A method for detecting internal solitary waves based on Rossby modal hydrodynamic parameters

Abstract

The invention discloses an internal solitary wave detection method based on Rossby modal hydrodynamic parameters, which relates to the field of internal solitary wave detection and includes the following steps: obtaining acoustic signals in a target area; performing acoustic inversion; reconstructing the amplitude of a sound velocity profile to obtain a number of sound velocity profile amplitude values; obtaining an amplitude function that varies with depth; calculating a nonlinear parameter in a KdV equation of a nonlinear internal solitary wave in shallow water without considering the influence of a background flow field; judging whether the nonlinear parameter is greater than a threshold value, and if so, determining that an internal solitary wave is generated; otherwise, determining that an internal solitary wave is not generated. The method represents the disturbance of the sound velocity profile by the change of the sound velocity profile amplitude, calculates the change of the nonlinear parameter based on the KdV equation of a nonlinear internal solitary wave in shallow water, and clearly monitors and predicts the generation, propagation, and amplitude of the internal solitary wave in real time through the relationship between the value of the nonlinear parameter and the threshold value, thereby realizing a large-scale, real-time, and economical internal solitary wave detection and early warning.

Description

Technical Field

[0001] The invention relates to the field of internal solitary wave detection, and in particular to an internal solitary wave detection method based on Rossby modal hydrodynamic parameters. Background Art

[0002] Internal solitary waves in the ocean are a type of nonlinear large-amplitude wave phenomenon that occurs in the ocean's density mutation layer. These waves are usually excited by strong currents passing through areas of rapid changes in the seafloor topography, such as steep slopes or ridges. Unlike linear internal tidal waves that are commonly found in stratified oceans and are excited by positive pressure currents, internal solitary waves are widely distributed in the world's oceans. Internal solitary waves with amplitudes of tens to hundreds of meters carry huge amounts of energy, and their energy decays slowly during propagation. During the propagation of these internal solitary waves, they may cause strong horizontal or vertical mixing of the water body due to small-scale phenomena such as breakup, friction with the rough seafloor topography, or shear instability. This strong mixing can pose a significant threat to underwater sonar systems, submarine operations, and offshore oil drilling platforms.

[0003] There are two main methods for detecting internal solitary waves, but both have certain defects:

[0004] 1. Internal solitary waves can be observed by deploying sensors in the water body for in-situ measurement. This method involves deploying multiple sensors in a specific sea area, including equipment for measuring temperature, salinity, sound speed, and flow rate, to capture and record small changes in the state of the water body at that location. By analyzing this data, the internal solitary wave phenomenon passing through the area can be effectively detected and identified. However, in-situ measurements make it difficult to accurately judge the water body that does not pass through the observation point, and the vast ocean makes it difficult to place equipment over a large area due to cost issues.

[0005] 2. Use synthetic aperture radar (SAR) and optical remote sensing observation methods to observe the state of the sea surface, and identify it based on features such as sea surface strip waves. However, this method is limited to the sea surface through satellite remote sensing observation, and it is difficult to accurately identify underwater internal solitary waves. It is also easy to miss or misreport internal solitary waves with less obvious sea surface features. At the same time, optical satellites are also easily affected by weather factors such as clouds and rainfall, making it difficult to provide real-time warnings. Summary of the invention

[0006] In view of the above-mentioned deficiencies in the prior art, the present invention provides an internal solitary wave detection method based on Rossby modal hydrodynamic parameters, which solves the problem that the prior art is difficult to detect internal solitary waves in real time and over a large range.

[0007] In order to achieve the above-mentioned object of the invention, the technical solution adopted by the present invention is:

[0008] A method for detecting internal solitary waves based on Rossby modal hydrodynamic parameters is provided, which comprises the following steps:

[0009] S1. transmitting a sound signal through a sound transmitting end in a target area, and receiving the sound signal through a sound receiving end to obtain an acoustic signal;

[0010] S2. Perform acoustic inversion on the acoustic signal to obtain the propagation time and direction of the internal wave, as well as the coefficients of different baroclinic modes;

[0011] S3, reconstructing the sound velocity profile amplitude through the sound velocity disturbance background value, the baroclinic mode and the coefficient corresponding to the baroclinic mode, and obtaining several sound velocity profile amplitude values;

[0012] S4, numerically fitting several sound velocity profile amplitude values ​​to obtain an amplitude function that varies with depth;

[0013] S5. Without considering the influence of the background flow field, an expression of a nonlinear parameter in the KdV equation representing a nonlinear internal solitary wave in shallow water by the maximum water depth, an amplitude function varying with depth, and a phase velocity is formed, and the nonlinear parameter is obtained;

[0014] S6. Determine whether the nonlinear parameter is greater than a threshold value. If so, it is determined that an internal solitary wave is generated; otherwise, it is determined that no internal solitary wave is generated.

[0015] Furthermore, in step S1, the sound transmitting end is a transducer, and the transducer is used to transmit sound signals in two directions parallel to the isobaths and in the direction where the isobaths become deeper; the sound receiving end is a hydrophone.

[0016] Furthermore, the expression for reconstructing the amplitude of the sound velocity profile in step S3 is:

[0017]

[0018] in It represents the amplitude value of the reconstructed sound velocity profile at depth z; Represents the background value of sound velocity disturbance at depth z; is a constant; is the baroclinic mode; .

[0019] Furthermore, the expression of the KdV equation for nonlinear internal solitary waves in shallow water is:

[0020]

[0021] in is the vertical displacement of the jump layer interface; is the internal wave propagation time; is the phase velocity; is the internal wave propagation direction; is a nonlinear parameter; is the dispersion parameter, , is the amplitude function that varies with depth; is the maximum water depth; Indicates depth; represents differential; the propagation time and propagation direction of the internal wave are obtained by inverting the acoustic signal.

[0022] Furthermore, in step S5, the expression of the nonlinear parameter in the KdV equation of the nonlinear internal solitary wave in shallow water represented by the maximum water depth, the amplitude function varying with depth and the phase velocity is:

[0023]

[0024] in is a nonlinear parameter; is the maximum water depth; Indicates depth; represents differential; is the amplitude function that varies with depth.

[0025] The beneficial effects of the present invention are as follows: the method represents the disturbance of the sound velocity profile by the change of the sound velocity profile amplitude, calculates the change of nonlinear parameters based on the KdV equation of nonlinear internal solitary waves in shallow water, and clearly monitors and predicts the generation, propagation and amplitude of internal solitary waves in real time through the relationship between the value of the nonlinear parameter and the threshold value. It only needs to obtain the maximum sea depth, the amplitude function that varies with depth, and the phase velocity to achieve a large-scale, real-time and economical internal solitary wave detection and early warning. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a schematic diagram of the process of this method;

[0027] Figure 2 This is an example of the change of the sound velocity profile when the internal solitary wave occurs in the embodiment;

[0028] Figure 3 This is an example of early warning of internal solitary waves by the method in the embodiment. DETAILED DESCRIPTION

[0029] The specific implementation modes of the present invention are described below so that those skilled in the art can understand the present invention. However, it should be clear that the present invention is not limited to the scope of the specific implementation modes. For those of ordinary skill in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the attached claims, these changes are obvious, and all inventions and creations utilizing the concept of the present invention are protected.

[0030] like Figure 1 As shown, the internal solitary wave detection method based on Rossby modal hydrodynamic parameters includes the following steps:

[0031] S1. transmitting a sound signal through a sound transmitting end in a target area, and receiving the sound signal through a sound receiving end to obtain an acoustic signal;

[0032] S2. Perform conventional acoustic inversion on the acoustic signal to obtain the propagation time and propagation direction of the internal wave, as well as the coefficients of different baroclinic modes;

[0033] S3, reconstructing the sound velocity profile amplitude through the sound velocity disturbance background value, the baroclinic mode and the coefficient corresponding to the baroclinic mode, and obtaining several sound velocity profile amplitude values;

[0034] S4, numerically fitting several sound velocity profile amplitude values ​​to obtain an amplitude function that varies with depth;

[0035] S5. Without considering the influence of the background flow field, an expression of a nonlinear parameter in the KdV equation representing a nonlinear internal solitary wave in shallow water by the maximum water depth, an amplitude function varying with depth, and a phase velocity is formed, and the nonlinear parameter is obtained;

[0036] S6. Determine whether the nonlinear parameter is greater than a threshold value. If so, it is determined that an internal solitary wave is generated; otherwise, it is determined that no internal solitary wave is generated.

[0037] In this embodiment, the sound transmitting end in step S1 is a transducer, which is used to transmit sound signals in two directions parallel to the isobath and in the direction where the isobath becomes deeper; the sound receiving end is a hydrophone. For sea areas with shallow seabed, the transducer can be placed directly on the seabed. For sea areas with deep seabed, mooring can be carried out by means of buoys.

[0038] In the specific implementation process, according to the fluid dynamics equation, the "steel cover approximation" commonly used in internal wave theory research is introduced, and the vertical motion of water protons can be simplified by the Sturm-Liouville problem:

[0039]

[0040] in is the flow rate of water protons, For the depth of the sea, is the phase velocity, is the buoyancy frequency. This equation is usually solved numerically. The buoyancy frequency is calculated using the average temperature profile and average salinity profile of the target sea area. Considering that the first three orders can describe most of the ocean disturbances, the baroclinic mode can be obtained. , , .

[0041] The expression for reconstructing the amplitude of the sound velocity profile in step S3 is:

[0042]

[0043] in It represents the amplitude value of the reconstructed sound velocity profile at depth z; It represents the background value of the sound velocity disturbance at the depth z, which can be obtained through the measured temperature profile and salinity profile; is a constant; is the baroclinic mode; .

[0044] The expression of the KdV equation for nonlinear internal solitary waves in shallow water is:

[0045]

[0046] in is the vertical displacement of the jump layer interface; is the internal wave propagation time; is the phase velocity; is the internal wave propagation direction; is a nonlinear parameter; is the dispersion parameter, , is the amplitude function that varies with depth; is the maximum water depth; Indicates depth; represents differential; the propagation time and propagation direction of the internal wave are obtained by inverting the acoustic signal.

[0047] In step S5, the expression of the nonlinear parameter in the KdV equation of the nonlinear internal solitary wave in shallow water represented by the maximum water depth, the amplitude function varying with depth and the phase velocity is:

[0048]

[0049] in is a nonlinear parameter; is the maximum water depth; Indicates depth; represents differential; is the amplitude function that varies with depth.

[0050] In the specific implementation process, the nonlinear parameters can be judged Whether it is above the detection threshold, the generation and propagation of internal solitary waves are monitored, and the nonlinear parameters are used to The period and amplitude of the internal solitary wave are analyzed by the size change. The specific value of the threshold can be set by the user of this method according to his own situation, so as to facilitate the corresponding early warning.

[0051] In one embodiment of the present invention, a temperature chain unit is placed near the Dongsha Islands in the South China Sea to detect the water body. The measurement frequency is 1 minute. The observed water disturbance is as follows: Figure 2 As shown in the figure (the horizontal and vertical axes are time and water disturbance value respectively), significant internal solitary wave activities were observed. Figure 3 As shown (the horizontal axis is time, and the vertical axis is the water disturbance value and the nonlinear parameter The amplitude of the sound velocity profile is reconstructed by this method, and the nonlinear parameters in the KdV equation of the nonlinear internal solitary wave in shallow water are further solved. . We can see that the nonlinear parameters The change of and the activity of the internal solitary wave form a good correspondence. In the place where the internal solitary wave is generated, the nonlinear parameter Correspondingly, the nonlinear parameters reach a peak value and the amplitude of the inner solitary wave is large. The peak value of is also large, and the nonlinear parameter It is a good measure of the strength of the internal solitary wave.

[0052] In summary, the present invention represents the disturbance of the sound velocity profile by the change of the sound velocity profile amplitude, calculates the change of nonlinear parameters based on the KdV equation of nonlinear internal solitary waves in shallow water, and clearly monitors and predicts the generation, propagation and amplitude of internal solitary waves in real time through the relationship between the value of the nonlinear parameter and the threshold. It only needs to obtain the maximum sea depth, the amplitude function that changes with depth, and the phase velocity to achieve a large-scale, real-time and economical internal solitary wave detection and early warning, which can avoid the high cost of previous deployment devices and the problem that only surface disturbances can be identified and possible missed judgments and misjudgments exist through satellite remote sensing.

Claims

1. An internal solitary wave detection method based on Rossby modal hydrodynamic parameters, characterized in that: The following steps are involved: S1. transmitting a sound signal through a sound transmitting end in a target area, and receiving the sound signal through a sound receiving end to obtain an acoustic signal; S2. Perform acoustic inversion on the acoustic signal to obtain the propagation time and direction of the internal wave, as well as the coefficients of different baroclinic modes; S3, reconstructing the sound velocity profile amplitude through the sound velocity disturbance background value, the baroclinic mode and the coefficient corresponding to the baroclinic mode, and obtaining several sound velocity profile amplitude values; S4, numerically fitting several sound velocity profile amplitude values ​​to obtain an amplitude function that varies with depth; S5. Without considering the influence of the background flow field, an expression of a nonlinear parameter in the KdV equation representing a nonlinear internal solitary wave in shallow water by the maximum water depth, an amplitude function varying with depth, and a phase velocity is formed, and the nonlinear parameter is obtained; S6, judging whether the nonlinear parameter is greater than a threshold value, if so, it is judged that an internal solitary wave is generated; otherwise, it is judged that no internal solitary wave is generated; The expression of the KdV equation for nonlinear internal solitary waves in shallow water is: in is the vertical displacement of the jump layer interface; is the internal wave propagation time; is the phase velocity; is the internal wave propagation direction; is a nonlinear parameter; is the dispersion parameter, , is the amplitude function that varies with depth; is the maximum water depth; Indicates depth; represents differential; the propagation time and propagation direction of the internal wave are obtained by inverting the acoustic signal; In step S5, the expression of the nonlinear parameter in the KdV equation of the nonlinear internal solitary wave in shallow water represented by the maximum water depth, the amplitude function varying with depth and the phase velocity is: in is a nonlinear parameter; is the maximum water depth; Indicates depth; represents differential; is the amplitude function that varies with depth.

2. The internal solitary wave detection method based on Rossby modal hydrodynamic parameters according to claim 1 is characterized in that: In step S1, the sound transmitting end is a transducer, which is used to transmit sound signals in two directions parallel to the isobaths and in the direction where the isobaths become deeper; the sound receiving end is a hydrophone.

3. The internal solitary wave detection method based on Rossby modal hydrodynamic parameters according to claim 1 is characterized in that: The expression for reconstructing the amplitude of the sound velocity profile in step S3 is: in It represents the amplitude value of the reconstructed sound velocity profile at depth z; Represents the background value of sound velocity disturbance at depth z; is a constant; is the baroclinic mode; .

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