A method for obtaining a view angle in a SAR forward-looking stripmap mode

Abstract

The application discloses a kind of view angle acquisition methods under SAR positive side view strip mode, according to the SAR radar transmitting pulse signal of continuous variation and flight trajectory information inversion SAR positive side view strip mode under view angle parameter, this method can be in unknown situation, by measuring the received radar transmitting signal power to obtain SAR positive side view strip mode under view angle parameter, by iteration, more accurate SAR positive side view strip mode view angle parameter is obtained, the view angle value obtained using the method can be radar calibration, and the pointing of radar antenna and wave control law are calibrated.The method improves the acquisition efficiency of view angle, and the view angle value obtained has higher precision.

Description

Technical Field

[0001] This invention relates to a SAR perspective acquisition method, specifically a method for acquiring perspective in the frontal side-view stripe operation mode of a synthetic aperture radar (SAR), belonging to the field of radar technology. Technical Background

[0002] Synthetic Aperture Radar (SAR) is a high-resolution Earth observation system that utilizes microwave imaging. SAR is widely used in disaster response, resource exploration, marine research, military reconnaissance, and many other fields. Several SAR imaging modes include stripmap mode, spotlight mode, and scan mode. The front-side-looking stripmap mode is the most commonly used SAR mode. In this imaging mode, the beam direction remains unchanged as the radar platform passes over the target. However, for SAR operating in front-side-looking stripmap mode, the viewing angle is a crucial parameter, but directly measuring the viewing angle in stripmap mode is difficult. Therefore, obtaining a relatively accurate viewing angle in front-side-looking stripmap mode has become a technical problem that needs to be solved. Summary of the Invention

[0003] The technical problem solved by this invention is to overcome the shortcomings of the prior art and propose a view acquisition method in SAR frontal side-view strip working mode. This method improves the view acquisition efficiency by using an iterative approach and the acquired view value has high accuracy.

[0004] The technical solution of this invention is: a method for obtaining the viewing angle in SAR frontal side-view strip working mode, the steps of which are as follows:

[0005] (1) Obtain SAR radar flight trajectory data and ground received signal power array based on the SAR radar coordinates corresponding to the ground sampling time series;

[0006] (2) Initial setting of SAR radar view center value β c and the viewing angle range d, which will reduce the SAR radar viewing angle range (β) c -d / 2) to (β) c The interval between +d / 2) is divided into (M-1) equal parts to obtain M SAR radar viewpoint values, which are used to construct the SAR radar search viewpoint array β(i), where i is a positive integer, i = 1, 2...M;

[0007] (3) Obtain the SAR radar view search array. For each search view, obtain the ground received signal power array. Based on the ground received signal power array for each search view and the ground received signal power array obtained in step (1), obtain the sum of squared errors of the received signal power for each search view. The search view value corresponding to the minimum sum of squared errors of the received signal power is denoted as β. tUsing this search perspective value β t Instead of the initial SAR radar view center value β set in step (2) c Then, halve the initially set viewing angle range d value and repeat the above process in step (3) until the search viewing angle value β that meets the accuracy requirements is obtained. t .

[0008] The specific implementation process of step (1) is as follows: set the coordinates of the ground receiving station R point as (Xr, Yr, 0), and form a sampling time sequence t according to the sampling time interval. k k is a positive integer, k = 1, 2, ..., N, corresponding to the sampling time series t k The coordinates of point P on the SAR radar are (Xp k Yp k Zp k ), based on the coordinates of point P (Xp) of the SAR radar. k Yp k Zp k The radar flight trajectory data and the corresponding sampling time series t were obtained. k Ground received signal power array Pm k ;

[0009] Where Xr represents the X-axis coordinate of ground receiving station R, Yr represents the Y-axis coordinate of ground receiving station R (Xr > 0, Yr > 0), and Xp k This indicates that point P of the SAR radar is at t k X-axis coordinate at time, Yp k This indicates that point P of the SAR radar is at t k Y-axis coordinate at time, Zp k This indicates that point P of the SAR radar is at t k The Z-axis coordinate at time [time].

[0010] The specific implementation process of step (3) is as follows:

[0011] (a) Based on the coordinates of the ground receiving station R point (Xr, Yr, 0) and the coordinates of the SAR radar P point (Xp) k Yp k Zp k To obtain the receiving range of the ground receiving station, the receiving range sequence R of the ground receiving station is obtained. k for:

[0012]

[0013] (b) Let the coordinates of the auxiliary point E be (Xp) k The coordinates of the auxiliary point F are (Xp, Yr, 0). k Yp kThe coordinates of point T, the intersection of the SAR radar line of sight and the XOY plane, are (Xp 0). k Yt k The coordinates of auxiliary point H are (Xr, Yt). k ,0),Yt k Let point T be at t k Given the Y-axis coordinate at time t, and under the search view array β(i), obtain the radar antenna azimuth off-axis angle sequence θ corresponding to the search view array β(i). k (i) Distance to off-axis angle sequence

[0014]

[0015] φ k (i)=|β(i)-γ k (i)| (4)

[0016] In the formula: γ k (i) is the angle between EP and FP;

[0017]

[0018] In the formula: a1 k (i) represents the distance between two points HT, b1 k (i) represents the distance between points PT;

[0019] a2 k (i)=|Yr-Yp k |,b2 k (i)=|Zp k |

[0020] In the formula: a2 k (i) represents the distance between points E and F, and b2 k (i) represents the distance between two points PF;

[0021] (c) Based on the SAR radar power direction gain diagram and azimuth off-axis angle sequence θ k (i) Distance to off-axis angle sequence The gain Gk(i) of the SAR radar in the PR direction is obtained, and the ground received signal power array Pr under each search view of the SAR radar view search array is obtained through equation (5). k (i):

[0022]

[0023] In the formula: Pt is the SAR radar transmit power, Gr is the receive antenna gain, λ is the SAR radar wavelength, and L is the system loss;

[0024] (d) Combine the ground received signal power array and sampling time series t for each search view value of the SAR radar view search array. k The corresponding ground received signal power arrays are compared to obtain the sum of squared errors δ(i) of the received signal power for each search view value in the SAR radar view search array, where:

[0025] (e) Search for the sum of squared errors of the received signal power δ(i) corresponding to each search viewpoint value, and denote the minimum value of the sum of squared errors of the received signal power δ(i) as δ min And determine the search perspective value β corresponding to the minimum value. t ;

[0026] (f) Using the search perspective value β obtained in step (e) t Instead of the initial setting of the SAR radar view center value β in step (2) c Then, the initial view range d value is halved, the search view array β(i) is reconstructed, and steps (a) to (e) are repeated until the search view value β is obtained. t Achieve the required precision.

[0027] The advantages of this invention compared to existing technologies are as follows: This invention retrieves the viewing angle parameters in the SAR front-side-view strip mode based on the continuously changing SAR radar transmitted pulse signal and flight trajectory information. This method can obtain the viewing angle parameters in the SAR front-side-view strip mode by measuring the power of the received radar transmitted signal when the viewing angle is unknown. Through iteration, relatively accurate SAR front-side-view strip mode viewing angle parameters can be obtained. The viewing angle values ​​obtained by this method can be used for radar calibration, and to calibrate the radar antenna pointing and beam control rules. Attached Figure Description

[0028] Figure 1 This is a flowchart illustrating the acquisition process from the perspective of this invention.

[0029] Figure 2 This is a schematic diagram illustrating the geometric relationship between the SAR radar of this invention and the ground;

[0030] Figure 3 Ground received signal power array curves in embodiments of the present invention;

[0031] Figure 4 Ground receiving distance sequence curves in embodiments of the present invention;

[0032] Figure 5 The second iteration azimuth off-axis angle sequence curve in this embodiment of the invention;

[0033] Figure 6 The second iteration distance-to-off-axis angle sequence curve in this embodiment of the invention;

[0034] Figure 7 The second iteration received signal power array curve in this embodiment of the invention;

[0035] Figure 8 The signal power error sum-of-squares curve obtained after three iterations in this embodiment of the invention. Detailed Implementation

[0036] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0037] This invention relates to a method for obtaining the aiming point in SAR strip operation mode. Referring to a three-dimensional Cartesian coordinate system, the XOY plane is defined as the ground plane, the projection of the radar flight trajectory direction onto the ground plane is the X-axis, the perpendicular line from the ground plane is the Z-axis, and the angle between PT and PF is the viewpoint in strip operation mode. The process is as follows: Figure 1 As shown, it includes the following steps:

[0038] Step 1: Acquire radar flight trajectory data and received signal power data.

[0039] The specific implementation process is as follows:

[0040] (a) Set the coordinates of the ground receiving station R as (Xr, Yr, 0), where Xr represents the X-axis coordinate of R and Yr represents the Y-axis coordinate of R (Xr > 0, Yr > 0). The sampling time series t is obtained by dividing the time interval according to the sampling time interval. k k is a positive integer, k = 1, 2, ..., N. The radar flight trajectory data is acquired to obtain the corresponding sampling time series t. k Radar point P coordinates (Xp) k Yp k Zp k ), where Xp k This indicates that point P is at time t. k X-axis coordinate at time, Yp k This indicates that point P is at time t. k Y-axis coordinate at time, Zp k This indicates that point P is at time t. k The Z-axis coordinate at time t corresponds to the sampling time series t. k Received signal power array Pm k .

[0041] Step 2: Initialize the center value and range of the view parameters in strip mode, and construct the search view array. Initialize the center value and range of the view, and set the initial center value β of the view. c Furthermore, the initial value of the view range is set to d, and the view range (β) is... c -d / 2) to (β) cDivide the interval between +d / 2) into (M-1) equal parts to obtain M viewpoint values, and construct a search viewpoint array β(i), where i is a positive integer, i = 1, 2...M.

[0042] Step 3: Obtain the viewpoint value.

[0043] By gradually adjusting the viewing angle value and iterating through M viewing angle values ​​β(i), the theoretical signal power data obtained from geometric relationships and radar equations is compared with the actual receiver signal power to obtain the sum of squared errors, specifically:

[0044] (a) Obtain the reception range of the ground receiving station, the reception range sequence R of the ground receiving station. k for:

[0045]

[0046] (b) such as Figure 2 As shown, let the coordinates of the auxiliary point E be (Xp k The coordinates of the auxiliary point F are (Xp, Yr, 0). k Yp k The coordinates of point T, the intersection of the radar line of sight and the XOY plane, are (Xp 0). k Yt k The coordinates of auxiliary point H are (Xr, Yt). k ,0),Yt k Let point T be at t k The Y-axis coordinate at each moment. At each set viewing angle β(i), obtain the corresponding radar antenna azimuth off-axis angle sequence θ. k (i) Distance to off-axis angle sequence The details are as follows:

[0047]

[0048] φ k (i)=|β(i)-γ k (i)| (4)

[0049] In the formula: γ k (i) is the angle between EP and FP;

[0050]

[0051] In the formula: a1 k (i) represents the distance between two points HT, b1 k (i) represents the distance between points PT;

[0052] a2 k (i)=|Yr-Yp k |,b2 k (i)=|Zp k |

[0053] In the formula: a2 k (i) represents the distance between points E and F, and b2 k (i) represents the distance between two points PF;

[0054] (c) Based on the SAR radar power direction gain diagram and azimuth off-axis angle sequence θ k (i) Distance to off-axis angle sequence Obtain the gain G of the SAR radar in the PR direction. k (i) The ground received signal power array Pr under each search view of the SAR radar view search array is obtained through equation (5). k (i):

[0055]

[0056] In the formula: Pt is the SAR radar transmit power, Gr is the receive antenna gain, λ is the SAR radar wavelength, and L is the system loss;

[0057] (d) Combine the ground received signal power array and sampling time series t for each search view value of the SAR radar view search array. k The corresponding ground received signal power arrays are compared to obtain the sum of squared errors δ(i) of the received signal power for each search view value in the SAR radar view search array, where:

[0058] (e) Search for the sum of squared errors of the received signal power δ(i) corresponding to each search viewpoint value, and denote the minimum value of the sum of squared errors of the received signal power δ(i) as δ min And determine the search perspective value β corresponding to the minimum value. t ;

[0059] (f) Using the search perspective value β obtained in step (e) t Instead of the initial setting of the SAR radar view center value β in step (2) c Then, the initial view range d value is halved, the search view array β(i) is reconstructed, and steps (a) to (e) are repeated until the search view value β is obtained. t The required accuracy is achieved. The search perspective value β obtained in this invention... t Used for radar calibration, to calibrate the pointing and beam control patterns of radar antennas.

[0060] The viewing angle value is obtained for an ideal airborne SAR radar operating in a front-side look-ahead mode. For example... Figure 2As shown, the coordinate unit in this embodiment is meters (m). The airborne SAR radar operates in a frontal side-view stripe mode, with a true viewing angle of 43°. The required viewing angle acquisition error is no greater than 0.01°. The radar transmit power Pt is 1000W, the radar antenna azimuth dimension D1 is 1m, the range dimension D2 is 0.5m, and Gt is the center pointing gain of 28dB.

[0061] The off-axis angular gain of the transmit power is G k (i),

[0062]

[0063] The radar operates at a frequency of f = 3 GHz, yielding a wavelength λ = 0.1 m. Its flight trajectory is within the XOZ plane at an altitude of 5000 m along the X-axis, with a speed of 200 m / s. The ground receiving station's coordinates are (5000, 4000, 0), the receiving antenna gain is 20 dB, and the system loss L is 3 dB. Let the time it takes for the airborne radar to reach the same X-coordinate point at the ground receiving station be 0 s. Using a pulse repetition frequency PRF = 200 Hz as the sampling frequency and a sample count N = 4001, with the sampling sequence centered at 0 s, we obtain the sampling time sequence t. k (k is a positive integer from 1 to 4001), and the corresponding flight trajectory coordinate sequence is calculated. The ground received signal power array Pm is obtained by simulation based on geometric relationships and radar equations. k ,like Figure 3 As shown.

[0064] Specifically, the steps are as follows:

[0065] Step 1: Acquire radar flight trajectory data and received signal power data;

[0066] Given that the coordinates (Xr, Yr, 0) of the ground receiving station R are (5000, 4000, 0), the sampling time series t is obtained by dividing the sampling time interval. k k is a positive integer, k = 1 to 4001. Input the radar flight trajectory to obtain the corresponding sampling time series t. k radar coordinates (Xp) k Yp k Zp k The receiver then acquires the received signal power sequence Pm corresponding to the sampling time sequence. k .

[0067] Step 2: Initialize the center and range of the view parameters in strip mode, and construct the search view array.

[0068] Initialize the viewpoint center value and range. Set the initial viewpoint center value βc to 45 degrees, and set the initial viewpoint range d to 20 degrees. Divide the viewpoint range (βc-d / 2) to (βc+d / 2) into 1000 equal parts, resulting in 1001 viewpoint values. Construct a search viewpoint array β(i), where i is a positive integer, i = 1, 2, ..., 1001.

[0069] Step 3: Obtain the viewpoint value.

[0070] (a) Calculation of receiving distance: The receiving distance sequence R of the ground receiving station is calculated according to formula (1). k ,like Figure 4 .

[0071] (b) such as Figure 2 As shown, under each set viewing angle β(i), the corresponding radar antenna azimuth off-axis angle sequence θ is obtained according to formulas (2) to (4). k (i) Distance to off-axis angle sequence

[0072] (c) Based on the power direction gain diagram and the off-axis angle sequence θ k (i), Obtain the radar gain G in the PR direction. k (i) The received signal power array Pr is obtained through equation (5). k (i);

[0073] (d) Compare the received signal power array and the ground received data array under each set viewing angle value, calculate the sum of squared errors δ(i) and store it;

[0074] (e) Search for the sum of squared power errors δ(i) corresponding to each of the 1001 search viewpoints, and obtain the minimum value of the sum of squared errors δ(i), denoted as δ. min And determine the viewing angle value β corresponding to this minimum value. t .

[0075] (f) Update the iteration parameters, taking the viewpoint value β obtained in the previous step. t Substitute β c Then, halve the distance range d value, reconstruct the search view array β(i), and repeat steps (a) to (e) until the search view value β is obtained. t The specified accuracy has been achieved. Taking the result of the second iteration, i=101 as an example, the search viewpoint value is 39°, resulting in the azimuth off-axis angle sequence θ. k (101), the result is as follows Figure 5 Distance to off-axis angle sequence Figure 6 As shown, under the search coordinates, the received signal power array Pr k(101), such as Figure 7 As shown;

[0076] After three iterations, the sum of squared signal power errors corresponding to the search viewpoint values ​​is as follows: Figure 8 As shown.

[0077] After the iteration, the search results are shown in Table 1:

[0078] Table 1 Search Results from a Perspective

[0079] Number of iterations 1 2 3 <![CDATA[β t ]]> 43.0080 43.0030 43.0005

[0080] After three iterations, the output result of 43.0005° was compared with the preset true viewing angle value of 43°. The error was 0.0005°, which met the set accuracy requirements.

[0081] The contents not described in detail in the specification are common knowledge to those skilled in the art.

Claims

1. A method for acquiring viewing angle in SAR front-side-looking strip working mode, characterized in that... The steps are as follows: (1) Obtain SAR radar flight trajectory data and ground received signal power array based on the SAR radar coordinates corresponding to the ground sampling time series; (2) Initial setting of SAR radar view center value β c and the viewing angle range d, and the SAR radar viewing angle range β c -d / 2 to β c The interval between +d / 2 is divided into (M-1) equal parts to obtain M SAR radar viewpoint values, which are then used to construct a SAR radar viewpoint search array β(i), where i is a positive integer, i = 1, 2...M; (3) Obtain the SAR radar view search array. For each search view, obtain the ground received signal power array. Based on the ground received signal power array for each search view and the ground received signal power array obtained in step (1), obtain the sum of squared errors of the received signal power for each search view. The search view value corresponding to the minimum sum of squared errors of the received signal power is denoted as β. t Using this search perspective value β t Instead of the initial SAR radar view center value β set in step (2) c Then, halve the initially set view range d value and repeat the above process in step (3) until the obtained search view value β is obtained. t Achieve the required precision.

2. The method for obtaining the viewing angle in the SAR frontal side-view strip working mode according to claim 1, characterized in that: The specific implementation process of step (1) is as follows: set the coordinates of the ground receiving station R point as (Xr, Yr, 0), and form a sampling time sequence t according to the sampling time interval. k k is a positive integer, k = 1, 2, ..., N, corresponding to the sampling time series t k The coordinates of point P on the SAR radar are (Xp k Yp k Zp k ), based on the coordinates of point P (Xp) of the SAR radar. k Yp k Zp k The radar flight trajectory data and the corresponding sampling time series t were obtained. k Ground received signal power array Pm k ; Where Xr represents the X-axis coordinate of ground receiving station R, Yr represents the Y-axis coordinate of ground receiving station R, Xr > 0, Yr > 0, Xp k This indicates that point P of the SAR radar is at t k X-axis coordinate at time, Yp k This indicates that point P of the SAR radar is at t k Y-axis coordinate at time, Zp k This indicates that point P of the SAR radar is at t k The Z-axis coordinate at time [time].

3. The method for obtaining the viewing angle in the SAR frontal side-view strip working mode according to claim 2, characterized in that: The specific implementation process of step (3) is as follows: (a) Based on the coordinates of the ground receiving station R point (Xr, Yr, 0) and the coordinates of the SAR radar P point (Xp) k Yp k Zp k To obtain the receiving range of the ground receiving station, the receiving range sequence R of the ground receiving station is obtained. k for: (b) Let the coordinates of the auxiliary point E be (Xp) k The coordinates of the auxiliary point F are (Xp, Yr, 0). k Yp k The coordinates of point T, the intersection of the SAR radar line of sight and the XOY plane, are (Xp 0). k Yt k The coordinates of auxiliary point H are (Xr, Yt). k ,0),Yt k Let point T be at t k Given the Y-axis coordinate at time t, and under the radar view search array β(i), obtain the radar antenna azimuth off-axis angle sequence θ corresponding to the radar view search array β(i). k (i) Distance to off-axis angle sequence φ k (i); f k (i)=|β(i)-γ k (i)| (4) In the formula: γ k (i) is the angle between EP and FP; In the formula: a1 k (i) represents the distance between two points HT, b1 k (i) represents the distance between points PT; a2 k (i)=|Yr-Yp k |,b2 k (i)=|Zp k | In the formula: a2 k (i) represents the distance between points E and F, and b2 k (i) represents the distance between two points PF; (c) Based on the SAR radar power direction gain diagram and azimuth off-axis angle sequence θ k (i) Distance to off-axis angle sequence φ k (i) , obtain the gain G of the SAR radar in the PR direction. k (i) The ground received signal power array Pr under each search view of the SAR radar view search array is obtained through equation (5). k (i): In the formula: Pt is the SAR radar transmit power, Gr is the receive antenna gain, λ is the SAR radar wavelength, and L is the system loss; (d) Combine the ground received signal power array and sampling time series t for each search view value of the SAR radar view search array. k The corresponding ground received signal power arrays are compared to obtain the sum of squared errors δ(i) of the received signal power for each search view value in the SAR radar view search array, where: (e) Search for the sum of squared errors of the received signal power δ(i) corresponding to each search viewpoint value, and denote the minimum value of the sum of squared errors of the received signal power δ(i) as δ min And determine the search perspective value β corresponding to the minimum value. t ; (f) Using the search perspective value β obtained in step (e) t Instead of the initial setting of the SAR radar view center value β in step (2) c Then, the initial view range d value is halved, the search view array β(i) is reconstructed, and steps (a) to (e) are repeated until the search view value β that meets the accuracy requirements is obtained. t .

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