Large space-variant motion error compensation method based on airship platform SAR

Abstract

The invention discloses a large space-variant motion error compensation method based on an airship platform SAR, motion parameters of all orders of a target are fitted through an inertial navigation system, motion errors are described as space-variant errors and non-space-variant errors, and the motion errors of the platform can be accurately described. Especially for the problem of cross coupling of course and tangential course motion errors, scene space-variant correction can be carried out more accurately. According to the method, consistency compensation is carried out on non-space-variant errors in a distance frequency domain, two-dimensional decoupling is carried out on the space-variant errors through a Lagrange averaging method, and compensation and correction are carried out through nonlinear scale transformation achieved through CZT, so that the operand is greatly reduced, and when large-width SAR data are processed, high calculation efficiency can be kept; the actual requirements of airship platform SAR imaging under the requirements of large breadth and high precision are met, and especially in real-time imaging and engineering application, the speed and effect of data processing can be remarkably improved.

Description

Technical Field

[0001] The invention belongs to the technical field of SAR imaging, and in particular relates to a large space-variable motion error compensation method based on airship platform SAR. Background Art

[0002] In synthetic aperture radar (SAR) imaging, motion error will cause the Doppler characteristics of the echo signal to change, which will significantly affect the depth of focus and reduce the imaging quality. Generally, aerial platforms such as aircraft are less affected by air turbulence and have relatively low motion errors. Unlike airborne radar imaging, airship platforms have a larger volume and slower movement speed, a longer synthetic aperture time, and mainly rely on air buoyancy to balance their own gravity and overcome air resistance through propeller thrust. In actual working processes, airships are more susceptible to atmospheric disturbances, have poor flight stability, and are difficult to maintain an ideal motion trajectory, resulting in large motion errors. In addition, airship SAR has the characteristics of long distance, wide bandwidth and high resolution, which makes the cross-coupling and scene space-variation problems caused by motion errors more significant. Traditional motion compensation (MOCO) methods usually use two-step MOCO, which assumes that distance and azimuth are independent and ignores the coupling and space-variation of motion errors. Therefore, it cannot meet the precise imaging requirements of airship platform SAR under nonlinear motion conditions. Although time-domain algorithms such as the Fast Factorized Back-Projection Algorithm (FFBPA) can achieve high-precision imaging under nonlinear conditions, the huge amount of calculation caused by their wide bandwidth leads to very high computational complexity and long operation time, which makes it difficult to meet the needs of engineering applications.

[0003] Xidian University disclosed a method for motion compensation of airborne SAR based on inertial navigation system (INS) parameters in its patent application, "A method for motion compensation of airborne SAR based on inertial navigation system parameters" (CN 11367031 A). The method includes: establishing a radar coordinate system and a motion error model, and collecting inertial navigation system parameters in real time; then establishing the instantaneous slant range equation of the airborne SAR, deriving the instantaneous slant range error formula, and decomposing it into the motion error of the carrier along the heading and the tangent heading; performing consistent compensation envelope in the range frequency domain and azimuth time domain after the range pulse compression, and finally compensating the phase in the two-dimensional time domain. Compared with the traditional two-step MOCO method, this scheme considers the spatial variation of the range direction when compensating the phase, thereby improving the imaging quality. However, this method still has certain shortcomings: the spatial variation of the range is not considered when compensating the envelope, and the coupling relationship of the motion error is assumed to be approximate, so it cannot meet the high-precision requirements of the airship platform SAR in wide-width imaging under large error conditions.

[0004] Existing imaging algorithms usually assume that the airship platform flies in a straight line along an ideal heading. However, in practical applications, the airship platform is more susceptible to airflow during SAR imaging, resulting in large motion errors, which affects the imaging quality and may even lead to the failure of imaging. In order to obtain ideal SAR imaging results, effective motion compensation is required for the collected raw echo data. Existing motion compensation methods can be divided into two categories according to different data sources:

[0005] 1. Compensation method based on motion data: This method relies on the inertial navigation system (INS) and GPS receiver on the platform to obtain the three-dimensional motion velocity parameters of the platform. The motion errors along the heading and the tangent heading are obtained by solving, and the "two-step" MOCO method is applied to frequency domain imaging algorithms such as RDA and RMA. This method assumes that the coupling of motion errors and space variations are somewhat similar, but airship platforms often have large errors, and this method cannot effectively handle complex motion errors.

[0006] 2. Non-parametric compensation method based on raw data: This method directly estimates the phase error caused by motion error through echo data to compensate for defocus. This type of method is often used in scenes such as drone-mounted SAR and vehicle-mounted SAR, which have a small width. However, airship SAR usually has a large scene width and a large amount of raw echo data, which leads to high computational complexity and low efficiency of this method, making it difficult to meet the needs of engineering applications. Summary of the invention

[0007] In order to solve the above problems existing in the prior art, the present invention provides a large-scale space-variable motion error compensation method based on airship platform SAR. The technical problem to be solved by the present invention is achieved through the following technical solutions:

[0008] The present invention provides a large space-variable motion error compensation method based on airship platform SAR, the method comprising:

[0009] Get the target echo signal at any point;

[0010] Fitting the various order motion parameters of the target through the inertial navigation system to obtain the fitting error;

[0011] Based on the fitting error, the motion error of the target in the arbitrary point target echo signal is described as a non-space-varying error and a space-varying error, and the target echo signal after pulse compression is obtained;

[0012] Performing consistency compensation on the non-space-varying error in the target echo signal after pulse compression in the range frequency domain to obtain a target echo signal after consistent compensation;

[0013] The space-varying error in the target echo signal after consistent compensation is decoupled in two dimensions by Lagrangian mean method to obtain the decoupled target echo signal;

[0014] The space-varying error in the decoupled target echo signal is compensated step by step based on CZT transformation, and the target echo signal after step compensation is subjected to two-dimensional IFFT to obtain the imaging result.

[0015] In one embodiment of the present invention, the expression of the arbitrary point target echo signal is as follows:

[0016]

[0017] Where t represents the fast time variable, t a represents the azimuth slow time variable, r1 represents the slant distance vector from any point to the platform at the reference time, λ represents the wavelength of the transmitted signal, τ represents the delay time of the received signal, j represents the imaginary unit, c represents the speed of light, μ represents the range modulation frequency, exp() represents the exponential operation with the natural constant e as the base, represents the real instantaneous slope distance corresponding to any point, w r () represents the distance envelope, w a () indicates the azimuth envelope.

[0018] In one embodiment of the present invention, the inertial navigation system is used to fit the various order motion parameters of the target to obtain the fitting error, including:

[0019] The velocity information of the target is obtained through the inertial navigation system, and the motion parameters of each order corresponding to the target are obtained by linear fitting;

[0020] According to the motion parameters of each order corresponding to the target, the instantaneous slope distance of the reference point and the slope distance history vector of any point are obtained;

[0021] The fitting error is obtained based on the instantaneous slope distance of the reference point and the slope distance history vector of any point.

[0022] In one embodiment of the present invention, the fitting error includes the fitting error corresponding to the arbitrary point and the fitting error corresponding to the reference point; wherein,

[0023] The expression of the fitting error corresponding to the arbitrary point is as follows:

[0024]

[0025] The expression of the fitting error corresponding to the reference point is as follows:

[0026]

[0027] Among them, t a represents the azimuth slow time variable, represents the real instantaneous slant distance corresponding to any point, r1 represents the slant distance vector from any point to the platform at the reference time, R(t a ,r1) represents the slope distance vector of any point, v represents the velocity, a0 represents the first-order acceleration, a1 represents the second-order acceleration, represents the real instantaneous slant distance corresponding to the reference point, r0 represents the slant distance vector from the reference point to the platform at the reference time, R(t a ,r0) represents the instantaneous slope distance of the reference point.

[0028] In one embodiment of the present invention, the expression of the target echo signal after pulse compression is as follows:

[0029]

[0030] Among them, s1(f r ,t a ) represents the target echo signal after pulse compression, f r represents the distance frequency, t a represents the azimuth slow time variable, j represents the imaginary unit, and f c represents the carrier frequency, c represents the speed of light, exp() represents the exponential operation based on the natural constant e, R(t a ,r1) represents the slant distance vector of any point, r1 represents the slant distance vector from any point to the platform at the reference time, represents the real instantaneous slant distance corresponding to the reference point, r0 represents the slant distance vector from the reference point to the platform at the reference time, R(t a ,r0) represents the instantaneous slope distance of the reference point.

[0031] In one embodiment of the present invention, the compensation function when performing consistency compensation is as follows:

[0032]

[0033] Among them, f r represents the distance frequency, t a represents the azimuth slow time variable, j represents the imaginary unit, and f c represents the carrier frequency, c represents the speed of light, and exp() represents the exponential operation based on the natural constant e. It represents the real instantaneous slant distance corresponding to the reference point, and r0 represents the slant distance vector from the reference point to the platform at the reference time.

[0034] In one embodiment of the present invention, the expression of the target echo signal after consistent compensation is as follows:

[0035]

[0036] Among them, f r represents the distance frequency, t a represents the azimuth slow time variable, j represents the imaginary unit, and f c represents the carrier frequency, c represents the speed of light, exp() represents the exponential operation based on the natural constant e, R(t a ,r1) represents the slant distance vector of any point, r1 represents the slant distance vector from any point to the platform at the reference time, R(t a ,r0) represents the instantaneous slant distance of the reference point, and r0 represents the slant distance vector from the reference point to the platform at the reference time.

[0037] In one embodiment of the present invention, a space-varying error in a target echo signal after consistent compensation is two-dimensionally decoupled by a Lagrangian mean method to obtain a decoupled target echo signal, including:

[0038] Based on the Lagrange mean method, the space-varying error in the target echo signal after consistent compensation is orthogonally expanded to obtain the expanded space-varying error;

[0039] The gradient of the expanded space-varying error is calculated to obtain a decoupled target echo signal.

[0040] In one embodiment of the present invention, the expression of the decoupled target echo signal is as follows:

[0041]

[0042] Among them, f r represents the distance frequency, t a represents the azimuth slow time variable, exp() represents the exponential operation with the natural constant e as the base, j represents the imaginary unit, and f c represents the carrier frequency, c represents the speed of light, g=|r1|-|r0|, represents the partial derivative operation, r0 represents the slant distance vector from the reference point to the platform at the reference time, |r0 represents the slant distance from the reference point to the platform at the reference time, represents the Doppler center from the platform to the reference point at the reference time, r1 represents the slant distance vector from any point to the platform at the reference time, |r1| represents the slant distance from any point to the platform at the reference time, fdc represents the Doppler center from the platform to any point at the reference time, R(r1|,fdc) represents the slant distance |r1| and Doppler center f from the platform to any point at the reference time dc The binary implicit function of .

[0043] In the scheme provided by the present invention, the motion error is described as a cross-coupled space-varying error and a non-space-varying error by fitting the various order motion parameters of the target through an inertial navigation system (INS), and the motion error can be accurately described as the space-varying error and the non-space-varying error of the platform. Compared with the prior art, the present invention can more accurately perform scene space-varying correction when facing a large motion error, especially the cross-coupling problem of the heading and tangent heading motion errors. The non-space-varying error is compensated for consistency in the range-frequency domain, the space-varying error is decoupled in two dimensions by the Lagrange mean method, and the nonlinear scale transformation is realized by CZT transformation for compensation and correction. Compared with the traditional non-parametric compensation method, the present invention greatly reduces the amount of calculation. This feature enables the present invention to maintain a high computational efficiency when processing wide-width SAR data, meet the actual needs of airship platform SAR imaging under wide-width and high-precision requirements, especially in real-time imaging and engineering applications, and can significantly improve the speed and effect of data processing. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 A schematic diagram of the steps of a method for compensating large space-variable motion errors based on an airship platform SAR provided by an embodiment of the present invention;

[0045] Figure 2 A schematic diagram of the flow of CZT transformation in a large space-variable motion error compensation method based on an airship platform SAR provided by an embodiment of the present invention;

[0046] Figure 3 This is a diagram of simulation results of a large-scale space-variable motion error compensation method based on airship platform SAR provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0047] The present invention is further described in detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0048] Although traditional satellites, aircraft and other platforms have certain advantages in remote sensing imaging, they still have many limitations, such as insufficient observation time, limited imaging coverage, and the impact of climatic conditions on platform performance. These problems affect the execution efficiency and imaging quality of traditional platforms in key tasks, especially in continuous monitoring and immediate response capabilities in harsh environments.

[0049] The airship platform carried by the embodiment of the present invention has unique technical advantages and can effectively make up for the shortcomings of existing platforms in these aspects. By extending the platform's hovering time, the airship can continuously and stably perform high-precision SAR imaging of a specific area for a long time, breaking through the time and space limitations of satellite and aircraft platforms, and significantly improving the imaging coverage and imaging quality. The high-altitude stability and flexibility of the airship make it an ideal remote monitoring platform, which can ensure real-time perception of the target and provide timely and accurate information support for decision-making.

[0050] With the continuous advancement of SAR technology, the transmission bandwidth and synthetic aperture are constantly improving, making the distance and azimuth resolution of SAR systems higher and higher. However, this also brings new challenges: the Doppler process differences of different imaging units in the beam coverage area caused by motion errors gradually appear, which may lead to a decrease in imaging quality, especially in complex terrain and large-scale scenes. In order to meet these challenges, the motion compensation algorithm proposed in the embodiment of the present invention can effectively correct the cross-coupling and scene space-variation problems, overcome technical bottlenecks such as edge blur and insufficient focus depth in the imaging process, and ensure that clear SAR images can be obtained stably and with high quality in a large error environment.

[0051] The large-space-variable motion error compensation method based on the airship platform SAR proposed in the embodiment of the present invention can solve the problem of unstable imaging quality under large error conditions in traditional methods, and greatly improve the adaptability of the SAR system in complex and dynamic environments. This enables the airship platform to stably and reliably perform high-precision SAR imaging tasks under all-day and all-weather conditions, greatly enhancing the platform's responsiveness to various tactical requirements.

[0052] The embodiment of the present invention provides a method for compensating large space-variable motion errors based on an airship platform SAR. Figure 1 As shown, it may include:

[0053] S1, obtain the target echo signal at any point.

[0054] The expression of the echo signal of any point target in the two-dimensional time domain is as follows:

[0055]

[0056] Where t represents the fast time variable, t arepresents the azimuth slow time variable, λ represents the wavelength of the transmitted signal, τ represents the delay time of the received signal, j represents the imaginary unit, c represents the speed of light, μ represents the distance modulation frequency, exp() represents the exponential operation with the natural constant e as the base, represents the real instantaneous slope distance corresponding to any point r1, w r () represents the distance envelope, w a () indicates the azimuth envelope.

[0057] S2, fitting the various order motion parameters of the target through the inertial navigation system to obtain the fitting error, which may include:

[0058] S21, obtaining the speed information of the target through the inertial navigation system, and obtaining the motion parameters of each order corresponding to the target by linear fitting.

[0059] The target's velocity information can include the three axes of north, east and sky. The expressions of the various order motion parameters corresponding to the target obtained by linear fitting are as follows:

[0060] e(t a )=v+…+(n+1)!a n t a n+1 ;

[0061] Among them, e(t a ) represents the north-east velocity vector obtained at each moment, v represents the velocity, ! represents the factorial operation, a n Represents n-order acceleration, and the fitting order n mainly depends on the influence of high-order acceleration on imaging.

[0062] S22, obtaining the instantaneous slant distance of the reference point and the slant distance history vector of any point according to the motion parameters of each order corresponding to the target;

[0063] The expression of the instantaneous slope distance of the reference point is as follows:

[0064]

[0065] Among them, t a represents the azimuth slow time variable, r0 represents the slant distance vector from the reference point to the platform at the reference time, v represents the velocity, a0 represents the first-order acceleration, and a1 represents the second-order acceleration.

[0066] The expression of the slope distance vector of any point is as follows:

[0067]

[0068] Where r1 represents the slant distance vector from any point to the platform at the reference time.

[0069] S23, obtaining a fitting error according to the instantaneous slant distance of the reference point and the slant distance history vector of any point.

[0070] The fitting error includes the fitting error corresponding to any point and the fitting error corresponding to the reference point;

[0071] The expression of the fitting error corresponding to any point is as follows:

[0072]

[0073] The expression of the fitting error corresponding to the reference point is as follows:

[0074]

[0075] Among them, t a represents the azimuth slow time variable, represents the real instantaneous slant distance corresponding to any point, r1 represents the slant distance vector from any point to the platform at the reference time, R(t a ,r1) represents the slope distance vector of any point, v represents the velocity, a0 represents the first-order acceleration, a1 represents the second-order acceleration, represents the real instantaneous slant distance corresponding to the reference point, r0 represents the slant distance vector from the reference point to the platform at the reference time, R(t a ,r0) represents the instantaneous slope distance of the reference point. and It is calculated directly from the instantaneous velocity information measured by the inertial navigation system (INS).

[0076] S3, based on the fitting error, the motion error of the target in the target echo signal at any point is described as a non-space-varying error and a space-varying error, and the target echo signal after pulse compression is obtained.

[0077] Ignore the amplitude terms irrelevant to imaging, use the fitting error of the reference point to replace the fitting error of any point, and the echo data of any point after pulse compression can be expressed in the range, frequency, azimuth and time domains as follows:

[0078]

[0079] Among them, s1(f r ,t a ) represents the target echo signal after pulse compression, f r represents the distance frequency, t a represents the azimuth slow time variable, j represents the imaginary unit, and f c represents the carrier frequency, c represents the speed of light, exp() represents the exponential operation based on the natural constant e, R(t a ,r1) represents the slant distance vector of any point, r1 represents the slant distance vector from any point to the platform at the reference time, represents the real instantaneous slant distance corresponding to the reference point, r0 represents the slant distance vector from the reference point to the platform at the reference time, R(t a ,r0) represents the instantaneous slope distance of the reference point.

[0080] The non-space-varying error of any point is represented by the reference point, and a consistent compensation function is designed to remove it. The compensation function for consistent compensation is as follows:

[0081]

[0082] Among them, f r represents the distance frequency, t a represents the azimuth slow time variable, j represents the imaginary unit, and f c represents the carrier frequency, c represents the speed of light, and exp() represents the exponential operation based on the natural constant e. It represents the real instantaneous slant distance corresponding to the reference point, and r0 represents the slant distance vector from the reference point to the platform at the reference time.

[0083] It can be understood that by fitting the various order motion parameters of the target through the inertial navigation system (INS), the motion error is described as a cross-coupled space-varying error and a non-space-varying error, which can accurately describe the motion error of the platform. Compared with the prior art, the embodiments of the present invention can more accurately perform scene space-varying correction when facing large motion errors, especially the cross-coupling problem of heading and tangent heading motion errors.

[0084] S4, performing consistency compensation on the non-space-varying error in the target echo signal after pulse compression in the range frequency domain to obtain a target echo signal after consistency compensation.

[0085] The expression of the target echo signal after consistent compensation is as follows:

[0086]

[0087] Among them, f r represents the distance frequency, t a represents the azimuth slow time variable, j represents the imaginary unit, and f c represents the carrier frequency, c represents the speed of light, exp() represents the exponential operation based on the natural constant e, R(t a ,r1) represents the slant distance vector of any point, r1 represents the slant distance vector from any point to the platform at the reference time, R(t a ,r0) represents the instantaneous slant distance of the reference point, and r0 represents the slant distance vector from the reference point to the platform at the reference time.

[0088] S5, performing two-dimensional decoupling of the space-varying error in the target echo signal after consistent compensation by Lagrangian mean method to obtain a decoupled target echo signal, may include:

[0089] S51, performing orthogonal expansion on the space-varying error in the target echo signal after consistent compensation based on the Lagrange mean method to obtain the expanded space-varying error.

[0090] Specifically, for the target echo signal after consistent compensation, R(t a ,r1) is decomposed as follows:

[0091]

[0092] At this time, the residual phase error in the above formula presents two-dimensional space variation and cross coupling relative to the reference point, t a represents the azimuth slow time variable, represents the i-th derivative of the Doppler frequency, t a i represents the i-th order derivative of the azimuth slow time variable, and the value range of i is a positive integer. Preferably, i can be 2 or 3. a ,r1) is regarded as the slant distance |r1| from the platform to any point at the reference time and the Doppler center f dc The binary implicit function is R(r1|,fdc). And replace R(ta,r1) and R(ta,r0) in the above formula, and based on the Lagrange mean method, the space-varying error in the target echo signal after consistent compensation is orthogonally expanded to obtain the expanded space-varying error.

[0093]

[0094] Among them, |r0| represents the slant distance from the reference point to the platform at the reference time, represents the Doppler center from the platform to the reference point at the reference time, and g = |r1|-|r0|, It can be seen from the above formula that the cross-coupled space-variant error R(ta,r1)-R(ta,r0) is decomposed into two terms that are only related to |r1| and fdc.

[0095] S52, calculating the gradient of the expanded space-variant error to obtain a decoupled target echo signal.

[0096] In order to calculate the partial derivative in the formula, we can find the gradient of R(r1|,fdc),

[0097]

[0098] Among them, according to the gradient operation rule, there is:

[0099]

[0100] Since the slant range plane where the image is located is and Two vectors are generated and exist That is, the two are orthogonal; therefore, the SAR image can be regarded as an orthogonal two-dimensional plane composed of two linearly independent coordinate axes.

[0101] Multiply the above formula by and because get:

[0102]

[0103] So we can get the partial derivative of the above formula:

[0104]

[0105] The partial derivative in the formula is expressed in the form of gradient operation. At this time, the expression of the decoupled target echo signal is as follows:

[0106]

[0107] Among them, f r represents the distance frequency, t a represents the azimuth slow time variable, exp() represents the exponential operation with the natural constant e as the base, j represents the imaginary unit, and f c represents the carrier frequency, c represents the speed of light, g=|r1|-|r0|, represents the partial derivative operation, r0| represents the slope distance from the reference point to the platform at the reference time, represents the Doppler center from the platform to the reference point at the reference time, |r1| represents the slant distance from any point to the platform at the reference time, fdc represents the Doppler center from the platform to any point at the reference time, and R(r1|,fdc) represents the slant distance |r1| and Doppler center f from the platform to any point at the reference time. dc The binary implicit function of .

[0108] S6, based on CZT transformation, the space-varying error in the decoupled target echo signal is compensated step by step, and a two-dimensional IFFT is performed on the target echo signal after step compensation to obtain an imaging result.

[0109] because and It is a nonlinear function and cannot be simply solved by phase multiplication. In order to solve the above problem, the embodiment of the present invention adopts the following method: Figure 2The CZT transformation shown in FIG. 1 is used to remove the space-variant error. The nonlinear scale transformation is achieved by three-dimensional scaling, so that the space-variant error distribution can be compensated. Among them, the Chirp scaling factor s c The expression is as follows:

[0110]

[0111] Among them, T s represents the coherent accumulation period, f c Indicates the carrier frequency, f r represents the distance frequency, t a Represents the azimuth slow-time variable.

[0112] Perform two-dimensional IFFT on the target echo signal after step compensation to obtain the imaging result.

[0113] The CZT transformation is used to realize nonlinear scale transformation for compensation and correction. Compared with the traditional non-parametric compensation method, the embodiment of the present invention greatly reduces the amount of calculation. This feature enables the embodiment of the present invention to maintain high computing efficiency when processing large-width SAR data, meet the actual needs of airship platform SAR imaging under large-width and high-precision requirements, especially in real-time imaging and engineering applications, and can significantly improve the speed and effect of data processing.

[0114] The beneficial effect of the large-space-variable motion error compensation method based on the airship platform SAR proposed in the embodiment of the present invention is verified by simulation below.

[0115] The simulation results of the embodiment of the present invention are obtained by simulating the parameters shown in Table 1. Figure 3 .

[0116] Table 1 Simulation parameters

[0117]

[0118]

[0119] from Figure 3 It can be seen that Figure 3 (a) is a two-dimensional slice diagram of the edge point target of the proposed algorithm under the condition of small motion error. Figure 3 (b) is a two-dimensional slice diagram of the edge point target based on the RDA algorithm of the "two-step MOCO" under the condition of small motion error. It can be seen that the large-space-variable motion error compensation method based on the airship platform SAR proposed in the embodiment of the present invention has slight defocusing at some edge points. Figure 3(c) and (d) are two cases in which the motion error is large. As the motion error becomes larger, the focusing effect of the traditional RDA algorithm based on "two-step MOCO" becomes worse, and there is no compensation for cross-coupling and scene variation, while the proposed algorithm can effectively correct it.

[0120] The embodiment of the present invention fits the various-order motion parameters of the target through an inertial navigation system (INS), describes the motion error as a cross-coupled space-varying error and a non-space-varying error, and can accurately describe the motion error of the platform. Compared with the prior art, the present invention can more accurately perform scene space-varying correction when facing large motion errors, especially the cross-coupling problem of heading and tangent heading motion errors. Consistency compensation is performed on the non-space-varying error in the range-frequency domain, the space-varying error is two-dimensionally decoupled by the Lagrange mean method, and the nonlinear scale transformation is implemented by CZT transformation for compensation and correction. Compared with the traditional non-parametric compensation method, the present invention greatly reduces the amount of calculation. This feature enables the present invention to maintain a high computational efficiency when processing wide-width SAR data, meet the actual needs of airship platform SAR imaging under wide-width and high-precision requirements, especially in real-time imaging and engineering applications, and can significantly improve the speed and effect of data processing.

[0121] From the application level, in addition, the technology of the embodiments of the present invention can also be widely used in natural disaster monitoring, environmental protection, urban planning, agricultural monitoring, etc. Especially after a natural disaster occurs, the airship platform can quickly build a monitoring network without the support of ground infrastructure, obtain real-time images of the disaster area, and provide rescue decision support. With the continuous maturity of technology and the expansion of application scenarios, the airship platform SAR system is expected to become an important part of future information scene applications.

[0122] In summary, the embodiments of the present invention not only expand the application boundaries of traditional SAR technology by improving the stability, accuracy and adaptability of the SAR imaging system, but also greatly enhance the information acquisition and response capabilities in various fields, providing strong support for my country's modern security protection.

[0123] It should be noted that in the description of the present invention, it should be understood that the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0124] The above description is only a preferred embodiment of the present invention and is not intended to limit the protection scope of the present invention. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention are included in the protection scope of the present invention.

Claims

1. A method for compensating large-scale air-variable motion errors based on airship platform SAR, characterized in that: include: Get the target echo signal at any point; Fitting the various order motion parameters of the target through the inertial navigation system to obtain the fitting error; Based on the fitting error, the motion error of the target in the arbitrary point target echo signal is described as a non-space-varying error and a space-varying error, and the target echo signal after pulse compression is obtained; Performing consistency compensation on the non-space-varying error in the target echo signal after pulse compression in the range frequency domain to obtain a target echo signal after consistent compensation; The space-varying error in the target echo signal after consistent compensation is decoupled in two dimensions by Lagrangian mean method to obtain the decoupled target echo signal; The space-varying error in the decoupled target echo signal is compensated step by step based on CZT transformation, and the target echo signal after step compensation is subjected to two-dimensional IFFT to obtain the imaging result.

2. The method for compensating large-scale space-variable motion errors based on airship platform SAR according to claim 1, characterized in that: The expression of the arbitrary point target echo signal is as follows: Where t represents the fast time variable, t a represents the azimuth slow time variable, r1 represents the slant distance vector from any point to the platform at the reference time, λ represents the wavelength of the transmitted signal, τ represents the delay time of the received signal, j represents the imaginary unit, c represents the speed of light, μ represents the range modulation frequency, exp() represents the exponential operation with the natural constant e as the base, represents the real instantaneous slope distance corresponding to any point, w r () represents the distance envelope, w a () indicates the azimuth envelope.

3. The method for compensating large-scale space-variable motion errors based on airship platform SAR according to claim 1, characterized in that: The method of fitting the various order motion parameters of the target by the inertial navigation system to obtain the fitting error includes: The velocity information of the target is obtained through the inertial navigation system, and the motion parameters of each order corresponding to the target are obtained by linear fitting; According to the motion parameters of each order corresponding to the target, the instantaneous slope distance of the reference point and the slope distance history vector of any point are obtained; The fitting error is obtained based on the instantaneous slope distance of the reference point and the slope distance history vector of any point.

4. The method for compensating large-scale space-variable motion errors based on airship platform SAR according to claim 1, characterized in that: The fitting error includes the fitting error corresponding to any point and the fitting error corresponding to the reference point; wherein, The expression of the fitting error corresponding to the arbitrary point is as follows: The expression of the fitting error corresponding to the reference point is as follows: Among them, t a represents the azimuth slow time variable, represents the real instantaneous slant distance corresponding to any point, r1 represents the slant distance vector from any point to the platform at the reference time, R(t a ,r1) represents the slope distance vector of any point, v represents the velocity, a0 represents the first-order acceleration, a1 represents the second-order acceleration, represents the real instantaneous slant distance corresponding to the reference point, r0 represents the slant distance vector from the reference point to the platform at the reference time, R(t a ,r0) represents the instantaneous slope distance of the reference point.

5. The method for compensating large-scale space-variable motion errors based on airship platform SAR according to claim 1, characterized in that: The expression of the target echo signal after pulse compression is as follows: Among them, s1(f r ,t a ) represents the target echo signal after pulse compression, f r represents the distance frequency, t a represents the azimuth slow time variable, j represents the imaginary unit, and f c represents the carrier frequency, c represents the speed of light, exp() represents the exponential operation based on the natural constant e, R(t a ,r1) represents the slant distance vector of any point, r1 represents the slant distance vector from any point to the platform at the reference time, represents the real instantaneous slant distance corresponding to the reference point, r0 represents the slant distance vector from the reference point to the platform at the reference time, R(t a ,r0) represents the instantaneous slope distance of the reference point.

6. The method for compensating large-scale space-variable motion errors based on airship platform SAR according to claim 1, characterized in that: The compensation function for consistency compensation is as follows: Among them, f r represents the distance frequency, t a represents the azimuth slow time variable, j represents the imaginary unit, and f c represents the carrier frequency, c represents the speed of light, and exp() represents the exponential operation based on the natural constant e. It represents the real instantaneous slant distance corresponding to the reference point, and r0 represents the slant distance vector from the reference point to the platform at the reference time.

7. The method for compensating large-scale space-variable motion errors based on airship platform SAR according to claim 1, characterized in that: The expression of the target echo signal after the consistent compensation is as follows: Among them, f r represents the distance frequency, t a represents the azimuth slow time variable, j represents the imaginary unit, and f c represents the carrier frequency, c represents the speed of light, exp() represents the exponential operation based on the natural constant e, R(t a ,r1) represents the slant distance vector of any point, r1 represents the slant distance vector from any point to the platform at the reference time, R(t a ,r0) represents the instantaneous slant distance of the reference point, and r0 represents the slant distance vector from the reference point to the platform at the reference time.

8. The method for compensating large-scale space-variable motion errors based on airship platform SAR according to claim 1, characterized in that: The method of performing two-dimensional decoupling of the space-varying error in the target echo signal after consistent compensation by the Lagrangian mean method to obtain the decoupled target echo signal includes: Based on the Lagrange mean method, the space-varying error in the target echo signal after consistent compensation is orthogonally expanded to obtain the expanded space-varying error; The gradient of the expanded space-varying error is calculated to obtain a decoupled target echo signal.

9. The method for compensating large-scale space-variable motion errors based on airship platform SAR according to claim 1, characterized in that: The expression of the decoupled target echo signal is as follows: Among them, f r represents the distance frequency, t a represents the azimuth slow time variable, exp() represents the exponential operation with the natural constant e as the base, j represents the imaginary unit, and f c represents the carrier frequency, c represents the speed of light, g=|r1|-|r0|, represents the partial derivative operation, r0 represents the slant distance vector from the reference point to the platform at the reference time, |r0| represents the slant distance from the reference point to the platform at the reference time, represents the Doppler center from the platform to the reference point at the reference time, r1 represents the slant distance vector from any point to the platform at the reference time, |r1| represents the slant distance from any point to the platform at the reference time, and f dc represents the Doppler center from the platform to any point at the reference time, R(|r1|,f dc ) represents the slant distance |r1| from the platform to any point at the reference time and the Doppler center f dc The binary implicit function of .

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