Method and device for inverting ocean internal wave current field

Abstract

The present invention provides a method and device for inverting the ocean internal wave current field, which are applied to the technical field of ocean remote sensing applications. The method includes: obtaining a synthetic aperture radar (SAR) single-look complex image and determining the Doppler centroid frequency grid of the SAR single-look complex image; determining a first sea surface radial velocity according to the Doppler centroid frequency grid and determining the first sea surface radial velocity as the range dimension component of the two-dimensional ocean internal wave surface current field; determining the internal wave propagation direction according to the SAR single-look complex image, and determining the azimuth dimension component of the two-dimensional ocean internal wave surface current field according to the internal wave propagation direction and the first sea surface radial velocity; inputting the range dimension component and the azimuth dimension component into the IDopRIM model for iterative calculation to output a second sea surface radial velocity and an azimuthal current field, and obtaining the two-dimensional current field of the ocean internal wave according to the second sea surface radial velocity and the azimuthal current field.

Description

Technical Field

[0001] The present invention relates to the technical field of marine remote sensing applications, and particularly to a method and device for inverting the internal wave current field of the ocean. Background Art

[0002] The ocean current field refers to the situation and distribution of seawater flow in the ocean. It includes information such as the flow velocity, flow direction, and movement trajectory of seawater. The measurement of the ocean current field is of particular importance for research and applications in aspects such as marine environmental monitoring, global climate change prediction, marine search, and emergency response.

[0003] In the prior art, a synthetic aperture radar (SAR) can invert the sea surface current field by measuring the Doppler frequency shift information caused by sea surface movement. The theoretical basis of the mainstream Doppler centroid offset method is the Doppler radar imaging model (DopRIM), which inverts the sea surface radial current field by analyzing the contribution sources of each part of the Doppler centroid offset in the SAR image.

[0004] However, when existing current field inversion algorithms separate the contributions of ocean currents and ocean waves from the Doppler centroid offset obtained from SAR images, it is generally considered that the two are independent and linearly additive, and an empirical model is used to calculate the Doppler contribution of wind waves. Such methods ignore the Doppler contribution of the coupled action of ocean currents and ocean waves, thereby introducing errors in the inversion of the internal wave sea surface current field and resulting in inaccurate inversion results of the sea surface current field. Summary of the Invention

[0005] The present invention provides a method and device for inverting the internal wave current field of the ocean to solve the problem of inaccurate inversion results of the sea surface current field in the prior art.

[0006] The present invention provides a method for inverting the internal wave current field of the ocean, including: acquiring a single-look complex image of a synthetic aperture radar (SAR) and determining the Doppler centroid frequency grid of the SAR single-look complex image; determining a first sea surface radial velocity according to the Doppler centroid frequency grid and determining the distance dimension component of the two-dimensional internal wave surface current field of the ocean as the first sea surface radial velocity; determining the internal wave propagation direction according to the SAR single-look complex image and determining the azimuth dimension component of the two-dimensional internal wave surface current field according to the internal wave propagation direction and the first sea surface radial velocity; inputting the distance dimension component and the azimuth dimension component into the IDopRIM model for iterative calculation to output a second sea surface radial velocity and an azimuthal current field, and obtaining the two-dimensional current field of the internal wave of the ocean according to the second sea surface radial velocity and the azimuthal current field.

[0007] According to an ocean internal wave current field inversion method provided by the present invention, the determination of the Doppler centroid frequency grid of the SAR single-look complex image includes: performing Fourier transform on the data within the window of the SAR single-look complex image in the azimuth direction to obtain the azimuth power spectrum; averaging the azimuth power spectrum along the range direction to obtain the average power spectrum; performing circular correlation on the average power spectrum and a reference function, and determining the zero-crossing point of the correlation result as the Doppler centroid of the data within the window; and determining the Doppler centroid frequency grid based on the Doppler centroids of all windows of the SAR single-look complex image.

[0008] According to an ocean internal wave current field inversion method provided by the present invention, the determination of the first sea surface radial velocity according to the Doppler centroid frequency grid includes: calculating a first Doppler shift caused by the relative motion of the satellite platform and the rotating earth; calculating a second Doppler shift caused by the sea surface wind wave motion; removing the first Doppler shift and the second Doppler shift from the Doppler centroid frequency grid to obtain a third Doppler shift caused by the sea surface current field; and determining the first sea surface radial velocity according to the third Doppler shift.

[0009] According to an ocean internal wave current field inversion method provided by the present invention, the determination of the internal wave propagation direction according to the SAR single-look complex image and the determination of the azimuth dimension component of the two-dimensional ocean internal wave surface current field according to the internal wave propagation direction and the first sea surface radial velocity include: preprocessing the SAR single-look complex image to obtain a backscattering coefficient image; using the Fourier transform method to determine the internal wave direction of the backscattering coefficient image according to the energy distribution in the frequency domain, and obtaining the internal wave propagation direction through position averaging processing; determining the internal wave propagation direction relative to the SAR antenna line-of-sight direction according to the internal wave propagation direction and the satellite azimuth angle; and determining the azimuth dimension component of the two-dimensional ocean internal wave surface current field according to the internal wave propagation direction relative to the SAR antenna line-of-sight direction and the first sea surface radial velocity.

[0010] According to an ocean internal wave current field inversion method provided by the present invention, the step of inputting the range dimension component and the azimuth dimension component into the IDopRIM model for iterative calculation to output the second sea surface radial velocity and the azimuthal flow field, and obtaining the two-dimensional ocean internal wave current field based on the second sea surface radial velocity and the azimuthal flow field includes: inputting the range dimension component, the azimuth dimension component, and wind field data into the IDopRIM model to obtain the sea surface Doppler velocity considering the coupling effect of waves and the current field; determining the Doppler frequency shift caused by the coupling effect of large-scale waves and the current field according to the sea surface Doppler velocity and the first sea surface radial velocity at the previous moment, and determining the second sea surface radial velocity at the current moment according to the Doppler frequency shift; when the error between the first sea surface radial velocity at the previous moment and the second sea surface radial velocity at the current moment satisfies the error threshold condition, outputting the second sea surface radial velocity and the azimuthal flow field, and obtaining the two-dimensional ocean internal wave current field based on the second sea surface radial velocity and the azimuthal flow field.

[0011] According to an ocean internal wave current field inversion method provided by the present invention, the method further includes: when the error between the first sea surface radial velocity at the previous moment and the second sea surface radial velocity at the current moment does not satisfy the error threshold condition, constructing a new two-dimensional ocean internal wave surface current field according to the second sea surface radial velocity and the azimuthal flow field, and re-inputting the new two-dimensional ocean internal wave surface current field into the IDopRIM model for iterative calculation.

[0012] The present invention also provides an ocean internal wave current field inversion device, including the following modules: an acquisition module and a processing module; the acquisition module is used to acquire a synthetic aperture radar (SAR) single-look complex image; the processing module is used to determine the Doppler centroid frequency grid of the SAR single-look complex image; determining the first sea surface radial velocity according to the Doppler centroid frequency grid, and determining the first sea surface radial velocity as the range dimension component of the two-dimensional ocean internal wave surface current field; determining the internal wave propagation direction according to the SAR single-look complex image, and determining the azimuth dimension component of the two-dimensional ocean internal wave surface current field according to the internal wave propagation direction and the first sea surface radial velocity; inputting the range dimension component and the azimuth dimension component into the IDopRIM model for iterative calculation to output the second sea surface radial velocity and the azimuthal flow field, and obtaining the two-dimensional ocean internal wave current field based on the second sea surface radial velocity and the azimuthal flow field; wherein, the IDopRIM model is a sea surface scattering Doppler model considering the coupling effect of waves and the current field.

[0013] An ocean internal wave current field inversion device provided by the present invention, the processing module is configured to perform Fourier transform on the data within the window of the SAR single-look complex image in the azimuth direction to obtain the azimuth power spectrum; average the azimuth power spectrum along the range direction to obtain the average power spectrum; perform circular correlation on the average power spectrum and a reference function, and determine the Doppler centroid of the data within the window at the zero crossing of the correlation result; determine the Doppler centroid frequency grid based on the Doppler centroids of all windows of the SAR single-look complex image.

[0014] An ocean internal wave current field inversion device provided by the present invention, the processing module is configured to calculate a first Doppler frequency shift caused by the relative motion between the satellite platform and the rotating earth; calculate a second Doppler frequency shift caused by the sea surface wind wave motion; remove the first Doppler frequency shift and the second Doppler frequency shift from the Doppler centroid frequency grid to obtain a third Doppler frequency shift caused by the sea surface current field; determine the first sea surface radial velocity according to the third Doppler frequency shift.

[0015] An ocean internal wave current field inversion device provided by the present invention, the processing module is configured to preprocess the SAR single-look complex image to obtain a backscattering coefficient image; use the Fourier transform method to determine the internal wave direction of the backscattering coefficient image according to the energy distribution in the frequency domain, and obtain the internal wave propagation direction through position averaging; determine the internal wave propagation direction relative to the SAR antenna line of sight according to the internal wave propagation direction and the satellite azimuth angle; determine the azimuth dimension component of the two-dimensional ocean internal wave surface current field according to the internal wave propagation direction relative to the SAR antenna line of sight and the first sea surface radial velocity.

[0016] An ocean internal wave current field inversion device provided by the present invention, the processing module is configured to input the range dimension component, the azimuth dimension component, and the wind field data into the IDopRIM model to obtain the sea surface Doppler velocity considering the coupling effect of waves and the current field; determine the Doppler frequency shift caused by the coupling effect of large-scale waves and the current field according to the sea surface Doppler velocity and the first sea surface radial velocity at the previous moment, and determine the second sea surface radial velocity at the current moment according to the Doppler frequency shift; when the error between the first sea surface radial velocity at the previous moment and the second sea surface radial velocity at the current moment satisfies the error threshold condition, output the second sea surface radial velocity and the azimuth current field, and obtain the two-dimensional current field of the ocean internal wave according to the second sea surface radial velocity and the azimuth current field.

[0017] An ocean internal wave current field inversion device provided by the present invention, the processing module is configured to, when the error between the first sea surface radial flow velocity at the previous moment and the second sea surface radial flow velocity at the current moment does not satisfy the error threshold condition, construct a new two-dimensional ocean internal wave surface current field according to the second sea surface radial flow velocity and the azimuthal current field, and re-enter the IDopRIM model for iterative calculation.

[0018] The present invention also provides an electronic device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the program, it implements the ocean internal wave current field inversion method as described in any one of the above.

[0019] The present invention also provides a non-transitory computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, it implements the ocean internal wave current field inversion method as described in any one of the above.

[0020] The present invention also provides a computer program product, including a computer program. When the computer program is executed by a processor, it implements the ocean internal wave current field inversion method as described in any one of the above.

[0021] The ocean internal wave current field inversion method and device provided by the present invention can determine the range dimension component and azimuth dimension component of the two-dimensional ocean internal wave surface current field. Therefore, compared with the prior art solution that only inverses the radial current field, the inversion method of the present application can more accurately reflect the spatial variation characteristics of the actual current field; since the IDopRIM model is a sea surface scattering Doppler model that considers the coupling effect of waves and the current field, the iterative calculation method of the present application fully considers the coupling effect of waves and the current field, and solves the problem that the traditional Doppler centroid offset method ignores the influence of the wave-current coupling effect on the current field inversion. By estimating and correcting the Doppler shift caused by the coupling effect, not only can the accuracy of the current field inversion be significantly improved, but also the stability of the algorithm is enhanced, enabling it to be more reliably applied to the measurement and analysis of the current field under various complex sea conditions. Description of the Drawings

[0022] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0023] Figure 1 It is a schematic flowchart of the ocean internal wave current field inversion method provided by the present invention;

[0024] Figure 2It is a schematic structural diagram of the ocean internal wave current field inversion device provided by the present invention;

[0025] Figure 3 It is a schematic structural diagram of the electronic device provided by the present invention. Specific embodiments

[0026] To make the objectives, technical solutions, and advantages of the present application clearer, the technical solutions in the present application will be clearly and completely described below with reference to the accompanying drawings in the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the scope of protection of the present application.

[0027] It should be noted that in the embodiments of the present application, words such as "exemplary" or "for example" are used to represent examples, illustrations, or explanations. Any embodiment or design solution described as "exemplary" or "for example" in the embodiments of the present application should not be construed as being more preferred or having more advantages than other embodiments or design solutions. Rather, the use of words such as "exemplary" or "for example" is intended to present relevant concepts in a specific manner.

[0028] It should be noted that in this document, the term "comprising", "including" or any other variant thereof is intended to cover a non-exclusive inclusion, such that a process, method, article, or device comprising a series of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or device. Without further limitation, an element defined by the phrase "comprising a..." does not exclude the presence of additional identical elements in the process, method, article, or device comprising that element. In addition, it should be pointed out that the scope of the methods and devices in the embodiments of the present application is not limited to performing functions in the order shown or discussed, and may also include performing functions in a substantially simultaneous manner or in a reverse order according to the functions involved. For example, the described methods may be performed in an order different from that described, and various steps may be added, omitted, or combined. Additionally, features described with reference to certain examples may be combined in other examples.

[0029] To facilitate a clear description of the technical solutions in the embodiments of the present application, in the embodiments of the present application, terms such as "first" and "second" are used to distinguish identical or similar items with basically the same functions and roles. Those skilled in the art can understand that terms such as "first" and "second" do not limit the quantity and execution order.

[0030] Some exemplary embodiments are described for purposes of illustration in the embodiments of the present application. It should be understood that the present application can be implemented in other ways not specifically shown in the drawings.

[0031] As Figure 1 shown, the embodiments of the present application provide a method for retrieving the internal wave current field in the ocean. This method for retrieving the internal wave current field in the ocean can be applied to a device for retrieving the internal wave current field in the ocean. The method for retrieving the internal wave current field in the ocean may include S101 - S104:

[0032] S101. The device for retrieving the internal wave current field in the ocean acquires a single - look complex image of a synthetic aperture radar (SAR) and determines the Doppler centroid frequency grid of the SAR single - look complex image.

[0033] Optionally, the device for retrieving the internal wave current field in the ocean can obtain the Doppler frequency shift information caused by the sea surface movement through the single - look complex image of the synthetic aperture radar.

[0034] It should be noted that the SAR single - look complex image is a specific type of SAR image. "Single - look" means that during the processing of synthetic aperture radar data, the echo signal is only imaged once. The relative concept is "multi - look" processing.

[0035] Optionally, the device for retrieving the internal wave current field in the ocean determines the Doppler centroid frequency grid of the SAR single - look complex image, including: performing a Fourier transform on the data within the window of the SAR single - look complex image in the azimuth direction to obtain the azimuth power spectrum; averaging the azimuth power spectrum along the range direction to obtain the average power spectrum; performing a circular correlation between the average power spectrum and a reference function, and determining the zero - crossing point of the correlation result as the Doppler centroid of the data within the window; determining the Doppler centroid frequency grid based on the Doppler centroids of all windows of the SAR single - look complex image.

[0036] Specifically, the device for retrieving the internal wave current field in the ocean can determine the Doppler centroid frequency grid through the following steps 11 - step 14:

[0037] Step 11. Determine the window size. The window size can be 512 pixels (azimuth direction) × 128 pixels (range direction). Perform a Fourier transform on the data within the window in the azimuth direction to obtain the azimuth power spectrum:

[0038] ;

[0039] Wherein, represents the azimuth power spectrum, represents the fast Fourier transform, is the input SAR echo data, , , is the number of azimuth echo points, to is the number of range cells.

[0040] Step 12: Average the power spectrum along the range direction and azimuth direction to obtain the average power spectrum .

[0041] ;

[0042] Step 13: Perform circular correlation between the average power spectrum and the reference function to find the zero crossing of the correlation result and obtain the Doppler centroid of this window.

[0043] ;

[0044] where is the Doppler bandwidth, represents frequency.

[0045] Step 14: Traverse the SAR single-look complex image, and perform the above Steps 11 - 13 on the data within the window in sequence to obtain the Doppler centroid frequency grid of the entire image.

[0046] S102: The ocean internal wave current field inversion device determines the first sea surface radial velocity according to the Doppler centroid frequency grid, and determines the first sea surface radial velocity as the range dimension component of the two-dimensional ocean internal wave surface current field.

[0047] Optionally, the ocean internal wave current field inversion device determines the first sea surface radial velocity according to the Doppler centroid frequency grid, including: calculating the first Doppler shift caused by the relative motion between the satellite platform and the rotating earth; calculating the second Doppler shift caused by the sea surface wind wave motion; removing the first Doppler shift and the second Doppler shift from the Doppler centroid frequency grid to obtain the third Doppler shift caused by the sea surface current field; determining the first sea surface radial velocity according to the third Doppler shift.

[0048] Specifically, the ocean internal wave current field inversion device can first calculate the first Doppler shift through the following formula according to the fitting polynomial given in the SAR single-look complex image, as well as parameters such as the required Doppler coefficient, slant range time, and standard slant range time :

[0049] ;

[0050] where is the Doppler coefficient, represents the slant range time, represents the standard slant range time.

[0051] After that, the ocean internal wave current field inversion device can use the CDOP model to calculate the second Doppler shift caused by the sea surface wind wave movement. , specifically including the following steps:

[0052] (1) Obtain the SAR image background field wind field data. Use the ERA5 (ECMWF reanalysis v5) analysis wind field data released by the European Centre for Medium Weather Forecasts (ECMWF). The original spatial resolution of the data is 0.25°. Resample the data to match the Doppler centroid frequency grid of the SAR single-look complex image to obtain the SAR image background field wind field data.

[0053] (2) The second Doppler shift caused by the sea surface wind wave movement . According to the wind field data and radar parameters, use the CDOP model to calculate the second Doppler shift caused by the wind wave movement :

[0054] ;

[0055] ;

[0056] ;

[0057] ;

[0058] ;

[0059] Among them, are the expressions of each layer function respectively, and represent the coefficients related to the radar polarization mode, is the incident angle, and are the wind directions in the radar line-of-sight direction ( , ), is the wind speed at a height of ten meters above the sea surface, is the radar polarization mode, and are the adjustment coefficients related to the radar polarization mode, is equal to 1 to 11, is the adjustment coefficient, is a vector containing terms related to angles and wind speeds, where: contains terms related to the wind direction, reflects the influence of the wind direction on the function, contains terms related to the incident angle, reflects the effect of the incident angle, contains terms related to the wind speed, indicating the influence of the wind speed in the function.

[0060] Finally, remove the first Doppler shift and the second Doppler shift from the Doppler centroid frequency grid to obtain a third Doppler shift caused by the sea surface current field ; determine the first sea surface radial velocity according to the third Doppler shift .

[0061] Optionally, the ocean internal wave current field inversion device can determine the first sea surface radial velocity according to the formula ; where is the first sea surface radial velocity, is the wave number of the radar incident wave, represents the incident angle sin value.

[0062] S103. The ocean internal wave current field inversion device determines the internal wave propagation direction according to the SAR single-look complex image, and determines the azimuth dimension component of the two-dimensional ocean internal wave surface current field according to the internal wave propagation direction and the first sea surface radial velocity.

[0063] Optionally, the ocean internal wave current field inversion device determines the internal wave propagation direction according to the SAR single-look complex image, and determines the azimuth dimension component of the two-dimensional ocean internal wave surface current field according to the internal wave propagation direction and the first sea surface radial velocity, including: preprocessing the SAR single-look complex image to obtain a backscattering coefficient image; using the Fourier transform method to determine the internal wave direction of the backscattering coefficient image according to the energy distribution in the frequency domain, and obtaining the internal wave propagation direction through position averaging processing; determining the internal wave propagation direction relative to the SAR antenna line of sight according to the internal wave propagation direction and the satellite azimuth angle; determining the azimuth dimension component of the two-dimensional ocean internal wave surface current field according to the internal wave propagation direction relative to the SAR antenna line of sight and the first sea surface radial velocity.

[0064] Specifically, the ocean internal wave current field inversion device can first preprocess the SAR single-look complex image. The preprocessing operations include radiometric calibration, geometric calibration, filtering, etc. Among them, the purpose of radiometric calibration is to eliminate or reduce the radiometric errors caused by factors such as the sensor itself and the atmosphere, so that the images acquired at different positions and different times are comparable in radiance. The purpose of geometric calibration is to correct the geometric deformations of the SAR single-look complex image caused by factors such as the position and attitude of the sensor platform and the earth's curvature during the acquisition process, so that the positions of the ground objects in the image correspond to the actual geographical coordinates, facilitating subsequent analysis and applications. The purpose of filtering is to remove the noise in the SAR image and improve the image quality. After completing these operations, the backscattering coefficient image can be obtained.

[0065] After that, since the gradient transformation direction of the internal wave is parallel to the propagation direction of the internal wave, the wave direction of the internal wave can be determined according to the energy distribution in the frequency domain. That is, first select multiple positions from top to bottom along the wave crest line of the internal wave. With the marked positions as the centers, set the window size to 512×512 pixels, and successively use the Fourier transform method to obtain the Fourier frequency domain spectrum. The energy distribution direction in the frequency domain is the propagation direction of the internal wave within this window. Then average the propagation directions of the internal waves at multiple positions as the propagation direction of the internal wave.

[0066] Then, assuming the propagation direction of the internal wave is , and the detected satellite azimuth angle is , then the propagation direction of the internal wave relative to the SAR antenna line of sight is expressed as:

[0067] ;

[0068] Judge the magnitude of the propagation direction of the internal wave according to the following formula:

[0069] ;

[0070] Finally, since the range dimension component of the internal wave can be expressed as: ; where is the first sea surface radial velocity in S102;

[0071] Therefore, the azimuth dimension component of the internal wave can be expressed as: .

[0072] It should be noted that the range dimension component and the azimuth dimension component of the internal wave together constitute the initial value of the two-dimensional ocean internal wave surface current field.

[0073] S104. The ocean internal wave current field inversion device inputs the distance dimension component and the azimuth dimension component into the IDopRIM model for iterative calculation to output the second sea surface radial velocity and the azimuthal flow field, and obtains the two-dimensional ocean internal wave current field based on the second sea surface radial velocity and the azimuthal flow field.

[0074] Among them, the IDopRIM (Improved DopRIM) model is a sea surface scattering Doppler model that takes into account the coupling effect of waves and the current field.

[0075] Optionally, the ocean internal wave current field inversion device inputs the distance dimension component and the azimuth dimension component into the IDopRIM model for iterative calculation to output the second sea surface radial velocity and the azimuthal flow field, and obtains the two-dimensional ocean internal wave current field based on the second sea surface radial velocity and the azimuthal flow field, including: inputting the distance dimension component, the azimuth dimension component, and the wind field data into the IDopRIM model to obtain the sea surface Doppler velocity considering the coupling effect of waves and the current field; determining the Doppler frequency shift caused by the coupling effect of large-scale waves and the current field according to the sea surface Doppler velocity and the first sea surface radial velocity at the previous moment, and determining the second sea surface radial velocity at the current moment according to the Doppler frequency shift; when the error between the first sea surface radial velocity at the previous moment and the second sea surface radial velocity at the current moment satisfies the error threshold condition, output the second sea surface radial velocity and the azimuthal flow field, and obtain the two-dimensional ocean internal wave current field based on the second sea surface radial velocity and the azimuthal flow field; when the error between the first sea surface radial velocity at the previous moment and the second sea surface radial velocity at the current moment does not satisfy the error threshold condition, construct a new two-dimensional ocean internal wave surface current field according to the second sea surface radial velocity and the azimuthal flow field, and re-enter it into the IDopRIM model for iterative calculation.

[0076] Specifically, the ocean internal wave current field inversion device can use the above-mentioned distance dimension component , azimuth dimension component , and the first sea surface radial velocity as the iterative initial values, input the current field data (i.e., the distance dimension component and the azimuth dimension component) and the detected wind field data into the IDopRIM model to obtain the sea surface Doppler velocity .

[0077] For the sea surface target observed by the radar, the relative motion velocity in the radar line-of-sight direction causes the radar Doppler frequency shift

[0078] ;

[0079] Among them, and represent the radar incident wave frequency and wave number respectively, c represents the speed of light.

[0080] The DopRIM model is based on the two-scale theory of sea surface scattering and the derivation of sea surface Doppler velocity. Based on the two-scale theory of sea surface scattering, the sea surface can be regarded as a small-scale rough surface superimposed on periodic large-scale waves. The horizontal component of the relative movement of the small surface element of the sea surface target with respect to the radar can be expressed as:

[0081] ;

[0082] where, represents the radar incident angle, represents the sea surface background flow velocity in the radial direction of radar observation, represents the average velocity of the small surface element relative to the background flow field, is a component related to the movement; 、 are parameters related to sea surface characteristics and fluctuations.

[0083] The IDopRIM model describes the differences in the sea surface morphology in the downwind and upwind directions by introducing hydrodynamic modulation to the sea wave spectrum model of medium and high wind speeds (>10 m / s), and solves the problem of overestimation of the IDopRIM model under small incident angles and medium and high wind speed upwind conditions. The sea wave spectrum with hydrodynamic modulation adopted by the IDopRIM model is expressed as:

[0084] ;

[0085] where, is the hydrodynamic modulation function, defined as:

[0086] ;

[0087] ;

[0088] ;

[0089] In the formula, represents the probability density function of the sea surface slope distribution in the wind direction, is the root mean square slope of the sea surface in the wind direction, is the projection of the sea surface slope in the direction of the wind direction, and the relationship between the two can be expressed as:

[0090] .

[0091] After that, based on the sea surface Doppler velocity and the first sea surface radial velocity at the previous moment , calculate the Doppler frequency shift caused by large-scale wind waves and wave-current coupling, and use the Doppler centroid offset method to calculate the second sea surface radial velocity at the current moment .

[0092] Then, judge whether it meets the error threshold condition, and the error threshold condition is less than the error threshold e; if it meets, stop the iteration and output the inversion result of the two-dimensional flow field of internal waves in the ocean: the second sea surface radial velocity and the azimuthal flow field ; if it does not meet, then according to the second sea surface radial velocity and the azimuthal flow field construct a new two-dimensional surface flow field of internal waves in the ocean and re-enter it into the IDopRIM model for iterative calculation.

[0093] In the embodiments of the present application, since the distance dimension component and the azimuth dimension component of the two-dimensional surface flow field of internal waves in the ocean can be determined, compared with the prior art solution that only inverses the radial flow field, the inversion method of the present application can more accurately reflect the spatial variation characteristics of the actual flow field; since the IDopRIM model is a sea surface scattering Doppler model that considers the coupling effect of waves and the flow field, the iterative calculation method of the present application fully considers the coupling effect of waves and the flow field, and solves the problem that the traditional Doppler centroid offset method ignores the influence of the wave-current coupling effect on the flow field inversion. By estimating and correcting the Doppler shift caused by the coupling effect, not only can the accuracy of the flow field inversion be significantly improved, but also the stability of the algorithm is enhanced, enabling it to be more reliably applied to the flow field measurement and analysis under various complex sea conditions.

[0094] The above mainly introduces the solution provided by the embodiments of the present application from the perspective of the method. To implement the above functions, it includes the corresponding hardware structure and / or software module for executing each function. Those skilled in the art should easily realize that, combined with the units and algorithm steps of each example described in the embodiments disclosed in this article, the embodiments of the present application can be implemented in the form of hardware or a combination of hardware and computer software. Whether a certain function is executed in the way of hardware or computer software driving hardware depends on the specific application and design constraints of the technical solution. Professional technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present application.

[0095] It should be noted that the device in the embodiments of the present application includes a virtual device and a physical device. The virtual device may be an internal wave current field inversion device in the ocean, and the physical device may include an electronic device, a computer storage medium, and a computer program product.

[0096] In the method for inverting the internal wave current field in the ocean provided by the embodiments of the present application, the execution subject may be an internal wave current field inversion device in the ocean, or a control module for inverting the internal wave current field in the internal wave current field inversion device. In the embodiments of the present application, taking the internal wave current field inversion device in the ocean as an example to execute the internal wave current field inversion method, the internal wave current field inversion device provided by the embodiments of the present application is described.

[0097] It should be noted that the embodiments of the present application can divide the functional modules of the internal wave current field inversion device in the ocean according to the above method examples. For example, each functional module can be divided corresponding to each function, or two or more functions can be integrated into one processing module. The above integrated module can be implemented in the form of hardware or in the form of a software functional module. Optionally, the division of modules in the embodiments of the present application is illustrative, and is only a logical function division. There may be other division methods in actual implementation.

[0098] As Figure 2 shown, the embodiments of the present application provide an internal wave current field inversion device 200 in the ocean. The internal wave current field inversion device 200 in the ocean includes: an acquisition module 201 and a processing module 202. The acquisition module 201 is used to acquire a synthetic aperture radar (SAR) single-look complex image; the processing module 202 is used to determine the Doppler centroid frequency grid of the SAR single-look complex image; determine the first sea surface radial velocity according to the Doppler centroid frequency grid, and determine the first sea surface radial velocity as the range dimension component of the two-dimensional internal wave surface current field in the ocean; determine the internal wave propagation direction according to the SAR single-look complex image, and determine the azimuth dimension component of the two-dimensional internal wave surface current field in the ocean according to the internal wave propagation direction and the first sea surface radial velocity; input the range dimension component and the azimuth dimension component into the IDopRIM model for iterative calculation to output the second sea surface radial velocity and the azimuthal current field, and obtain the two-dimensional internal wave current field in the ocean according to the second sea surface radial velocity and the azimuthal current field; wherein, the IDopRIM model is a sea surface scattering Doppler model considering the coupling effect of waves and the current field.

[0099] Optionally, the processing module 202 is configured to perform Fourier transform on the data within the window of the SAR single-look complex image in the azimuth direction to obtain an azimuth power spectrum; average the azimuth power spectrum along the range direction to obtain an average power spectrum; perform circular correlation on the average power spectrum and a reference function, and determine the zero-crossing point of the correlation result as the Doppler centroid of the data within the window; and determine the Doppler centroid frequency grid based on the Doppler centroids of all windows of the SAR single-look complex image.

[0100] Optionally, the processing module 202 is configured to calculate a first Doppler frequency shift caused by the relative motion between the satellite platform and the rotating earth; calculate a second Doppler frequency shift caused by the sea surface wind and wave motion; remove the first Doppler frequency shift and the second Doppler frequency shift from the Doppler centroid frequency grid to obtain a third Doppler frequency shift caused by the sea surface current field; and determine the first sea surface radial velocity based on the third Doppler frequency shift.

[0101] Optionally, the processing module 202 is configured to preprocess the SAR single-look complex image to obtain a backscattering coefficient image; use the Fourier transform method to determine the wave direction of internal waves in the backscattering coefficient image according to the energy distribution in the frequency domain, and obtain the internal wave propagation direction through position averaging processing; determine the internal wave propagation direction relative to the SAR antenna line of sight according to the internal wave propagation direction and the satellite azimuth angle; and determine the azimuth dimension component of the two-dimensional ocean internal wave surface current field according to the internal wave propagation direction relative to the SAR antenna line of sight and the first sea surface radial velocity.

[0102] Optionally, the processing module 202 is configured to input the range dimension component, the azimuth dimension component, and the wind field data into the IDopRIM model to obtain the sea surface Doppler velocity considering the coupling effect of waves and the current field; determine the Doppler frequency shift caused by the coupling effect of large-scale waves and the current field according to the sea surface Doppler velocity and the first sea surface radial velocity at the previous moment, and determine the second sea surface radial velocity at the current moment according to the Doppler frequency shift; and output the second sea surface radial velocity and the azimuthal current field when the error between the first sea surface radial velocity at the previous moment and the second sea surface radial velocity at the current moment satisfies the error threshold condition, and obtain the two-dimensional current field of ocean internal waves according to the second sea surface radial velocity and the azimuthal current field.

[0103] Optionally, when the error between the first sea surface radial velocity at the previous moment and the second sea surface radial velocity at the current moment does not satisfy the error threshold condition, the processing module 202 is configured to construct a new two-dimensional ocean internal wave surface current field according to the second sea surface radial velocity and the azimuthal current field, and re-enter the IDopRIM model for iterative calculation.

[0104] In the embodiments of the present application, since the distance - dimension component and the azimuth - dimension component of the two - dimensional ocean internal wave surface flow field can be determined, compared with the prior - art solution that only inverses the radial flow field, the inversion method of the present application can more accurately reflect the spatial variation characteristics of the actual flow field; since the IDopRIM model is a sea - surface scattering Doppler model that considers the coupling effect between waves and the flow field, the iterative calculation method of the present application fully considers the coupling effect between waves and the flow field, and solves the problem that the traditional Doppler centroid offset method ignores the influence of the wave - current coupling effect on the flow - field inversion. By estimating and correcting the Doppler shift caused by the coupling effect, not only can the accuracy of the flow - field inversion be significantly improved, but also the stability of the algorithm is enhanced, enabling it to be more reliably applied to the flow - field measurement and analysis under various complex sea conditions.

[0105] Figure 3 An entity - structure schematic diagram of an electronic device is exemplified, as Figure 3 shown. The electronic device may include: a processor 310, a communications interface 320, a memory 330, and a communication bus 340. Among them, the processor 310, the communications interface 320, and the memory 330 complete mutual communication through the communication bus 340. The processor 310 can call the logical instructions in the memory 330 to execute the method for inverting the ocean internal wave flow field. The method includes: obtaining a synthetic aperture radar (SAR) single - look complex image and determining the Doppler centroid frequency grid of the SAR single - look complex image; determining the first sea - surface radial velocity according to the Doppler centroid frequency grid and determining the distance - dimension component of the two - dimensional ocean internal wave surface flow field as the first sea - surface radial velocity; determining the internal wave propagation direction according to the SAR single - look complex image and determining the azimuth - dimension component of the two - dimensional ocean internal wave surface flow field according to the internal wave propagation direction and the first sea - surface radial velocity; inputting the distance - dimension component and the azimuth - dimension component into the IDopRIM model for iterative operation to output the second sea - surface radial velocity and the azimuth - direction flow field, and obtaining the two - dimensional flow field of the ocean internal wave according to the second sea - surface radial velocity and the azimuth - direction flow field.

[0106] In addition, when the logical instructions in the above-mentioned memory 330 are implemented in the form of software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art, or a part of the technical solution, can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes: various media that can store program codes, such as USB flash drives, mobile hard disks, read-only memories (ROM, Read-Only Memory), random access memories (RAM, Random Access Memory), magnetic disks, or optical discs.

[0107] On the other hand, the present invention also provides a computer program product. The computer program product includes a computer program that can be stored on a non-transitory computer-readable storage medium. When the computer program is executed by a processor, the computer can execute the ocean internal wave current field inversion method provided by the above-mentioned various methods. The method includes: acquiring a synthetic aperture radar (SAR) single-look complex image and determining the Doppler centroid frequency grid of the SAR single-look complex image; determining a first sea surface radial velocity according to the Doppler centroid frequency grid and determining the first sea surface radial velocity as the range dimension component of the two-dimensional ocean internal wave surface current field; determining the internal wave propagation direction according to the SAR single-look complex image and determining the azimuth dimension component of the two-dimensional ocean internal wave surface current field according to the internal wave propagation direction and the first sea surface radial velocity; inputting the range dimension component and the azimuth dimension component into the IDopRIM model for iterative operation to output a second sea surface radial velocity and an azimuthal current field, and obtaining the two-dimensional current field of the ocean internal wave according to the second sea surface radial velocity and the azimuthal current field.

[0108] In another aspect, the present invention also provides a non-transitory computer-readable storage medium, on which a computer program is stored. When the computer program is executed by a processor, it implements the method for inverting the ocean internal wave current field provided by the above-mentioned various methods. The method includes: obtaining a synthetic aperture radar (SAR) single-look complex image and determining the Doppler centroid frequency grid of the SAR single-look complex image; determining a first sea surface radial velocity according to the Doppler centroid frequency grid and determining the first sea surface radial velocity as the range dimension component of the two-dimensional ocean internal wave surface current field; determining the internal wave propagation direction according to the SAR single-look complex image and determining the azimuth dimension component of the two-dimensional ocean internal wave surface current field according to the internal wave propagation direction and the first sea surface radial velocity; inputting the range dimension component and the azimuth dimension component into the IDopRIM model for iterative calculation to output a second sea surface radial velocity and an azimuthal current field, and obtaining the two-dimensional current field of the ocean internal wave according to the second sea surface radial velocity and the azimuthal current field.

[0109] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed to multiple network units. Some or all of the modules can be selected according to actual needs to achieve the purpose of the solution of this embodiment. Those of ordinary skill in the art can understand and implement it without creative effort.

[0110] Through the description of the above embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus a necessary general hardware platform, and of course, it can also be implemented by hardware. Based on such an understanding, the essence of the above technical solution, or the part that contributes to the prior art, can be embodied in the form of a software product. The computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disc, etc., and includes several instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) to execute the methods described in each embodiment or some parts of the embodiments.

[0111] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments or equivalently replace some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for inverting ocean internal wave flow fields, characterized in that: include: Acquire a synthetic aperture radar (SAR) single-view complex image, and determine a Doppler centroid frequency grid of the SAR single-view complex image; Determine a first sea surface radial velocity according to the Doppler centroid frequency grid, and determine the first sea surface radial velocity as a distance dimension component of a two-dimensional ocean internal wave surface flow field; Determining the internal wave propagation direction according to the SAR single-view complex image, and determining the azimuth component of the two-dimensional ocean internal wave surface flow field according to the internal wave propagation direction and the first sea surface radial flow velocity; Inputting the distance dimension component and the azimuth dimension component into the IDopRIM model for iterative calculation to output a second sea surface radial velocity and an azimuth flow field, and obtaining a two-dimensional flow field of ocean internal waves according to the second sea surface radial velocity and the azimuth flow field; The IDopRIM model is a sea surface scattering Doppler model that takes into account the coupling effect of waves and flow fields; The step of inputting the distance dimension component and the azimuth dimension component into the IDopRIM model for iterative calculation to output a second sea surface radial velocity and an azimuth flow field, and obtaining a two-dimensional ocean internal wave flow field according to the second sea surface radial velocity and the azimuth flow field comprises: The distance dimension component, the azimuth dimension component and the wind field data are input into the IDopRIM model to obtain the sea surface Doppler velocity that takes into account the coupling effect of waves and flow fields; the Doppler frequency shift caused by the coupling effect of large-scale waves and flow fields is determined according to the sea surface Doppler velocity and the first sea surface radial velocity at the previous moment, and the second sea surface radial velocity at the current moment is determined according to the Doppler frequency shift; when the error between the first sea surface radial velocity at the previous moment and the second sea surface radial velocity at the current moment meets the error threshold condition, the second sea surface radial velocity and the azimuth flow field are output, and the two-dimensional ocean internal wave flow field is obtained according to the second sea surface radial velocity and the azimuth flow field; when the error between the first sea surface radial velocity at the previous moment and the second sea surface radial velocity at the current moment does not meet the error threshold condition, a new two-dimensional ocean internal wave surface flow field is constructed according to the second sea surface radial velocity and the azimuth flow field, and the new two-dimensional ocean internal wave surface flow field is re-input into the IDopRIM model for iterative calculation.

2. The method for inverting ocean internal wave flow field according to claim 1, characterized in that: The step of determining the Doppler centroid frequency grid of the SAR single-view complex image comprises: Performing Fourier transform on the data in the window of the SAR single-view complex image in azimuth to obtain an azimuth power spectrum; Averaging the azimuth power spectrum along the range direction to obtain an average power spectrum; Performing circular correlation between the average power spectrum and a reference function, and determining the zero-crossing point of the correlation result as the Doppler centroid of the data in the window; The Doppler centroid frequency grid is determined based on the Doppler centroids of all windows of the SAR single-look complex image.

3. The method for inverting ocean internal wave flow field according to claim 1, characterized in that: The determining of the first sea surface radial velocity according to the Doppler centroid frequency grid comprises: Calculate the first Doppler shift caused by the relative motion of the satellite platform and the rotating earth; Calculate the second Doppler shift caused by the motion of wind and waves on the sea surface; removing the first Doppler frequency shift and the second Doppler frequency shift from the Doppler centroid frequency grid to obtain a third Doppler frequency shift caused by the sea surface flow field; The first sea surface radial flow velocity is determined according to the third Doppler frequency shift.

4. The method for inverting ocean internal wave flow field according to claim 1, characterized in that: The method of determining the internal wave propagation direction according to the SAR single-view complex image, and determining the azimuth component of the two-dimensional ocean internal wave surface flow field according to the internal wave propagation direction and the first sea surface radial flow velocity, comprises: Preprocessing the SAR single-view complex image to obtain a backscatter coefficient image; The internal wave direction of the backscatter coefficient image is determined according to the energy distribution in the frequency domain by using the Fourier transform method, and the internal wave propagation direction is obtained by position averaging processing; Determining the internal wave propagation direction relative to the SAR antenna line of sight according to the internal wave propagation direction and the satellite azimuth; The azimuth component of the two-dimensional ocean internal wave surface flow field is determined according to the internal wave propagation direction relative to the SAR antenna line of sight and the first sea surface radial flow velocity.

5. An ocean internal wave flow field inversion device, characterized in that: include: Acquisition module and processing module; The acquisition module is used to acquire a synthetic aperture radar SAR single-view complex image; The processing module is used to determine the Doppler centroid frequency grid of the SAR single-view complex image; determine the first sea surface radial velocity according to the Doppler centroid frequency grid, and determine the first sea surface radial velocity as the distance dimension component of the two-dimensional ocean internal wave surface flow field; determine the internal wave propagation direction according to the SAR single-view complex image, and determine the azimuth dimension component of the two-dimensional ocean internal wave surface flow field according to the internal wave propagation direction and the first sea surface radial velocity; input the distance dimension component and the azimuth dimension component into the IDopRIM model for iterative calculation to output the second sea surface radial velocity and the azimuth flow field, and obtain the ocean internal wave two-dimensional flow field according to the second sea surface radial velocity and the azimuth flow field; wherein the IDopRIM model is a sea surface scattering Doppler model that takes into account the coupling effect of waves and flow fields; The processing module is used to input the distance dimension component, the azimuth dimension component and the wind field data into the IDopRIM model to obtain the sea surface Doppler velocity that takes into account the coupling effect of waves and flow fields; determine the Doppler frequency shift caused by the coupling effect of large-scale waves and flow fields according to the sea surface Doppler velocity and the first sea surface radial velocity at the previous moment, and determine the second sea surface radial velocity at the current moment according to the Doppler frequency shift; when the error between the first sea surface radial velocity at the previous moment and the second sea surface radial velocity at the current moment meets the error threshold condition, output the second sea surface radial velocity and the azimuth flow field, and obtain the two-dimensional ocean internal wave flow field according to the second sea surface radial velocity and the azimuth flow field; when the error between the first sea surface radial velocity at the previous moment and the second sea surface radial velocity at the current moment does not meet the error threshold condition, construct a new two-dimensional ocean internal wave surface flow field according to the second sea surface radial velocity and the azimuth flow field, and re-input it into the IDopRIM model for iterative calculation.

6. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that: When the processor executes the computer program, the ocean internal wave flow field inversion method as claimed in any one of claims 1 to 4 is implemented.

7. A non-transitory computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by a processor, the ocean internal wave flow field inversion method as claimed in any one of claims 1 to 4 is implemented.

8. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the ocean internal wave flow field inversion method as claimed in any one of claims 1 to 4 is implemented.

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