A high-orbit ship target imaging resolution analysis method

Abstract

The present invention provides a high-orbit ship target imaging resolution analysis method, comprising constructing a simplified high-orbit echo ambiguity function; constructing a sway model of a sinusoidal variation of the ship target rotation angle; obtaining a rotation matrix based on the constructed sine variation of the ship target rotation angle sway model; taking the derivative of the rotation matrix to obtain the ship sway angular velocity; substituting the obtained ship sway angular velocity into the constructed simplified high-orbit echo ambiguity function to obtain an updated high-orbit echo ambiguity function; and determining the high-orbit ship target imaging resolution based on the updated high-orbit echo ambiguity function. The method of the present invention uses the ambiguity function as an analysis tool to simplify the high-orbit SAR imaging ambiguity function; uses the rotational angular velocity formed by the ship sway as a resolution evaluation condition, integrates the ship sway motion into the ambiguity function, and intuitively provides the high-orbit ship target imaging resolution evaluation result.

Description

Technical Field

[0001] The present application relates to the field of radar technology, in particular to synthetic aperture radar imaging signal processing technology, and in particular to a high-orbit ship target imaging resolution analysis method. Background Art

[0002] When high-orbit satellites image ship targets, they can only do so within a sub-aperture with a shorter synthetic aperture time, taking into account the defocusing effect caused by the ship's swaying. Analyzing based on the SAR imaging principle, a shorter sub-aperture synthetic aperture time will result in lower azimuth resolution; however, if analyzed based on the ISAR imaging principle, since the ship target rotates at a larger angle within the shorter sub-aperture synthetic aperture time, the ship target can still achieve high azimuth resolution by relying on its own swaying motion. This results in a contradiction between SAR and ISAR imaging resolution analysis when high-orbit satellites image ship targets.

[0003] Taking into account the influence of ship's swaying motion, the high-orbit ship target imaging process involves both the SAR imaging process of the high-orbit satellite's relative motion to the ship target and the ISAR imaging process of the ship's own swaying motion. Within the sub-aperture time, the SAR imaging process achieves low-resolution imaging, while the ISAR imaging process achieves high-resolution imaging. When considering the ship's own swaying motion, there is a contradiction between the ISAR imaging resolution analysis and the ISAR imaging resolution analysis. It is inaccurate to perform resolution analysis solely from traditional SAR or ISAR analysis methods. In addition, current domestic and foreign research on high-orbit SAR imaging resolution mostly focuses on static targets in the scene, and no research on imaging resolution analysis of swaying ship targets has been published.

[0004] In summary, there is an urgent need for a method that can resolve the contradiction between SAR and ISAR resolution analysis in high-orbit ship target imaging. Summary of the Invention

[0005] In response to the above technical problems, the present invention provides a high-orbit ship target imaging resolution analysis method to solve the technical problem that there is a contradiction between SAR resolution analysis and ISAR resolution analysis of high-orbit ship target imaging in the existing technology.

[0006] The present invention is specifically implemented by the following technical solutions:

[0007] A high-orbit ship target imaging resolution analysis method includes the following steps:

[0008] Step 1: Construct a simplified high-orbit echo ambiguity function;

[0009] Step 2: Construct a sine-changing swaying model of the ship target's rotation angle;

[0010] Step 3: Obtain the rotation matrix based on the constructed ship target rotation angle sinusoidal variation swing model;

[0011] Step 4: Derivative the rotation matrix to obtain the ship's sway angular velocity;

[0012] Step 5: Substitute the ship's sway angular velocity obtained in step 4 into the simplified high-orbit echo ambiguity function constructed in step 1 to obtain an updated high-orbit echo ambiguity function;

[0013] Step 6: Determine the high-orbit ship target imaging resolution based on the updated high-orbit echo ambiguity function.

[0014] The present invention also has the following technical features:

[0015] Furthermore, the simplified high orbit echo ambiguity function described in step 1 is:

[0016]

[0017] Where A and B are any two adjacent scattering points on the ship target, is the distance vector from the high-orbit SAR satellite to the scattering point B, is the distance vector from the high-orbit SAR satellite to the scattering point A, c is the speed of light, λ is the wavelength of the signal transmitted by the high-orbit SAR satellite, and j is a complex unit; P ( · ) is the inverse Fourier transform of the echo normalized energy spectrum, Q ( · ) is the inverse Fourier transform of the normalized antenna pattern, is the unit vector of the line of sight from the satellite to the scattering point A, ω ∑ In order to consider the composite angular velocity of the Earth's rotation and the motion of the high-orbit SAR satellite, ω ∑ The direction unit vector.

[0018] Furthermore, in the simplified high-orbit echo ambiguity function,

[0019]

[0020] Where, is the velocity vector of the high-orbit SAR satellite, is the velocity vector of the scattering point A, is the position vector of the high-orbit SAR satellite, is the projection operator, ω e is the angular velocity of the Earth's rotation.

[0021] Furthermore, the sinusoidal variation swing model of the ship target rotation angle described in step 2 is:

[0022]

[0023] Where θ roll is the rolling angle of the ship target, θ pitch is the pitch angle of the ship target, θ yaw is the yaw angle of the ship target swing, q1 is the roll amplitude, q2 is the pitch amplitude, q3 is the yaw amplitude, T1 is the roll period, T2 is the pitch period, T3 is the yaw period, φ1 is the initial roll angle, φ2 is the initial pitch angle, φ3 is the initial yaw angle, t m Slow time for orientation.

[0024] Furthermore, the rotation matrix described in step 3 is as follows:

[0025]

[0026] Where, is the rotation matrix, θ roll is the rolling angle of the ship target, θ pitch is the pitch angle of the ship target, θ yaw Yaw angle for ship target swing.

[0027] Furthermore, the ship's rolling angular velocity can be determined by the following formula:

[0028]

[0029] Where, is the ship's rolling angular velocity, is the rotation matrix, t m Slow time for orientation.

[0030] Furthermore, the updated high orbit echo ambiguity function is:

[0031]

[0032] Where A and B are any two adjacent scattering points on the ship target, is the distance vector from the high-orbit SAR satellite to the scattering point B, is the distance vector from the high-orbit SAR satellite to the scattering point A, c is the speed of light, λ is the wavelength of the signal transmitted by the high-orbit SAR satellite, and j is a complex unit; P ( · ) is the inverse Fourier transform of the echo normalized energy spectrum, Q ( · ) is the inverse Fourier transform of the normalized antenna pattern, is the unit vector of the line of sight from the satellite to the scattering point A, ω ΣIn order to consider the composite angular velocity of the Earth's rotation and the motion of the high-orbit SAR satellite, ω Σ The direction unit vector, is the ship's rolling angular velocity.

[0033] Furthermore, the imaging resolution of the high-orbit ship target is determined by the following formula:

[0034]

[0035] Where, ρ a is the imaging resolution of high-orbit ship targets, is the distance vector from the high-orbit SAR satellite to the scattering point B, is the distance vector from the high-orbit SAR satellite to the scattering point A, λ is the wavelength of the signal transmitted by the high-orbit SAR satellite, ω ∑ In order to consider the composite angular velocity of the Earth's rotation and the motion of the high-orbit SAR satellite, ω ∑ The direction unit vector, is the ship's angular velocity, T a is the signal bearing duration.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] (1) The proposed method uses fuzzy function as an analysis tool to simplify the fuzzy function of high-orbit SAR imaging. The angular velocity formed by the ship's swaying is used as the resolution evaluation condition, and the ship's swaying motion is integrated into the fuzzy function, which intuitively gives the high-orbit ship target imaging resolution evaluation result.

[0038] (2) The method of the present invention performs resolution analysis through a fuzzy function. The analysis method is not affected by the high-orbit imaging mode and is applicable to high-orbit ship imaging applications under various sea conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] The present application may be better understood by referring to the following description taken in conjunction with the accompanying drawings, which together with the following detailed description are incorporated into and form a part of this specification. In the drawings:

[0040] Figure 1 Flowchart of the method of the present invention.

[0041] Figure 2 Geometric model for imaging high-orbit ship targets.

[0042] Figure 3These are the target imaging simulation experiment results in Example 1, where (a) is the ship target scattering point model constructed in the simulation experiment, (b) is the full-aperture imaging result of the stationary ship target, (c) is the sub-aperture imaging result of the stationary ship target, and (d) is the sub-aperture imaging result of the rocking ship target.

[0043] Figure 4 This is the scattering point imaging result of Example 1. DETAILED DESCRIPTION

[0044] The present invention will be described in detail below with reference to the accompanying drawings and embodiments to facilitate a better understanding of the present invention by those skilled in the art. It should be noted that in the following description, detailed descriptions of known functions and designs will be omitted when they might obscure the main aspects of the present invention.

[0045] The imaging resolution of high-orbit ship targets is determined by three rotational components: the equivalent rotational component of the satellite flying relative to the target, the rotational component caused by the rotation of the earth, and the ship's own swaying rotational component. Among them, since the ship's own rotation period and rotation radius are very small, the equivalent rotational angular velocity is much greater than the equivalent rotational angular velocity of the satellite flight and the rotation of the earth, which plays a decisive role in the imaging resolution of high-orbit ship targets.

[0046] Example

[0047] In accordance with the above technical solution, this embodiment provides a high-orbit ship target imaging resolution analysis method. The method analyzes the nature of the relative rotation angle determining the azimuth resolution, uses the fuzzy function as an analysis tool, simplifies the high-orbit SAR imaging fuzzy function, and integrates the ship's swaying motion into the fuzzy function to provide a high-orbit ship target imaging resolution evaluation result, including the following steps:

[0048] Step 1: Construct a simplified high-orbit echo ambiguity function;

[0049] Specifically, it includes constructing the following high-orbit echo ambiguity function

[0050]

[0051] Where A and B are any two adjacent scattering points on the ship target; t is the distance to the target time; t m S is the azimuth slow time; A (t,t m ) is the echo signal of scattering point A; S B (t,t m ) is the echo signal of scattering point B; For S B (t,t m )'s conjugation; is the position vector of the scattering point A; is the position vector of the scattering point B.

[0052] In the above formula, the echo signal of scattering point A is determined according to the following formula:

[0053] S A (t,t m )=W a (t m )s(t-τ A (t m ))exp(j2πf0(t-τ A (t m )))

[0054] The echo signal of scattering point B is determined according to the following formula:

[0055] S B (t,t m )=W a (t m )s(t-τ B (t m ))exp(j2πf0(t-τ B (t m )))

[0056] Where s(t) is the signal waveform, f0 is the center carrier frequency, τ A (t m ) is the echo delay of scattering point A, τ B (t m ) is the echo delay of scattering point B, W a (t m ) is the signal envelope, and j is a complex unit.

[0057] S A (t,t m ) and S B (t,t m ) is substituted into the high-orbit echo ambiguity function constructed above to obtain the following simplified high-orbit echo ambiguity function:

[0058]

[0059] Where A and B are any two adjacent scattering points on the ship target; is the distance vector from the high-orbit SAR satellite to point B, is the distance vector from the high-orbit SAR satellite to point A, c is the speed of light, λ is the wavelength of the signal transmitted by the high-orbit SAR satellite, j is a complex unit, P ( · ) is the inverse Fourier transform of the echo normalized energy spectrum; Q ( ·) is the inverse Fourier transform of the normalized antenna pattern; is the unit vector of the line of sight from the satellite to the scattering point A; ω Σ To take into account the composite angular velocity of the Earth's rotation and the motion of the high-orbit SAR satellite; ω ∑ The direction of the unit vector, T is the transpose;

[0060] According to the existing low-orbit SAR azimuth resolution formula, while considering the influence of the earth's rotation on the azimuth resolution, the simplified high-orbit echo ambiguity function is It can be determined by the following formula:

[0061]

[0062] Where, is the velocity vector of the high-orbit SAR satellite, is the velocity vector of the scattering point A, is the position vector of the high-orbit SAR satellite; is the distance vector from the high-orbit SAR satellite to the scattering point A, is the projection operator, is the unit vector of the line of sight from the satellite to the scattering point A, ω e is the angular velocity of the Earth's rotation.

[0063] Step 2: Construct a sine-changing swaying model of the ship target's rotation angle;

[0064] Due to the influence of wind and waves at sea, ships will inevitably sway on the sea surface. Therefore, in the imaging analysis of high-orbit ship targets, in addition to considering the rotation effect of the earth's rotation, it is also necessary to consider the impact of the three-dimensional swaying motion of the ship target itself on the imaging resolution. Therefore, the three-dimensional swaying motion is reflected by the following sine variation swaying model of the ship target rotation angle:

[0065]

[0066] Where θ roll is the rolling angle of the ship target, θ pitch is the pitch angle of the ship target, θ yaw is the yaw angle of the ship target swing, q1 is the roll amplitude, q2 is the pitch amplitude, q3 is the yaw amplitude, T1 is the roll period, T2 is the pitch period, T3 is the yaw period, φ1 is the initial roll angle, φ2 is the initial pitch angle, φ3 is the initial yaw angle, t m Slow time for orientation.

[0067] Step 3: Based on the constructed ship target rotation angle sinusoidal swing model, the rotation matrix is ​​obtained as follows:

[0068]

[0069] Where, is the rotation matrix, θ roll is the rolling angle of the ship target, θ pitch is the pitch angle of the ship target, θ yaw Yaw angle for ship target swing.

[0070] Step 4: Derivative the rotation matrix to obtain the ship's sway angular velocity as follows;

[0071]

[0072] Where, is the ship's rolling angular velocity, is the rotation matrix, t m Slow time for orientation.

[0073] Step 5: Substitute the ship's sway angular velocity obtained in step 4 into the simplified high-orbit echo ambiguity function constructed in step 1 to obtain the updated high-orbit echo ambiguity function as follows:

[0074]

[0075] Where A and B are any two adjacent scattering points on the ship target, is the distance vector from the high-orbit SAR satellite to the scattering point B, is the distance vector from the high-orbit SAR satellite to the scattering point A, c is the speed of light, λ is the wavelength of the signal transmitted by the high-orbit SAR satellite, and j is a complex unit; P ( · ) is the inverse Fourier transform of the echo normalized energy spectrum, Q ( · ) is the inverse Fourier transform of the normalized antenna pattern, is the unit vector of the line of sight from the satellite to the scattering point A, ω ∑ In order to consider the composite angular velocity of the Earth's rotation and the motion of the high-orbit SAR satellite, ω ∑ The direction unit vector, is the ship's rolling angular velocity.

[0076] Step 6: Determine the imaging resolution of the high-orbit ship target based on the updated high-orbit echo ambiguity function;

[0077] The imaging resolution is determined by the following formula:

[0078]

[0079] Where, ρ ais the imaging resolution of high-orbit ship targets, is the distance vector from the high-orbit SAR satellite to the scattering point B, is the distance vector from the high-orbit SAR satellite to the scattering point A, λ is the wavelength of the signal transmitted by the high-orbit SAR satellite, ω ∑ In order to consider the composite angular velocity of the Earth's rotation and the motion of the high-orbit SAR satellite, ω ∑ The direction unit vector, is the ship's angular velocity, T a is the signal bearing duration.

[0080] The effects of the present invention are also verified through simulation experiments in this embodiment, including:

[0081] High-orbit ship imaging simulation test

[0082] First, a sinusoidal swing model of the ship target rotation angle is constructed as follows: Figure 2 As shown, the ship target imaging result is obtained as follows Figure 3 As shown, Figure 3 (a) is the ship target scattering point model constructed in the simulation experiment. Figure 3 (b) is the full-aperture imaging result of a stationary ship target. Figure 3 (c) is the sub-aperture imaging result of a stationary ship target. Figure 3 (d) is the sub-aperture imaging result of the swaying ship target. Figure 3 (c) with Figure 3 (d) It can be seen that the sub-aperture imaging results under the stationary and swaying states of the ship well verify the impact of the ship's swaying on the resolution of the present invention.

[0083] Resolution evaluation simulation test

[0084] In the high-orbit imaging environment, a coordinate system is established with the ship body, and the ship's swing center (0, 0, 0) is used as the reference point. Five rotating scattering points are placed on its right side at intervals of 2 meters along the azimuth direction. The coordinates are (2, 0, 0), (4, 0, 0), (6, 0, 0), (8, 0, 0), and (10, 0, 0). The five scattering points are swung and rotated with a rotation amplitude of 6° and a rotation period of 55 seconds around the reference point. The BP imaging algorithm is used for imaging processing, and the scattering point imaging results are obtained as follows: Figure 4 As shown in the figure, the 3dB bandwidth of each scattering point in the scattering point imaging result is used as the basis for evaluating the azimuth resolution. Finally, the resolution of the five scattering points is calculated. According to the high-orbit ship target imaging resolution model constructed in the present invention, the simulation parameters in Table 1 are substituted and the obtained imaging resolution is 0.944. The comparison results are shown in Table 2.

[0085]

[0086]

[0087] Table 1. Simulation parameters of high-orbit ship target imaging resolution

[0088] in, is a unit vector, and the final calculated imaging resolution is 0.944.

[0089]

[0090] Table 2. Statistical results of ship rotation scattering point resolution

[0091] As can be seen from Table 2, the error between the resolution results calculated using the method of the present invention and the resolution results obtained by simulation is less than 1%, which proves the accuracy and effectiveness of the resolution analysis method proposed in the present invention.

[0092] The above descriptions are merely examples of various embodiments of the present application, but the scope of protection of the present application is not limited thereto. Any modifications or substitutions that can be readily conceived by a person skilled in the art within the technical scope disclosed in the present application should be included within the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. A high-orbit ship target imaging resolution analysis method, characterized in that: The following steps are involved: Step 1: Construct a simplified high-orbit echo ambiguity function; Step 2: Construct a sine-changing swaying model of the ship target's rotation angle; Step 3: Obtain the rotation matrix based on the constructed ship target rotation angle sinusoidal variation swing model; Step 4: Derivative the rotation matrix to obtain the ship's sway angular velocity; Step 5: Substitute the ship's sway angular velocity obtained in step 4 into the simplified high-orbit echo ambiguity function constructed in step 1 to obtain an updated high-orbit echo ambiguity function; Step 6: Determine the imaging resolution of the high-orbit ship target based on the updated high-orbit echo ambiguity function; The imaging resolution of the high-orbit ship target is determined by the following formula: Where, ρ a is the imaging resolution of high-orbit ship targets, is the distance vector from the high-orbit SAR satellite to the scattering point B, is the distance vector from the high-orbit SAR satellite to the scattering point A, λ is the wavelength of the signal transmitted by the high-orbit SAR satellite, ω ∑ In order to consider the composite angular velocity of the Earth's rotation and the motion of the high-orbit SAR satellite, ω ∑ The direction unit vector, is the ship's angular velocity, T a is the signal bearing duration, and T is the transpose.

2. The high-orbit ship target imaging resolution analysis method according to claim 1, characterized in that: The simplified high orbit echo ambiguity function described in step 1 is: Where A and B are any two adjacent scattering points on the ship target, is the distance vector from the high-orbit SAR satellite to the scattering point B, is the distance vector from the high-orbit SAR satellite to the scattering point A, c is the speed of light, λ is the wavelength of the signal transmitted by the high-orbit SAR satellite, and j is a complex unit; P ( · ) is the inverse Fourier transform of the echo normalized energy spectrum, Q ( · ) is the inverse Fourier transform of the normalized antenna pattern, is the unit vector of the line of sight from the satellite to the scattering point A, ω ∑ In order to consider the composite angular velocity of the Earth's rotation and the motion of the high-orbit SAR satellite, ω ∑ The direction unit vector.

3. The high-orbit ship target imaging resolution analysis method according to claim 2, characterized in that: The simplified high-orbit echo ambiguity function is: Where, is the velocity vector of the high-orbit SAR satellite, is the velocity vector of the scattering point A, is the position vector of the high-orbit SAR satellite, is the projection operator, ω e is the angular velocity of the Earth's rotation.

4. The high-orbit ship target imaging resolution analysis method according to claim 1, characterized in that: The sinusoidal variation swing model of the ship target rotation angle described in step 2 is: Where θ roll is the rolling angle of the ship target, θ pitch is the pitch angle of the ship target, θ yaw is the yaw angle of the ship target swing, q1 is the roll amplitude, q2 is the pitch amplitude, q3 is the yaw amplitude, T1 is the roll period, T2 is the pitch period, T3 is the yaw period, φ1 is the initial roll angle, φ2 is the initial pitch angle, φ3 is the initial yaw angle, t m Slow time for orientation.

5. The high-orbit ship target imaging resolution analysis method according to claim 4, characterized in that: The rotation matrix described in step 3 is as follows: Where, is the rotation matrix, θ roll is the rolling angle of the ship target, θ pitch is the pitch angle of the ship target, θ yaw Yaw angle for ship target swing.

6. The high-orbit ship target imaging resolution analysis method according to claim 1, characterized in that: The ship's rolling angular velocity can be determined by the following formula: Where, is the ship's angular velocity, is the rotation matrix, t m Slow time for orientation.

7. The high-orbit ship target imaging resolution analysis method according to claim 1, characterized in that: The updated high orbit echo ambiguity function is: Where A and B are any two adjacent scattering points on the ship target, is the distance vector from the high-orbit SAR satellite to the scattering point B, is the distance vector from the high-orbit SAR satellite to the scattering point A, c is the speed of light, λ is the wavelength of the signal transmitted by the high-orbit SAR satellite, and j is a complex unit; P ( · ) is the inverse Fourier transform of the echo normalized energy spectrum, Q ( · ) is the inverse Fourier transform of the normalized antenna pattern, is the unit vector of the line of sight from the satellite to the scattering point A, ω ∑ In order to consider the composite angular velocity of the Earth's rotation and the motion of the high-orbit SAR satellite, ω ∑ The direction unit vector, is the ship's rolling angular velocity, and T is the transpose.

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