Method and device for compensating two-dimensional time-varying error of azimuth multichannel synthetic aperture radar

Abstract

The invention provides an azimuth multichannel synthetic aperture radar two-dimensional time-varying error compensation method and device, which can be applied to the technical field of radars. The method comprises the following steps: estimating and compensating the attitude error of each channel according to the attitude information and velocity vector of the flight process of an aircraft carrying a synthetic aperture radar; doppler centers of sampling point echoes in different distance directions of each channel are calculated by adopting a vector method, channel pattern errors are estimated, and the pattern errors are compensated by utilizing an amplitude equalization method; performing two-dimensional Fourier transform on the echo of the channel after the attitude error and directional diagram error compensation is completed to obtain a two-dimensional frequency domain echo; performing two-dimensional frequency domain echo interference on the two-dimensional frequency domain echo, and estimating and compensating the distance time delay error of each channel; and performing two-dimensional frequency domain echo interference on the two-dimensional frequency domain echoes of the channels after distance time delay error compensation, and estimating and compensating the fixed phase error of each channel. Therefore, various actual errors of the channel are compensated, the image quality is improved, and the method is suitable for small-squint-angle signal reconstruction and imaging.

Description

Technical Field

[0001] The present disclosure relates to the field of radar technology, and more particularly, to a two-dimensional time-varying error compensation method and device for an azimuth multi-channel synthetic aperture radar. Background Art

[0002] Imaging systems with high resolution and wide swath modes are an important development trend for future synthetic aperture radar (SAR) systems. However, traditional single-channel SARs are restricted by the minimum antenna area, and it is impossible to simultaneously meet the requirements of high resolution and wide swath imaging. High resolution in the azimuth direction requires a large Doppler bandwidth, and the system pulse repetition frequency needs to be greater than the Doppler bandwidth to ensure non-ambiguous images. However, a large system pulse repetition frequency will result in a reduction in the imaging swath width. To solve this contradiction, azimuth multi-channel SAR systems have been proposed, which can reduce the system's requirements for the system pulse repetition frequency. However, the above methods are all proposed on the premise of assuming no various actual errors. The actual airborne azimuth multi-channel SAR system is affected by various factors such as aircraft vibration, atmospheric turbulence, and system errors, resulting in an unsatisfactory imaging result after azimuth multi-channel reconstruction and serious azimuth ambiguity.

[0003] To correct the azimuth multi-channel errors of the actual system, various error estimation methods have been proposed. Chen et al. proposed an internal calibration method that uses an additional system to obtain channel errors, but this method greatly increases the complexity of the system and has a low cost performance in the actual system. Feng et al. proposed the azimuth cross-correlation method, which can quickly and effectively estimate channel errors, but its performance highly depends on the estimation of the Doppler center. Other scholars have also proposed to use the property that the noise subspace is orthogonal to the signal subspace to achieve inter-channel error estimation under the condition of azimuth undersampling. However, such methods require redundant channels, which will make the actual SAR system more complex. In the image domain methods, Zhang et al. proposed a channel error correction method based on weighted minimum entropy, which uses the coarsely focused image to estimate the phase error. However, similar to other image domain algorithms, it still needs to further perform imaging processing to obtain a non-ambiguous and finely focused image, and the time cost of repeated imaging is relatively large. Summary of the Invention

[0004] In view of the above problems, the present disclosure provides a two-dimensional time-varying error compensation method and device for an azimuth multi-channel synthetic aperture radar that compensates for various actual errors of channels and improves image quality.

[0005] According to a first aspect of the present disclosure, a two-dimensional time-varying error compensation method for an azimuth multi-channel synthetic aperture radar is provided, including: estimating and compensating the attitude errors of each channel of the synthetic aperture radar according to the attitude information and velocity vector of the aircraft carrying the synthetic aperture radar during flight; calculating the Doppler center of the echoes of each channel at different range sampling points by the vector method, estimating the channel pattern error and compensating the pattern error by the amplitude equalization method; performing two-dimensional Fourier transform on the echoes of the channels after compensating the attitude error and the pattern error to obtain two-dimensional frequency-domain echoes; performing two-dimensional frequency-domain echo interference on the two-dimensional frequency-domain echoes to estimate the range delay errors of each channel and compensate them; performing two-dimensional frequency-domain echo interference on the two-dimensional frequency-domain echoes of the channels after compensating the range delay errors to estimate the fixed phase errors of each channel and compensate them.

[0006] According to an embodiment of the present disclosure, estimating the attitude errors of each channel of the synthetic aperture radar according to the attitude information and velocity vector of the aircraft carrying the synthetic aperture radar during flight includes:

[0007] Calculating the antenna axial vectors of each channel during the actual flight of the aircraft according to the attitude information of the aircraft carrying the synthetic aperture radar and the antenna axial vectors of each channel of the synthetic aperture radar under ideal conditions;

[0008] Calculating the velocity vectors of each channel during the actual flight of the aircraft according to the velocity vector;

[0009] Estimating the attitude errors of each channel according to the antenna axial vectors and velocity vectors of each channel during the actual flight of the aircraft.

[0010] According to an embodiment of the present disclosure, calculating the Doppler center of the echoes of each channel at different range sampling points by the vector method includes:

[0011] Establishing the line-of-sight vectors corresponding to each channel;

[0012] Calculating the Doppler center of the echoes of each channel at different range sampling points according to the line-of-sight vectors and the velocity vectors of each channel during the actual flight of the aircraft.

[0013] According to an embodiment of the present disclosure, compensating the pattern error by the amplitude equalization method includes:

[0014] Based on the Doppler center of the echoes of each range sampling point, performing amplitude equalization on the echoes of each range sampling point in the Doppler domain to complete the compensation of the channel pattern error.

[0015] According to an embodiment of the present disclosure, performing two-dimensional frequency-domain echo interference on the two-dimensional frequency-domain echoes to estimate the range delay errors of each channel includes:

[0016] The two-dimensional frequency-domain echoes of the reference channel in the two-dimensional frequency-domain echoes are respectively multiplied conjugately with the two-dimensional frequency-domain echoes of other non-reference channels, and the range-time delay errors of each channel are estimated according to the results of the conjugate multiplication.

[0017] According to an embodiment of the present disclosure, two-dimensional frequency-domain echo interference is performed on the two-dimensional frequency-domain echoes of the channels after range-time delay error compensation to estimate the fixed phase errors of each channel, including:

[0018] After each channel completes range-time delay error compensation, the two-dimensional frequency-domain echoes of the reference channel are respectively multiplied conjugately with the two-dimensional frequency-domain echoes of the non-reference channels again to obtain a plurality of impulse functions;

[0019] The phases of the plurality of impulse functions are respectively calculated, and the phases are used as the fixed phase errors of the corresponding channels.

[0020] According to an embodiment of the present disclosure, the method further includes:

[0021] Performing azimuth downsampling and range compression on the echoes of each channel;

[0022] Based on each channel after various error compensations, signal reconstruction is performed according to the range-compressed signal;

[0023] According to the attitude and position information of the reference channel, two-dimensional focusing is performed on the reconstructed signal by using the single-channel two-step motion compensation method to generate a reconstructed image.

[0024] Another aspect of the embodiments of the present disclosure provides an azimuth multi-channel synthetic aperture radar two-dimensional time-varying error compensation device, including:

[0025] An attitude error estimation and compensation module, configured to estimate and compensate the attitude errors of each channel of the synthetic aperture radar according to the attitude information and velocity vector of the aircraft carrying the synthetic aperture radar during flight;

[0026] A pattern error estimation and compensation module, configured to calculate the Doppler center of the echoes of each channel at different range sampling points by using a vector method, estimate the pattern errors of the channels, and compensate the pattern errors by using an amplitude equalization method;

[0027] A two-dimensional Fourier transform module, configured to perform two-dimensional Fourier transform on the echoes of the channels after attitude error and pattern error compensation to obtain two-dimensional frequency-domain echoes;

[0028] A range-time delay error estimation and compensation module, configured to perform two-dimensional frequency-domain echo interference on the two-dimensional frequency-domain echoes to estimate and compensate the range-time delay errors of each channel;

[0029] The fixed phase error estimation and compensation module is used to perform two-dimensional frequency domain echo interference on the two-dimensional frequency domain echo of the channel after range time delay error compensation, estimate the fixed phase error of each channel, and perform compensation.

[0030] One or more of the above embodiments have the following beneficial effects: It can at least partially solve the problems of azimuth ambiguity and poor reconstructed image quality caused by azimuth multi-channel errors, and thus can estimate and completely compensate for multi-channel errors caused by various factors in the actual scene, reduce azimuth ambiguity, and the complexity of this method is low, and the imaging time cost is small. It is especially suitable for signal reconstruction and imaging with small squint angles that are inevitable during actual flight. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Through the following description of the embodiments of the present disclosure with reference to the drawings, the above content and other objects, features, and advantages of the present disclosure will become clearer. In the drawings:

[0032] Figure 1 Schematically shows a flowchart of a two-dimensional time-varying error compensation method for azimuth multi-channel synthetic aperture radar according to an embodiment of the present disclosure;

[0033] Figure 2 Schematically shows a schematic diagram of an imaging geometric model of azimuth multi-channel synthetic aperture radar according to an embodiment of the present disclosure;

[0034] FIG. 3(a) schematically shows a schematic diagram of an image in the case of undersampling according to an embodiment of the present disclosure;

[0035] FIG. 3(b) schematically shows a schematic diagram of a reconstructed image generated without compensating multi-channel errors in the case of undersampling according to an embodiment of the present disclosure;

[0036] FIG. 3(c) schematically shows a schematic diagram of a reconstructed image generated by compensating multi-channel errors using a traditional error compensation method in the case of undersampling according to an embodiment of the present disclosure;

[0037] FIG. 3(d) schematically shows a schematic diagram of a reconstructed image generated by compensating multi-channel errors using the compensation method of the present disclosure in the case of undersampling according to an embodiment of the present disclosure;

[0038] Figure 4 Schematically shows a structural diagram of an azimuth multi-channel synthetic aperture radar two-dimensional time-varying error compensation device according to an embodiment of the present disclosure.

[0039] It should be noted that, for clarity, in the drawings used to describe the embodiments of the present disclosure, the size of the overall / local structure or the overall / local area may be enlarged or reduced, that is, these drawings are not drawn according to the actual scale. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0040] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present disclosure. In the following detailed description, for the sake of explanation, numerous specific details are set forth to provide a comprehensive understanding of the embodiments of the present disclosure. However, evidently, one or more embodiments can also be implemented without these specific details. In addition, in the following description, descriptions of well-known structures and technologies are omitted to avoid unnecessarily confusing the concepts of the present disclosure.

[0041] The terms used herein are merely for describing specific embodiments and are not intended to limit the present disclosure. The terms "including", "comprising", etc. used herein indicate the presence of the described features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0042] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0043] In the case of using expressions such as "at least one of A, B, and C, etc.", generally, it should be interpreted according to the meaning commonly understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include, but not be limited to, a system having only A, only B, only C, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.).

[0044] Embodiments of the present disclosure provide a method for compensating two-dimensional time-varying errors of an azimuth multi-channel synthetic aperture radar. This method completely compensates for channel errors caused by various factors such as the actual movement of the aircraft and system design, reduces azimuth ambiguity, and improves the image quality after signal reconstruction.

[0045] Figure 1 A flowchart of the method for compensating two-dimensional time-varying errors of an azimuth multi-channel synthetic aperture radar according to an embodiment of the present disclosure is schematically shown.

[0046] As Figure 1 shown, method 100 includes:

[0047] In operation S110, according to the attitude information and velocity vector of the aircraft carrying the synthetic aperture radar during flight, estimate the attitude errors of each channel of the synthetic aperture radar and perform compensation.

[0048] In some embodiments, during flight, an aircraft (such as an airplane) will inevitably have various attitude changes over time due to factors such as airflows and airframe vibrations. As a result, attitude errors will occur in the channels, and the manifestation of the attitude error is the slant range error. The slant range error will cause the azimuth-time-varying phase error in the echoes between channels. Therefore, the time-varying slant range error corresponds to the time-varying phase error.

[0049] In some embodiments, the attitude information includes attitude angles such as the roll angle, pitch angle, and heading angle of the airplane during flight; among them, the attitude information can be obtained through an inertial measurement unit (IMU) carried by the airplane.

[0050] In some embodiments, the velocity vector can also be obtained through the inertial measurement unit (IMU) carried by the airplane, and this velocity vector is a three-dimensional velocity vector.

[0051] In some embodiments, the vector method is used to estimate and compensate the attitude errors of each channel of the synthetic aperture radar, which can suppress the severe azimuth-time-varying phase error between channels.

[0052] In operation S120, the vector method is used to calculate the Doppler center of the echoes of the sampling points in different range bins of each channel, estimate the channel pattern error, and compensate the pattern error using the amplitude equalization method.

[0053] In some embodiments, in an actual system, due to the differences between the antenna design and manufacturing on the synthetic aperture radar, the antenna patterns of different channels cannot be exactly the same, and there will be amplitude and envelope errors. Considering the variation of the down-looking angle in a wide-swath scenario, the main differences in the patterns of different channels lie in the amplitude and beam width. When the imaging swath is large, the variation of the down-looking angle corresponding to different ranges is large, and the echoes at different ranges have different slant angles. Therefore, the pattern compensation of the channels needs to vary with the range gate. Thus, the pattern errors of each channel are estimated and compensated in the Doppler domain of the echoes. Based on this, this embodiment proposes using the vector method to calculate the Doppler center of the echoes of the sampling points in different range bins of each channel, estimating the amplitude error of the channel pattern in the range time domain - azimuth frequency domain, and completing the compensation of the channel pattern error using the amplitude equalization method in the Doppler domain (or the azimuth frequency domain) based on the Doppler center of the echoes of the sampling points in different range bins.

[0054] In some embodiments, the influence of the pattern error on signal reconstruction is considered, especially in a wide-swath scenario, and corresponding estimation and compensation methods are proposed, further improving the quality of signal reconstruction.

[0055] In operation S130, the echoes of the channels for which the attitude error and pattern error compensation have been completed are subjected to two-dimensional Fourier transform to obtain two-dimensional frequency-domain echoes.

[0056] In some embodiments, there is also a time delay error between channels. Since the time delay of a signal in the time domain can be equivalent to a linear phase in the frequency domain, after compensating for the attitude error and the pattern error, the echoes of each channel are subjected to a two-dimensional Fourier transform to transform them into the two-dimensional frequency domain. In the two-dimensional frequency domain, the fixed phase error and the range delay error of each channel are estimated.

[0057] In operation S140, two-dimensional frequency domain echo interference is performed on the two-dimensional frequency domain echoes to estimate the range delay error of each channel and perform compensation.

[0058] In some embodiments, during the process of signal reconstruction, when sampling the echo signal, the sampling start times of different channels will be different, which will cause a fixed range delay error between channels. The attitude error mentioned above will also cause a non-fixed range delay error between channels. The fixed range delay error and the non-fixed range delay error are collectively referred to as the range delay error. When the attitude error compensation is completed, the non-fixed range delay error is also compensated. Therefore, the range delay error compensated by the two-dimensional frequency domain echo interference method later is actually the compensation for the fixed range delay error.

[0059] In operation S150, two-dimensional frequency domain echo interference is performed on the two-dimensional frequency domain echoes of the channels after range delay error compensation to estimate the fixed phase error of each channel and perform compensation.

[0060] In some embodiments, a channel is generally composed of a radio frequency circuit. There are differences in the performance of components such as amplifiers and mixers in the radio frequency circuits of different channels. This difference will cause amplitude and phase errors between channels. Since most of the amplitude errors have been compensated during the pattern error compensation process, the influence of the remaining amplitude errors on signal reconstruction is extremely small and can be ignored.

[0061] In some embodiments, the two-dimensional frequency domain echo interference method is used to estimate the range delay error and the fixed phase error of the channel, and it is not necessary to implement error estimation in the image domain, saving the time cost of separately imaging multiple channels.

[0062] Figure 2 Schematically shows a schematic diagram of the geometric model of azimuth multi-channel synthetic aperture radar imaging according to an embodiment of the present disclosure.

[0063] As Figure 2 shown, an aircraft carrying a synthetic aperture radar (SAR) flies along the X-axis. The direction indicated by the X-axis is the azimuth direction, and the direction indicated by the Y-axis perpendicular to the X-axis is the range direction. The transmit / receive channels of the synthetic aperture radar are an important part thereof. The synthetic aperture radar can adopt a working mode with one transmit channel and multiple receive channels. Figure 2 The transmit channel is represented by in It is shown that the flight altitude of the aircraft is , the number of channels is , the position coordinates of the ground point target are , represents the incident angle of the ground point target relative to the reference channel, represents the mapping bandwidth, represents the spacing between adjacent channels, 、 respectively represent the slant range history of the th receiving channel and the slant range history from the reference channel to the ground point target;

[0064] According to the equivalent phase center principle, the echo received by the channel during the flight of the aircraft can be expressed as:

[0065]

[0066] wherein, represents the range-time and the azimuth-time at the th receiving channel, represents the complex constant related to the th receiving channel, 、 、 、 、 、 are respectively the range window function, azimuth window function, speed of light, echo wavelength, radar flight speed, frequency modulation slope, 、 、 respectively represent the slant range history of the th receiving channel, the position of the th receiving channel relative to the reference channel, and the abscissa position of the ground point target; wherein, the reference channel can be a receiving channel or a transmitting channel;

[0067] Furthermore, ; ;

[0068]

[0069] wherein, represents the arrival direction angle of the echo in the azimuth direction. Furthermore, the arrival direction angles of the echoes of each channel are the same.

[0070] In some embodiments, ; wherein, represents the azimuth frequency.

[0071] In some embodiments, due to reasons such as atmospheric turbulence and aircraft vibration, the actual flight path of the aircraft is not an ideal straight line. The coordinates of points on the actual flight path of the aircraft can be expressed as , where , , respectively represent the motion errors of the aircraft on the X-axis, Y-axis, and Z-axis. Therefore, the actual slant range history from the reference channel to the ground point target is expressed as follows:

[0072]

[0073] where is the motion error of a single channel, and its approximate expression is:

[0074]

[0075] In some embodiments, if various errors such as motion error, attitude error, pattern error, range delay error, and fixed phase error of the above channels are not compensated, the time-domain echo signal after pulse compression is obtained by the following formula:

[0076]

[0077]

[0078] where represents the bandwidth of the echo signal, , , respectively represent the range delay error, fixed phase error, and time-varying phase error of the th receiving channel relative to the reference channel; further, the attitude error is reflected by the slant range error, and the slant range error will cause time-varying phase error. Therefore, the attitude error can be compensated by compensating the time-varying phase error.

[0079] In some embodiments, the motion error of the channel is compensated by a multi-channel signal model.

[0080] In some embodiments, in operation S110, according to the attitude information and velocity vector of the vehicle carrying the synthetic aperture radar during flight, the attitude error of each channel of the synthetic aperture radar is estimated, including:

[0081] Calculating the antenna axial vector of each channel during the actual flight of the vehicle according to the attitude information of the vehicle carrying the synthetic aperture radar during flight and the antenna axial vector of each channel of the synthetic aperture radar under ideal conditions;

[0082] Calculate the velocity vectors of each channel during the actual flight of the aircraft according to the velocity vectors.

[0083] Estimate the attitude errors of each channel according to the antenna axial vectors and velocity vectors of each channel during the actual flight of the aircraft.

[0084] For example, the attitude information of an aircraft during flight can be represented by an attitude matrix. The expression of the attitude matrix is as follows:

[0085]

[0086] where represents the roll angle of the aircraft at azimuth time , represents the pitch angle of the aircraft at azimuth time , represents the heading angle of the aircraft at azimuth time ;

[0087] Under ideal conditions, the antenna axial vector of a channel can be expressed as:

[0088] , where represents vector transpose;

[0089] Calculate the antenna axial vector of each channel during the actual flight of the aircraft according to the following formula:

[0090]

[0091] Since the actual motion trajectory of the aircraft is not a uniform straight line, the velocity vector of the th receiving channel should be expressed as:

[0092]

[0093] where is the three-dimensional velocity vector of the aircraft, and represents the modulo operation;

[0094] Furthermore, since there are differences between and , the attitude error that needs to be compensated can be obtained, that is,

[0095] , where represents the attitude error of the th receiving channel;

[0096] ​By converting the attitude error of the channel into the slant range error, the time-varying phase error of the channel can be obtained:

[0097]

[0098] wherein, represents the time-varying phase error of the th receiving channel, and respectively represent the Y-axis component and the Z-axis component of the attitude error of the th receiving channel, is the fixed slant range error of the th receiving channel inevitably caused during system installation.

[0099] In some embodiments, the time-varying phase error of the channel is compensated through a multi-channel signal model, thereby completing the compensation of the attitude error.

[0100] In some embodiments, after the attitude error is compensated, the pattern error of the channel is estimated; specifically, the time-domain pattern of the th receiving channel can be expressed as:

[0101]

[0102] wherein, represents the amplitude coefficient of , , , , respectively represent the azimuth beamwidth coefficient, the azimuth beamwidth, the azimuth arrival direction angle of the echo, and the azimuth slant angle at the range time ;

[0103] Since the pattern compensation needs to vary with the range gate, the parameter can be used to represent the Doppler center corresponding to , and the pattern error of the channel is estimated in the Doppler domain;

[0104] Further, the Doppler center corresponding to the channel within a period of azimuth time is considered to be constant, and the result of averaging the antenna axial vector of the channel along the azimuth time is denoted as , and the vector method is used to calculate the Doppler center varying in the range direction.

[0105] In some embodiments, in operation S120, the vector method is used to calculate the Doppler center of the echoes of the sampling points in different range directions of each channel, including:

[0106] Establish the line-of-sight vectors corresponding to each channel;

[0107] Calculate the Doppler center of the echoes from the sampling points at different distances in each channel according to the line-of-sight vector and the velocity vectors of each channel during the actual flight of the aircraft.

[0108] In some embodiments, the line-of-sight vector is defined as , 、 are the components of the line-of-sight vector on the X-axis and Y-axis respectively; represents the range-time, corresponding to the sampling points at different range bins;

[0109] Furthermore, is also defined as the slant range of the echo varying with the range bin, that is:

[0110]

[0111] Since the line-of-sight vector is perpendicular to , the vector inner product of these two is 0, and thus the calculation formula of is as follows:

[0112]

[0113] Wherein, 、 、 represent the axis components of the vector respectively;

[0114] Based on the line-of-sight vector and the velocity vector of the channel during the flight of the aircraft, calculate the Doppler center of the channel echo, and the calculation formula is as follows:

[0115]

[0116] In some embodiments, in operation S120, compensating the pattern error by using the amplitude equalization method includes:

[0117] Based on the Doppler center of the echoes from the sampling points at different range bins, perform amplitude equalization on the echoes of each sampling point in the Doppler domain to complete the compensation of the channel pattern error;

[0118] Furthermore, the above amplitude equalization method is used to compensate the channel pattern error through the multi-channel signal model.

[0119] In some embodiments, after completing the compensation of the attitude error and the pattern error, the echo signals of the channels with fixed amplitude-phase error and range-delay error can be expressed as:

[0120]

[0121] Among them, and are respectively the two-dimensional frequency-domain echoes of the th receiving channel and the two-dimensional frequency-domain echo of the reference channel after completion of attitude error and pattern error compensation. is the range frequency, is the azimuth time delay, which depends on the channel interval . After completion of attitude error compensation, the time-varying part in has been compensated. Therefore, next, only the fixed delay error in needs to be estimated.

[0122] In some embodiments, in operation S140, two-dimensional frequency-domain echo interference is performed on the two-dimensional frequency-domain echo to estimate the range time delay error of each channel, including:

[0123] The two-dimensional frequency-domain echo of the reference channel in the two-dimensional frequency-domain echo is respectively conjugated and multiplied with the two-dimensional frequency-domain echoes of other non-reference channels, and based on the result of the conjugated multiplication, the range time delay error of each channel is estimated.

[0124] For example, conjugating and multiplying and can obtain the range time delay error of the th receiving channel. The following formula is specifically used for conjugated multiplication:

[0125]

[0126] Among them, represents two-dimensional Fourier transform, represents two-dimensional FFT, represents the conjugation operation, represents the Hadamard product;

[0127] The obtained range time delay error of the th receiving channel is expressed as:

[0128]

[0129] Among them, represents the number of rows of, represents the sampling frequency, represents the first index of the position of the maximum amplitude in the complex matrix .

[0130] In some embodiments, the range time delay error of the channel is compensated through a multi-channel signal model.

[0131] In some embodiments, in operation S150, two-dimensional frequency-domain echo interference is performed on the two-dimensional frequency-domain echo of the channel after range-time delay error compensation to estimate the fixed phase error of each channel, including:

[0132] After each channel completes range-time delay error compensation, the two-dimensional frequency-domain echo of the reference channel is conjugated and multiplied with the two-dimensional frequency-domain echo of the non-reference channel again to obtain a plurality of impulse functions;

[0133] Calculate the phases of the plurality of impulse functions respectively, and use the phases as the fixed phase errors of the corresponding channels.

[0134] For example, after each channel completes range-time delay error compensation, according to the above conjugate multiplication formula for and perform conjugate multiplication again to obtain the fixed phase error corresponding to the th receiving channel. The two-dimensional frequency domain corresponding to the fixed phase is an impulse function. Multiple receiving channels correspond to multiple impulse functions. The phase of the impulse function is the fixed phase error of the channel relative to the reference channel. Taking the th receiving channel as an example, its fixed phase error can be expressed as:

[0135]

[0136] where, represents the second index of the position of the maximum amplitude in the complex matrix , and represents taking the phase of the complex number.

[0137] In some embodiments, the fixed phase error of the channel is compensated by a multi-channel signal model.

[0138] In some embodiments, method 100 further includes:

[0139] Perform azimuth downsampling and range compression on the echo of each channel;

[0140] Based on each channel after various error compensations, perform signal reconstruction according to the range-compressed signal;

[0141] According to the attitude and position information of the reference channel, use the single-channel two-step motion compensation method to perform two-dimensional focusing on the reconstructed signal to generate a reconstructed image.

[0142] In some embodiments, by performing azimuth downsampling and range compression on the echoes of each channel, compensating for the errors of each channel using the error compensation method of Method 100, reconstructing the signal after range compression, combining the signals of each channel after error compensation into one signal, finally obtaining the attitude information and position information of the reference channel according to the inertial measurement unit (IMU), performing two-dimensional focusing on the reconstructed signal using the single-channel two-step motion compensation method to generate a reconstructed image, and verifying the error compensation effect of Method 100 according to the quality of the reconstructed image. After verification, the error compensation effect of Method 100 is very good, which can greatly reduce the blurred energy of the image. Therefore, Method 100 can be used in scenarios such as radar imaging; the error compensation mentioned here refers to all error compensation methods such as attitude error compensation, pattern error compensation, range delay error compensation, and fixed phase error compensation; the attitude information of the reference channel includes roll angle, pitch angle, and heading angle.

[0143] The effectiveness of the error estimation and compensation method proposed by Method 100 is verified using three-channel echo data. The reconstructed images obtained using Method 100 are respectively compared with the reconstructed images obtained using traditional compensation methods, the reconstructed images generated without error compensation, and the images obtained without error compensation and without signal reconstruction, as shown in Figures 3(a) - 3(d). It can be seen from the figures that the image obtained without error compensation and without signal reconstruction (Figure 3(a)) has a large amount of azimuth ambiguity and is difficult to identify. The reconstructed image generated without error compensation (Figure 3(b)) still has a lot of azimuth ambiguity and has not been significantly improved. The reconstructed image obtained using traditional compensation methods (Figure 3(c)) greatly suppresses the azimuth ambiguity. For example, the azimuth ambiguity in area A of the picture is well suppressed and area A is clearer, but there is still residual azimuth ambiguity in the picture and the suppression is incomplete. However, the azimuth ambiguity of the reconstructed image obtained using Method 100 (Figure 3(d)) is basically completely suppressed, presenting an observable two-dimensional image effect. This shows that the error estimation and compensation method proposed by Method 100 can greatly suppress the blurred phenomenon of the reconstructed picture and improve the image quality.

[0144] It should be noted that some steps of the above method can be executed independently or in combination, and can be executed in parallel or sequentially, and are not limited to the specific operation sequence shown in the figure.

[0145] Based on the above azimuth multi-channel synthetic aperture radar two-dimensional time-varying error compensation method, the present disclosure also provides an azimuth multi-channel synthetic aperture radar two-dimensional time-varying error compensation device. The following will be combined with Figure 4 Describe this device in detail.

[0146] Figure 4 Schematically shows the structural diagram of the azimuth multi-channel synthetic aperture radar two-dimensional time-varying error compensation device according to an embodiment of the present disclosure.

[0147] Figure 4 Schematically shows a structural block diagram of an azimuth multi-channel synthetic aperture radar two-dimensional time-varying error compensation device according to an embodiment of the present disclosure.

[0148] As Figure 4 shown, the device 400 of this embodiment includes an attitude error estimation and compensation module 410, a pattern error estimation and compensation module 420, a two-dimensional Fourier transform module 430, a range delay error estimation and compensation module 440, and a fixed phase error estimation and compensation module 450.

[0149] The attitude error estimation and compensation module 410 is configured to estimate and compensate the attitude errors of each channel of the synthetic aperture radar according to the attitude information and velocity vector of the aircraft carrying the synthetic aperture radar during flight. In one embodiment, the attitude error estimation and compensation module 410 can be used to perform the operation S110 described above, which will not be elaborated here.

[0150] The pattern error estimation and compensation module 420 is configured to calculate the Doppler center of the echoes of the sampling points in different range directions of each channel by using the vector method, estimate the channel pattern error, and compensate the pattern error by using the amplitude equalization method. In one embodiment, the pattern error estimation and compensation module 420 can be used to perform the operation S120 described above, which will not be elaborated here.

[0151] The two-dimensional Fourier transform module 430 is configured to perform a two-dimensional Fourier transform on the echoes of the channels after compensating for the attitude error and the pattern error to obtain two-dimensional frequency domain echoes. In one embodiment, the two-dimensional Fourier transform module 430 can be used to perform the operation S130 described above, which will not be elaborated here.

[0152] The range delay error estimation and compensation module 440 is configured to perform two-dimensional frequency domain echo interference on the two-dimensional frequency domain echoes to estimate and compensate the range delay errors of each channel. In one embodiment, the range delay error estimation and compensation module 440 can be used to perform the operation S140 described above, which will not be elaborated here.

[0153] The fixed phase error estimation and compensation module 450 is configured to perform two-dimensional frequency domain echo interference on the two-dimensional frequency domain echoes of the channels after compensating for the range delay error to estimate and compensate the fixed phase errors of each channel. In one embodiment, the fixed phase error estimation and compensation module 450 can be used to perform the operation S150 described above, which will not be elaborated here.

[0154] According to an embodiment of the present disclosure, the device 400 can achieve the effects of reducing the blurred energy of the reconstructed image and improving the quality of the reconstructed image, and is more suitable for signal reconstruction and imaging with a small squint angle.

[0155] For parts not mentioned in the device section, they can be understood by referring to the various embodiments of the above method. That is, the device section includes modules respectively used to execute the steps of any one of the method embodiments described above. Moreover, the implementation manners, the technical problems solved, the functions achieved, and the technical effects achieved by each module / unit / sub-unit, etc. in the device section embodiments are respectively the same as or similar to those of the corresponding steps in the method section embodiments, and will not be elaborated here.

[0156] According to an embodiment of the present disclosure, any multiple modules among the attitude error estimation and compensation module 410, the pattern error estimation and compensation module 420, the two-dimensional Fourier transform module 430, the range-delay error estimation and compensation module 440, and the fixed phase error estimation and compensation module 450 can be combined and implemented in one module, or any one of them can be split into multiple modules. Or, at least part of the functions of one or more of these modules can be combined with at least part of the functions of other modules and implemented in one module.

[0157] The flowcharts and block diagrams in the accompanying drawings illustrate the possible architectures, functions, and operations of the methods and devices according to various embodiments of the present disclosure. In this regard, each block in the flowchart or block diagram may represent a part of a method step or a module. It should also be noted that in some alternative implementations, the functions marked in the blocks may occur in a different order from that marked in the accompanying drawings. For example, two consecutive blocks shown may actually be executed substantially in parallel, and they may sometimes be executed in the reverse order, depending on the functions involved.

[0158] Those skilled in the art can understand that the features described in the various embodiments of the present disclosure can be combined and / or combined in various ways, even if such combinations or combinations are not explicitly described in the present disclosure. In particular, without departing from the spirit and teachings of the present disclosure, the features described in the various embodiments of the present disclosure can be combined and / or combined in various ways. All such combinations and / or combinations fall within the scope of the present disclosure.

[0159] The above describes the embodiments of the present disclosure. However, these embodiments are only for illustrative purposes and do not limit the scope of the present disclosure. Although the embodiments are described separately above, this does not mean that the measures in each embodiment cannot be used advantageously in combination. The scope of the present disclosure is defined by the appended claims and their equivalents. Without departing from the scope of the present disclosure, those skilled in the art can make various substitutions and modifications, and all such substitutions and modifications should fall within the scope of the present disclosure.

Claims

1. A two-dimensional time-varying error compensation method for azimuth multi-channel synthetic aperture radar, characterized in that The method includes: Estimating and compensating the attitude errors of each channel of the synthetic aperture radar according to the attitude information and velocity vector of the aircraft carrying the synthetic aperture radar during flight; Calculating the Doppler center of the echoes of sampling points in different range directions of each channel by using the vector method, estimating the channel pattern error, and compensating the pattern error by using the amplitude equalization method; Performing two-dimensional Fourier transform on the echoes of the channels after compensating the attitude error and pattern error to obtain two-dimensional frequency-domain echoes; Performing two-dimensional frequency-domain echo interference on the two-dimensional frequency-domain echoes to estimate the range time-delay errors of each channel and compensating them; Performing two-dimensional frequency-domain echo interference on the two-dimensional frequency-domain echoes of the channels after compensating the range time-delay errors to estimate the fixed phase errors of each channel and compensating them.

2. The method according to claim 1, wherein The estimating the attitude errors of each channel of the synthetic aperture radar according to the attitude information and velocity vector of the aircraft carrying the synthetic aperture radar during flight includes: Calculating the antenna axial vectors of each channel during the actual flight of the aircraft according to the attitude information of the aircraft carrying the synthetic aperture radar during flight and the antenna axial vectors of each channel of the synthetic aperture radar under ideal conditions; Calculating the velocity vectors of each channel during the actual flight of the aircraft according to the velocity vector; Estimating the attitude errors of each channel according to the antenna axial vectors and velocity vectors of each channel during the actual flight of the aircraft.

3. The method according to claim 2, characterized in that, The calculating the Doppler center of the echoes of sampling points in different range directions of each channel by using the vector method includes: Establishing the line-of-sight vectors corresponding to each channel; Calculating the Doppler center of the echoes of sampling points in different range directions of each channel according to the line-of-sight vectors and the velocity vectors of each channel during the actual flight of the aircraft.

4. The method according to claim 3, characterized in that, The compensating the pattern error by using the amplitude equalization method includes: Based on the Doppler center of the echoes of sampling points in different range directions, performing amplitude equalization on the echoes of each sampling point in the Doppler domain to complete the compensation of the channel pattern error.

5. The method according to claim 1, wherein The performing two-dimensional frequency-domain echo interference on the two-dimensional frequency-domain echoes to estimate the range time-delay errors of each channel includes: Multiplying the two-dimensional frequency-domain echo of the reference channel in the two-dimensional frequency-domain echoes by the conjugate of the two-dimensional frequency-domain echoes of other non-reference channels respectively, and estimating the range time-delay errors of each channel according to the results of the conjugate multiplication.

6. The method according to claim 5, wherein The performing two-dimensional frequency-domain echo interference on the two-dimensional frequency-domain echoes of the channels after compensating the range time-delay errors to estimate the fixed phase errors of each channel includes: After each channel completes the compensation of the range time-delay error, multiplying the two-dimensional frequency-domain echo of the reference channel by the conjugate of the two-dimensional frequency-domain echoes of non-reference channels respectively again to obtain a plurality of impulse functions; Calculating the phases of the plurality of impulse functions respectively, and taking the phases as the fixed phase errors of the corresponding channels.

7. The method according to claim 1, characterized in that The method further includes: Performing azimuth downsampling and range compression on the echoes of each channel; Based on each channel after various error compensations, performing signal reconstruction according to the range-compressed signal; According to the attitude and position information of the reference channel, performing two-dimensional focusing on the reconstructed signal by using the single-channel two-step motion compensation method to generate a reconstructed image.

8. An azimuth multi-channel synthetic aperture radar two-dimensional time-varying error compensation device, characterized in that, The device includes: An attitude error estimation and compensation module, which is used to estimate and compensate the attitude errors of each channel of the synthetic aperture radar according to the attitude information and velocity vector of the aircraft carrying the synthetic aperture radar during flight; A pattern error estimation and compensation module, which is used to calculate the Doppler center of the echoes of the sampling points in different range directions of each channel by using the vector method, estimate the channel pattern error and compensate the pattern error by using the amplitude equalization method; A two-dimensional Fourier transform module, which is used to perform a two-dimensional Fourier transform on the echoes of the channels that have completed attitude error and pattern error compensation to obtain two-dimensional frequency-domain echoes; A range delay error estimation and compensation module, which is used to perform two-dimensional frequency-domain echo interference on the two-dimensional frequency-domain echoes to estimate and compensate the range delay errors of each channel; A fixed phase error estimation and compensation module, which is used to perform two-dimensional frequency-domain echo interference on the two-dimensional frequency-domain echoes of the channels after range delay error compensation to estimate and compensate the fixed phase errors of each channel.

Images