Method for measuring two-dimensional flow field of sea surface based on along-track interferometry

Abstract

The application provides a kind of star-ground two-dimensional sea surface flow field measurement method based on order track interference, by determining observation scene, with observation scene center as geometric center to establish star-ground SAR observation geometric model;According to the geometric model, determine the time baseline in each group of receiving station, and obtain the SAR echo data when satellite passes through observation scene;The imaging of each group of received SAR echo data is interfered and multi-view processing to obtain interference phase, then according to the time baseline of each group of receiving station and corresponding interference phase, calculate the two-dimensional sea surface flow field data in the region to be measured flow field area.The application only needs to be laid out receiving station on the ground to realize high-precision, high spatial resolution two-dimensional sea surface flow field data inversion with low cost;In addition, the application can use any transit SAR satellite as signal transmitting source, only needs to adjust the angle of direct wave receiving station antenna, can continuously observe the same scene to obtain high time resolution flow field data.

Description

Technical Field

[0001] This invention belongs to the field of interferometric synthetic aperture radar technology, specifically relating to a two-dimensional sea surface flow field measurement method based on orbital interferometry and dual-base satellite-ground system. Background Technology

[0002] Synthetic Aperture Radar (SAR) is a technology that uses electromagnetic waves in the microwave spectrum as a detection medium and employs synthetic aperture to acquire two-dimensional imaging information of the observed object. Compared with traditional optical imaging, SAR has the advantages of long-range detection and all-weather, all-day operation.

[0003] Radial flow field measurement over the sea surface is one of the most important applications of in-orbit interferometric SAR (ATI-SAR). Figure 1 This is a schematic diagram for measuring the radial sea surface flow field using in-orbit interferometric SAR. In in-orbit interferometric SAR, two antennas are set up along the direction of platform movement, with a distance B between them. One antenna transmits and receives linear frequency modulated (LFM) signals, while the other antenna receives LFM signals. The radial velocity is measured by utilizing the slant range difference caused by the time difference between the echo imaging of the two antennas.

[0004] The time interval between the imaging of the antenna received signal before and after ATI-SAR is v s Given the platform velocity, the phases of the two antenna echoes after imaging are respectively... Therefore, the radial inversion velocity can be expressed as:

[0005]

[0006] Where λ is the wavelength of the electromagnetic wave, and M is the number of views.

[0007] Based on in-orbit interferometric SAR, a slant-looking dual-beam system is used to measure radial flow velocities in two directions. After vector synthesis, a two-dimensional flow field measurement of the sea surface can be achieved. In the figure below, the x-axis represents the platform's motion direction, the z-axis represents the direction from the Earth's center upwards from the platform, and the y-axis is determined according to the right-hand screw rule. The inverted flow field vector is decomposed along the x-axis and y-axis.

[0008] refer to Figure 2 , Figure 2 It is a dual-beam system configuration. Figure 2 The front and rear beams each form a parallel-track interferometry system, and the radial velocity components of the flow field are measured for the front and rear beams:

[0009]

[0010] Set the incident angles of the front and rear beams to θ respectively. fore θ aftThe angles between the projections of the front and rear beams onto the xoy plane and the y-axis are ρ and ρ, respectively. fore ρ aft The velocity of the inverted two-dimensional flow field is then...

[0011]

[0012] Currently, many satellites, both domestically and internationally, possess in-orbit interferometry capabilities to measure radial ocean current velocities, such as GF-3 and TanDEM. However, these are not yet in operational production, and their one-dimensional flow field data cannot meet the demands of scientific research, production, and daily life for two-dimensional flow field data. Dual-beam ATI satellite systems capable of two-dimensional flow field measurement are still under development, with uncertain timelines for production. Furthermore, these systems are all single-satellite systems with long revisit periods and low temporal resolution. Summary of the Invention

[0013] To address the aforementioned problems in the existing technology, this invention provides a method for measuring two-dimensional sea surface flow fields based on orbital interferometry between space and ground. The technical problem to be solved by this invention is achieved through the following technical solution:

[0014] The present invention provides a method for measuring two-dimensional sea surface flow field based on orbital interferometry in a space-to-ground dual-base system, comprising:

[0015] Step 1: Obtain the flow field region to be measured on Earth and the satellite beam illumination region, and use the union of the two spatial regions as the observation scene;

[0016] Step 2: Using the center of the observation scene as the geometric center, establish a three-dimensional satellite-ground dual-base SAR observation geometric model that expresses the relative positions of the satellite and multiple sets of receiving stations located outside the observation scene;

[0017] Each set of receiving stations includes at least one conventional receiving station capable of receiving direct satellite wave signals and at least two ATI receiving stations used to measure the flow field region under test.

[0018] Step 3: Determine the time baseline within each group of receiving stations based on the relative positions of the satellite and the ATI receiving station in each group in the satellite-ground dual-base SAR observation geometric model.

[0019] Step 4: Calculate the radar gate opening and closing time of the ATI receiving station when the satellite passes through the observation scene, and wait for the satellite radar beam to scan the observation scene to obtain SAR echo data transmitted by the satellite and reflected by the flow field, as well as direct wave data of the satellite received by the conventional receiving station during the radar power-on time.

[0020] Step 5: Based on the time baseline within each receiving station, perform interferometric and multi-view processing on the imaging of the SAR echo data received by each receiving station to obtain the interferometric phase corresponding to the time baseline of each receiving station.

[0021] Step 6: Calculate the two-dimensional flow field data of the sea surface within the flow field area to be measured, based on the time baseline and corresponding interference phase of each receiving station.

[0022] The beneficial effects of this invention are:

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] First, this invention provides a satellite-ground dual-base method for measuring two-dimensional sea surface flow field based on in-orbit interferometry. It only requires the deployment of receiving stations on the ground to achieve high-precision, high-spatial-resolution two-dimensional sea surface flow field data inversion, which is extremely low in cost compared to measuring two-dimensional flow field data by aircraft or satellite.

[0025] Secondly, the present invention uses SAR satellites that can be used as signal transmission sources for any passing observation scenario. Only the antenna angle of the direct wave receiving station needs to be adjusted to complete the measurement of flow field data. Compared with the prior art, the measurement method of the present invention can obtain high temporal resolution flow field data by continuously observing the same scenario.

[0026] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of radial sea surface flow field measurement using in-orbit interferometric SAR in existing technology;

[0028] Figure 2 This is a schematic diagram of a dual-beam system configuration;

[0029] Figure 3 This is a flowchart illustrating a two-dimensional sea surface flow field measurement method based on orbital interferometry provided by the present invention.

[0030] Figure 4 This is a schematic diagram of the geodetic model for dual-base SAR observation provided by the present invention;

[0031] Figure 5 This is a schematic diagram of flow field decomposition in the observation scenario provided by the present invention. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0033] like Figure 3 As shown, the present invention provides a method for measuring two-dimensional sea surface flow field based on orbital interferometry in a space-to-ground dual-base system, comprising:

[0034] Step 1: Obtain the flow field region to be measured on Earth and the satellite beam illumination region, and use the union of the two spatial regions as the observation scene;

[0035] Step 2: Using the center of the observation scene as the geometric center, establish a three-dimensional satellite-ground dual-base SAR observation geometric model that expresses the relative positions of the satellite and multiple sets of receiving stations located outside the observation scene;

[0036] Each set of receiving stations includes at least one conventional receiving station capable of receiving direct satellite wave signals and at least two ATI receiving stations used to measure the flow field region under test.

[0037] In one specific embodiment, step 2 includes:

[0038] Step 21: Using the center of the observation scene as the geometric center, the satellite beam scanning direction as the x-axis, and the geocentric vector pointing to the origin as the z-axis, determine the three-dimensional geometric coordinate y-axis according to the right-hand screw rule;

[0039] Step 22: Set up multiple ATI receiving stations outside the observation scene along the x-axis;

[0040] Step 23: Establish a three-dimensional satellite-ground dual-base SAR observation geometric model that expresses the relative positions of the satellite and multiple sets of receiving stations.

[0041] Reference for Geometric Model of Space-Ground Bi-base SAR Observation Figure 4 As shown, two sets of receiving stations are set up at a high point outside the observation scene along the x-axis, with a large enough distance between them to ensure that the vectors from the observation scene to the two receiving stations are perpendicular to each other on the ground. Each set of receiving stations requires at least three stations: one for receiving direct satellite signals and the other two as ATI receiving stations positioned along the x-axis to measure the flow field. Alternatively, multiple receiving stations can be used as ATI receiving stations, equidistantly distributed to form multi-baseline in-orbit interferometric data, improving the accuracy of flow field inversion.

[0042] Step 3: Determine the time baseline within each group of receiving stations based on the relative positions of the satellite and the ATI receiving station in each group in the satellite-ground dual-base SAR observation geometric model.

[0043] In one specific embodiment, step 3 includes:

[0044] Step 31: For any ATI receiving station in a group, calculate the slant distance history from the ocean current located at the center of the observation scene to each ATI receiving station in that group.

[0045] Ignoring the effects of Earth's curvature, assuming the satellite's downward angle is θ, its trajectory is a straight line during the imaging time, and the ocean current flows at a velocity [v]... x ,vy If the satellite moves along the path [v, 0], then its trajectory is [v]. s [t,Htanθ,H], the coordinates of receiving station P1 are [x1,y1,z1], and the coordinates of receiving station P2 are [x2,y2,z2]. The slant distance path from the ocean current located at the center of the scene to receiving stations P1 and P2 is as follows:

[0046]

[0047]

[0048] Step 32: Perform Taylor expansion on the slant range history corresponding to each ATI receiving station in any group to obtain the signal Doppler history of each ATI receiving station.

[0049] set up A Taylor expansion of the slant distance history in step 31 at t=0 yields:

[0050]

[0051]

[0052] Based on the above two equations, the Doppler processes of signals P1 and P2 are obtained as follows:

[0053]

[0054]

[0055] Step 33: Calculate the zero-Doppler moment of the received signal for each ATI receiving station based on the signal Doppler history of each ATI receiving station in any group.

[0056] Let f d1 =0,f d2 =0, the zero Doppler times of the received signals P1 and P2 are respectively

[0057]

[0058]

[0059] Step 34: Subtract the zero Doppler times of the received signals from two ATI receiving stations within any group to obtain the time baseline.

[0060] Therefore, the time baseline for any group is

[0061] τ = t1 - t2. (12)

[0062] Step 4: Calculate the radar gate opening and closing time of the ATI receiving station when the satellite passes through the observation scene, and wait for the satellite radar beam to scan the observation scene to obtain SAR echo data transmitted by the satellite and reflected by the flow field, as well as direct wave data of the satellite received by the conventional receiving station during the radar power-on time.

[0063] In one specific embodiment, step 4 includes:

[0064] Step 41, based on the nearest slant distance R from the satellite to the observation scene n The closest slant distance r from the receiving station to the observation scene n Calculate the radar gate opening time of the ATI receiver station;

[0065] Step 42, based on the farthest slant distance R from the satellite to the observation scene f The farthest slant distance r from the receiving station to the observation scene f Calculate the radar gate closing time;

[0066] Step 43: Wait for the satellite radar beam to pass through the observation scene, and acquire SAR echo data transmitted by the satellite and reflected by the flow field during the radar power-on time of the receiving station, as well as direct wave data of the satellite received by the conventional receiving station.

[0067] The moment the satellite beam begins to illuminate the observation scene is when the receiver radar is powered on; the moment the satellite beam leaves the observation scene is when the echo signal receiver radar is powered off. The azimuth of the receiver echo signal is the direction in which the satellite beam scans the ground. Unlike ordinary satellite / airborne SAR, because the receiver is fixed, the closest slant range of the SAR system is the closest slant range R from the satellite to the scene. n The closest slant distance r from the receiver to the scene n The sum, i.e., the radar gate opening time, can be expressed as:

[0068] t on =(R n +r n ) / c;(13)

[0069] The farthest slant range of the SAR system is the farthest slant range R from the satellite to the scene. f The farthest slant distance r from the receiver to the scene f The sum of. It is worth noting that r f This refers to the maximum distance between a point in the scene and the receiver, not the farthest slant range mentioned in conventional SAR systems. Therefore, the radar gate closing time can be expressed as...

[0070] t off =(R f +r f ) / c(14)

[0071] Where c is the speed of sound.

[0072] Once the time is determined, wait for the satellite to pass overhead to receive the SAR echo signal.

[0073] Step 5: Based on the time baseline within each receiving station, perform interferometric and multi-view processing on the imaging of the SAR echo data received by each receiving station to obtain the interferometric phase corresponding to the time baseline of each receiving station.

[0074] Depend on Figure 4 As shown, the satellite transmits signals in a front-side look-ahead mode over the scene. P1 and P2, and P3 and P4 are two sets of ATI receivers placed outside the scene to receive the signals returned from the sea surface. Assuming the satellite's zero Doppler time is 0, at 0 a particle is located at point T on the sea surface. After passing the time baseline τ, the particle moves to point T′. The particle's azimuth and range velocities are v0 and v0, respectively. az v ra The distance traveled is v·τ.

[0075] If the scene is flat and there is no ocean current, then the Doppler paths of the signals received by P1 and P2 are the same, and the imaging time is 0. The interference phase after imaging by receivers P1 and P2 can be expressed as:

[0076]

[0077] Similarly, the interference phase after imaging by the P3 and P4 receivers can be expressed as:

[0078]

[0079] Therefore, the two sets of ATI receivers have inherent interference phases, and the interference phases are different at different positions, exhibiting two-dimensional spatial variation along the azimuth and range directions.

[0080] When the scene is a sea surface, the imaging time of receivers P1 and P2 varies with τ. fore Due to the time difference, P1 receives the echo returned by the particle at point T, and P2 receives the echo reflected by the particle at point T′. Therefore, when receivers P1 and P2 observe the same target point, there is a slant range difference, i.e., after registration, there is an in-orbit interferometric phase. The in-orbit interferometric phase of P1 and P2 can be divided into three parts: one part is caused by the change in slant range from the satellite to the target point, another part is caused by the slant range from the target point to the receiver, and finally, there is a fixed slant range difference between receivers P1 and P2.

[0081] When the scene is a sea surface, the imaging time of receivers P1 and P2 varies with τ. foreDue to the time difference, P1 receives the echo returned by the particle at point T, and P2 receives the echo reflected by the particle at point T′. Therefore, when receivers P1 and P2 observe the same target point, there is a slant range difference, i.e., after registration, there is in-orbit interference phase. The in-orbit interference difference between P1 and P2 can be divided into three parts: one part is caused by the change in slant range from the satellite to the target point, another part is caused by the slant range from the target point to the receiver, and the last part is the fixed slant range difference between receivers P1 and P2. Since the fixed slant range difference can be calculated and is known, it is ignored in the subsequent derivation.

[0082]

[0083] Among them, v r v fore For velocity on the y-axis, The projection on the surface.

[0084]

[0085] Similarly, the interference phase of receivers P3 and P4 can be expressed as:

[0086]

[0087] v aft =vcosθ aft (20)

[0088] like Figure 5 As shown, the flow field velocity can be decomposed along the x-axis and y-axis into The angle between the y-axis and the y-axis is ρ aft ρ fore .

[0089] but

[0090]

[0091]

[0092] Step 6: Calculate the two-dimensional flow field data of the sea surface within the flow field area to be measured, based on the time baseline and corresponding interference phase of each receiving station.

[0093] The velocity of the two-dimensional flow field at the sea surface is

[0094]

[0095] in,

[0096]

[0097] This invention provides a satellite-ground dual-base SAR observation geometric model for measuring two-dimensional sea surface flow fields based on in-orbit interferometry. The method involves defining the observation scene and establishing the model with the center of the observation scene as the geometric center. The time baseline within each receiving station is determined according to the geometric model, and SAR echo data from satellites passing through the observation scene is acquired. Interferometric and multi-look processing is performed on the imaging of each set of received SAR echo data to obtain the interferometric phase. Then, based on the time baseline and corresponding interferometric phase of each receiving station, the two-dimensional sea surface flow field data within the measured flow field area is calculated. This invention only requires the deployment of receiving stations on the ground to achieve high-precision, high spatial resolution two-dimensional sea surface flow field data inversion at a low cost. Furthermore, this invention can use any passing SAR satellite as the signal source; by simply adjusting the antenna angle of the direct-wave receiving station, continuous observation of the same scene can be performed to obtain high temporal resolution flow field data.

[0098] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0099] Although this application has been described herein in conjunction with various embodiments, those skilled in the art will understand and implement other variations of the disclosed embodiments by reviewing the accompanying drawings, the disclosure, and the appended claims in carrying out the claimed application. In the claims, the word "comprising" does not exclude other components or steps, and "a" or "an" does not exclude a plurality.

[0100] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for measuring two-dimensional sea surface flow field based on orbital interferometry between space and ground, characterized in that, include: Step 1: Obtain the flow field region to be measured on Earth and the satellite beam illumination region, and use the union of the two spatial regions as the observation scene; Step 2: Using the center of the observation scene as the geometric center, establish a three-dimensional satellite-ground dual-base SAR observation geometric model that expresses the relative positions of the satellite and multiple sets of receiving stations located outside the observation scene; Each set of receiving stations includes at least one conventional receiving station capable of receiving direct satellite wave signals and at least two ATI receiving stations used to measure the flow field region under test. Step 3: Based on the relative positions of the satellite and the ATI receiving station within each group in the satellite-ground dual-base SAR observation geometric model, determine the time baseline within each group of receiving stations; Step 3 includes: Step 31: For any ATI receiving station in a group, calculate the slant distance history from the ocean current located at the center of the observation scene to each ATI receiving station in that group. Step 32: Perform Taylor expansion on the slant range history corresponding to each ATI receiving station in any group to obtain the signal Doppler history of each ATI receiving station. Step 33: Calculate the zero-Doppler moment of the received signal for each ATI receiving station based on the signal Doppler history of each ATI receiving station in any group. Step 34: Subtract the zero Doppler moments of the received signals from any two ATI receiving stations within a group to obtain the time baseline; Step 4: Calculate the radar gate opening and closing time of the ATI receiving station when the satellite passes through the observation scene, and wait for the satellite radar beam to scan the observation scene to obtain SAR echo data transmitted by the satellite and reflected by the flow field, as well as direct wave data of the satellite received by the conventional receiving station during the radar power-on time. Step 5: Based on the time baseline within each receiving station, perform interferometric and multi-view processing on the imaging of the SAR echo data received by each receiving station to obtain the interferometric phase corresponding to the time baseline of each receiving station. Step 6: Calculate the two-dimensional flow field data of the sea surface within the flow field area to be measured, based on the time baseline and corresponding interference phase of each receiving station.

2. The method for measuring two-dimensional sea surface flow field based on orbital interferometry using a dual-base system according to claim 1, characterized in that, Step 2 includes: Step 21: Using the center of the observation scene as the geometric center, the satellite beam scanning direction as the x-axis, and the geocentric vector pointing to the origin as the z-axis, determine the three-dimensional geometric coordinate y-axis according to the right-hand screw rule; Step 22: Set up multiple ATI receiving stations outside the observation scene along the x-axis; Step 23: Establish a three-dimensional satellite-ground dual-base SAR observation geometric model that expresses the relative positions of the satellite and multiple sets of receiving stations.

3. The method for measuring two-dimensional sea surface flow field based on orbital interferometry using a dual-base system according to claim 1, characterized in that, The slant range histories of the two ATI receiving stations within any group in step 31 are expressed as follows: Among them, the satellite's downward angle is The trajectory is a straight line during the imaging time, and the ocean current moves at a speed of... The motion, the satellite's trajectory is ATI receiving station within the group Coordinates are AIT receiving station within the group Coordinates are ; set up , , For the slant range history in step 31 Performing a Taylor expansion, we get: In step 32, the signal Doppler trajectories of the two ATI receiving stations within any group are respectively expressed as follows: In step 33, the zero-Doppler times of the received signals from the two ATI receiving stations in any group are respectively The time baseline for any group in step 34 is 。 4. The method for measuring two-dimensional sea surface flow field based on orbital interferometry using a dual-base system according to claim 3, characterized in that, Step 4 includes: Step 41, based on the nearest slant distance from the satellite to the observation scene. The closest slant distance from the receiving station to the observation scene Calculate the radar gate opening time of the ATI receiver station; Step 42, based on the farthest slant distance from the satellite to the observation scene. The farthest slant distance from the receiving station to the observation scene Calculate the radar gate closing time; Step 43: Wait for the satellite radar beam to pass through the observation scene, and acquire SAR echo data transmitted by the satellite and reflected by the flow field during the radar power-on time of the receiving station, as well as direct wave data of the satellite received by the conventional receiving station.

5. The method for measuring two-dimensional sea surface flow field based on orbital interferometry using a dual-base system according to claim 4, characterized in that, Radar gate opening time is ； The radar gate closing time is in, The speed of sound.

6. The method for measuring two-dimensional sea surface flow field based on orbital interferometry using a dual-base system according to claim 5, characterized in that, The interference phase corresponding to the time baselines of the two sets of receiving stations in step 5 is: in, , This represents the time baseline of the two sets of receiving stations, and the projection vector of the satellite-to-target beam onto the observation scene is: The axis, the projection vector of the target point onto the ATI receiving station beam in the observation scene is... velocity vector and axis, The included angles are respectively , The incident angle and reflection angle of the satellite transmission and signal reflection beams are respectively and , , and The included angle of the axis is , .

7. The method for measuring two-dimensional sea surface flow field based on orbital interferometry using a dual-base satellite-ground system, as described in claim 6, is characterized in that... The two-dimensional flow field data of the sea surface within the flow field region to be measured in step 6 are as follows: in, .

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