CN114252880A - Method and system for simultaneously realizing bunching and stripe SAR imaging by coding array - Google Patents
Method and system for simultaneously realizing bunching and stripe SAR imaging by coding array Download PDFInfo
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Abstract
The invention relates to a method and a system for realizing bunching and stripe SAR imaging of a coding array at the same time, wherein the method comprises the following steps: the radar array is arranged along the azimuth direction of SAR imaging, and a separate coding pulse signal is given to each radiation array element of the radar array; the separate coded pulse signals enable echo signals generated by target reflection to be separable in time, space or frequency; or the echo signals can be separated after decoding processing; when the radar works, each radiating array element of the radar array transmits a respective coded pulse signal, and each radiating array element receives echo signals of the coded pulse signals transmitted by the radiating array element and other radiating array elements; collecting the echo signals received by each radiation array element, and decoding; and according to the decoded echo signals, simultaneously performing beamforming and strip SAR imaging processing to obtain beamforming and strip SAR imaging results. The invention simultaneously realizes the requirements of the working method and the system of the synthetic aperture radar in two imaging modes, and improves the imaging efficiency.
Description
Technical Field
The invention belongs to the technical field of radars, and particularly relates to a method and a system for realizing bunching and stripe SAR imaging simultaneously by a coding array.
Background
Synthetic Aperture Radars (SAR) enable high resolution imaging of a target, which improve range resolution by pulse compression and azimuth resolution by synthetic aperture.
Synthetic aperture radars have different imaging modes including stripe imaging, beamforming imaging, etc., as shown in fig. 1.
In the prior art, the strip SAR imaging is the earliest and most widely applied SRA imaging mode at present, the imaging area of the strip SAR imaging is a strip-shaped area parallel to the motion direction of a carrier (or a carrying platform such as a satellite), a radar beam is generally perpendicular to a flight track, namely, the radar beam is in front side view, the strip-shaped SAR imaging can also work in an oblique view mode, and the included angle between the radar beam and a rain flight track is unchanged in an ideal state in the imaging process. The azimuth resolution of the strip SAR imaging mode is limited by the size of the radar antenna, namely the azimuth resolution cannot be better than half of the length of the azimuth antenna, and the azimuth resolution of the SAR is limited because the azimuth resolution cannot be reduced without limit in the actual system design.
In the prior art, a beaming SAR imaging mode provides a method for improving azimuth resolution, and in the imaging process, a radar beam is controlled to fixedly point to the same area, so that a target can be observed in a larger visual angle range, and the accumulation time of a synthetic aperture in a small area is increased. And the azimuth resolution is improved, so that the improvement of the azimuth resolution of SAR imaging is not limited by the azimuth size of the antenna.
However, the beaming SAR imaging can only perform high-resolution imaging of the azimuth direction on a small area, and cannot image a ground continuous strip on one side of a flight path like a strip SAR imaging mode, thereby reducing the imaging efficiency.
Therefore, the need exists in the art for a synthetic aperture radar working method and system capable of overcoming the defects that the traditional strip SAR imaging is limited by improving the azimuth resolution and the bunching SAR imaging cannot be continuously imaged and observed with high efficiency, and simultaneously realizing two imaging modes.
Disclosure of Invention
In view of the above analysis, the present invention aims to disclose a method and a system for implementing simultaneous imaging and detection of a coding array, which overcome the shortcomings of the traditional imaging radar and moving object detection radar, and meet the requirement for improving the system performance of the simultaneous imaging and detection of the radar.
The invention discloses a method for realizing simultaneous beamforming and stripe SAR imaging by a coding array, which comprises the following steps:
the radar array is arranged along the azimuth direction of SAR imaging, and a separate coding pulse signal is given to each radiation array element of the radar array; the separate coded pulse signals enable echo signals generated by target reflection to be separable in time, space or frequency; or the echo signals can be separated after decoding processing;
when the radar works, each radiating array element of the radar array transmits a respective coded pulse signal, and each radiating array element receives echo signals of the coded pulse signals transmitted by the radiating array element and other radiating array elements;
collecting the echo signals received by each radiation array element, and decoding; and according to the decoded echo signals, simultaneously performing beamforming and strip SAR imaging processing to obtain beamforming and strip SAR imaging results.
Further, the beamforming SAR imaging processing is to form a virtual beamforming imaging scanning beam by using target echo signals of each array element, which are not encoded with pulse signals at the same time, so as to obtain virtual beamforming scanning radar data; and then, performing bunching SAR imaging processing on the data to obtain a bunching SAR image.
Further, the strip SAR imaging processing is to form a virtual strip imaging beam by using target echo signals of each array element, which are not encoded with pulse signals at the same time, to obtain virtual strip imaging radar data, and then to perform strip SAR imaging processing by using the data to obtain a strip SAR image.
Further, the individual coded pulse signals are frequency division coded pulse signals, time-phase combined coded pulse signals or time-phase-frequency combined coded pulse signals;
the single coded pulse signal is a frequency division coded pulse signal; during transmission, each array element adopts different frequencies for transmission, and a transmission channel is isolated through the frequency; during receiving, after each array element receives an echo signal, echo signals corresponding to transmitting signals of different array elements are separated through frequency domain filtering;
the single coded pulse signal is a time-phase combined coded pulse signal, and the basic constraint of coding is that each coding channel is orthogonal to each other; when transmitting, each array element adopts different codes to transmit; during receiving, after each array element receives an echo signal, the echo signals corresponding to the transmitting signals of different array elements are separated through decoding processing;
the single coded pulse signal is a time-phase-frequency combined coded pulse signal, and the basic constraint of coding is that each coding channel is orthogonal to each other; when transmitting, each array element adopts different codes to transmit; during receiving, after each array element receives the echo signal, the echo signals corresponding to the transmitting signals of different array elements are separated through decoding processing.
Further, the acquiring the echo signal received by each radiating array element, and the decoding process includes:
for the frequency division encoding pulse signal, decoding processing is carried out in a frequency domain filtering mode;
for the time-phase combined coded pulse signal, a decoding matrix is obtained through the coding matrix, and then the echo signal is decoded by the decoding matrix; the decoding matrix corresponds to the encoding matrix and comprises pulse decoding modes corresponding to the pulse encoding modes of all array elements;
for the time-phase-frequency combined coded pulse signal, a decoding matrix is obtained through the coding matrix, and then the echo signal is processed by the decoding matrix; decoding the echo signal in a frequency filtering mode; the decoding matrix corresponds to the encoding matrix and comprises pulse decoding modes corresponding to the pulse encoding modes of all the array elements.
Further, in the beamforming SAR imaging process,
for decoded inclusion of N2Selecting corresponding channel data for subsequent processing according to the imaging resolution of target echo data of the independent channel signals, wherein N is the number of array elements(ii) a The method comprises the following steps:
1) frequency processing:
for frequency division coding, after filtering processing is carried out on received data, frequency synthesis is carried out, and the frequency bandwidth after synthesis is not lower than the frequency bandwidth corresponding to the imaging resolution requirement;
for time-phase combined coding, after filtering processing and decoding processing are carried out on received data, frequency synthesis is carried out, and the frequency bandwidth after synthesis is not lower than the frequency bandwidth corresponding to the imaging resolution requirement;
for time-phase-frequency combined coding, after filtering processing and decoding processing are carried out on received data, frequency synthesis is carried out, and the frequency bandwidth after synthesis is not lower than the frequency bandwidth corresponding to the imaging resolution requirement;
2) and (3) beam synthesis processing:
determining the width theta of the synthesized beam according to the imaging distance and the imaging range; determining the number of array elements participating in imaging processing according to the width theta of the synthesized beam; azimuthal resolution ρ from beamforming imagingaDetermining a beamforming imaging angle thetas；
Calculating the beam bunching starting position and the beam bunching ending position according to the imaging center position, the distance between the radar and the imaging center and the beam bunching imaging angle, and calculating the beam bunching instantaneous pointing angle at each sampling position in the radar flight process from the beam bunching starting position to the beam bunching ending position;
and for each sampling position, determining the phase shift phase of each array element participating in beam forming processing by using the beam-forming instantaneous pointing angle of the position, performing phase correction on data obtained by each array element at the position, accumulating the data of different array elements corresponding to the same moment to complete beam forming, and obtaining virtual beam-forming scanning radar data of the radar at the position through synthesis.
Further the synthesized beamwidth
L is the length of the ground mark irradiated by the radar beam at the imaging distance along the direction vertical to the wave propagation direction; rmaxThe farthest distance for imaging;
the number of the array elements for beam synthesis is determined according to the fact that the antenna beam width corresponding to the antenna length determined by the number of the array elements is not less than the synthesized beam width theta;
the angle of beam bunching imaging
Where λ is the center frequency wavelength of the transmitted signal.
Further, in the stripe SAR imaging process,
for decoded inclusion of N2Selecting corresponding channel data for subsequent processing according to the imaging resolution of target echo data of the independent channel signals, wherein N is the number of array elements; the method comprises the following steps:
1) frequency processing:
for frequency division coding, after filtering processing is carried out on received data, frequency synthesis is carried out, and the frequency bandwidth after synthesis is not lower than the frequency bandwidth corresponding to the imaging resolution requirement;
for time-phase combined coding, after filtering processing and decoding processing are carried out on received data, frequency synthesis is carried out, and the frequency bandwidth after synthesis is not lower than the frequency bandwidth corresponding to the imaging resolution requirement;
for time-phase-frequency combined coding, after filtering processing and decoding processing are carried out on received data, frequency synthesis is carried out, and the frequency bandwidth after synthesis is not lower than the frequency bandwidth corresponding to the imaging resolution requirement;
2) and (3) beam synthesis processing:
imaging azimuthal resolution ρ from stripe SARaDetermining the number of array elements participating in imaging processing; the number of array elements used for beam forming is determined by that the length of an antenna determined by the number of the array elements is not more than half of the azimuth resolution;
for each sampling position, determining the phase shift phase of each array element participating in beam synthesis processing by using the beam instantaneous pointing angle of the position, performing phase correction on data obtained by each array element at the position, accumulating the data of different array elements corresponding to the same moment to complete beam synthesis, and obtaining virtual strip imaging radar data of the radar at the position through synthesis;
3) imaging processing:
and carrying out SAR strip imaging processing by using the virtual strip imaging radar data obtained by synthesis to obtain a strip SAR image.
The invention also discloses a system for realizing the method for simultaneously realizing beam bunching and stripe SAR imaging based on the coding array, which comprises the following steps:
the array coding signal generating unit is used for generating a single pulse coding signal transmitted by each radiating array element; the separate coded pulse signals enable echo signals generated by target reflection to be separable in time, space or frequency; or the echo signals can be separated after decoding processing;
the radar array comprises N array elements, each array element transmits a pulse code signal and receives target echo signals of all the array elements transmitting the pulse code signals;
the data acquisition unit is used for acquiring target echo signals received by each radiation array element to form target echo data;
the array signal decoding processing unit is used for decoding the acquired target echo data and separating N corresponding to the receiving and transmitting channel combination formed by different radiation array elements2Target echo data of individual channel signals;
the virtual beam forming unit is used for calculating target echo data corresponding to different transceiving channel combinations to generate a virtual beaming imaging scanning beam and a virtual strip imaging beam, and processing the virtual beaming imaging scanning beam and the virtual strip imaging radar data to obtain the virtual beaming scanning radar data and the virtual strip imaging radar data;
the spotlight SAR imaging processor is used for carrying out imaging processing according to the virtual spotlight scanning radar data to obtain a spotlight SAR image;
and the stripe SAR image processor is used for carrying out imaging processing according to the virtual stripe imaging radar data to obtain a stripe SAR image.
The comprehensive display unit is used for carrying out visualization processing on the bunching SAR image and the stripe SAR image to form a video stream containing the bunching SAR image, the stripe SAR image and information of the bunching SAR image and the stripe SAR image;
and the control unit is used for controlling the coding array to realize the signal generation, the receiving and transmitting, the acquisition, the processing and the data display generation of the simultaneous imaging system.
The invention can realize at least one of the following beneficial effects:
(1) the invention can simultaneously acquire the radar data which can be used for strip SAR imaging and bunching SAR imaging, and improves the imaging efficiency.
(2) The method can simultaneously acquire the strip SAR image and the bunching SAR image of the continuous observation area.
(3) The azimuth resolution of the beamformed SAR image acquired simultaneously by the method is not limited by the overall physical size of the array antenna.
Drawings
The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout.
FIG. 1 is a schematic diagram of the operation of a strip and beamer SAR imaging according to the prior art;
FIG. 2 is a schematic diagram of a method for simultaneously implementing beamforming and stripe SAR imaging in an embodiment of the present invention;
FIG. 3 is a diagram illustrating simultaneous beamforming in an embodiment of the present invention;
fig. 4 is a schematic diagram of a radar system for simultaneously implementing beamforming and stripe SAR imaging in an embodiment of the present invention.
Detailed Description
The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form a part hereof, and which together with the embodiments of the invention serve to explain the principles of the invention.
An embodiment of the present invention discloses a method for realizing simultaneous beamforming and stripe SAR imaging by a coding array, which is shown in fig. 2 and includes the following steps:
s1, arranging the radar arrays along the azimuth direction of SAR imaging, and endowing each radiation array element of the radar arrays with an individual coded pulse signal;
the separate coded pulse signals enable echo signals generated by target reflection to be separable in time or space or frequency; or the echo signals may be separable after the decoding process.
Preferably, the separate coded pulse signal is a frequency division coded pulse signal. During transmission, each array element adopts different frequencies to transmit, and the transmitting channels are isolated through the frequencies, and during receiving, after each array element receives echo signals, the echo signals corresponding to the transmitting signals of different array elements are separated through frequency domain filtering;
preferably, the individual code pulse signals are time-phase combined code pulse signals, and the basic constraint of the code is that the code channels are orthogonal to each other. During transmission, each array element adopts different codes for transmission, and during reception, after each array element receives echo signals, the echo signals corresponding to the transmission signals of different array elements are separated through decoding processing;
preferably, the individual coded pulse signals are time-phase-frequency combined coded pulse signals, and the basic constraint of coding is that the coding channels are orthogonal to each other, and each array element is transmitted by using different codes. During receiving, after each array element receives an echo signal, the echo signals corresponding to the transmitting signals of different array elements are separated through decoding processing;
step S2, when the radar works, each radiating array element of the radar array transmits respective coded pulse signals;
specifically, each radiating array element of the radar array transmits a respective coded pulse signal according to the fact that a separate coded pulse signal is given to the radiating array element of each radar array.
Step S3, receiving an echo signal of the coded pulse by the radar array;
each radiating array element receives an echo signal of a self-transmitted coded pulse signal and echo signals of coded pulse signals transmitted by other radiating array elements; and the problem of transmitting signal interference between channels is solved through frequency isolation or coding and decoding isolation.
Step S4, collecting echo signals received by each radiation array element, and decoding the echo signals;
for the frequency division encoding pulse signal, decoding processing is carried out in a frequency domain filtering mode;
for the time-phase combined coded pulse signal, a decoding matrix is obtained through the coding matrix, and then the echo signal is processed by the decoding matrix to complete decoding processing;
for the time-phase-frequency combined coding pulse signal, a decoding matrix is obtained through the coding matrix, then the echo signal is processed by the decoding matrix, and the decoding processing is completed in combination with a frequency filtering mode.
Step S5, according to the decoded echo signals, simultaneously performing beamforming and strip SAR imaging processing to obtain beamforming and strip SAR imaging results;
specifically, the spotlight SAR imaging method comprises the following steps:
the target echo signals of different coded pulses of each array element can be utilized to form virtual beamforming imaging scanning beams to obtain virtual beamforming scanning radar data, and then beamforming SAR imaging processing is carried out on the data to obtain a beamforming SAR image. The specific treatment comprises the following steps:
for the decoded echo data, N is included2And selecting the data of the channels with determined number for subsequent processing according to the imaging resolution ratio, wherein the data (N is the number of array elements) of the signals of the independent channels:
1) frequency processing:
for frequency division coding, after filtering processing is carried out on received data, frequency synthesis is carried out, and the frequency bandwidth after synthesis is not lower than the frequency bandwidth corresponding to the imaging resolution requirement;
for time-phase combined coding, after filtering processing and decoding processing are carried out on received data, frequency synthesis is carried out, and the frequency bandwidth after synthesis is not lower than the frequency bandwidth corresponding to the imaging resolution requirement;
for time-phase-frequency combined coding, after filtering processing and decoding processing are carried out on received data, frequency synthesis is carried out, and the frequency bandwidth after synthesis is not lower than the frequency bandwidth corresponding to the imaging resolution requirement;
2) and (3) beam synthesis processing:
FIG. 3 is a diagram illustrating simultaneous beamforming in an embodiment of the present invention;
determining a synthetic beam width theta according to the imaging distance and the imaging range requirement, wherein the radar beam irradiates the ground mark at the imaging distance and the length L perpendicular to the wave propagation direction is formed by the synthetic beam width theta and the imaging farthest distance RmaxIn the determination of the number of times,
the length L should not be less than the line connecting any two points in the imaging range, i.e.
And determining the number of array elements participating in imaging processing according to the requirement of the synthesized beam width theta, wherein the antenna beam width corresponding to the antenna length determined by the number of array elements used for beam synthesis is not lower than the requirement of the synthesized beam width theta, thereby determining the number of array elements used for beam synthesis.
Azimuthal resolution ρ from beamforming imagingaDetermining a beamforming imaging angle thetas，
Where λ is the center frequency wavelength of the transmitted signal.
And calculating the beam bunching starting position and the beam bunching ending position according to the imaging center position, the distance between the radar and the imaging center and the beam bunching imaging angle, and calculating the beam bunching instantaneous pointing angle at each sampling position in the radar flight process from the beam bunching starting position to the beam bunching ending position.
And for each sampling position, determining the phase shift phase of each array element participating in beam forming processing by using the beam-forming instantaneous pointing angle of the position, performing phase correction on data obtained by each array element at the position, accumulating the data of different array elements corresponding to the same moment to complete beam forming, and obtaining virtual beam-forming scanning radar data of the radar at the position through synthesis.
3) Imaging processing:
and performing beamforming SAR imaging processing by using the virtual beamforming scanning radar data of different positions from the beamforming initial position to the beamforming end position obtained through synthesis to obtain a beamforming SAR image.
Specifically, the strip SAR imaging method comprises the following steps:
the target echo signals of different coded pulses of each array element can be utilized to form virtual strip imaging beams to obtain virtual strip imaging radar data, and then the data is used for carrying out strip SAR imaging processing to obtain a strip SAR image. The specific treatment comprises the following steps:
for the decoded echo data, N is included2And selecting the data of the channels with determined number for subsequent processing according to the imaging resolution ratio, wherein the data (N is the number of array elements) of the signals of the independent channels:
1) frequency processing:
for frequency division coding, after filtering processing is carried out on received data, frequency synthesis is carried out, and the frequency bandwidth after synthesis is not lower than the frequency bandwidth corresponding to the imaging resolution requirement;
for time-phase combined coding, after filtering processing and decoding processing are carried out on received data, frequency synthesis is carried out, and the frequency bandwidth after synthesis is not lower than the frequency bandwidth corresponding to the imaging resolution requirement;
for time-phase-frequency combined coding, after filtering processing and decoding processing are carried out on received data, frequency synthesis is carried out, and the frequency bandwidth after synthesis is not lower than the frequency bandwidth corresponding to the imaging resolution requirement;
2) and (3) beam synthesis processing:
imaging azimuthal resolution ρ from stripe SARaDetermining the number of array elements participating in the imaging process, wherein the length of the antenna determined by the number of array elements used for beam forming is not more than half of the azimuth resolution, thereby determining the number of array elements used for beam forming.
For each sampling position, determining the phase shift phase of each array element participating in beam synthesis processing by using the beam instantaneous pointing angle (the front side view imaging is 90 degrees) of the position, performing phase correction on data obtained by each array element at the position, accumulating the data of different array elements corresponding to the same time to complete beam synthesis, and obtaining virtual strip imaging radar data of the radar at the position through synthesis.
3) Imaging processing:
and carrying out SAR strip imaging processing by using the virtual strip imaging radar data obtained by synthesis to obtain a strip SAR image.
Step S6, comprehensively displaying the radar image and the target detection result;
and step S7, displaying the radar image and the moving target information subjected to the integrated display processing on the display device.
Another embodiment of the present invention discloses a coded array implementation simultaneous beamforming and stripe SAR imaging system, as shown in fig. 4, including:
an array code signal generating unit configured to generate a separate pulse code signal transmitted by each radiating array element;
the separate encoded signals are separable in time or space or frequency for the echo signals produced by the encoded signals at the target, or by a decoding process.
The radar array comprises N array elements, and the columns are arranged along the azimuth direction of SAR imaging; each array element transmits a pulse coding signal and receives target echo signals of all the array elements transmitting the pulse coding signals; the circulator is respectively connected with the transmitter, the receiver and the array element and is used for transmitting a radiation signal output by the transmitter to the array element for radiation or outputting a target echo signal received by the array element to the receiver for receiving and processing. And the circulator realizes the receiving and transmitting isolation of the radar.
For each array element of the radar array, the ability to transmit an independent coded signal should be provided when transmitting, and the ability to receive an independent echo signal should be provided when receiving.
Connected with the transmitter of each array element is an individual pulse code signal which is generated by the array code signal generating unit and corresponds to the array element;
the output of the receiver of each array element is connected with a data acquisition unit;
the data acquisition unit is configured to acquire a target echo signal received by each radiation array element to form target echo data;
the data acquisition unit can be used for independently acquiring the echo signals of each array element, or mixing the echo signals of N array elements together (N >1), and then acquiring the mixed signals.
The array signal decoding processing unit is configured to decode the acquired target echo data and separate out target echo data corresponding to a receiving and transmitting channel combination formed by different radiation array elements;
for frequency division coding, echo data acquired corresponding to echo signals received by each array element are subjected to frequency domain filtering processing through a filter bank corresponding to the number of the array elements, and each filter outputs echo signals corresponding to the frequency of a transmitting array element;
for time-phase combined coding, echo data acquired corresponding to echo signals received by each array element is calculated with a decoding matrix to obtain output decoding signals corresponding to the number of the array elements.
For time-phase-frequency combined coding, echo data acquired corresponding to echo signals received by each array element are calculated with a decoding matrix, and frequency domain filtering processing is respectively carried out to obtain output decoding signals corresponding to the number of the array elements.
The virtual beam forming unit is configured to calculate target echo data corresponding to different transceiving channel combinations to generate a virtual beamforming scanning beam and a virtual stripe imaging beam, and process the virtual beamforming scanning radar data and the virtual stripe imaging radar data;
the imaging processor is configured to perform imaging processing on target echo data corresponding to different transceiving channel combinations to obtain a bunching SAR image and a stripe SAR image;
because the bunching SAR imaging processing and the stripe SAR imaging processing are required to be carried out simultaneously, and the data sources of the bunching SAR imaging processing and the stripe SAR imaging processing are different, the imaging processor comprises two independent signal processors, namely a bunching SAR imaging processor and a stripe SAR image processor.
According to different requirements of specific application environment and processing real-time performance, the virtual beam forming unit and the imaging processor can adopt a general commercial computer and an industrial control computer, and can also adopt a special signal processing platform formed by a signal processing board consisting of a plurality of DSPs, FPGAs and the like.
The comprehensive display unit is configured for performing visualization processing on the bunching SAR image and the stripe SAR image to form a video stream containing the bunching SAR image, the stripe SAR image and information of the bunching SAR image and the stripe SAR image;
and the control unit is configured for controlling the coding array to realize signal generation, transceiving, acquisition, processing and display data generation of the simultaneous beamforming and stripe SAR imaging system.
The control unit generates system working synchronous signals, the system working synchronous signals comprise signal generation synchronous signals, signal acquisition synchronous signals and receiving and transmitting protection synchronous signals, each array element is provided with independent signal generation synchronous signals, signal acquisition synchronous signals and receiving and transmitting protection synchronous signals, strict synchronous relation is kept between the signal generation synchronous signals and the signal acquisition synchronous signals corresponding to each array element, and the synchronous requirement is not lower than the time synchronous requirement of SAR imaging.
It should be noted that the above description omits some more specific technical details that are well known to those skilled in the art and that may be necessary for the implementation of the embodiments of the present invention in order to make the embodiments of the present invention easier to understand. For example, the above description omits a general description of an existing radar or radar system. It should be understood that a continuous pulse radar according to embodiments of the present invention may have other components or assemblies in addition to the transmitters, receivers, and signal recoverers described above that are present in existing radars or radar systems. The foregoing description is by way of example only and is not intended as limiting.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.
Claims (10)
1. A method for realizing simultaneous beamforming and stripe SAR imaging by a coding array is characterized by comprising the following steps:
the radar array is arranged along the azimuth direction of SAR imaging, and a separate coding pulse signal is given to each radiation array element of the radar array; the separate coded pulse signals enable echo signals generated by target reflection to be separable in time, space or frequency; or the echo signals can be separated after decoding processing;
when the radar works, each radiating array element of the radar array transmits a respective coded pulse signal, and each radiating array element receives echo signals of the coded pulse signals transmitted by the radiating array element and other radiating array elements;
collecting the echo signals received by each radiation array element, and decoding; and according to the decoded echo signals, simultaneously performing beamforming and strip SAR imaging processing to obtain beamforming and strip SAR imaging results.
2. The method according to claim 1, wherein in the beamforming SAR imaging processing, a virtual beamforming scanning beam is formed by using target echo signals of different coded pulse signals of each array element to obtain virtual beamforming scanning radar data; and then, performing bunching SAR imaging processing on the data to obtain a bunching SAR image.
3. The method of claim 1, wherein in the strip SAR imaging processing, a virtual strip imaging beam is formed by using target echo signals of different coded pulse signals of each array element to obtain virtual strip imaging radar data, and then the data is used for strip SAR imaging processing to obtain a strip SAR image.
4. The method according to any one of claims 1 to 3, wherein the individual coded pulse signals are frequency-divided coded pulse signals, time-phase combined coded pulse signals or time-phase-frequency combined coded pulse signals;
the single coded pulse signal is a frequency division coded pulse signal; during transmission, each array element adopts different frequencies for transmission, and a transmission channel is isolated through the frequency; during receiving, after each array element receives an echo signal, echo signals corresponding to transmitting signals of different array elements are separated through frequency domain filtering;
the single coded pulse signal is a time-phase combined coded pulse signal, and the basic constraint of coding is that each coding channel is orthogonal to each other; when transmitting, each array element adopts different codes to transmit; during receiving, after each array element receives an echo signal, the echo signals corresponding to the transmitting signals of different array elements are separated through decoding processing;
the single coded pulse signal is a time-phase-frequency combined coded pulse signal, and the basic constraint of coding is that each coding channel is orthogonal to each other; when transmitting, each array element adopts different codes to transmit; during receiving, after each array element receives the echo signal, the echo signals corresponding to the transmitting signals of different array elements are separated through decoding processing.
5. The method of claim 4, wherein the collecting the echo signals received by each radiating element, and performing decoding processing comprises:
for the frequency division encoding pulse signal, decoding processing is carried out in a frequency domain filtering mode;
for the time-phase combined coded pulse signal, a decoding matrix is obtained through the coding matrix, and then the echo signal is decoded by the decoding matrix; the decoding matrix corresponds to the encoding matrix and comprises pulse decoding modes corresponding to the pulse encoding modes of all array elements;
for the time-phase-frequency combined coded pulse signal, a decoding matrix is obtained through the coding matrix, and then the echo signal is processed by the decoding matrix; decoding the echo signal in a frequency filtering mode; the decoding matrix corresponds to the encoding matrix and comprises pulse decoding modes corresponding to the pulse encoding modes of all the array elements.
6. The method of claim 4, wherein, in a beamforming SAR imaging process,
for decoded inclusion of N2Selecting corresponding channel data for subsequent processing according to the imaging resolution of target echo data of the independent channel signals, wherein N is the number of array elements; the method comprises the following steps:
1) frequency processing:
for frequency division coding, after filtering processing is carried out on received data, frequency synthesis is carried out, and the frequency bandwidth after synthesis is not lower than the frequency bandwidth corresponding to the imaging resolution requirement;
for time-phase combined coding, after filtering processing and decoding processing are carried out on received data, frequency synthesis is carried out, and the frequency bandwidth after synthesis is not lower than the frequency bandwidth corresponding to the imaging resolution requirement;
for time-phase-frequency combined coding, after filtering processing and decoding processing are carried out on received data, frequency synthesis is carried out, and the frequency bandwidth after synthesis is not lower than the frequency bandwidth corresponding to the imaging resolution requirement;
2) and (3) beam synthesis processing:
determining the width theta of the synthesized beam according to the imaging distance and the imaging range; determining the number of array elements participating in imaging processing according to the width theta of the synthesized beam; azimuthal resolution ρ from beamforming imagingaDetermining a beamforming imaging angle thetas；
Calculating the beam bunching starting position and the beam bunching ending position according to the imaging center position, the distance between the radar and the imaging center and the beam bunching imaging angle, and calculating the beam bunching instantaneous pointing angle at each sampling position in the radar flight process from the beam bunching starting position to the beam bunching ending position;
and for each sampling position, determining the phase shift phase of each array element participating in beam forming processing by using the beam-forming instantaneous pointing angle of the position, performing phase correction on data obtained by each array element at the position, accumulating the data of different array elements corresponding to the same moment to complete beam forming, and obtaining virtual beam-forming scanning radar data of the radar at the position through synthesis.
7. The method of claim 6,
the synthesized beam width
L is the length of the ground mark irradiated by the radar beam at the imaging distance along the direction vertical to the wave propagation direction; rmaxThe farthest distance for imaging;
the number of the array elements for beam synthesis is determined according to the fact that the antenna beam width corresponding to the antenna length determined by the number of the array elements is not less than the synthesized beam width theta;
the angle of beam bunching imaging
Where λ is the center frequency wavelength of the transmitted signal.
8. The method of claim 4, characterized in that, in a strip SAR imaging process,
for decoded inclusion of N2Selecting corresponding channel data for subsequent processing according to the imaging resolution of target echo data of the independent channel signals, wherein N is the number of array elements; the method comprises the following steps:
1) frequency processing:
for frequency division coding, after filtering processing is carried out on received data, frequency synthesis is carried out, and the frequency bandwidth after synthesis is not lower than the frequency bandwidth corresponding to the imaging resolution requirement;
for time-phase combined coding, after filtering processing and decoding processing are carried out on received data, frequency synthesis is carried out, and the frequency bandwidth after synthesis is not lower than the frequency bandwidth corresponding to the imaging resolution requirement;
for time-phase-frequency combined coding, after filtering processing and decoding processing are carried out on received data, frequency synthesis is carried out, and the frequency bandwidth after synthesis is not lower than the frequency bandwidth corresponding to the imaging resolution requirement;
2) and (3) beam synthesis processing:
imaging azimuthal resolution ρ from stripe SARaDetermining the number of array elements participating in imaging processing; the number of array elements used for beam forming is determined by that the length of an antenna determined by the number of the array elements is not more than half of the azimuth resolution;
for each sampling position, determining the phase shift phase of each array element participating in beam synthesis processing by using the beam instantaneous pointing angle of the position, performing phase correction on data obtained by each array element at the position, accumulating the data of different array elements corresponding to the same moment to complete beam synthesis, and obtaining virtual strip imaging radar data of the radar at the position through synthesis;
3) imaging processing:
and carrying out SAR strip imaging processing by using the virtual strip imaging radar data obtained by synthesis to obtain a strip SAR image.
9. A system for implementing simultaneous beamforming and banding SAR imaging methods based on the coding array of any of claims 1-8, comprising:
the array coding signal generating unit is used for generating a single pulse coding signal transmitted by each radiating array element; the separate coded pulse signals enable echo signals generated by target reflection to be separable in time, space or frequency; or the echo signals can be separated after decoding processing;
the radar array comprises N array elements, each array element transmits a pulse code signal and receives target echo signals of all the array elements transmitting the pulse code signals;
the data acquisition unit is used for acquiring target echo signals received by each radiation array element to form target echo data;
an array signal decoding and processing unit for the collected target echoDecoding the data to separate N corresponding to the receiving and transmitting channel combination formed by different radiation array elements2Target echo data of individual channel signals;
the virtual beam forming unit is used for calculating target echo data corresponding to different transceiving channel combinations to generate a virtual beaming imaging scanning beam and a virtual strip imaging beam, and processing the virtual beaming imaging scanning beam and the virtual strip imaging radar data to obtain the virtual beaming scanning radar data and the virtual strip imaging radar data;
the spotlight SAR imaging processor is used for carrying out imaging processing according to the virtual spotlight scanning radar data to obtain a spotlight SAR image;
and the stripe SAR image processor is used for carrying out imaging processing according to the virtual stripe imaging radar data to obtain a stripe SAR image.
10. The system of claim 9, further comprising,
the comprehensive display unit is used for carrying out visualization processing on the bunching SAR image and the stripe SAR image to form a video stream containing the bunching SAR image, the stripe SAR image and information of the bunching SAR image and the stripe SAR image;
and the control unit is used for controlling the coding array to realize signal generation, transceiving, acquisition, processing and display data generation of the system for simultaneous imaging.
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