A method and device for compensating two-dimensional time-varying errors in azimuth multi-channel synthetic aperture radar

Abstract

This disclosure provides a two-dimensional time-varying error compensation method and apparatus for azimuth multi-channel synthetic aperture radar, applicable to the field of radar technology. The method includes: estimating and compensating for the attitude error of each channel based on the attitude information and velocity vector of the aircraft carrying the synthetic aperture radar during flight; calculating the Doppler center of the echoes from different range sampling points of each channel using a vector method, estimating the channel pattern error, and compensating for the pattern error using an amplitude equalization method; performing a two-dimensional Fourier transform on the echoes of the channels after attitude and pattern error compensation to obtain two-dimensional frequency domain echoes; performing two-dimensional frequency domain echo interferometry on the two-dimensional frequency domain echoes to estimate and compensate for the range delay error of each channel; and performing two-dimensional frequency domain echo interferometry on the two-dimensional frequency domain echoes of the channels after range delay error compensation to estimate and compensate for the fixed phase error of each channel. This compensates for various actual errors in the channels, improves image quality, and is suitable for small oblique angle signal reconstruction and imaging.

Description

Technical Field

[0001] This disclosure relates to the field of radar technology, and more specifically, to a two-dimensional time-varying error compensation method and apparatus for azimuth multi-channel synthetic aperture radar. Background Technology

[0002] High-resolution and wide-swath imaging systems are a crucial trend in the future development of synthetic aperture radar (SAR) systems. However, traditional single-channel SAR is constrained by the minimum antenna area, making it impossible to simultaneously achieve high resolution and wide swath imaging. High azimuth resolution requires a large Doppler bandwidth, and the system pulse repetition frequency needs to be greater than the Doppler bandwidth to ensure a blur-free image. However, a large system pulse repetition frequency leads to a reduction in the imaging swath width. To resolve this contradiction, azimuth multi-channel SAR systems have been proposed, which can reduce the system's requirement for system pulse repetition frequency. However, the above methods are proposed under the assumption of no practical errors. In reality, airborne azimuth multi-channel SAR systems are affected by various factors such as aircraft vibration, atmospheric turbulence, and system errors, resulting in unsatisfactory imaging results after azimuth multi-channel reconstruction and severe azimuth ambiguity.

[0003] To correct azimuth multi-channel errors in practical systems, various error estimation methods have been proposed. Chen et al. proposed an internal calibration method using an additional system to obtain channel errors, but this method significantly increases system complexity and has low cost-effectiveness in practical systems. Feng et al. proposed an azimuth cross-correlation method, which can quickly and effectively estimate channel errors, but its performance is heavily dependent on the estimation of the Doppler center. Other scholars have proposed using the orthogonality between the noise subspace and the signal subspace to achieve inter-channel error estimation under azimuth undersampling conditions; however, these methods require redundant channels, making practical SAR systems more complex. In image domain methods, Zhang et al. proposed a channel error correction method based on weighted minimum entropy, using coarsely focused images to estimate phase errors. However, similar to other image domain algorithms, further imaging processing is required to obtain a blurred, finely focused image, resulting in a high time cost for repeated imaging. Summary of the Invention

[0004] In view of the above problems, this disclosure provides a two-dimensional time-varying error compensation method and apparatus for azimuth multi-channel synthetic aperture radar to compensate for various actual errors in the channels and improve image quality.

[0005] According to the first aspect of this disclosure, a two-dimensional time-varying error compensation method for a multi-channel synthetic aperture radar is provided, comprising: estimating and compensating for the attitude error of each channel of the synthetic aperture radar based on the attitude information and velocity vector of the aircraft carrying the synthetic aperture radar during flight; calculating the Doppler center of the echoes from different range sampling points of each channel using a vector method, estimating the channel pattern error, and compensating for the pattern error using an amplitude equalization method; performing a two-dimensional Fourier transform on the echoes of the channels for which attitude and pattern errors have been compensated to obtain two-dimensional frequency domain echoes; performing two-dimensional frequency domain echo interferometry on the two-dimensional frequency domain echoes to estimate and compensate for the range delay error of each channel; and performing two-dimensional frequency domain echo interferometry on the two-dimensional frequency domain echoes of the channels after range delay error compensation to estimate and compensate for the fixed phase error of each channel.

[0006] According to embodiments of this disclosure, the attitude error of each channel of the synthetic aperture radar is estimated based on the attitude information and velocity vector of the aircraft equipped with synthetic aperture radar during flight, including:

[0007] Based on the attitude information of the aircraft equipped with synthetic aperture radar during flight and the antenna axial vectors of each channel of the synthetic aperture radar under ideal conditions, the antenna axial vectors of each channel of the aircraft during actual flight are calculated.

[0008] Calculate the velocity vector of each channel during the actual flight of the aircraft based on the velocity vector;

[0009] Based on the antenna axial vector and velocity vector of each channel during the actual flight of the aircraft, the attitude error of each channel is estimated.

[0010] According to embodiments of this disclosure, the Doppler center of the echo from the sampling point at different distances in each channel is calculated using a vector method, including:

[0011] Establish the line-of-sight vectors for each channel;

[0012] Based on the line-of-sight vector and the velocity vector of each channel during the actual flight of the aircraft, the Doppler center of the echo from the sampling point at different distances of each channel is calculated.

[0013] According to embodiments of this disclosure, compensating for pattern errors using the amplitude equalization method includes:

[0014] Based on the Doppler center of the echoes from sampling points at different ranges, amplitude equalization is performed on the echoes from each sampling point in the Doppler domain to compensate for channel pattern errors.

[0015] According to embodiments of this disclosure, two-dimensional frequency domain echo interferometry is performed on the two-dimensional frequency domain echo to estimate the distance delay error of each channel, including:

[0016] The two-dimensional frequency domain echo of the reference channel in the two-dimensional frequency domain echo is multiplied by conjugate with the two-dimensional frequency domain echo of other non-reference channels respectively. Based on the conjugate multiplication result, the distance delay error of each channel is estimated.

[0017] According to embodiments of this disclosure, two-dimensional frequency domain echo interferometry is performed on the two-dimensional frequency domain echoes of the channels after distance delay error compensation to estimate the fixed phase error of each channel, including:

[0018] After each channel completes distance delay error compensation, the two-dimensional frequency domain echo of the reference channel is multiplied by the two-dimensional frequency domain echo of the non-reference channel again to obtain multiple impulse functions.

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

[0020] According to embodiments of this disclosure, the method further includes:

[0021] Azimuth downsampling and range compression are performed on the echoes of each channel;

[0022] Based on each channel after multiple error compensations, signal reconstruction is performed according to the signal after distance compression.

[0023] Based on the attitude and position information of the reference channel, the reconstructed signal is focused in two dimensions using a single-channel two-step motion compensation method to generate a reconstructed image.

[0024] Another aspect of this disclosure provides a two-dimensional time-varying error compensation device for azimuth multi-channel synthetic aperture radar, comprising:

[0025] The attitude error estimation and compensation module is used to estimate and compensate for the attitude error of each channel of the synthetic aperture radar based on the attitude information and velocity vector of the aircraft carrying the synthetic aperture radar during flight.

[0026] The pattern error estimation and compensation module is used to calculate the Doppler center of the echo from the sampling point at different distances in each channel using the vector method, estimate the channel pattern error, and compensate for the pattern error using the amplitude equalization method.

[0027] The two-dimensional Fourier transform module is used to perform a two-dimensional Fourier transform on the echo of the channel that has completed attitude error and pattern error compensation, so as to obtain a two-dimensional frequency domain echo.

[0028] The distance delay error estimation and compensation module is used to perform two-dimensional frequency domain echo interferometry on the two-dimensional frequency domain echo, estimate the distance delay error of each channel and compensate for it.

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

[0030] The above one or more embodiments have the following beneficial effects: they can at least partially solve the problems of azimuth blurring and poor image quality caused by azimuth multi-channel errors, and thus can estimate and fully compensate for multi-channel errors caused by various factors in actual scenarios, reduce azimuth blurring, and the method has low complexity and low imaging time cost, and is especially suitable for signal reconstruction and imaging at small oblique angles that are unavoidable in actual flight. Attached Figure Description

[0031] The foregoing contents, as well as other objects, features, and advantages of this disclosure, will become clearer from the following description of embodiments with reference to the accompanying drawings, in which:

[0032] Figure 1 A flowchart illustrating a two-dimensional time-varying error compensation method for azimuth multi-channel synthetic aperture radar according to an embodiment of the present disclosure is shown schematically.

[0033] Figure 2 A schematic diagram of an azimuth multichannel synthetic aperture radar imaging geometry model according to an embodiment of the present disclosure is shown.

[0034] Figure 3(a) schematically illustrates an image under the condition of undersampling according to an embodiment of the present disclosure;

[0035] Figure 3(b) schematically illustrates a reconstructed image generated without compensation for multi-channel errors in the case of undersampling according to an embodiment of the present disclosure;

[0036] Figure 3(c) schematically illustrates a reconstructed image generated by compensating for multi-channel errors using a conventional error compensation method in the case of undersampling according to an embodiment of the present disclosure;

[0037] Figure 3(d) schematically illustrates a reconstructed image generated by compensating for 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 A schematic diagram of a two-dimensional time-varying error compensation device for azimuth multi-channel synthetic aperture radar according to an embodiment of the present disclosure is shown.

[0039] It should be noted that, for clarity, the dimensions of the overall / partial structure or the overall / partial region in the drawings used to describe the embodiments of this disclosure may be enlarged or reduced, i.e., these drawings are not drawn to actual scale. Detailed Implementation

[0040] The embodiments of the present disclosure will now be described with reference to the accompanying drawings. However, it should be understood that these descriptions are exemplary only and are not intended to limit the scope of the disclosure. In the following detailed description, numerous specific details are set forth to provide a thorough understanding of the embodiments of the present disclosure for ease of explanation. However, it will be apparent that one or more embodiments may be practiced without these specific details. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concepts of the present disclosure.

[0041] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. The terms “comprising,” “including,” etc., as used herein indicate the presence of the stated 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 are to be interpreted in a manner consistent with the context of this specification, and not in an idealized or overly rigid way.

[0043] When using expressions such as "at least one of A, B and C", they should generally be interpreted in accordance with the meaning that is commonly understood by those skilled in the art (e.g., "a system having at least one of A, B and C" should include, but is not limited to, a system having A alone, a system having B alone, a system having C alone, a system having A and B, a system having A and C, a system having B and C, and / or a system having A, B and C, etc.).

[0044] The embodiments of this disclosure provide a two-dimensional time-varying error compensation method for azimuth multi-channel synthetic aperture radar. This method fully compensates for channel errors caused by various factors such as actual aircraft motion and system design, reduces azimuth ambiguity, and improves the image quality after signal reconstruction.

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

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

[0047] In operation S110, the attitude error of each channel of the synthetic aperture radar is estimated and compensated based on the attitude information and velocity vector of the aircraft carrying the synthetic aperture radar during flight.

[0048] In some embodiments, during flight, an aircraft (such as an airplane) will inevitably experience various attitude changes with azimuth and time due to airflow and body vibration, which will cause attitude errors in the channel. The attitude error is manifested as slant range error. Slant range error will cause azimuth time-varying phase error in the echo between channels. Therefore, time-varying slant range error corresponds to time-varying phase error.

[0049] In some embodiments, attitude information includes attitude angles such as roll angle, pitch angle, and yaw angle of the aircraft during flight; wherein, attitude information can be obtained by an inertial measurement unit (IMU) on board the aircraft.

[0050] In some embodiments, the velocity vector can also be obtained by an inertial measurement unit (IMU) on board the aircraft, and the velocity vector is a three-dimensional velocity vector.

[0051] In some embodiments, the vector method is used to estimate and compensate for the attitude error 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 Doppler center of the echo from the sampling point at different distances in each channel is calculated using the vector method, the channel pattern error is estimated, and the pattern error is compensated using the amplitude equalization method.

[0053] In some embodiments, in actual systems, due to differences in antenna design and manufacturing on synthetic aperture radar, the antenna patterns of different channels cannot be exactly the same, resulting in amplitude and envelope errors. Considering the downward viewing angle changes in wide-span scenarios, the differences in the patterns of different channels mainly lie in the differences in amplitude and beamwidth. When the imaging swath is large, the downward viewing angle changes significantly at different distances, and the echoes at different distances have different oblique viewing angles. Therefore, the pattern compensation of the channels needs to vary with the range gate. Thus, the pattern error of each channel is estimated and compensated in the Doppler domain of the echo. Based on this, this embodiment proposes to use the vector method to calculate the Doppler center of the echoes from sampling points at different ranges of each channel, estimate the amplitude error of the channel pattern in the range time domain-azimuth frequency domain, and use the amplitude equalization method to complete the compensation of the channel pattern error in the Doppler domain (or azimuth frequency domain) based on the Doppler center of the echoes from sampling points at different ranges.

[0054] In some embodiments, the impact of pattern error on signal reconstruction is considered, especially in wide-span scenarios, and corresponding estimation and compensation methods are proposed to further improve the quality of signal reconstruction.

[0055] In operation S130, a two-dimensional Fourier transform is performed on the echo of the channel that has completed attitude error and pattern error compensation to obtain a two-dimensional frequency domain echo.

[0056] In some embodiments, there is also a time delay error between channels. Since the time delay of the signal in the time domain can be equivalent to a linear phase in the frequency domain, after completing the attitude error and pattern error compensation, a two-dimensional Fourier transform is performed on the echo of each channel to transform it to the two-dimensional frequency domain. In the two-dimensional frequency domain, the fixed phase error and distance delay error of each channel are estimated.

[0057] In operation S140, two-dimensional frequency domain echo interferometry is performed on the two-dimensional frequency domain echo to estimate and compensate for the distance delay error of each channel.

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

[0059] In operation S150, two-dimensional frequency domain echo interferometry is performed on the two-dimensional frequency domain echo of the channel after distance delay error compensation to estimate and compensate for the fixed phase error of each channel.

[0060] In some embodiments, a channel is generally composed of radio frequency circuits. The amplifiers, mixers and other components in the radio frequency circuits of different channels have different performance. This difference will lead to amplitude and phase errors between channels. Since most of the amplitude error has been compensated in the pattern error compensation process, the remaining amplitude error has a very small impact on signal reconstruction and can be ignored.

[0061] In some embodiments, the distance delay error and fixed phase error of the channel are estimated using the two-dimensional frequency domain echo interferometry method, which eliminates the need for error estimation in the image domain and saves the time cost of imaging multiple channels separately.

[0062] Figure 2 A schematic diagram of an azimuth multichannel synthetic aperture radar imaging geometry model according to an embodiment of the present disclosure is shown.

[0063] like Figure 2 As shown, an aircraft equipped with a synthetic aperture radar (SAR) flies along the X-axis, which points in the azimuth direction. The Y-axis, perpendicular to the X-axis, points in the range direction. The transmit / receive channels of the SAR are an important component. SAR can operate in a mode with one transmit channel and multiple receive channels. Figure 2 For use in the middle launch channel This indicates that the receiving channel uses... It indicates that the aircraft's flight altitude is The number of channels is Ground point targets The position coordinates are , This represents the angle of incidence of a ground point target relative to the reference channel. Indicates the mapping bandwidth. Indicates the spacing between adjacent channels. , They represent the first The slant range history of each receiving channel and the slant range history from the reference channel to the ground target;

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

[0065]

[0066] in, Representing distance to time With direction and time First The echo received by each receiving channel Indicates the relationship with the first Complex constants related to each receiving channel , , , , , These are the range window function, azimuth window function, speed of light, echo wavelength, radar flight speed, and frequency modulation slope, respectively. , , They represent the first The slant range history of the first receiving channel, the first The position of the receiving channel relative to the reference channel, and the horizontal coordinate position of the ground point target; wherein, the reference channel can be either a receiving channel or a transmitting channel;

[0067] Furthermore, ; ;

[0068]

[0069] in, This indicates the direction angle of arrival of the echo in the azimuth direction. Furthermore, the direction angle of arrival of the echoes in each channel is the same.

[0070] In some embodiments, ;in, Indicates the azimuth frequency.

[0071] In some embodiments, due to atmospheric turbulence, aircraft vibration, etc., the actual trajectory of the aircraft is not an ideal straight line, and the coordinates of a point on the actual trajectory can be represented as follows: ,in, , , These represent the motion errors of the aircraft along the X, Y, and Z axes, respectively. Therefore, the actual slant range history from the reference channel to the ground target is... The expression is as follows:

[0072]

[0073] in, The motion error for a single channel can be approximated as:

[0074]

[0075] In some embodiments, if compensation is not made for various errors such as motion error, attitude error, pattern error, distance delay error, and fixed phase error of the above channels, the resulting pulse-compressed time-domain echo signal The formula is as follows:

[0076]

[0077]

[0078] in, This indicates the echo signal bandwidth. , , They represent the first The distance delay error, fixed phase error, and time-varying phase error of each receiving channel relative to the reference channel are considered. Furthermore, the attitude error is reflected through the slant range error, which leads to the time-varying phase error. Therefore, the attitude error can be compensated by compensating for the time-varying phase error.

[0079] In some embodiments, motion errors of the channels are compensated using a multi-channel signal model.

[0080] In some embodiments, during operation S110, the attitude error of each channel of the synthetic aperture radar is estimated based on the attitude information and velocity vector of the aircraft equipped with the synthetic aperture radar during flight, including:

[0081] Based on the attitude information of the aircraft equipped with synthetic aperture radar during flight and the antenna axial vectors of each channel of the synthetic aperture radar under ideal conditions, the antenna axial vectors of each channel of the aircraft during actual flight are calculated.

[0082] Calculate the velocity vector of each channel during the actual flight of the aircraft based on the velocity vector;

[0083] Based on the antenna axial vector and velocity vector of each channel during the actual flight of the aircraft, the attitude error of each channel is estimated.

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

[0085]

[0086] in, Represents the aircraft's position and time. The roll angle at that time Represents the aircraft's position and time. pitch angle at time Represents the aircraft's position and time. The heading angle at that time;

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

[0088] ,in, Indicates vector transpose;

[0089] The antenna axial vector of each channel during actual flight is calculated using the following formula. :

[0090]

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

[0092]

[0093] in, Let be the three-dimensional velocity vector of the aircraft. Indicates a modulo operation;

[0094] Furthermore, due to , The existence of differences allows us to obtain the posture that needs compensation.

[0095] State error, that is, ,in, Indicates the first Attitude error of each receiving channel;

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

[0097]

[0098] in, Indicates the first Time-varying phase error of each receiving channel, , They represent the first The Y-axis and Z-axis components of the attitude error of each receiving channel This is an unavoidable issue during system installation. Fixed slant range error for each receiving channel.

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

[0100] In some embodiments, after attitude error compensation, the channel pattern error is estimated; specifically, the first Time-domain pattern of each receiving channel It can be represented as:

[0101]

[0102] in, represent amplitude coefficient, , , , These represent the azimuth beamwidth factor, azimuth beamwidth, azimuth arrival angle of the echo, and range time, respectively. The oblique angle of the location;

[0103] Since pattern compensation needs to vary with the distance gate, it can be done using parameters. represent The corresponding Doppler center is used to estimate the channel pattern error in the Doppler domain;

[0104] Furthermore, assuming the Doppler center corresponding to the channel is constant over a certain azimuth time interval, the result of averaging the channel's antenna axial vector along the azimuth direction over time is denoted as... The Doppler center with range variation is calculated using the vector method.

[0105] In some embodiments, during operation S120, the Doppler center of the echo from each channel at different distances to the sampling point is calculated using a vector method, including:

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

[0107] Based on the line-of-sight vector and the velocity vector of each channel during the actual flight of the aircraft, the Doppler center of the echo from the sampling point at different distances of each channel is calculated.

[0108] In some embodiments, gaze vector Defined as , , These are the components of the line-of-sight vector on the X and Y axes, respectively. This indicates the distance-time dimension, corresponding to different distance-time sampling points;

[0109] Furthermore, It is also defined as the echo slant range that varies with the range gate, i.e.:

[0110]

[0111] Due to the line-of-sight vector and Since they are perpendicular, their vector dot product is 0, hence we get... The calculation formula is as follows:

[0112]

[0113] in, , , They represent vectors respectively of Axial components;

[0114] Based on gaze vector and the velocity vector of the channel during aircraft flight Doppler center of the channel echo The calculation formula is as follows:

[0115]

[0116] In some embodiments, during operation S120, compensating for pattern errors using amplitude equalization includes:

[0117] Based on the Doppler center of the echoes from sampling points at different ranges, amplitude equalization is performed on the echoes from each sampling point in the Doppler domain to compensate for channel pattern errors.

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

[0119] In some embodiments, after attitude error and pattern error compensation are completed, the echo signal of the channel with fixed amplitude and phase error and range delay error can be expressed as:

[0120]

[0121] in, , These are the first two sets of data after attitude error and pattern error compensation. Two-dimensional frequency domain echo of each receiving channel and two-dimensional frequency domain echo of the reference channel. For range frequency, The azimuth delay depends on the channel spacing. After attitude error compensation is completed, The time-varying part has already been compensated, therefore, the next step is only to estimate... Fixed delay error in .

[0122] In some embodiments, during operation S140, performing two-dimensional frequency domain echo interferometry on the two-dimensional frequency domain echo to estimate the distance delay error of each channel includes:

[0123] The two-dimensional frequency domain echo of the reference channel in the two-dimensional frequency domain echo is multiplied by conjugate with the two-dimensional frequency domain echo of other non-reference channels respectively. Based on the conjugate multiplication result, the distance delay error of each channel is estimated.

[0124] For example, for and By performing conjugate multiplication, we can obtain the first... The distance delay error of each receiving channel is specifically calculated using the following formula through conjugate multiplication:

[0125]

[0126] in, Represents a two-dimensional Fourier transform. Represents a two-dimensional FFT. This indicates the conjugate operation. Represents the Hadamard product;

[0127] The obtained number Distance delay error of each receiving channel Represented as:

[0128]

[0129] in, represent the number of rows, Represents the sampling frequency. Represents a complex matrix The first index of the position of the maximum amplitude.

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

[0131] In some embodiments, during operation S150, two-dimensional frequency domain echo interferometry is performed on the two-dimensional frequency domain echoes of the channels after distance delay error compensation to estimate the fixed phase error of each channel, including:

[0132] After each channel completes distance delay error compensation, the two-dimensional frequency domain echo of the reference channel is multiplied by the two-dimensional frequency domain echo of the non-reference channel again to obtain multiple impulse functions.

[0133] The phases of multiple impulse functions are calculated separately, and the phases are used as the fixed phase errors of the corresponding channels.

[0134] For example, after each channel completes distance delay error compensation, the above conjugate multiplication formula is applied to... and Perform conjugate multiplication again to obtain the first... The fixed phase error corresponding to each receiving channel is represented by a two-dimensional frequency domain impulse function. Multiple receiving channels correspond to multiple impulse functions, and the phase of the impulse function is the fixed phase error of the channel relative to the reference channel. Taking the first receiving channel as an example... Taking a single receiving channel as an example, its fixed phase error It can be represented as:

[0135]

[0136] in, Represents a complex matrix The second index of the position of the maximum amplitude. This represents taking the phase of a complex number.

[0137] In some embodiments, a multi-channel signal model is used to compensate for the fixed phase error of the channel.

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

[0139] Azimuth downsampling and range compression are performed on the echoes of each channel;

[0140] Based on each channel after multiple error compensations, signal reconstruction is performed according to the signal after distance compression.

[0141] Based on the attitude and position information of the reference channel, the reconstructed signal is focused in two dimensions using a single-channel two-step motion compensation method to generate a reconstructed image.

[0142] In some embodiments, by downsampling the echoes of each channel and compressing the range, the error compensation method of method 100 is used to compensate for the errors of each channel. The range-compressed signal is reconstructed, and the error-compensated signals of each channel are merged into one signal. Finally, the attitude and position information of the reference channel are obtained according to the inertial measurement unit (IMU). The reconstructed signal is then focused in two dimensions using a single-channel two-step motion compensation method to generate a reconstructed image. The error compensation effect of method 100 is verified based on the quality of the reconstructed image. The verification shows that the error compensation effect of method 100 is very good and can greatly reduce the blur energy of the image. Therefore, method 100 can be used in radar imaging and other scenarios. The error compensation mentioned here refers to all error compensation methods, including 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 yaw angle.

[0143] The effectiveness of the error estimation and compensation method proposed in Method 100 was verified using three-channel echo data. The reconstructed image obtained using Method 100 was compared with the reconstructed image obtained by the traditional compensation method, the reconstructed image generated without error compensation, and the image 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 lot of azimuth blur, making the image difficult to identify. The reconstructed image generated without error compensation (Figure 3(b)) still has a lot of azimuth blur and has not been significantly improved. The reconstructed image obtained using the traditional compensation method (Figure 3(c)) greatly suppresses the azimuth blur. For example, the azimuth blur at region A in the image is well suppressed, and region A is clearer. However, there is still residual azimuth blur in the image, indicating that the suppression is not complete. In contrast, the azimuth blur of the reconstructed image obtained using Method 100 (Figure 3(d)) is basically completely suppressed, presenting a considerable two-dimensional image effect. This shows that the error estimation and compensation method proposed in Method 100 can greatly suppress the blur phenomenon of the reconstructed image and improve the image quality.

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

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

[0146] Figure 4 A schematic diagram of a two-dimensional time-varying error compensation device for azimuth multi-channel synthetic aperture radar according to an embodiment of the present disclosure is shown.

[0147] Figure 4 A schematic block diagram of a two-dimensional time-varying error compensation device for azimuth multi-channel synthetic aperture radar according to an embodiment of the present disclosure is shown.

[0148] like Figure 4 As shown, the device 400 in 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 distance 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 used to estimate and compensate for the attitude error of each channel of the synthetic aperture radar based on 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 repeated here.

[0150] The pattern error estimation and compensation module 420 is used to calculate the Doppler center of the echo from the sampling point at different distances in each channel using the vector method, estimate the channel pattern error, and compensate for the pattern error 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 repeated here.

[0151] The two-dimensional Fourier transform module 430 is used to perform a two-dimensional Fourier transform on the echo of the channel that has completed attitude error and pattern error compensation, to obtain a two-dimensional frequency domain echo. In one embodiment, the two-dimensional Fourier transform module 430 can be used to perform the operation S130 described above, which will not be repeated here.

[0152] The distance delay error estimation and compensation module 440 is used to perform two-dimensional frequency domain echo interferometry on the two-dimensional frequency domain echo, estimate the distance delay error of each channel, and compensate for it. In one embodiment, the distance delay error estimation and compensation module 440 can be used to perform the operation S140 described above, which will not be repeated here.

[0153] The fixed phase error estimation and compensation module 450 is used to perform two-dimensional frequency domain echo interferometry on the two-dimensional frequency domain echo of the channel after distance delay error compensation, estimate the fixed phase error of each channel, and perform compensation. 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 repeated here.

[0154] According to embodiments of this disclosure, the device 400 can reduce the blur energy of the reconstructed image and improve the quality of the reconstructed image, making it more suitable for signal reconstruction and imaging at small oblique angles.

[0155] For any parts not mentioned in the apparatus section, please refer to the various embodiments of the above method for understanding. That is, the apparatus section includes modules for performing each step of any of the method embodiments described above. Furthermore, the implementation methods, technical problems solved, functions achieved, and technical effects of each module / unit / subunit in the apparatus section embodiments are the same as or similar to the implementation methods, technical problems solved, functions achieved, and technical effects of the corresponding steps in the method section embodiments, and will not be repeated here.

[0156] According to embodiments of this 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 into one module, or any one of these modules can be split into multiple modules. Alternatively, at least some of the functions of one or more of these modules can be combined with at least some of the functions of other modules and implemented in one module.

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

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

[0159] The embodiments of this disclosure have been described above. However, these embodiments are for illustrative purposes only and are not intended to limit the scope of this disclosure. Although various embodiments have been described above, this does not mean that the measures in the various embodiments cannot be used advantageously in combination. The scope of this disclosure is defined by the appended claims and their equivalents. Various substitutions and modifications can be made by those skilled in the art without departing from the scope of this disclosure, and all such substitutions and modifications should fall within the scope of this disclosure.

Claims

1. A two-dimensional time-varying error compensation method for azimuth multi-channel synthetic aperture radar, characterized in that, The method includes: Based on the attitude information and velocity vector of the aircraft equipped with synthetic aperture radar during flight, the attitude error of each channel of synthetic aperture radar is estimated and compensated. The Doppler center of the echo from the sampling point at different distances in each channel is calculated using the vector method, the channel pattern error is estimated, and the pattern error is compensated using the amplitude equalization method. A two-dimensional Fourier transform is performed on the echo of the channel that has completed attitude error and pattern error compensation to obtain a two-dimensional frequency domain echo. Two-dimensional frequency domain echo interferometry is performed on the two-dimensional frequency domain echo to estimate and compensate for the distance delay error of each channel; Two-dimensional frequency domain echo interferometry is performed on the two-dimensional frequency domain echo of the channel after distance delay error compensation to estimate and compensate for the fixed phase error of each channel.

2. The method according to claim 1, characterized in that, The estimation of attitude errors of each channel of the synthetic aperture radar based on the attitude information and velocity vector of the aircraft equipped with synthetic aperture radar during flight includes: Based on the attitude information of the aircraft equipped with synthetic aperture radar during flight and the antenna axial vectors of each channel of the synthetic aperture radar under ideal conditions, the antenna axial vectors of each channel of the aircraft during actual flight are calculated. Calculate the velocity vector of each channel during the actual flight of the aircraft based on the velocity vector; Based on the antenna axial vector and velocity vector of each channel during the actual flight of the aircraft, the attitude error of each channel is estimated.

3. The method according to claim 2, characterized in that, The calculation of the Doppler center of the echo from the sampling point at different distances in each channel using the vector method includes: Establish the line-of-sight vectors for each channel; Based on the line-of-sight vector and the velocity vector of each channel during the actual flight of the aircraft, the Doppler center of the echo from each channel to the sampling point at different distances is calculated.

4. The method according to claim 3, characterized in that, The method of compensating for the pattern error using amplitude equalization includes: Based on the Doppler center of the echoes from sampling points at different ranges, amplitude equalization is performed on the echoes from each sampling point in the Doppler domain to compensate for channel pattern errors.

5. The method according to claim 1, characterized in that, The step of performing two-dimensional frequency domain echo interferometry on the two-dimensional frequency domain echo to estimate the distance delay error of each channel includes: The two-dimensional frequency domain echo of the reference channel in the two-dimensional frequency domain echo is multiplied by conjugate with the two-dimensional frequency domain echo of other non-reference channels respectively. Based on the conjugate multiplication result, the distance delay error of each channel is estimated.

6. The method according to claim 5, characterized in that, The two-dimensional frequency domain echo interferometry of the two-dimensional frequency domain echoes of the channels after distance delay error compensation, and the estimation of the fixed phase error of each channel, includes: After each channel completes distance delay error compensation, the two-dimensional frequency domain echo of the reference channel is multiplied by the two-dimensional frequency domain echo of the non-reference channel again to obtain multiple impulse functions. The phases of the multiple impulse functions are calculated respectively, and the phases are used as the fixed phase errors of the corresponding channels.

7. The method according to claim 1, characterized in that, The method further includes: Azimuth downsampling and range compression are performed on the echoes of each channel; Based on each channel after multiple error compensations, signal reconstruction is performed according to the signal after distance compression. Based on the attitude and position information of the reference channel, the reconstructed signal is focused in two dimensions using a single-channel two-step motion compensation method to generate a reconstructed image.

8. A two-dimensional time-varying error compensation device for azimuth multi-channel synthetic aperture radar, characterized in that, The device includes: The attitude error estimation and compensation module is used to estimate and compensate for the attitude error of each channel of the synthetic aperture radar based on the attitude information and velocity vector of the aircraft carrying the synthetic aperture radar during flight. The pattern error estimation and compensation module is used to calculate the Doppler center of the echo from the sampling point at different distances in each channel using the vector method, estimate the channel pattern error, and compensate the pattern error using the amplitude equalization method. The two-dimensional Fourier transform module is used to perform a two-dimensional Fourier transform on the echo of the channel that has completed attitude error and pattern error compensation, so as to obtain a two-dimensional frequency domain echo. The distance delay error estimation and compensation module is used to perform two-dimensional frequency domain echo interferometry on the two-dimensional frequency domain echo, estimate the distance delay error of each channel and compensate for it. The fixed phase error estimation and compensation module is used to perform two-dimensional frequency domain echo interferometry on the two-dimensional frequency domain echo of the channel after distance delay error compensation, estimate the fixed phase error of each channel and perform compensation.

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