Ocean internal wave feature extraction method based on acoustic echo intensity

Abstract

The invention discloses an ocean internal wave feature extraction method based on acoustic echo intensity, which comprises the following steps of: arranging acoustic emission receivers at three different positions in a target sea area, acquiring acoustic echo intensity profile data at the different positions, and extracting an ocean internal wave feature according to an acoustic echo intensity profile gradient maximum value and an occurrence frequency; and calibrating the generation depth, amplitude and period information of the internal wave, and calculating the propagation direction and propagation speed of the internal wave according to the distance between every two stations and the time delay. According to the technical scheme, key information such as the wavelength, the period, the amplitude, the propagation speed and the propagation direction of the internal waves can be accurately and rapidly extracted, and the method is suitable for monitoring and early warning of the ocean internal waves.

Description

Technical Field

[0001] The present invention belongs to the field of information technology technology, and in particular relates to a method for extracting ocean internal wave features based on acoustic echo intensity. Background Art

[0002] Internal waves are undulations within a stably stratified ocean water column. Unlike surface waves, their maximum amplitude occurs below the sea surface. They have a phase velocity of approximately 1 meter per second, amplitudes ranging from a few to tens of meters, wavelengths from nearly 100 meters to tens of kilometers, and periods ranging from minutes to tens of hours. They are a key factor in mixing seawater and forming its fine structure. The fluctuations in the isopycnal surfaces caused by internal waves alter the magnitude and direction of sound speed, significantly affecting sonar, hindering the navigation of underwater vessels, and potentially damaging offshore facilities. Therefore, the observation of internal waves and the analysis and extraction of their characteristics are of great practical significance.

[0003] Ocean internal waves vary randomly in time and space, with a wide frequency range, requiring rapid and intensive sampling over extended periods of time. Recently developed general-purpose oceanographic survey instruments can meet these observational requirements. The most commonly used observation device is an anchored, self-contained current meter, which can simultaneously measure seawater temperature, salinity, depth, and other parameters. Internal waves can also be detected using acoustic waves and other methods. Arranging multiple anchored devices and instruments into a three-dimensional instrument array allows calculation of the phase velocity of internal wave propagation and the inference of the wave's origin and destination.

[0004] The sea area where the ocean internal waves pass through will cause strong vertical velocity shear to the seawater inside the area. This strong vertical shear causes abnormal vertical distribution of small particle scatterers in the water body, which provides a strong condition for using sound wave intensity to detect the distribution of ocean internal waves.

[0005] The above-mentioned anchored buoy measures internal waves by contact, but this method may cause entanglement and other effects on ship navigation. Therefore, non-contact measurement methods of internal waves, such as using acoustic detection to observe ocean internal waves, are extremely important for sea areas with a high navigation density. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for extracting ocean internal wave characteristics based on acoustic echo intensity.

[0007] To achieve the above object, the present invention adopts the following technical solutions: A method for extracting ocean internal wave features based on acoustic echo intensity, comprising: Deploy three acoustic wave transmitters and receivers at fixed points in the target sea area; The three acoustic wave transmitters and receivers transmit acoustic waves upward or downward, receive echo signals reflected by scatterers in the seawater, and obtain the profile distribution of acoustic wave echo intensity at different seawater depths at the three stations; According to the acoustic echo intensity profile distribution at each station, the gradient test algorithm is used to calculate the acoustic echo intensity gradient distribution at each station, and the time range and depth where the echo intensity maximum occurs are found; The location of the maximum echo intensity is marked, and the frequency of the signal is calculated using the wavelet transform method. Signals whose echo intensity maximum frequency falls within the internal wave frequency band are marked as ocean internal waves. The depth, fluctuation amplitude, and period of the ocean internal waves are obtained from the depth of the maximum distribution of the acoustic echo intensity gradient at each station, the range of signal fluctuations at different depths, and the frequency of the signal. The time delay of the ocean internal wave is obtained based on the time range of the maximum echo intensity between each two stations; According to the distance between each two stations and the time delay of the ocean internal waves, the propagation direction and speed of the internal waves are obtained.

[0008] Preferably, when three acoustic wave transmitters and receivers are deployed in the ocean, the stations are distributed in an isosceles triangle, and the distance between the stations should be 10 to 100 kilometers.

[0009] Preferably, when the three acoustic wave transmitters and receivers are deployed in the ocean, the directions of the acoustic wave transmitter and receiver probes deviate from the vertical by 0 to 30 degrees.

[0010] Preferably, the three sound wave transmitters and receivers have a time interval between transmitting adjacent sound waves of 30 seconds to 1 minute.

[0011] Preferably, three sound wave transmitters and receivers are mounted on a buoy on the sea surface to transmit sound waves downward.

[0012] Preferably, three acoustic wave transmitters and receivers are placed on the seabed and transmit upward.

[0013] The present invention deploys acoustic transmitters and receivers at three different locations in the target sea area. By acquiring acoustic echo intensity profile data at each location, the depth, amplitude, and period of internal waves are calibrated based on the maximum gradient and frequency of the acoustic echo intensity profile. The propagation direction and velocity of internal waves are calculated based on the distance between each station and the time delay. The present invention has the advantage of using non-contact acoustic wave measurement to accurately and quickly extract key information such as internal wave wavelength, period, amplitude, propagation velocity, and direction, making it suitable for monitoring and early warning of marine internal waves. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0015] Figure 1 Flowchart of a method for extracting ocean internal wave features based on acoustic echo intensity according to an embodiment of the present invention; Figure 2 This is an application case of the ocean internal wave feature extraction method based on acoustic echo intensity in a certain sea area according to an embodiment of the present invention; wherein, Figure 2 a is the time series of acoustic echo intensity profile, Figure 2 b is the gradient of acoustic echo intensity at a depth of 100 meters, Figure 2 The arrow box line in a is given according to Figure 2 b Gradient for signal labeling.

[0016] Figure 3 This is a wavelet analysis case of the ocean internal wave feature extraction method based on acoustic echo intensity according to an embodiment of the present invention; wherein, Figure 3 Figure a is the wavelet spectrum of the acoustic echo intensity time series at a depth of 100 meters, and Figure b is the wavelet spectrum of the acoustic echo intensity time series at a depth of 110 meters. Figure 3 a and Figure 3 The b arrow box line is given according to Figure 2 The signal marking of the gradient in a, Figure 3 a and Figure 3 The thick black line in b is the 95% confidence curve of the signal.

[0017] Figure 4 This is a schematic diagram of the acoustic echo intensity profile observed by instruments deployed in a certain sea area and the extracted internal wave information according to the ocean internal wave feature extraction method based on acoustic echo intensity in an embodiment of the present invention; wherein the dotted line is the internal wave waveform.

[0018] Figure 5 Schematic diagram of the internal wave propagation direction vector analysis of three observation stations A, B, and C in a certain sea area using the ocean internal wave feature extraction method based on acoustic echo intensity according to an embodiment of the present invention; A, B, and C are the spatial distribution of the three observation stations in a certain sea area, connected by a dotted line, and c AB 、c BC are the phase velocities of internal wave propagation between stations AB and BC, respectively, which are indicated by thin solid lines with arrows. The actual propagation direction of the internal wave is , represented by a thick solid line with an arrow, and the thin broken line is an auxiliary line for vector analysis. Figure 5a represents the vector analysis case when the internal wave is transmitted from station B to station A and from station B to station C; Figure 5 The b represents the vector analysis case when the internal wave is transmitted from station B to station A and from station C to station B. DETAILED DESCRIPTION

[0019] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0020] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0021] Example 1: like Figure 1 As shown, an embodiment of the present invention provides a method for extracting ocean internal wave features based on acoustic echo intensity, comprising: Step S10: deploying three acoustic wave transmitters and receivers at fixed points in the target sea area; Step S20: The three acoustic wave transmitters and receivers transmit acoustic waves upward or downward, receive echo intensity signals reflected by seawater molecules or particles in the water, and obtain profile distributions of acoustic wave echo intensity at different seawater depths at the three stations; Step S30: Calculate the acoustic echo intensity gradient distribution at each station using a gradient test algorithm based on the acoustic echo intensity profile distribution at the station, and find the time range and depth where the echo intensity maximum occurs; Step S40: Mark the location of the maximum echo intensity, calculate the frequency of the signal using the wavelet transform method, and mark the signal whose frequency of the maximum echo intensity falls within the internal wave frequency band as an ocean internal wave. From the depth of the maximum distribution of the acoustic echo intensity gradient at each station, the range of signal fluctuations at different depths, and the frequency of the signal, the depth, fluctuation amplitude, and period of the ocean internal wave are obtained; Step S50: Obtain the time delay of the ocean internal wave according to the time range of the maximum echo intensity between each two stations; Step S60: Obtain the internal wave propagation direction and propagation speed based on the distance between each two stations and the time delay of the ocean internal waves.

[0022] As an implementation method of an embodiment of the present invention, when three acoustic wave transmitters and receivers are deployed in the ocean, the stations are distributed in an isosceles triangle, and the distance between the stations should be 10 to 100 kilometers.

[0023] As an implementation method of an embodiment of the present invention, when three acoustic wave transmitters and receivers are deployed in the ocean, the directions of the acoustic wave transmitter and receiver probes deviate from the vertical by 0 to 30 degrees.

[0024] As an implementation manner of the embodiment of the present invention, there are three sound wave transmitters and receivers, and the time interval between the sound wave transmitters and receivers transmitting adjacent sound waves is 30 seconds to 1 minute.

[0025] As an implementation method of the embodiment of the present invention, three sound wave transmitters and receivers are mounted on a buoy on the sea surface to transmit sound waves downward.

[0026] As an implementation method of the embodiment of the present invention, three acoustic wave transmitters and receivers are placed on the seabed and transmit upwards.

[0027] Example 2: Figure 2 The present invention provides an example of extracting ocean internal wave information using the acoustic echo intensity profile at a certain station. Figure 2 The gradient calculation of the a acoustic echo intensity profile is performed. Figure 2 b is the gradient of acoustic echo intensity at a depth of 100 meters. Obviously, Figure 2 In b, around 5:00 on September 4, the gradient change of echo intensity is large. Similarly, the gradient of echo intensity at different depths is plotted. Figure 2 The depth and time range given by the arrow box in a indicate abnormal signals, and the signals are marked.

[0028] Figure 3 An example of extracting ocean internal wave information using the acoustic echo intensity profile at a certain station is given. Figure 3 a is the wavelet spectrum of the acoustic echo intensity time series at a depth of 100 meters at the station. Figure 3 Figure b shows the wavelet spectrum of the acoustic echo intensity time series at a depth of 110 meters. Figure 3 The thick black line in the middle is the 95% confidence curve, indicating that the observed signal passes the confidence test and is an actual signal. Among them, the frequency within the internal wave spectrum is an internal wave signal. Figure 3 a and Figure 3 The arrows and boxes in b give the Figure 2 The signal marked by the gradient in a marks the spatiotemporal region. The signal period is 16-100 minutes, and judging from the period, it is an internal wave.

[0029] Figure 4This figure shows the acoustic echo intensity profile of an instrument deployed in a certain sea area, as well as the extracted internal wave information, using the ocean internal wave feature extraction method based on acoustic echo intensity according to an embodiment of the present invention. The dotted line represents the internal wave waveform. The extracted information shows that the first two waves have a longer period of approximately 100 minutes and a larger amplitude of approximately 40 meters. Subsequently, the waves have a shorter period of approximately 10-30 minutes and a smaller amplitude of approximately 10-30 meters.

[0030] Figure 5 A method for calculating the actual propagation direction of internal waves using instruments at three stations is presented. Using the acoustic echo intensity profile data from the three stations, the time delay of wave propagation can be calculated using pairwise data. The wave's direction can be inferred based on the order in which the wave passes through the stations. Combining the time delay calculated from pairwise data with spatial distance allows the wave propagation velocity to be calculated. Figure 5 When it is known that the internal wave is transmitted from station B to station A, the propagation phase velocity is C AB , station B transmits to station C, and the propagation phase velocity is C BC When the spatial distribution of the three stations ABC is combined with the phase velocity C AB 、C BC Size, using vector synthesis, the actual propagation direction of the internal wave is obtained as , transmitted from station B to the AC connection direction. Figure 5 When the internal wave is transmitted from station B to station A, the propagation phase velocity is C AB , station C transmits to station B, and the propagation phase velocity is C BC When the spatial distribution of the three stations ABC is combined with the phase velocity C AB 、C BC Size, using vector synthesis, the actual propagation direction of the internal wave is obtained as , transmitted from the BC station connection direction to the A station.

[0031] Combine Figures 1 to 4 The method for extracting ocean internal wave features based on acoustic echo intensity according to an embodiment of the present invention includes: Step 1. Observation station selection: Deploy three or more acoustic wave transmitters and receivers at fixed points in the target sea area. When deploying in the ocean, avoid placing the three acoustic wave transmitters and receivers in a straight line. The stations should be distributed in an isosceles triangle as much as possible, and the distance between stations should be 10 to 100 kilometers.

[0032] Step 2. Deployment of acoustic wave transmitters: When deployed in the ocean, acoustic wave transmitters and receivers can be mounted on buoys on the sea surface to transmit acoustic waves downward, or they can be placed on the seabed to transmit acoustic waves upward. The direction of the acoustic wave transmitter and receiver probe can deviate from the vertical by 0 to 30 degrees to obtain the echo intensity profile of the entire ocean layer.

[0033] Step 3. Observation instrument settings: The time interval between the sound wave transmitter and receiver emitting adjacent sound waves should be 30 seconds to 1 minute, should not exceed 3 minutes, and should not be less than 10 seconds.

[0034] Step 4. Observation data acquisition: Continuously observe the seawater within a certain depth range. The receiver receives the echo intensity signal reflected by seawater molecules or particulate scatterers in the water, and obtains the profile distribution of the sound wave echo intensity at different seawater depths at the above-mentioned station.

[0035] Step 5: Use the gradient algorithm to calculate the gradient distribution of the acoustic echo intensity profile at each station over time, find and extract the time and depth of the maximum echo intensity. The data matrix of the echo intensity profile over time is recorded as I ,matrix I of x The direction is the time dimension, y The direction is the vertical distribution profile, with upward being the positive direction. The time distribution matrix of the echo intensity profile is calculated by the following formula: I Gradient: ; in, , , x The unit is seconds, the step size is the sampling interval, y The unit is meter, and the step size is the vertical resolution of the fluctuation. I Gradient distribution GI , mark the areas with a value greater than 2 times or 3 times the variance, and their occurrence depth and time range.

[0036] Step 6: Mark the location of the maximum echo intensity and calculate the frequency of the signal using the wavelet transform method. The Morlet wavelet function is selected as the operator. The Morlet wavelet function is: ; in, is a dimensionless spatial scale, is a dimensionless frequency scale.

[0037] To obtain the matrix I Gradient distribution GI , according to the depth of the abnormal value, the depth of occurrence is selected as the time series x n , each element in the time series has a uniform time interval δt, which is the time sampling interval, and n = 0, 1 ... N –1 ( Nis the number of elements in the time series, or the total number of sampling samples in the time dimension), the discrete wavelet transform of this time series can be written as: ; in, s is the wavelet scale. The wavelet power spectrum is defined as .

[0038] Step 7. Mark the signals belonging to the internal wave frequency band in the echo intensity wavelet spectrum as ocean internal waves. From the depth of the maximum distribution of the acoustic echo intensity gradient at each station, the range of signal fluctuations at different depths, and the frequency of the signal, the depth, fluctuation amplitude, and period information of the ocean internal waves can be read from the horizontal axis depth and vertical axis time coordinates of the acoustic echo intensity gradient profile.

[0039] Step 8: Deploy three acoustic observation stations A, B, and C, and obtain the acoustic echo signal data with a sampling interval of 1 minute. The time series corresponding to the maximum acoustic echo intensity of the two observation stations A and B are t A and t B , construct the time delay correlation coefficient: ; Among them, Cov is the time series t A , t B_i The covariance of for t A , t B_i The standard deviation of i This is the time series of the acoustic echo intensity at station B t B Compared to t A The number of data points that differ between them is the corresponding time difference. i Can be positive or negative, representing the lead or lag of two time series. For example, i =1 is the constructed time series t A and t B There is a 1 minute difference between them.

[0040] Similarly, for the echo observation data between stations A and C, and between stations B and C, the delay correlation coefficient is constructed 、 . It should be noted that here i For variables, for different correlation coefficients, the corresponding i The values ​​are also different.

[0041] Step 9: Delay correlation coefficients between A and B, A and C, and B and C 、 、 , find the time interval corresponding to the maximum value of the correlation coefficient between different combinations 、 、 This is the result of the time delay of the internal wave signals observed between different stations during the propagation of ocean internal waves. 、 、 The signal time interval between different stations 、 、 It can be positive or negative. For example, for station AB, a positive value indicates that the internal wave signal is transmitted from A to B, and a negative value indicates that the internal wave signal is transmitted from B to A.

[0042] Step 10: Calculate the internal wave propagation speed based on the distance between each two stations and the time delay. For example, the horizontal distance between stations A and B is L AB , the signal time interval between stations A and B , the phase velocity of internal wave propagation between stations A and B is: ; Similarly, the propagation phase velocity of internal waves between stations A and C, and between stations B and C can be calculated respectively.

[0043] Step 11: Based on the geographical location of the observation station, establish a vector relationship by the magnitude of the phase velocity between the two stations, determine the order in which the internal wave passes through the three stations, and infer the actual propagation direction of the internal wave. Figure 5 As shown, the internal wave phase velocity and propagation direction can be given by vector synthesis based on the spatial distance between the three stations ABC, combined with the calculated phase velocity magnitude and sign between stations A and B, A and C, and B and C.

[0044] It should be noted that when plotting the echo intensity profile over time, attention should be paid to the time and vertical resolution of the horizontal and vertical axes.

[0045] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. A method for extracting ocean internal wave features based on acoustic echo intensity, characterized in that: include: Deploy three acoustic wave transmitters and receivers at fixed points in the target sea area; The three acoustic wave transmitters and receivers transmit acoustic waves upward or downward, receive echo signals reflected by scatterers in the seawater, and obtain the profile distribution of acoustic wave echo intensity at different seawater depths at the three stations; According to the acoustic echo intensity profile distribution at each station, the gradient test algorithm is used to calculate the acoustic echo intensity gradient distribution at each station, and the time range and depth where the echo intensity maximum occurs are found; The location of the maximum echo intensity is marked, and the frequency of the signal is calculated using the wavelet transform method. Signals whose echo intensity maximum frequency falls within the internal wave frequency band are marked as ocean internal waves. The depth, fluctuation amplitude, and period of the ocean internal waves are obtained from the depth of the maximum distribution of the acoustic echo intensity gradient at each station, the range of signal fluctuations at different depths, and the frequency of the signal. The time delay of the ocean internal wave is obtained based on the time range of the maximum echo intensity between each two stations; According to the distance between each two stations and the time delay of the ocean internal waves, the propagation direction and speed of the internal waves are obtained.

2. The method for extracting ocean internal wave characteristics based on acoustic echo intensity according to claim 1, wherein: When three acoustic wave transmitters and receivers are deployed in the ocean, the stations are distributed in an isosceles triangle, and the distance between the stations should be 10 to 100 kilometers.

3. The method for extracting ocean internal wave characteristics based on acoustic echo intensity according to claim 2, wherein: When the three acoustic wave transmitters and receivers are deployed in the ocean, the directions of the acoustic wave transmitter and receiver probes deviate from the vertical by 0 to 30 degrees.

4. The method for extracting ocean internal wave characteristics based on acoustic echo intensity according to claim 3, wherein: The three sound wave transmitters and receivers have a time interval between transmitting adjacent sound waves of 30 seconds to 1 minute.

5. The method for extracting ocean internal wave characteristics based on acoustic echo intensity according to claim 4, wherein: Three sound wave transmitters and receivers are mounted on buoys on the sea surface, emitting sound waves downwards.

6. The method for extracting ocean internal wave characteristics based on acoustic echo intensity according to claim 5, wherein: Three acoustic wave transmitters and receivers are placed on the seabed and transmit upwards.

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