wave in various directions, and provide a more reasonable basis for the correction of the time difference, thereby effectively reducing the measurement error caused by differences in seabed geological conditions and improving the accuracy and reliability of seabed topography measurement.

[0087] Furthermore, based on the difference between the time differences in adjacent directions, the spatial deviation is obtained, and combined with the sound speed correction coefficient, the time difference in each direction is corrected. This can more accurately correct the time difference in each direction, thereby balancing the impact of the sound speed difference in the sound wave transmission process, improving the accuracy of seabed depth measurement, and making the measurement results more realistically reflect the actual topography of the seabed.

[0088] The flowcharts and block diagrams in the accompanying drawings show the possible implementation architectures, functions and operations of the systems, methods and computer program products according to the embodiments of the present disclosure. In this regard, each box in the flowchart or block diagram can represent a module, program segment or part of the code, and the module, program segment or part of the code contains one or more executable instructions for implementing the specified logical functions. In some alternative implementations, the functions marked in the box can also occur in an order different from that marked in the accompanying drawings. For example, two consecutive boxes can actually be executed substantially in parallel, or they can sometimes be executed in the opposite order, which can depend on the functions involved. In the descriptions corresponding to the flowcharts and block diagrams in the accompanying drawings, the operations or steps corresponding to different boxes can also occur in an order different from that disclosed in the description, and sometimes there is no specific order between different operations or steps. For example, two consecutive operations or steps can actually be executed substantially in parallel, or they can sometimes be executed in the opposite order, which can depend on the functions involved. Each block in the block diagrams and / or flowcharts, and combinations of blocks in the block diagrams and / or flowcharts, may be implemented by a dedicated hardware-based system that performs the specified function or action, or may be implemented by a combination of dedicated hardware and computer instructions.

[0089] It is obvious to those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and that the present application can be implemented in other specific forms without departing from the basic characteristics of the present application. Therefore, from all perspectives, the above embodiments of the present application should be regarded as exemplary and non-restrictive.

Claims

1. A high-precision seabed in-situ testing method based on acoustic assistance, characterized in that: The method comprises the following steps: Real-time acquisition of echo signals in all directions when the multi-beam echo sounder scans the seabed, as well as the time difference between the transmitted signal and the received echo signal in all directions, including the direction perpendicular to the seabed; During a single scan, the water depth in the vertical direction is obtained, and the corrected sound speed in each direction is obtained by using the water depth in the vertical direction and the time difference; The frequency with the maximum energy intensity of the echo signal in each direction in the frequency domain is recorded as the main frequency. The sound velocity frequency deviation value in each direction is obtained by taking the difference between the transmission frequency of the transmission 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; the goodness of fit of the echo signal in each direction is obtained by performing sinusoidal fitting, and the direction that is symmetrical about the vertical direction in each direction is recorded as the symmetrical direction. The sound velocity correction value in each direction is obtained by taking the goodness of fit in each direction and its deviation from the goodness of fit in the symmetrical direction, combined with the sound velocity frequency deviation value. Positive coefficient; by comparing the time difference between each direction and its adjacent direction, combined with the angle between each direction and the vertical direction, obtaining the spatial deviation of each direction, and combining the sound speed correction coefficient, correcting the time difference in each direction; recording the intersection of the transmitted signal in each direction and the seabed as a scanning point, and taking half of the product of the corrected time difference in each direction and the corrected sound speed as the distance from the multibeam echo sounder to the scanning point in each direction; according to the distance and the angle, using the trigonometric function relationship, obtaining the seabed depth value of the scanning point in each direction, and constructing a seabed topography map; The calculation formula of the sound velocity frequency deviation value is: Where, represents the sound velocity frequency deviation 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; represents the main frequency in the i-th direction; exp( ) represents an exponential function with a natural constant as the base; represents the difference in the 3dB bandwidth of the main frequency between the ith direction and the perpendicular direction; The calculation formula of the sound velocity correction coefficient is: ; represents the sound velocity correction coefficient in the i-th direction; represents the sound velocity frequency deviation value in the i-th direction; Indicates the goodness of fit of the sine fitting of the echo signal in the i-th direction; extract the direction that is symmetrical about the vertical direction and record it as the symmetric direction of each direction, represents the deviation of the goodness of fit between the i-th direction and its symmetric direction; The calculation formula of the spatial deviation is: Where, Represents the spatial deviation of the i-th direction; the sequence number of each direction and the time difference constitute the two-dimensional feature point of each direction. When the time difference of each direction is greater than the time difference of its two adjacent directions, the inverse of the area enclosed by the two-dimensional feature points of each direction and its two adjacent directions is recorded as the enclosed area; otherwise, the area enclosed by the two-dimensional feature points of each direction and its two adjacent directions is recorded as the enclosed area; represents the area enclosed by the i-th direction and its two adjacent directions; cos() represents the cosine function; represents the angle between the i-th direction and the vertical direction; represents the mean value of the area enclosed by all consecutive adjacent two-dimensional feature points in three directions; The correction formula for correcting the time difference in each direction is: ; represents the time difference after correction in the i-th direction; represents the time difference before correction in the i-th direction; represents the sound velocity correction coefficient in the i-th direction; represents the spatial deviation in the i-th direction; Indicates that the preset scaling factor is not 0; Indicates the preset calibration step size.

2. The high-precision seabed in-situ testing method based on acoustic assistance according to claim 1, characterized in that: The calculation method of the corrected sound velocity is: Calculating the product of the time difference in the vertical direction and one half; The corrected sound velocity is the product of the water depth and the product.

3. A high-precision seabed in-situ 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, the steps of the acoustically assisted high-precision seabed in-situ testing method as described in any one of claims 1-2 are implemented.

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