Method for extracting characteristics of internal waves in the ocean based on acoustic echo intensity

Abstract

The application discloses a method for extracting oceanic internal wave characteristics based on acoustic echo intensity, acoustic emission receivers are arranged at three different stations in a target sea area, acoustic echo intensity profile data at the different stations are acquired, the occurrence depth, amplitude and period information of internal waves are calibrated according to the acoustic echo intensity profile gradient maximum value and occurrence frequency, and the internal wave propagation direction and propagation speed are calculated according to the distance between every two stations and the time delay. By using the technical scheme, the key information such as the internal wave wavelength, period, amplitude, propagation speed and propagation direction can be accurately and quickly extracted, and the method is suitable for monitoring and early warning of oceanic internal waves.

Description

Technical Field

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

[0002] Internal waves are vibrations within densely stratified ocean water. Unlike surface waves, the maximum amplitude of internal waves occurs below the sea surface. Their phase velocity is approximately 1 meter per second, amplitude ranges from several meters to tens of meters, wavelengths from nearly a hundred meters to tens of kilometers, and periods range from several minutes to tens of hours. They are a significant cause of seawater mixing and the formation of fine structures. The isodense surface fluctuations caused by internal waves alter both the magnitude and direction of sound velocity, greatly impacting sonar, affecting the navigation of underwater vessels, and potentially damaging maritime facilities. Therefore, the observation of internal waves and the analysis and extraction of their characteristics have strong practical significance.

[0003] Ocean internal waves vary randomly in space and time, with a wide frequency range, requiring rapid and dense sampling over a long period. Newly developed general-purpose oceanographic survey instruments can meet these observation requirements. The most commonly used observation device is the moored self-contained current meter, which can simultaneously measure seawater temperature, salinity, and depth. Ocean internal waves can also be detected using methods such as acoustic waves. By arranging multiple moored devices and instruments into a three-dimensional instrument array, the propagation phase velocity of ocean internal waves can be calculated, and the direction of propagation and trajectory of internal waves can be estimated.

[0004] The ocean waves that pass through the area will cause strong vertical velocity shearing to the seawater in the region. This strong vertical shearing causes anomalies in the vertical distribution of small particle scatterers in the water, which provides a powerful condition for detecting the distribution of ocean waves by using sound wave intensity.

[0005] The aforementioned moored underwater buoys measure internal waves through contact, but this method may cause entanglement or other effects on ship navigation. Therefore, non-contact measurement methods for internal waves, such as using acoustic detection to observe ocean internal waves, are extremely important in sea areas with 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 features based on acoustic echo intensity.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A method for extracting ocean internal wave features based on acoustic echo intensity, comprising:

[0009] Three acoustic wave transmitters and receivers were deployed at a fixed point in the target sea area;

[0010] Three acoustic wave transmitters and receivers transmit acoustic waves upwards or downwards and receive echo signals reflected by scatterers in the seawater to obtain the profile distribution of acoustic echo intensity at different seawater depths at the three stations.

[0011] Based on 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 to find the time range and depth where the maximum echo intensity occurs.

[0012] The location of the maximum echo intensity is marked, and the frequency of the signal is calculated using wavelet transform. Signals whose maximum echo intensity frequency belongs to the internal wave band are marked as ocean internal waves. From the depth of the maximum echo intensity gradient distribution at each station, the range of signal fluctuation at different depths, and the frequency of the signal, the depth, fluctuation amplitude, and period information of the ocean internal waves are obtained.

[0013] The time delay of ocean internal waves is obtained based on the time range of the maximum echo intensity between each two stations;

[0014] Based on the distance between each two stations and the time delay of the internal waves, the propagation direction and speed of the internal waves are obtained.

[0015] Preferably, when the three acoustic transmitters and receivers are deployed in the ocean, the stations are arranged in an isosceles triangle, and the distance between the stations should be 10 to 100 kilometers.

[0016] Preferably, when the three acoustic wave transmitters and receivers are deployed in the ocean, the probes of the acoustic wave transmitters and receivers are deviated from the vertical direction by 0 to 30 degrees.

[0017] Preferably, there are three sound wave transmitters and receivers, with the time interval between the transmission of adjacent sound waves being 30 seconds to 1 minute.

[0018] As a preferred option, three acoustic wave transmitters and receivers are mounted on a sea surface buoy to emit acoustic waves downwards.

[0019] As a preferred option, three acoustic wave transmitters and receivers are placed on the seabed and transmit upwards.

[0020] This invention deploys acoustic transmitters and receivers at three different locations in the target sea area. By acquiring acoustic echo intensity profile data at different locations, and based on the maximum gradient value and frequency of the acoustic echo intensity profile, the origin depth, amplitude, and period information of the internal wave are determined. The propagation direction and velocity of the internal wave are calculated based on the distance between each pair of stations and the time delay. The advantage of this invention is that it uses non-contact acoustic measurement to accurately and quickly extract key information such as the wavelength, period, amplitude, propagation velocity, and propagation direction of the internal wave, making it suitable for monitoring and early warning of ocean internal waves. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0022] Figure 1 This is a flowchart of a method for extracting ocean internal wave features based on acoustic echo intensity, according to an embodiment of the present invention.

[0023] 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' represents the time series of the acoustic echo intensity profile. Figure 2 Let b be the gradient of the acoustic echo intensity at a depth of 100 meters. Figure 2 The arrow box in 'a' gives the information based on... Figure 2 Signal labeling is performed using the b gradient.

[0024] Figure 3 This is a wavelet analysis example of the ocean internal wave feature extraction method based on acoustic echo intensity, as described in this embodiment of the invention; wherein, Figure 3 Figure a shows the wavelet spectrum of the acoustic echo intensity time series at a depth of 100 meters, and Figure b shows the wavelet spectrum of the acoustic echo intensity time series at a depth of 110 meters. Figure 3 a and Figure 3 The arrow in the box indicates the basis. Figure 2 Signal labeling based on gradient in a, Figure 3 a and Figure 3 The thick black line in b represents the 95% confidence curve of the signal.

[0025] Figure 4 This is a schematic diagram of the acoustic echo intensity profile and extracted internal wave information observed by a deployed instrument in a certain sea area, based on the ocean internal wave feature extraction method based on acoustic echo intensity according to an embodiment of the present invention; wherein, the dotted lines represent internal wave waveforms.

[0026] Figure 5 This is a schematic diagram illustrating the vector analysis of the propagation direction of internal waves at three observation stations A, B, and C in a certain sea area, based on the ocean internal wave feature extraction method based on acoustic echo intensity, according to an embodiment of the present invention. A, B, and C represent the spatial distribution of the three observation stations in the sea area, connected by a dashed line. AB c BC The phase velocities of the internal waves propagating between stations AB and BC are represented by thin solid lines with arrows, and the actual propagation direction of the internal waves is... The arrows are represented by thick solid lines with arrowheads, while the thin broken lines are auxiliary lines for vector analysis. Figure 5 'a' represents a vector analysis case when the internal wave propagates from station B to station A and from station B to station C. Figure 5 The value of 'b' represents a vector analysis case where the internal wave propagates from station B to station A and from station C to station B. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] Example 1:

[0030] like Figure 1 As shown, this embodiment of the invention provides a method for extracting ocean internal wave features based on acoustic echo intensity, including:

[0031] Step S10: Deploy 3 acoustic wave transmitters and receivers at fixed points in the target sea area;

[0032] Step S20: The three acoustic wave transmitters and receivers transmit acoustic waves upwards or downwards and receive the echo intensity signals reflected by seawater molecules or particulate matter scattering bodies in the water to obtain the profile distribution of acoustic wave echo intensity at different seawater depths at the three stations.

[0033] Step S30: Based on the acoustic echo intensity profile distribution at each station, use the gradient test algorithm to calculate the acoustic echo intensity gradient distribution at each station, and find the time range and depth where the maximum echo intensity occurs.

[0034] Step S40: Mark the location of the maximum echo intensity, calculate the frequency of the signal using wavelet transform, and mark the signal whose frequency of the maximum echo intensity belongs to the internal wave band as ocean internal wave. From the depth of the maximum echo intensity gradient distribution at each station, the range of signal fluctuation at different depths, and the frequency of the signal, obtain the depth, fluctuation amplitude, and period information of the ocean internal wave.

[0035] Step S50: Based on the time range of the maximum echo intensity between each two stations, obtain the time delay of the ocean internal wave;

[0036] Step S60: Based on the distance between each two stations and the time delay of the internal waves, obtain the propagation direction and speed of the internal waves.

[0037] As one 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.

[0038] As one embodiment of the present invention, when three acoustic wave transmitters and receivers are deployed in the ocean, the probe direction of the acoustic wave transmitters and receivers deviates from the vertical direction by 0 to 30 degrees.

[0039] As one embodiment of the present invention, there are 3 sound wave transmitters and receivers, and the time interval between the transmission of adjacent sound waves by the sound wave transmitters and receivers is 30 seconds to 1 minute.

[0040] In one embodiment of the present invention, three sound wave transmitters and receivers are mounted on a sea surface buoy to emit sound waves downwards.

[0041] In one embodiment of the present invention, three acoustic wave transmitters and receivers are placed on the seabed and emit upwards.

[0042] Example 2:

[0043] Figure 2 An example of extracting ocean internal wave information using acoustic echo intensity profiles from a specific station is given. Figure 2 Gradient calculations were performed on the alpha acoustic echo intensity profile. Figure 2 Let b be the gradient of the acoustic echo intensity at a depth of 100 meters. It is obvious that... Figure 2 In image b, around 5:00 AM on September 4th, the gradient change in echo intensity was significant. Similarly, the gradients of echo intensity at different depths were plotted. It was found that... Figure 2 The arrow box in 'a' indicates a signal anomaly within the depth and time range, and this signal is marked.

[0044] Figure 3 An example of extracting ocean internal wave information using the acoustic echo intensity profile of a certain station is given in this invention. Figure 3 'a' represents the wavelet spectrum of the acoustic echo intensity at a depth of 100 meters at this station. Figure 3 b gives the wavelet spectrum of the time series of acoustic echo intensity at a depth of 110 meters. Figure 3 The thick black line represents the 95% confidence curve, indicating that the observed signal has passed the confidence test and is the actual signal. Among them, the frequency within the inner wave spectrum is the inner wave signal. Figure 3 a and Figure 3 The arrows and boxes in b indicate the basis Figure 2 The signal is used to mark the spatiotemporal region by gradient gradation in 'a'. The period of this signal is 16-100 minutes, and based on the period, the signal belongs to the internal wave category.

[0045] Figure 4 This paper presents an acoustic echo intensity profile observed by a deployed instrument in a certain sea area, based on the ocean internal wave feature extraction method based on acoustic echo intensity according to an embodiment of the present invention, and the extracted internal wave information. The dotted lines represent the internal wave waveforms. From the extracted information, it can be seen that the first two waves have relatively long periods of about 100 minutes and large amplitudes of about 40 meters. Subsequently, the wave periods are shorter, about 10-30 minutes, and the wave amplitudes are smaller, about 10-30 meters.

[0046] Figure 5 This paper presents a method for calculating the actual propagation direction of internal waves using instruments at three stations. Using acoustic echo intensity profile data from the three stations, the time delay of wave propagation can be calculated using data from each pair of stations. The direction of origin of the wave can be inferred based on the order in which the wave passes the stations. By combining the time delay and spatial distance calculated from the data from each pair of stations, the wave propagation speed can be calculated. Figure 5 Let 'a' be the propagation velocity of the internal wave from station B to station A, and 'c' be the propagation speed of the internal wave. AB The data is transmitted from Bilibili to Bilibili, with a propagation velocity of C. BC At that time, based on the spatial distribution of the three stations A, B, and C, combined with the phase velocity C... AB C BC The magnitude, using vector synthesis, yields the actual propagation direction of the internal wave. It is transmitted from Bilibili to the AC connection direction. Figure 5 Let b be the propagation velocity of the internal wave from station B to station A, and C be the propagation speed. AB The data is transmitted from station C to station B, with a propagation phase velocity of C. BC At that time, based on the spatial distribution of the three stations A, B, and C, combined with the phase velocity C... AB C BC The magnitude, using vector synthesis, yields the actual propagation direction of the internal wave. The signal is transmitted from station B to station A via the connection between stations B and C.

[0047] Combination Figures 1 to 4 The ocean internal wave feature extraction method based on acoustic echo intensity according to embodiments of the present invention includes:

[0048] Step 1: Selection of observation sites: Deploy more than three 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 distribution of the sites should be as close as possible to an isosceles triangle, and the distance between the sites should be 10 to 100 kilometers.

[0049] Step 2, Deployment of acoustic transmitters: When deploying acoustic transmitters and receivers in the ocean, they can be mounted on a surface buoy to emit acoustic waves downwards, or they can be deployed on the seabed to emit acoustic waves upwards. The probe direction of the acoustic transmitter and receiver can be deviated from the vertical direction by 0 to 30 degrees to obtain the echo intensity profile of the entire ocean layer.

[0050] Step 3, setting up the observation instrument: the time interval between the transmission of adjacent sound waves by the sound wave transmitter and receiver should be 30 seconds to 1 minute, not exceeding 3 minutes, and not less than 10 seconds.

[0051] Step 4: Data Acquisition: Continuous observation of seawater within a certain depth range is conducted. The receiver receives the echo intensity signal reflected by seawater molecules or particulate matter in the water, and obtains the profile distribution of sound wave echo intensity at different seawater depths at the above-mentioned stations.

[0052] Step 5: Using the gradient algorithm, calculate the gradient distribution of the acoustic echo intensity profile over time at each station, and find and extract the time and depth at which the maximum echo intensity occurs. Let the data matrix of the echo intensity profile over time be denoted 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 echo intensity profile distribution matrix over time is calculated using the following formula. I gradient:

[0053] ;

[0054] in, , , x The unit is seconds, and the step size is the sampling interval. y The unit is meters, and the step size is the fluctuating vertical resolution. For the acquired matrix... I Gradient distribution GI For regions with a variance greater than 2 or 3 times the variance, mark the depth and time range of their occurrence.

[0055] Step 6: Mark the locations of the maximum echo intensity and calculate the frequency of the signal using wavelet transform. The Morlet wavelet function is selected as the operator. The Morlet wavelet function is:

[0056] ;

[0057] in, It is a dimensionless spatial scale. It is a dimensionless frequency scale.

[0058] For the obtained matrix I Gradient distribution GI Based on the depth of outlier occurrence, the occurrence depth is selected as the time series. x n In this time series, each element has a uniform time interval δt, which is the time sampling interval. n= 0, 1 … N –1( N (where is the number of elements in the time series, or the total number of samples in the time dimension). The discrete wavelet transform of this time series can be written as:

[0059] ;

[0060] in, s The wavelet scale. The wavelet power spectrum is defined as... .

[0061] 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 where the maximum value of the acoustic echo intensity gradient is distributed at each station, the range of signal fluctuation at different depths, and the frequency of the signal, read the depth, fluctuation amplitude, and period information of the ocean internal waves from the horizontal axis depth and vertical axis time coordinates of the acoustic echo intensity gradient profile.

[0062] Step 8: Deploy three acoustic observation stations A, B, and C, and obtain the acoustic echo signal data with a time sampling interval of 1 minute. Analyze the time series corresponding to the maximum acoustic echo intensity at observation stations A and B. t A and t B Construct the time delay correlation coefficient:

[0063] ;

[0064] Where Cov is a time series t A , t B_i covariance, for t A , t B_i standard deviation i Time series of sound wave echo intensity on Bilibili t B Compared to t A The number of data points that differ between the two points is the corresponding time difference. i It can be positive or negative, representing whether two time series are leading or lagging. For example, i =1 indicates the constructed time series. t A and t B There is a 1-minute difference between them.

[0065] Similarly, delay correlation coefficients were constructed for the echo observation data between stations A and C, and between stations B and C, respectively. , It is important to note that here... i As variables, for different correlation coefficients, the corresponding i The values ​​are also different.

[0066] Step 9: Analyze the delay correlation coefficients between stations A and B, A and C, and B and C. , , Find the time interval corresponding to the maximum correlation coefficient among different combinations. , , This is because, during the propagation of internal ocean waves, the waves pass through different stations at different times, resulting in a time delay in the observed internal wave signals between those stations. , , Signal time interval between different stations , , It can be a positive or negative value. For example, for stations A and B, 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.

[0067] Step 10: Calculate the internal wave propagation velocity based on the distance between each pair of 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 propagation phase velocity of the internal wave between stations A and B is:

[0068] ;

[0069] Similarly, the propagation phase velocity of the internal wave between stations A and C, and between stations B and C, can be calculated respectively.

[0070] Step 11: Based on the geographical location of the observation station, establish a vector relationship by considering the positive and negative values ​​of the phase velocities between two stations. Determine the order in which the internal wave passes through the three stations and infer the actual direction of propagation of the internal wave. Vector analysis is as follows: Figure 5 As shown, based on the spatial distances between the three stations A, B, and C, and combined with the calculated magnitudes and signs of the phase velocities between stations A and B, A and C, and B and C, the magnitude and propagation direction of the internal wave phase velocity can be given by vector synthesis.

[0071] It is important to note 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.

[0072] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Various modifications and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope 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: Three acoustic wave transmitters and receivers were deployed at a fixed point in the target sea area; Three acoustic wave transmitters and receivers transmit acoustic waves upwards or downwards and receive echo signals reflected by scatterers in the seawater to obtain the profile distribution of acoustic echo intensity at different seawater depths at the three stations. Based on 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 to find the time range and depth where the maximum echo intensity occurs. The location of the maximum echo intensity is marked, and the frequency of the signal is calculated using wavelet transform. Signals whose maximum echo intensity frequency belongs to the internal wave band are marked as ocean internal waves. From the depth of the maximum echo intensity gradient distribution at each station, the range of signal fluctuation at different depths, and the frequency of the signal, the depth, fluctuation amplitude, and period information of the ocean internal waves are obtained. The time delay of ocean internal waves is obtained based on the time range of the maximum echo intensity between each two stations; Based on the distance between each two stations and the time delay of the internal waves, the propagation direction and speed of the internal waves are obtained; When deploying three acoustic transmitters and receivers in the ocean, the stations should be arranged in an isosceles triangle, and the distance between the stations should be 10 to 100 kilometers. When three acoustic wave transmitters and receivers are deployed in the ocean, the probes of the acoustic wave transmitters and receivers are deviated from the vertical direction by 0 to 30 degrees. Three sound wave transmitters and receivers, with the time interval between the transmission of adjacent sound waves being 30 seconds to 1 minute.

2. The method for extracting ocean internal wave features based on acoustic echo intensity as described in claim 1, characterized in that, Three sound wave transmitters and receivers are mounted on a sea surface buoy and emit sound waves downwards.

3. The method for extracting ocean internal wave features based on acoustic echo intensity as described in claim 1, characterized in that, Three sound wave transmitters and receivers are placed on the seabed and transmit upwards.

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