Satellite-borne synthetic aperture radar sea surface vector flow reconstruction method

Abstract

The invention discloses a spaceborne synthetic aperture radar sea surface vector flow reconstruction method, and relates to the field of ocean current observation, and the method comprises the steps: obtaining a synthetic aperture radar image of a research region; the sea surface radial flow velocity is determined according to the synthetic aperture radar image; based on an earth rotation approximation theory and the sea surface radial flow velocity, determining an initial azimuth flow velocity; performing non-ground rotation correction on the initial azimuth flow velocity to obtain a final azimuth flow velocity; and according to the sea surface radial flow velocity and the final azimuth flow velocity, reconstructing a sea surface vector flow field, and obtaining the flow velocity and the flow direction of the reconstructed sea surface vector flow field. According to the invention, the sea surface vector flow field can be accurately obtained from the single-antenna spaceborne synthetic aperture radar, and the precision of the sea surface vector flow field is improved.

Description

Technical Field

[0001] The present application relates to the field of ocean current observation, and in particular to a method for reconstructing sea surface vector flow of a spaceborne synthetic aperture radar based on geostrophic approximation and non-geostrophic correction. Background Art

[0002] Ocean currents are complex systems composed of multiple dynamic elements, including geostrophic currents, wind-driven Ekman currents, wave-induced Stokes drift, inertial motion, and tidal currents. These ocean currents play a vital role in the global redistribution and exchange of ocean heat, salinity, nutrients, carbon sinks, and fresh water. They have a significant impact on ocean dynamic phenomena. In addition, in-depth research on ocean currents has great application value and practical significance for optimizing ship route planning, accurately developing fishery resources, efficiently implementing maritime search and rescue operations, and effectively tracking the diffusion path of pollutants.

[0003] With the rapid development of satellite remote sensing technology, satellites equipped with altimeters have become an important tool for mapping global sea surface flow fields. Spaceborne synthetic aperture radar (SAR) has the ability to detect the global ocean all day and all weather, and can provide high-resolution (1 km) and wide coverage (500 km) sea surface Doppler shift data. However, most SAR satellites currently in orbit are equipped with a single antenna, so they can only obtain one component of the ocean surface flow, that is, the radial flow velocity along the direction of the antenna, and cannot directly measure the azimuthal flow velocity along the direction of the satellite's flight. However, in oceanographic research and applications, the sea surface velocity vector is a more ideal data form. Therefore, how to reconstruct the sea surface velocity vector from a single-antenna SAR is a key technical issue to improve the accuracy of numerical model predictions. Summary of the invention

[0004] The purpose of this application is to provide a method for reconstructing sea surface vector flow from a spaceborne synthetic aperture radar, which can accurately obtain the sea surface vector flow field from a single-antenna SAR and improve the accuracy of the sea surface vector flow field.

[0005] To achieve the above objectives, this application provides the following solutions: The present application provides a method for reconstructing sea surface vector flow of a spaceborne synthetic aperture radar, comprising: Acquire synthetic aperture radar images of the study area; determining the sea surface radial velocity according to the synthetic aperture radar image; Based on the geostrophic approximation theory and the sea surface radial velocity, determine the preliminary azimuthal velocity; Performing non-geostrophic correction on the preliminary azimuthal flow velocity to obtain a final azimuthal flow velocity; The sea surface vector flow field is reconstructed according to the sea surface radial flow velocity and the final azimuthal flow velocity to obtain the flow velocity magnitude and flow direction of the reconstructed sea surface vector flow field.

[0006] According to the specific embodiments provided in this application, this application has the following technical effects: The present application provides a method for reconstructing sea surface vector flow of a spaceborne synthetic aperture radar, which makes full use of the theory of physical oceanography, first determines the preliminary azimuthal flow velocity based on the geostrophic approximation theory and the sea surface radial flow velocity, then performs non-geostrophic correction on the preliminary azimuthal flow velocity, thereby improving the accuracy of the azimuthal flow velocity, and further reconstructs the sea surface vector flow field based on the sea surface radial flow velocity and the final azimuthal flow velocity, thereby being able to accurately obtain the sea surface vector flow field from a single-antenna SAR and improving the accuracy of the sea surface vector flow field. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0008] Figure 1 This is a diagram of the application environment of a method for reconstructing sea surface vector flow using a space-borne synthetic aperture radar in one embodiment of the present application.

[0009] Figure 2 A schematic flow chart of a method for reconstructing sea surface vector flow using a spaceborne synthetic aperture radar provided in one embodiment of the present application.

[0010] Figure 3 A schematic diagram of the functional modules of a space-borne synthetic aperture radar sea surface vector flow reconstruction device provided in one embodiment of the present application.

[0011] Figure 4 A schematic diagram of the structure of a computer device provided in one embodiment of the present application. DETAILED DESCRIPTION

[0012] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0013] In order to make the above-mentioned objects, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0014] The method for reconstructing sea surface vector flow of a spaceborne synthetic aperture radar provided in the embodiment of the present application can be applied to Figure 1 In the application environment shown. Among them, the terminal 102 communicates with the server 104 through the network. The data storage system can store the data that the server 104 needs to process. The data storage system can be set up separately, or it can be integrated on the server 104, or it can be placed on the cloud or other servers. The terminal 102 can send a synthetic aperture radar image of the study area to the server 104, and the server 104 reconstructs the sea surface vector flow field after receiving the synthetic aperture radar image of the study area. The server 104 can feed back the reconstructed sea surface vector flow field to the terminal 102. In addition, in some embodiments, the space-borne synthetic aperture radar sea surface vector flow reconstruction method can also be implemented by the server 104 or the terminal 102 alone.

[0015] The terminal 102 may be, but is not limited to, various desktop computers, laptop computers, smart phones, tablet computers, IoT devices, and portable wearable devices. The IoT devices may be smart speakers, smart TVs, smart air conditioners, smart vehicle-mounted devices, etc. The portable wearable devices may be smart watches, smart bracelets, head-mounted devices, etc. The server 104 may be implemented as an independent server or a server cluster consisting of multiple servers, or may be a cloud server.

[0016] In an exemplary embodiment, Figure 2 As shown, a method for reconstructing sea surface vector flow of a spaceborne synthetic aperture radar is provided. The method is executed by a computer device, and specifically can be executed by a computer device such as a terminal or a server alone, or can be executed by a terminal and a server together. In the embodiment of the present application, the method is applied to Figure 1 The server 104 in the example is used for explanation, and the steps include the following steps 201 to 205.

[0017] Step 201: Acquire a synthetic aperture radar image of a study area, wherein the synthetic aperture radar image includes a Doppler frequency shift of the ocean surface.

[0018] In a specific application example, a Doppler frequency shift of the ocean surface is measured by a space-borne synthetic aperture radar to generate a synthetic aperture radar image.

[0019] Step 202: determining the sea surface radial flow velocity according to the synthetic aperture radar image.

[0020] In a specific application example, the Doppler shift observed by the radar includes non-geophysical Doppler shift and geophysical Doppler shift, wherein the geophysical Doppler shift is caused by ocean currents and wave motion. , the non-geophysical Doppler shift and the Doppler shift caused by wave motion in the Doppler shift of the ocean surface are corrected to obtain the Doppler shift caused by the ocean current. For the non-geophysical Doppler shift, the non-zero Doppler shift on land can be corrected by combining the linear fitting method; for the Doppler shift caused by wave motion, the semi-empirical Doppler velocity model can be used for correction.

[0021] According to the Doppler frequency shift caused by the ocean current, the formula Determine the radial velocity of the sea surface. Where, is the sea surface radial velocity, with a spatial resolution of 1 km, is the Doppler shift caused by the ocean current, is the wave number of the incident electromagnetic wave, is the radar incident angle, and All are known parameters.

[0022] Step 203, based on the geostrophic approximation theory and the sea surface radial velocity, determine the preliminary azimuthal velocity.

[0023] In a specific application example, it is assumed that the sea surface current is quasi-geostrophic, and the surface current is the geostrophic current. Since the geostrophic current is non-divergent ( ), and the sea surface radial velocity has been obtained in step 202 , so the following formula (1) can be used to determine the preliminary azimuthal flow velocity.

[0024] (1) in, is the initial azimuthal velocity, is the azimuthal velocity at the lower boundary of the ocean in the synthetic aperture radar image, is the lower edge of the ocean in the synthetic aperture radar image y Axis coordinates, is the radial velocity at the sea surface, and are coordinates in the rectangular coordinate system, The axis represents the radial direction, i.e. the direction of the antenna. The axis represents the azimuth, which is the direction in which the satellite is flying.

[0025] Specifically, the following formula (2) can be used to obtain The initial azimuthal flow velocity at the location.

[0026] (2) in, for The initial azimuthal velocity at position, is the lower boundary of the ocean in the synthetic aperture radar image The azimuthal current velocity at the location can be obtained through the Copernicus Marine Environment Monitoring Service (CMEMS) global high-resolution real-time forecast system. for The radial velocity of the sea surface at the location.

[0027] Step 204, performing non-geostrophic correction on the preliminary azimuthal flow velocity to obtain a final azimuthal flow velocity.

[0028] In a specific application example, the ocean surface current is not a geostrophic current in a strict sense, but also includes a non-geostrophic component, so it is necessary to calculate the non-geostrophic component to compensate for the preliminary azimuthal flow velocity. Step 204 includes the following steps 41 and 42.

[0029] Step 41, based on the preliminary azimuthal flow velocity, the non-geostrophic flow is determined using the surface horizontal momentum balance equation, which is expressed as formula (3) and formula (4).

[0030] (3) (4) in, is the final azimuthal flow velocity, For time, is the Coriolis force, is the acceleration due to gravity, is the sea surface height, is the turbulent eddy viscosity coefficient, The depth of the ocean.

[0031] By calculating the curl of formula (3) and formula (4), the vertical component of the sea surface flow vorticity can be obtained, as shown in formula (5).

[0032] (5) in, is the final vorticity of the sea surface flow, , is the divergence of the sea surface current, .

[0033] It should be noted that the right side of the equal sign in formula (3) , the right side of the equal sign in formula (4) And the right side of the equal sign in formula (5) It represents wind-driven current, and the speed of wind-driven current is about 2% of the wind speed, so a wind speed of 5 m / s produces a current speed of about 0.1 m / s. The size of the mesoscale ocean current is about 1-2 m / s, so the magnitude of wind-driven current is very small, so this application does not consider the impact of wind-driven current.

[0034] Assuming that the non-geostrophic flow velocity is much smaller than the geostrophic flow velocity, the linearization of formula (5) yields the expression of formula (6).

[0035] (6) in, It is a non-geostrophic flow. is the vorticity of the sea surface current, , substitute formula (2) into From this we can get formula (7).

[0036] (7) When using formula (6) and formula (7) to estimate the non-geostrophic flow, information about the change of vorticity over time is required, but since SAR observations are instantaneous, this information cannot be obtained. This application uses a mediation parameter Substitute the right side of the equal sign in formula (6) where: for The vorticity of the sea surface flow at location, is the time adjustment parameter. Solving formula (6) can obtain the non-geostrophic flow, as shown in formula (8).

[0037] (8) To eliminate the time adjustment parameter , combined with formula (2) and formula (8), and The relevant expressions are shown in formula (9).

[0038] (9) in, is the azimuthal velocity at the upper boundary of the ocean in the synthetic aperture radar image. This quantity can be obtained by combining the direction of the coastal current with the radial velocity of the sea surface. Calculated, is the azimuthal velocity at the lower boundary of the ocean in the synthetic aperture radar image, provided by CMEMS, is the upper boundary of the ocean in the synthetic aperture radar image y Axis coordinates.

[0039] Substituting formula (9) into formula (8) we can obtain the non-geostrophic flow The final expression of is as shown in formula (10).

[0040] (10) Step 42, determining a final azimuthal flow velocity based on the preliminary azimuthal flow velocity and the non-geostrophic flow.

[0041] In a specific application example, the following formula (11) is used to determine the final azimuthal flow velocity.

[0042] (11) in, is the final azimuthal flow velocity, is the initial azimuthal velocity, It is a non-geostrophic flow.

[0043] Step 205, reconstructing the sea surface vector flow field according to the sea surface radial flow velocity and the final azimuthal flow velocity, and obtaining the flow velocity magnitude and flow direction of the reconstructed sea surface vector flow field.

[0044] In a specific application example, the sea surface radial velocity and the final azimuthal velocity are projected into an east-west vertical coordinate system and a north-south vertical coordinate system respectively to obtain an east-west component and a north-south component of the sea surface current.

[0045] Based on the east-west component and the north-south component, the formula and Reconstruct the sea surface vector flow field to obtain the velocity and direction of the reconstructed sea surface vector flow field; is the velocity of the reconstructed sea surface vector flow field, is the direction of the reconstructed sea surface vector flow field, is the east-west component, It is the north-south component.

[0046] The sea surface vector flow field reconstructed from the sea surface radial velocity observed by SAR can be used by ocean forecasting business units and satellite remote sensing and other related departments.

[0047] This application first estimates the preliminary azimuthal flow velocity based on the geostrophic assumption of the ocean mesoscale current (i.e., the divergence of the ocean current is zero) by solving the divergence equation and using the known sea surface radial flow velocity. Then, the surface horizontal momentum equation is used to perform non-geostrophic correction on the preliminary azimuthal flow velocity to obtain a more accurate azimuthal flow velocity. Finally, the sea surface radial flow velocity and the final azimuthal flow velocity are vector-synthesized to obtain a complete sea surface vector flow field.

[0048] This application makes full use of physical oceanography theory, by ignoring items of smaller magnitude and simplifying equations using mediation parameters, thereby obtaining a calculation formula for azimuth velocity, which combines geostrophic approximation and non-geostrophic correction. It is worth noting that there are many inaccurate current estimates based solely on preliminary azimuth velocity, such as low estimates in high-value areas and high estimates in low-value areas. However, after non-geostrophic correction, the results are significantly improved, and the root mean square error is reduced to about 0.2 meters per second. Through the synergistic effect of step 203 and step 204, it is possible to accurately obtain the sea surface vector flow field from a single antenna SAR, and the spatial resolution of the flow field can reach 1 kilometer. The method provided in this application provides more accurate and comprehensive current data support for ocean circulation research, environmental monitoring, disaster warning, and improving the forecast accuracy of ocean numerical models.

[0049] Based on the same inventive concept, the embodiment of the present application also provides a satellite-borne synthetic aperture radar sea surface vector flow reconstruction device for implementing the satellite-borne synthetic aperture radar sea surface vector flow reconstruction method involved above. The implementation scheme for solving the problem provided by the device is similar to the implementation scheme recorded in the above method, so the specific limitations of one or more satellite-borne synthetic aperture radar sea surface vector flow reconstruction device embodiments provided below can refer to the limitations of the satellite-borne synthetic aperture radar sea surface vector flow reconstruction method above, and will not be repeated here.

[0050] In an exemplary embodiment, Figure 3 As shown, a satellite-borne synthetic aperture radar sea surface vector flow reconstruction device is provided, including: an image acquisition module 301, a radial flow determination module 302, an azimuth flow initial guessing module 303, an azimuth flow correction module 304 and a vector flow reconstruction module 305.

[0051] The image acquisition module 301 is used to acquire a synthetic aperture radar image of the study area.

[0052] The radial flow determination module 302 is used to determine the sea surface radial flow velocity according to the synthetic aperture radar image.

[0053] The azimuthal flow initial guessing module 303 is used to determine the preliminary azimuthal flow velocity based on the geostrophic approximation theory and the sea surface radial flow velocity.

[0054] The azimuth flow correction module 304 is used to perform non-geostrophic correction on the preliminary azimuth flow velocity to obtain a final azimuth flow velocity.

[0055] The vector flow reconstruction module 305 is used to reconstruct the sea surface vector flow field according to the sea surface radial flow velocity and the final azimuthal flow velocity, and obtain the flow velocity magnitude and flow direction of the reconstructed sea surface vector flow field.

[0056] In an exemplary embodiment, a computer device is provided. The computer device may be a server or a terminal. The internal structure diagram thereof may be as follows: Figure 4 As shown. The computer device includes a processor, a memory, an input / output interface (Input / Output, referred to as I / O) and a communication interface. Among them, the processor, the memory and the input / output interface are connected through a system bus, and the communication interface is connected to the system bus through the input / output interface. Among them, the processor of the computer device is used to provide computing and control capabilities. The memory of the computer device includes a non-volatile storage medium and an internal memory. The non-volatile storage medium stores an operating system, a computer program and a database. The internal memory provides an environment for the operation of the operating system and the computer program in the non-volatile storage medium. The database of the computer device is used to store synthetic aperture radar images of the study area. The input / output interface of the computer device is used to exchange information between the processor and an external device. The communication interface of the computer device is used to communicate with an external terminal through a network connection. When the computer program is executed by the processor, a method for reconstructing sea surface vector flow of a space-borne synthetic aperture radar is implemented.

[0057] Those skilled in the art will understand that Figure 4 The structure shown in the figure is only a block diagram of a part of the structure related to the solution of the present application, and does not constitute a limitation on the computer device to which the solution of the present application is applied. The specific computer device may include more or fewer components than those shown in the figure, or combine certain components, or have a different arrangement of components.

[0058] In an exemplary embodiment, a computer-readable storage medium is provided, storing a computer program, and when the computer program is executed by a processor, the steps in the above-mentioned method embodiments are implemented.

[0059] In an exemplary embodiment, a computer program product is provided, including a computer program, and when the computer program is executed by a processor, the steps in the above method embodiments are implemented.

[0060] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, stored data, displayed data, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of relevant data must comply with relevant regulations.

[0061] In this application, all actions to obtain signals, information or data are carried out in compliance with the relevant data protection laws and policies of the country where they are located and with the authorization given by the owner of the corresponding device.

[0062] Those skilled in the art can understand that all or part of the processes in the above-mentioned embodiment methods can be completed by instructing the relevant hardware through a computer program, and the computer program can be stored in a non-volatile computer-readable storage medium. When the computer program is executed, it can include the processes of the embodiments of the above-mentioned methods. Among them, any reference to the memory, database or other medium used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetoresistive random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM may be in various forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM).

[0063] The database involved in each embodiment provided in this application may include at least one of a relational database and a non-relational database. The non-relational database may include a distributed database based on blockchain, etc., but is not limited thereto. The processor involved in each embodiment provided in this application may be a general-purpose processor, a central processing unit, a graphics processor, a digital signal processor, a programmable logic device, a data processing logic device based on quantum computing, etc., but is not limited thereto.

[0064] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0065] This article uses specific examples to illustrate the principles and implementation methods of this application. The description of the above embodiments is only used to help understand the method and core ideas of this application. At the same time, for those skilled in the art, according to the ideas of this application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as limiting this application.

Claims

1. A method for reconstructing sea surface vector flow from a spaceborne synthetic aperture radar, characterized in that: The spaceborne synthetic aperture radar sea surface vector flow reconstruction method comprises: Acquire synthetic aperture radar images of the study area; determining the sea surface radial velocity according to the synthetic aperture radar image; Based on the geostrophic approximation theory and the sea surface radial velocity, determine the preliminary azimuthal velocity; Performing non-geostrophic correction on the preliminary azimuthal flow velocity to obtain a final azimuthal flow velocity; The sea surface vector flow field is reconstructed according to the sea surface radial flow velocity and the final azimuthal flow velocity to obtain the flow velocity magnitude and flow direction of the reconstructed sea surface vector flow field.

2. The method for reconstructing sea surface vector flow of spaceborne synthetic aperture radar according to claim 1, characterized in that: The synthetic aperture radar image includes a Doppler shift of the ocean surface; Determining the sea surface radial velocity according to the synthetic aperture radar image specifically includes: The non-geophysical Doppler shift and the Doppler shift caused by wave motion in the Doppler shift of the ocean surface are corrected to obtain the Doppler shift caused by the ocean current; According to the Doppler frequency shift caused by the ocean current, the formula Determine the sea surface radial velocity; where, is the radial velocity at the sea surface, is the Doppler shift caused by the ocean current, is the wave number of the incident electromagnetic wave, is the radar incident angle.

3. The method for reconstructing sea surface vector flow of spaceborne synthetic aperture radar according to claim 1, characterized in that: The preliminary azimuthal flow velocity is determined using the following formula: ； in, is the initial azimuthal velocity, is the azimuthal velocity at the lower boundary of the ocean in the synthetic aperture radar image, is the lower edge of the ocean in the synthetic aperture radar image y Axis coordinates, is the radial velocity at the sea surface, and are coordinates in the rectangular coordinate system, The axis represents the radial direction, The axis represents the direction.

4. The method for reconstructing sea surface vector flow from a spaceborne synthetic aperture radar according to claim 1, characterized in that: The preliminary azimuthal flow velocity is subjected to non-geostrophic correction to obtain a final azimuthal flow velocity, specifically comprising: Based on the preliminary azimuthal flow velocity, the non-geostrophic flow is determined using the surface horizontal momentum equation; A final azimuthal flow velocity is determined based on the preliminary azimuthal flow velocity and the non-geostrophic flow.

5. The method for reconstructing sea surface vector flow of spaceborne synthetic aperture radar according to claim 4, characterized in that: The non-geostrophic current is determined using the following formula: ； in, It is a non-geostrophic flow. is the azimuthal velocity at the upper boundary of the ocean in the synthetic aperture radar image, is the azimuthal velocity at the lower boundary of the ocean in the synthetic aperture radar image, is the upper boundary of the ocean in the synthetic aperture radar image y Axis coordinates, is the lower edge of the ocean in the synthetic aperture radar image y Axis coordinates, is the radial velocity at the sea surface, is the vorticity of the sea surface current, , is the lower boundary of the ocean in the synthetic aperture radar image The azimuthal flow velocity at the location, for The radial velocity of the sea surface at the location, and are coordinates in the rectangular coordinate system, The axis represents the radial direction, The axis represents the direction.

6. The method for reconstructing sea surface vector flow of spaceborne synthetic aperture radar according to claim 4, characterized in that: The final azimuthal flow velocity is determined using the following formula: ； in, is the final azimuthal flow velocity, is the initial azimuthal velocity, It is a non-geostrophic flow.

7. The method for reconstructing sea surface vector flow of spaceborne synthetic aperture radar according to claim 1, characterized in that: Reconstructing the sea surface vector flow field according to the sea surface radial flow velocity and the final azimuthal flow velocity specifically includes: Projecting the sea surface radial velocity and the final azimuthal velocity into an east-west vertical coordinate system and a north-south vertical coordinate system, respectively, to obtain an east-west component and a north-south component of the sea surface current; Based on the east-west component and the north-south component, the formula and Reconstruct the sea surface vector flow field to obtain the velocity and direction of the reconstructed sea surface vector flow field; is the velocity of the reconstructed sea surface vector flow field, is the direction of the reconstructed sea surface vector flow field, is the east-west component, It is the north-south component.

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