Ocean internal wave flow field inversion method and device

Abstract

The invention provides an ocean internal wave flow field inversion method and device, and is applied to the technical field of ocean remote sensing application. The method comprises the following steps: acquiring a synthetic aperture radar (SAR) single-view complex image, and determining a Doppler centroid frequency grid of the SAR single-view complex image; determining a first sea surface radial flow velocity according to the Doppler centroid frequency grid, and determining the first sea surface radial flow velocity as a distance dimension component of a two-dimensional ocean internal wave surface flow field; determining an internal wave propagation direction according to the SAR single-view complex image, and determining an 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 flow velocity; and inputting the distance dimension component and the azimuth dimension component into an IIDopRIM model for iterative operation so as to output a second sea surface radial flow velocity and an azimuth flow field, and obtaining an ocean internal wave two-dimensional flow field according to the second sea surface radial flow velocity and the azimuth flow field.

Description

Technical Field

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

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

[0003] In the existing technology, Synthetic Aperture Radar (SAR) can invert the sea surface flow field by measuring the Doppler frequency shift information caused by sea surface motion. The theoretical basis of the mainstream Doppler centroid shift method is the Doppler radar imaging model (DopRIM), which inverts the sea surface radial flow field by analyzing the contribution sources of each part of the Doppler centroid shift in the SAR image.

[0004] However, when existing flow field inversion algorithms separate the contributions of ocean currents and waves from the Doppler centroid offset obtained from SAR images, they generally assume that the two are independent and linearly additive, and use empirical models to calculate the Doppler contribution of wind and waves. This type of method ignores the Doppler contribution of the coupling of ocean currents and waves, thereby introducing errors in the inversion of internal wave sea surface flow fields, resulting in inaccurate inversion results of sea surface flow fields. Summary of the invention

[0005] The present invention provides an ocean internal wave flow field inversion method and device, which are used to solve the problem of inaccurate inversion results of sea surface flow field in the prior art.

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

[0007] According to a method for inverting an internal wave flow field in the ocean provided by the present invention, the method of determining the Doppler centroid frequency grid of the SAR single-view complex image comprises: performing Fourier transform on the data in a 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 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 in the window; and determining the Doppler centroid frequency grid based on the Doppler centroids of all windows of the SAR single-view complex image.

[0008] According to a method for inverting an ocean internal wave flow field provided by the present invention, the method of determining a first sea surface radial flow velocity based on the Doppler centroid frequency grid comprises: calculating a first Doppler frequency shift caused by the relative motion of a satellite platform and a rotating earth; calculating a second Doppler frequency shift caused by sea surface wind and wave motion; 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; and determining the first sea surface radial flow velocity based on the third Doppler frequency shift.

[0009] According to a method for inverting an ocean internal wave flow field provided by the present invention, the internal wave propagation direction is determined according to the SAR single-view complex image, and the azimuth dimension component of the two-dimensional ocean internal wave surface flow field is determined according to the internal wave propagation direction and the first sea surface radial flow velocity, including: preprocessing the SAR single-view complex image to obtain a backscattering coefficient image; using a 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; determining the azimuth dimension component of the two-dimensional ocean internal wave surface flow field according to the internal wave propagation direction relative to the SAR antenna line of sight and the first sea surface radial flow velocity.

[0010] According to a method for inverting an ocean internal wave flow field provided by the present invention, the distance dimension component and the azimuth dimension component are input into an IDopRIM model for iterative calculation to output a second sea surface radial velocity and an azimuth flow field, and the ocean internal wave two-dimensional flow field is obtained according to the second sea surface radial velocity and the azimuth flow field, including: inputting the distance dimension component, the azimuth dimension component and wind field data into the IDopRIM model to obtain a sea surface Doppler velocity that takes into account the coupling effect of waves and flow fields; determining 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 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 meets the error threshold condition, outputting the second sea surface radial velocity and the azimuth flow field, and obtaining the ocean internal wave two-dimensional flow field according to the second sea surface radial velocity and the azimuth flow field.

[0011] According to a method for inverting an ocean internal wave flow field provided by the present invention, the method also 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 meet the error threshold condition, constructing a new two-dimensional ocean internal wave surface flow field according to the second sea surface radial velocity and the azimuthal flow field, and re-inputting the IDopRIM model for iterative calculation.

[0012] The present invention also provides an ocean internal wave flow field inversion device, comprising the following modules: an acquisition module and a 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; a first sea surface radial velocity is determined according to the Doppler centroid frequency grid, and the first sea surface radial velocity is determined as the distance dimension component of a two-dimensional ocean internal wave surface flow field; an internal wave propagation direction is determined according to the SAR single-view complex image, and an azimuth dimension component of the two-dimensional ocean internal wave surface flow field is determined according to the internal wave propagation direction and the first sea surface radial velocity; the distance dimension component and the azimuth dimension component are input into an IDopRIM model for iterative calculation to output a second sea surface radial velocity and an azimuth flow field, and the ocean internal wave two-dimensional flow field is obtained 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.

[0013] According to an ocean internal wave flow field inversion device provided by the present invention, the processing module is used to perform Fourier transform on the data in the window of the SAR single-view complex image in azimuth 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 zero-crossing point of the correlation result as the Doppler centroid of the data in the window; and determine the Doppler centroid frequency grid based on the Doppler centroid of all windows of the SAR single-view complex image.

[0014] According to an ocean internal wave flow field inversion device provided by the present invention, the processing module is used to calculate a first Doppler frequency shift caused by the relative motion of a satellite platform and a rotating earth; calculate a second Doppler frequency shift caused by 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 flow field; and determine the first sea surface radial flow velocity according to the third Doppler frequency shift.

[0015] According to an ocean internal wave flow field inversion device provided by the present invention, the processing module is used to preprocess the SAR single-view 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 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; determine the azimuth component of the two-dimensional ocean internal wave surface flow field according to the internal wave propagation direction relative to the SAR antenna line of sight and the first sea surface radial flow velocity.

[0016] According to an ocean internal wave flow field inversion device provided by the present invention, 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 flow velocity at the previous moment, and determine the second sea surface radial flow velocity at the current moment according to the Doppler frequency shift; 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 meets the error threshold condition, output the second sea surface radial flow velocity and the azimuth flow field, and obtain the ocean internal wave two-dimensional flow field according to the second sea surface radial flow velocity and the azimuth flow field.

[0017] According to an ocean internal wave flow field inversion device provided by the present invention, the processing module is used to construct a new two-dimensional ocean internal wave surface flow field according to 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 meet the error threshold condition, and re-input the IDopRIM model for iterative calculation.

[0018] The present invention also provides an electronic device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, any of the above-mentioned methods for inverting the ocean internal wave flow field is implemented.

[0019] The present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon, and when the computer program is executed by a processor, the method for inverting the ocean internal wave flow field as described in any one of the above is implemented.

[0020] The present invention also provides a computer program product, comprising a computer program, wherein when the computer program is executed by a processor, the method for inverting the ocean internal wave flow field as described above is implemented.

[0021] The method and device for inverting the ocean internal wave flow field provided by the present invention can determine the distance dimension component and the azimuth dimension component of the two-dimensional ocean internal wave surface flow field. Therefore, compared with the prior art solution of only inverting 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 takes into account the coupling effect of waves and flow fields, the iterative calculation method of the present application fully considers the coupling effect of waves and flow fields, and solves the problem that the traditional Doppler centroid shift method ignores the influence of wave-current coupling on flow field inversion. By estimating and correcting the Doppler shift caused by the coupling effect, not only can the accuracy of flow field inversion be significantly improved, but also the stability of the algorithm is enhanced, so that it can be more reliably applied to flow field measurement and analysis under various complex sea conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 It is a schematic diagram of the flow chart of the ocean internal wave flow field inversion method provided by the present invention; Figure 2 It is a schematic diagram of the structure of the ocean internal wave flow field inversion device provided by the present invention; Figure 3 It is a structural schematic diagram of the electronic device provided by the present invention. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of this application clearer, the technical solutions in this application will be clearly and completely described below in conjunction with the drawings in this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0025] It should be noted that, in the embodiments of the present application, words such as "exemplary" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

[0026] It should be noted that, in this article, the terms "comprise", "include" or any other variant thereof are intended to cover non-exclusive inclusion, so that the process, method, article or device including a series of elements includes not only those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, the elements defined by the sentence "comprise one..." do not exclude the presence of other identical elements in the process, method, article or device including the 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 reverse order according to the functions involved, for example, the described method may be performed in an order different from that described, and various steps may also be added, omitted, or combined. In addition, the features described with reference to certain examples may be combined in other examples.

[0027] In order to facilitate a clear description of the technical solutions of the embodiments of the present application, in the embodiments of the present application, words such as "first" and "second" are used to distinguish between identical or similar items with substantially the same functions and effects. Those skilled in the art can understand that words such as "first" and "second" do not limit the quantity and order of execution.

[0028] The embodiments of the present application describe some exemplary embodiments for the purpose of explanation. It should be understood that the present application can be implemented in other ways that are not specifically shown in the drawings.

[0029] like Figure 1 As shown, the embodiment of the present application provides an ocean internal wave flow field inversion method, which can be applied to an ocean internal wave flow field inversion device. The ocean internal wave flow field inversion method may include S101-S104: S101. An ocean internal wave flow field inversion device obtains a synthetic aperture radar SAR single-view complex image and determines a Doppler centroid frequency grid of the SAR single-view complex image.

[0030] Optionally, the ocean internal wave flow field inversion device can obtain Doppler frequency shift information caused by sea surface motion through synthetic aperture radar single-view complex images.

[0031] It should be noted that SAR single-view complex image is a specific type of SAR image. "Single-view" means that in the process of synthetic aperture radar data processing, only one imaging process is performed on the echo signal. The relative concept is "multi-view" processing.

[0032] Optionally, the ocean internal wave flow field inversion device determines the Doppler centroid frequency grid of the SAR single-view complex image, including: 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; circularly correlating the average power spectrum with a reference function, and determining the zero-crossing point of the correlation result as the Doppler centroid of the data in the window; and determining the Doppler centroid frequency grid based on the Doppler centroids of all windows of the SAR single-view complex image.

[0033] Specifically, the ocean internal wave flow field inversion device can determine the Doppler centroid frequency grid by following steps 11 to 14: Step 11, determine the window size, which can be 512 pixels (azimuth) × 128 pixels (range), and perform Fourier transform on the data in the window in azimuth to obtain the azimuth power spectrum: ; in, represents the azimuthal power spectrum, represents the fast Fourier transform, To input SAR echo data, , , is the number of echo points in azimuth direction, arrive is the number of distance units.

[0034] Step 12: Average the power spectrum in the azimuth direction along the distance direction to obtain the average power spectrum .

[0035] ; Step 13: Compare the average power spectrum with the reference function Perform circular correlation, find the zero-crossing point of the correlation result, and obtain the Doppler centroid of the window.

[0036] ; in, is the Doppler bandwidth, Indicates frequency.

[0037] Step 14: traverse the SAR single-view complex image, and perform the above steps 11-13 on the data in the window in turn to obtain the Doppler centroid frequency grid of the entire image.

[0038] S102. The ocean internal wave flow field inversion device determines a first sea surface radial velocity according to the Doppler centroid frequency grid, and determines the first sea surface radial velocity as a distance dimension component of a two-dimensional ocean internal wave surface flow field.

[0039] Optionally, the ocean internal wave flow field inversion device determines a first sea surface radial flow velocity based on the Doppler centroid frequency grid, including: calculating a first Doppler frequency shift caused by the relative motion of the satellite platform and the rotating earth; calculating a second Doppler frequency shift caused by sea surface wind and wave motion; 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; and determining the first sea surface radial flow velocity based on the third Doppler frequency shift.

[0040] Specifically, the ocean internal wave flow field inversion device can first calculate the first Doppler frequency shift according to the fitting polynomial given in the SAR single-view complex image, as well as the required Doppler coefficient, slant range time, standard slant range time and other parameters by the following formula: : ; in, is the Doppler coefficient, represents the slant range time, Indicates the standard slope range time.

[0041] Afterwards, the ocean internal wave flow field inversion device can use the CDOP model to calculate the second Doppler frequency shift caused by the sea surface wind and wave motion. , specifically including the following steps: (1) Obtain SAR image background wind data. The wind data were analyzed using ERA5 (ECMWF reanalysis v5) released by the European Centre for Medium Weather Forecasts (ECMWF). The original spatial resolution of the data was 0.25°. The data was resampled to match the Doppler centroid frequency grid of the SAR single-view complex image to obtain the SAR image background wind data.

[0042] (2) Second Doppler frequency shift caused by wind and wave motion on the sea surface Based on wind field data and radar parameters, the CDOP model is used to calculate the second Doppler frequency shift caused by wind and wave motion. : ; ; ; ; ; in, are the expressions of each layer function, and represents the coefficient related to the radar polarization mode, is the incident angle, and is the wind direction in the radar line of sight ( , ), is the wind speed at a height of ten meters above the sea surface, is the polarization mode of the radar, and is the adjustment factor related to the radar polarization mode, Equal to 1 to 11, is the adjustment factor, is a vector containing terms related to angle and wind speed, where: Contains items related to wind direction, It reflects the influence of wind direction on the function. contains terms related to the angle of incidence, It reflects the effect of the angle of incidence. Contains terms related to wind speed, Shows the effect of wind speed in the function.

[0043] Finally, the first Doppler frequency shift is removed from the Doppler centroid frequency grid. and the second Doppler shift , the third Doppler frequency shift caused by the sea surface flow field is obtained According to the third Doppler frequency shift The first sea surface radial flow velocity is determined.

[0044] Optionally, the ocean internal wave flow field inversion device can be based on the formula Determine the first sea surface radial velocity; wherein, is the first sea surface radial velocity, is the radar incident wave number, Indicates the angle of incidence The sine value of .

[0045] S103. The ocean internal wave flow field inversion device determines the internal wave propagation direction according to the SAR single-view complex image, and determines the azimuthal 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.

[0046] Optionally, the ocean internal wave flow field inversion device determines the internal wave propagation direction according to the SAR single-view complex image, and determines 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, including: preprocessing the SAR single-view complex image to obtain a backscattering coefficient image; using a 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; determining the azimuth component of the two-dimensional ocean internal wave surface flow field according to the internal wave propagation direction relative to the SAR antenna line of sight and the first sea surface radial flow velocity.

[0047] Specifically, the ocean internal wave flow field inversion device can first preprocess the SAR single-view complex image. The preprocessing operations include radiation correction, geometric correction, filtering, etc., wherein the purpose of radiation correction is to eliminate or reduce the radiation error caused by the sensor itself, the atmosphere and other factors, so that the images acquired at different positions and at different times are comparable in radiation brightness. The purpose of geometric correction is to correct the geometric deformation caused by the position, attitude, earth curvature and other factors of the sensor platform during the acquisition process of the SAR single-view complex image, so that the position of the ground objects in the image corresponds to the actual geographic coordinates, so as to facilitate subsequent analysis and application. The purpose of filtering is to remove noise in the SAR image and improve the image quality. After completing these operations, the backscatter coefficient image can be obtained.

[0048] Afterwards, since the gradient transformation direction of the internal wave is parallel to the propagation direction of the internal wave, the direction of the internal wave can be determined based on the energy distribution in the frequency domain. That is, multiple positions are selected from top to bottom along the crest line of the internal wave, with the marked position as the center, and the window size is set to 512×512 pixels. The Fourier transform method is used to obtain the Fourier frequency domain spectrum. The energy distribution direction in the frequency domain is the propagation direction of the internal wave in the window. The propagation directions of the internal waves at multiple positions are then averaged as the propagation direction of the internal wave.

[0049] Then, assuming that the internal wave propagation direction is , the detected satellite azimuth is , then the internal wave propagation direction relative to the SAR antenna line of sight is It is expressed as: ; Determine the propagation direction of the internal wave according to the following formula Size: ; Finally, due to the distance component of the internal wave It can be expressed as: ;in, is the first sea surface radial velocity in S102; Therefore, the azimuthal component of the internal wave It can be expressed as: .

[0050] It should be noted that the distance dimension component and the azimuth dimension component of the internal wave together constitute the initial value of the two-dimensional ocean internal wave surface flow field.

[0051] S104, the ocean internal wave flow field inversion device inputs 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 obtains the ocean internal wave two-dimensional flow field based on the second sea surface radial velocity and the azimuth flow field.

[0052] The IDopRIM (Improved DopRIM) model is a sea surface scattering Doppler model that takes into account the coupling effect of waves and flow fields.

[0053] Optionally, the ocean internal wave flow field inversion device inputs 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 obtains the ocean internal wave two-dimensional flow field based on the second sea surface radial velocity and the azimuth flow field, including: inputting the distance dimension component, the azimuth dimension component and 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; determining the Doppler frequency shift caused by the coupling effect of large-scale waves and flow fields based on the sea surface Doppler velocity and the first sea surface radial velocity at the previous moment, and determining the Doppler frequency shift based on the Doppler frequency shift. Determine the second sea surface radial velocity at the current moment; 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 azimuthal flow field, and obtain the ocean internal wave two-dimensional flow field according to 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 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 azimuthal flow field, and re-input the IDopRIM model for iterative calculation.

[0054] Specifically, the ocean internal wave flow field inversion device can convert the above distance dimension component , azimuth dimension and the first sea surface radial velocity Set as the initial value of the iteration, and convert the flow field data (i.e., distance dimension component and azimuth dimension component), the detected wind field data Input IDopRIM model to get sea surface Doppler velocity .

[0055] For sea surface targets observed by radar, their relative motion speed in the direction of radar line of sight is The radar Doppler shift caused It can be expressed as: ; in, and denote the radar incident wave frequency and wave number respectively, c Represents the speed of light.

[0056] The DopRIM model is based on the dual-scale theory of sea surface scattering and the derivation of sea surface Doppler velocity. Based on the dual-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 motion of the small surface element of the sea surface target relative to the radar is It can be expressed as: ; in, represents the radar incident angle, represents the sea surface background velocity in the radar observation radial direction, represents the average velocity of the small surface element relative to the background flow field, It is a component related to movement; , It is a parameter related to sea surface characteristics and fluctuations.

[0057] The IDopRIM model introduces hydrodynamic modulation into the wave spectrum model of medium and high wind speeds (>10 m / s) to describe the difference in sea surface morphology in the downwind and upwind directions, solving the problem of overestimation of the IDopRIM model under small incident angles and medium and high wind speed upwind conditions. The wave spectrum of hydrodynamic modulation used by the IDopRIM model is expressed as: ; in, is the hydrodynamic modulation function, defined as: ; ; ; In the formula, It represents the probability density function of the surface slope distribution in the wind direction, is the root mean square slope of the sea surface in the wind direction, for Direction of sea surface slope In the projection of wind direction, the relationship between the two can be expressed as: .

[0058] Then, according to 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 shift method to calculate the second sea surface radial velocity at the current moment .

[0059] Then, judge Whether the error threshold condition is met, the error threshold condition is Less than the error threshold e; if it is satisfied, the iteration is stopped and the inversion result of the two-dimensional flow field of the ocean internal wave is output: the second sea surface radial velocity and azimuthal flow field If not satisfied, then according to the second sea surface radial velocity and azimuthal flow field A new two-dimensional ocean internal wave surface flow field is constructed and re-input into the IDopRIM model for iterative calculation.

[0060] In the embodiment 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 of only inverting 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 takes into account the coupling effect of waves and flow fields, the iterative calculation method of the present application fully considers the coupling effect of waves and flow fields, and solves the problem that the traditional Doppler centroid shift method ignores the influence of wave-current coupling on flow field inversion. By estimating and correcting the Doppler shift caused by the coupling effect, not only can the accuracy of flow field inversion be significantly improved, but also the stability of the algorithm is enhanced, so that it can be more reliably applied to flow field measurement and analysis under various complex sea conditions.

[0061] The above mainly introduces the solution provided by the embodiment of the present application from the perspective of the method. In order to realize the above functions, it includes hardware structures and / or software modules corresponding to the execution of each function. Those skilled in the art should easily realize that, in combination with the units and algorithm steps of each example described in the embodiment disclosed herein, the embodiment of the present application can be implemented in the form of hardware or a combination of hardware and computer software. Whether a function is executed in the form of hardware or computer software driving hardware depends on the specific application and design constraints of the technical solution. Professional and technical personnel 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.

[0062] It should be noted that the device in the embodiment of the present application includes a virtual device and a physical device. The virtual device may be an ocean internal wave flow field inversion device, and the physical device may include an electronic device, a computer storage medium, and a computer program product.

[0063] The ocean internal wave current field inversion method provided in the embodiment of the present application can be executed by an ocean internal wave current field inversion device, or a control module for ocean internal wave current field inversion in the ocean internal wave current field inversion device. In the embodiment of the present application, the ocean internal wave current field inversion method performed by the ocean internal wave current field inversion device is taken as an example to illustrate the ocean internal wave current field inversion device provided in the embodiment of the present application.

[0064] It should be noted that the embodiment of the present application can divide the functional modules of the ocean internal wave flow field inversion device according to the above method example. For example, each functional module can be divided according 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 software functional modules. Optionally, the division of modules in the embodiment of the present application is schematic and is only a logical functional division. There may be other division methods in actual implementation.

[0065] like Figure 2 As shown, the embodiment of the present application provides an ocean internal wave and current field inversion device 200. The ocean internal wave and current field inversion device 200 includes: an acquisition module 201 and a processing module 202. The acquisition module 201 is used to acquire a synthetic aperture radar SAR single-view complex image; the processing module 202 is used to determine the 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 the distance dimension component of a 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 a second sea surface radial velocity and an 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.

[0066] Optionally, the processing module 202 is used to perform Fourier transform on the data in the window of the SAR single-view complex image in azimuth to obtain an azimuth power spectrum; average the azimuth power spectrum along the range direction to obtain an average power spectrum; circularly correlate the average power spectrum with a reference function, and determine the zero-crossing point of the correlation result as the Doppler centroid of the data in the window; and determine the Doppler centroid frequency grid based on the Doppler centroid of all windows of the SAR single-view complex image.

[0067] Optionally, the processing module 202 is used 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 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 flow field; and determine the first sea surface radial flow velocity based on the third Doppler frequency shift.

[0068] Optionally, the processing module 202 is used to preprocess the SAR single-view complex image to obtain a backscatter coefficient image; use the Fourier transform method to determine the internal wave direction of the backscatter 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; determine the azimuth component of the two-dimensional ocean internal wave surface flow field according to the internal wave propagation direction relative to the SAR antenna line of sight and the first sea surface radial flow velocity.

[0069] Optionally, the processing module 202 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 flow field of ocean internal waves according to the second sea surface radial velocity and the azimuth flow field.

[0070] Optionally, the processing module 202 is used to construct a new two-dimensional ocean internal wave surface flow field according to 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 meet the error threshold condition, and re-input the IDopRIM model for iterative calculation.

[0071] In the embodiment 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 of only inverting 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 takes into account the coupling effect of waves and flow fields, the iterative calculation method of the present application fully considers the coupling effect of waves and flow fields, and solves the problem that the traditional Doppler centroid shift method ignores the influence of wave-current coupling on flow field inversion. By estimating and correcting the Doppler shift caused by the coupling effect, not only can the accuracy of flow field inversion be significantly improved, but also the stability of the algorithm is enhanced, so that it can be more reliably applied to flow field measurement and analysis under various complex sea conditions.

[0072] Figure 3 An example of a physical structure diagram of an electronic device is shown in FIG. Figure 3As shown, the electronic device may include: a processor 310 , a communications interface 320 , a memory 330 and a communication bus 340 , wherein the processor 310 , the communications interface 320 , and the memory 330 communicate with each other via the communication bus 340 . The processor 310 can call the logic instructions in the memory 330 to execute the ocean internal wave flow field inversion method, which includes: acquiring a synthetic aperture radar SAR single-view complex image, and determining the Doppler centroid frequency grid of the SAR single-view 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 distance dimension component of the 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 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 calculation to output a second sea surface radial velocity and an azimuth flow field, and obtaining the ocean internal wave two-dimensional flow field according to the second sea surface radial velocity and the azimuth flow field.

[0073] In addition, the logic instructions in the above-mentioned memory 330 can be implemented in the form of a software functional unit and can be stored in a computer-readable storage medium when it is sold or used as an independent product. Based on such an understanding, the technical solution of the present invention, in essence, or the part that contributes to the prior art or the part of the technical solution, can be embodied in the form of a software product, and the computer software product is stored in a storage medium, including a number of instructions for a computer device (which can be a personal computer, a server, or a network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, mobile hard disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), disk or optical disk, etc. Various media that can store program codes.

[0074] On the other hand, the present invention also provides a computer program product, which includes a computer program. The computer program 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 flow field inversion method provided by the above-mentioned methods, and the method includes: obtaining a synthetic aperture radar SAR single-view complex image, and determining the Doppler centroid frequency grid of the SAR single-view 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 distance dimension component of the 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 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 calculation to output a second sea surface radial velocity and an azimuth flow field, and obtaining the ocean internal wave two-dimensional flow field according to the second sea surface radial velocity and the azimuth flow field.

[0075] On the other hand, the present invention also provides a non-transitory computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, is implemented to execute the ocean internal wave flow field inversion method provided by the above-mentioned methods, the method comprising: acquiring a synthetic aperture radar SAR single-view complex image, and determining the Doppler centroid frequency grid of the SAR single-view 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 distance dimension component of the 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 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 calculation to output a second sea surface radial velocity and an azimuth flow field, and obtaining the ocean internal wave two-dimensional flow field according to the second sea surface radial velocity and the azimuth flow field.

[0076] The device embodiments described above are merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components displayed as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative labor.

[0077] Through the description of the above implementation methods, those skilled in the art can clearly understand that each implementation method can be implemented by means of software plus a necessary general hardware platform, and of course, can also be implemented by hardware. Based on this understanding, the above technical solution is essentially or the part that contributes to the prior art can be embodied in the form of a software product, and the computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, a disk, an optical disk, etc., including a number of instructions for 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.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions 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.

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. The method for inverting ocean internal wave flow field according to claim 1, characterized in that: 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: 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 taking into account the coupling effect of waves and flow fields; Determine the Doppler frequency shift caused by the coupling of large-scale waves and flow fields according to the sea surface Doppler velocity and the first sea surface radial flow velocity at the previous moment, and determine the second sea surface radial flow 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, the second sea surface radial velocity and the azimuthal flow field are output, and the two-dimensional flow field of ocean internal waves is obtained based on the second sea surface radial velocity and the azimuthal flow field.

6. The method for inverting the ocean internal wave flow field according to claim 5, characterized in that: The method further comprises: 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 based on the second sea surface radial velocity and the azimuthal flow field, and the IDopRIM model is re-input for iterative calculation.

7. 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.

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

9. 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 method for inverting the ocean internal wave and current field as claimed in any one of claims 1 to 6 is implemented.

10. A computer program product, comprising a computer program, characterized in that When the computer program is executed by a processor, the method for inverting the ocean internal wave and current field as claimed in any one of claims 1 to 6 is implemented.

Images