CN114384519B - Ultrahigh-resolution satellite-borne synthetic aperture radar imaging method and device - Google Patents
Ultrahigh-resolution satellite-borne synthetic aperture radar imaging method and device Download PDFInfo
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Abstract
The invention provides an ultrahigh-resolution satellite-borne synthetic aperture radar imaging method and device, and relates to the technical field of satellite-borne synthetic aperture radar imaging processing. The method comprises the following steps: obtaining a baseband echo signal of the satellite-borne SAR; acquiring a motion track of a satellite antenna phase center under a WGS84 coordinate system; according to the motion trail, determining a ground specific target point of which the zero Doppler position is at a first preset pixel position; calculating a distance process between the ground specific target point and a satellite antenna phase center, and determining a matched filter which enables the ground specific target point to be focused to a first preset pixel position according to the distance process; performing two-dimensional Fourier transform on the baseband echo signal to obtain a two-dimensional frequency domain signal; and performing matched filtering on the two-dimensional frequency domain signal by using a matched filter, and performing two-dimensional inverse Fourier transform on the two-dimensional frequency domain signal subjected to matched filtering to obtain a focusing target image of the ground specific target point.
Description
Technical Field
The present disclosure relates to the technical field of Synthetic Aperture Radar (SAR) imaging processing, and in particular, to the technical field of ultrahigh Resolution (VHR) imaging processing and two-dimensional space-variant processing, and more particularly, to an imaging method and apparatus for an ultrahigh Resolution SAR.
Background
Conventional SAR imaging methods are typically based on the assumption of uniform linear motion of the antenna. Let the movement speed bevThen the distance history of a certain point in the irradiation range is a hyperbolic model
In whichR 0Being the closest distance of the point to the antenna track,ηin order to be the time of the azimuth,
，η - 、η + at the moment of the start and stop of the synthetic aperture at that point,η 0the point zero doppler time (at which point the distance from the antenna track is shortest). According to the conventional omega-kappa algorithm, firstly, the nearest distance is taken as a reference distance through matched filteringR ref And finishing accurate focusing of each point, and finishing accurate focusing of other closest distance points by using stop interpolation.
For the satellite-borne SAR, in the process of acquiring a scene of data, an antenna track is an arc segment of a satellite orbit in a short time (several seconds to tens of seconds), and the uniform velocity straight line assumption of a conventional imaging model cannot be satisfied. For an on-board SAR system with a short synthetic aperture time (less than 5 seconds), in order to utilize a conventional hyperbolic model, a hyperbolic model fit can be made to the distance history of each point in the irradiation range. Due to the geometric difference of illumination, the equivalent speeds of different distances and different square points in the illumination scenevThe velocity parameters after fitting the hyperbolic model all changed. In this case, the conventional satellite-borne SAR processing is usually adapted to approximately the equivalent speed vCs (chirp scaling) algorithm as a function of distance.
However, for an ultra-high resolution (higher than 0.3 m) satellite-borne SAR system, hyperbolic model fitting is performed on the distance histories of each point with large error, so that accurate focusing cannot be achieved through a conventional omega-kappa algorithm or a CS algorithm.
Disclosure of Invention
In view of the above technical problems in the prior art, the present disclosure provides an ultrahigh resolution spaceborne synthetic aperture radar imaging method and apparatus.
The disclosure provides an ultrahigh resolution spaceborne synthetic aperture radar imaging method, which includes: obtaining a baseband echo signal of the satellite-borne SAR; acquiring the motion of the phase center of the satellite antenna under a WGS84 coordinate systemA trajectory; according to the motion track, determining a ground specific target point with a zero Doppler position at a first preset pixel position, wherein the first preset pixel position is [ [ phi ] ] [ [ alpha ] ]n r ，n a ]，n r Andn a respectively the number of pixels of a first preset distance direction and the number of pixels of a first preset direction of the baseband echo signal; calculating a distance process between the ground specific target point and a satellite antenna phase center, and determining a matched filter which enables the ground specific target point to be focused to a first preset pixel position according to the distance process; performing two-dimensional Fourier transform on the baseband echo signal to obtain a two-dimensional frequency domain signal; performing matched filtering on the two-dimensional frequency domain signal by using a matched filter; and performing two-dimensional inverse Fourier transform on the two-dimensional frequency domain signal subjected to matching filtering to obtain a focusing target image of the ground specific target point.
The present disclosure provides a method and apparatus for imaging an ultra-high resolution spaceborne synthetic aperture radar, including: the signal acquisition module is used for acquiring a baseband echo signal of the satellite-borne SAR; the motion track acquisition module is used for acquiring a motion track of a satellite antenna phase center under a WGS84 coordinate system; a specific target point determining module, configured to determine, according to the motion trajectory, a ground specific target point at which the zero doppler position is located at a first preset pixel position, where the first preset pixel position is set as [ [ solution ] ]n r ，n a ]，n r Andn a respectively obtaining a first preset distance pixel number and a first preset azimuth pixel number of the baseband echo signal; the matched filter determining module is used for calculating a distance process between the ground specific target point and the satellite antenna phase center and determining a matched filter which enables the ground specific target point to be focused to a first preset pixel position according to the distance process; the signal transformation module is used for carrying out two-dimensional Fourier transformation on the baseband echo signal to obtain a two-dimensional frequency domain signal; the matched filtering determining module is used for performing matched filtering on the two-dimensional frequency domain signal by using a matched filter; a focusing target image determining module for performing two-dimensional inverse Fourier transform on the two-dimensional frequency domain signal after the matched filtering to obtain a ground A focused target image of the surface-specific target point.
Compared with the prior art, the ultrahigh-resolution spaceborne synthetic aperture radar imaging method and device provided by the disclosure at least have the following beneficial effects:
(1) for an ultra-high resolution (higher than 0.3 m) satellite-borne SAR system, when an imaging algorithm based on traditional hyperbolic distance history model fitting fails, the accurate two-dimensional matched filter of a specific target position can still be obtained by the method, so that accurate focusing of the specific target position is realized.
(2) After obtaining the accurate two-dimensional matched filter of a specific target position, the method realizes the accurate focusing of a scene in a certain area range by taking the specific target position as the center, namely two-dimensional space-variant processing, and simultaneously provides a method for verifying the focusing effect of the area.
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The above and other objects, features and advantages of the present disclosure will become more apparent from the following description of embodiments of the present disclosure with reference to the accompanying drawings, in which:
fig. 1 schematically illustrates a flow diagram of an ultra-high resolution spaceborne synthetic aperture radar imaging method according to an embodiment of the present disclosure;
FIG. 2 schematically illustrates a flow diagram of a baseband echo signal according to an embodiment of the present disclosure;
Fig. 3 schematically illustrates a flow chart for determining a ground-specific target point according to an embodiment of the present disclosure;
FIG. 4 schematically shows a flow chart for computing an orientation time-frequency correspondence according to an embodiment of the present disclosure;
figure 5 schematically illustrates a flow diagram of an ultra-high resolution on-board synthetic aperture radar imaging method according to another embodiment of the present disclosure;
FIG. 6 schematically illustrates an operational flow diagram of an ultra-high resolution spaceborne synthetic aperture radar imaging method according to another embodiment of the disclosure;
FIG. 7 schematically illustrates a flow chart of focus effect verification for a focus area image according to another embodiment of the present disclosure;
fig. 8 schematically shows a block diagram of an apparatus of an ultra-high resolution spaceborne synthetic aperture radar imaging method according to an embodiment of the present disclosure;
fig. 9 schematically shows a block diagram of an apparatus of an ultra-high resolution spaceborne synthetic aperture radar imaging method according to another embodiment of the disclosure.
Detailed Description
For the purpose of promoting a better understanding of the objects, aspects and advantages of the present disclosure, reference is made to the following detailed description taken in conjunction with the accompanying drawings. It is to be understood that the described embodiments are only a few, and not all, of the disclosed embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments disclosed herein without making any creative effort, shall fall within the protection scope of the present disclosure.
The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the disclosure. The terms "comprises," "comprising," and the like, as used herein, specify the presence of stated features, steps, operations, and/or components, but do not preclude the presence or addition of one or more other features, steps, operations, or components.
All terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs, unless otherwise defined. It is noted that the terms used herein should be interpreted as having a meaning that is consistent with the context of this specification and should not be interpreted in an idealized or overly formal sense.
Some block diagrams and/or flowcharts are shown in the figures. It will be understood that some blocks of the block diagrams and/or flowchart illustrations, or combinations of blocks in the block diagrams and/or flowchart illustrations, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the instructions, which execute via the processor, create means for implementing the functions/acts specified in the block diagrams and/or flowchart block or blocks.
Accordingly, the techniques of this disclosure may be implemented in hardware and/or software (including firmware, microcode, etc.). In addition, the techniques of this disclosure may take the form of a computer program product on a computer-readable medium having instructions stored thereon for use by or in connection with an instruction execution system. In the context of this disclosure, a computer-readable medium may be any medium that can contain, store, communicate, propagate, or transport the instructions. For example, the computer readable medium can include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, device, or propagation medium. Specific examples of the computer readable medium include: magnetic storage devices, such as magnetic tape or Hard Disk Drives (HDDs); optical storage devices, such as compact disks (CD-ROMs); a memory, such as a Random Access Memory (RAM) or a flash memory; and/or wired/wireless communication links.
First, it should be noted that the ultrahigh Resolution (VHR) mentioned in the embodiments of the present disclosure refers to a Resolution higher than 0.3 m. For an ultra-high resolution satellite-borne SAR system, when hyperbolic model fitting is carried out on the distance process of each point, the error is large, so that accurate focusing cannot be carried out through a conventional omega-kappa algorithm or a CS algorithm.
Fig. 1 schematically shows a flow chart of an ultra-high resolution spaceborne synthetic aperture radar imaging method according to an embodiment of the present disclosure.
The present disclosure is set forth under the condition of a front side view stripe mode spaceborne SAR. As shown in FIG. 1, the ultra-high resolution spaceborne synthetic aperture radar imaging method of the embodiment includes operations S110 to S170.
In operation S110, a baseband echo signal of the SAR is acquired.
In operation S120, a motion trajectory of the satellite antenna phase center is acquired in the WGS84 coordinate system.
In operation S130, a ground-specific target point with a zero doppler position at a first preset pixel position is determined according to the motion trajectory.
Wherein the first preset pixel position is [ 2 ]n r ，n a ]，n r Andn a respectively baseband echo signalsThe first preset distance pixel number and the first preset azimuth pixel number of the sign. In particular, the amount of the solvent to be used, n a The number of sampling points in the range direction of the baseband echo signal is set to 1 or more and lessN r An integer of (a);n a the number of azimuth pulses of the baseband echo signal is set to 1 or more and 1 or lessN a Is an integer of (2).
In operation S140, a distance history between the ground specific target point and the satellite antenna phase center is calculated, and a matched filter for focusing the ground specific target point to a first predetermined pixel position is determined according to the distance history.
In operation S150, a two-dimensional fourier transform is performed on the baseband echo signal to obtain a two-dimensional frequency domain signal.
In operation S160, the two-dimensional frequency domain signal is matched filtered using a matched filter.
In operation S170, the two-dimensional inverse fourier transform is performed on the matched and filtered two-dimensional frequency domain signal to obtain a focused target image of the ground specific target point.
Therefore, for the ultra-high resolution satellite-borne SAR system, when the imaging algorithm based on the traditional hyperbolic distance history model fitting fails, the precise two-dimensional matched filter of the ground specific target point can be obtained, so that the precise focusing of the ground specific target point is realized.
The ultrahigh resolution spaceborne synthetic aperture radar imaging method of the embodiment of the disclosure outlined in fig. 1 is described in detail below with fig. 2-4.
Fig. 2 schematically shows a flow diagram of a baseband echo signal according to an embodiment of the present disclosure.
As shown in fig. 2, the baseband echo signal of the satellite-borne SAR in operation S110 may be specifically obtained according to the following operations S1101 to S1102.
In operation S1101, baseband echo data in a quadrature-demodulated two-dimensional time domain is acquired.
In operation S1102, the baseband echo data is distance-wise compressed to obtain a baseband echo signal.
Baseband loopThe wave signal is a distance-compressed signal and can be described as a distance-compressed signal for convenience of descriptions(τ，η) Wherein, in the step (A),τandηrespectively, range-direction time and azimuth-direction time. According to the baseband echo signal, the number of distance sampling points can be determinedN r Number of pulses in the sum directionN a 。
In the WGS84 coordinate system, the locus of motion of the phase center of the satellite antenna can be expressed asX(η)，Y(η)，Z(η)]。
Fig. 3 schematically illustrates a flow chart for determining a ground-specific target point according to an embodiment of the present disclosure.
As shown in fig. 3, the determining the ground-specific target point at which the zero doppler position is located at the first preset pixel position in operation S130 may specifically include operations S1301 to S1302.
In operation S1301, on the ground within a beam irradiation range of the satellite antenna in the WGS84 coordinate system, the shortest distance of the ground specific target point to the movement locus of the satellite antenna phase center is made a preset distance.
The preset distanceR c Comprises the following steps:
wherein, the first and the second end of the pipe are connected with each other,R minis the nearest slope distance of the baseband echo signal;cis the speed of light;f s is the data sampling rate.
In operation S1302, a distance from a ground-specific target point to a motion trajectory of a satellite antenna phase center is made to be the firstn a A minimum value is reached at every pulse.
Wherein the content of the first and second substances,n a the azimuth pulse number of the baseband echo signaln a The time of a pulse can also be expressed asH c The time instant is also called the azimuth zero doppler time instant.
The position of the ground-specific target point thus determined can be represented asP c [x c ，y c ，z c ]The ground-specific target point satisfies both of the above operations S1301 and S1302.
In the embodiment of the present disclosure, the distance history between the ground specific target point and the satellite antenna phase center in operation S140 is described abover c (η) Calculated according to the following formula:
wherein the content of the first and second substances,X(η)，Y(η)，Z(η) The three-dimensional coordinates of the motion trail of the satellite antenna phase center under the WGS84 coordinate system;x c ，y c ，z c for specifying target points on the ground under the WGS84 coordinate systemP c Three-dimensional coordinates of (a).
Fig. 4 schematically shows a flowchart for calculating an orientation time-frequency correspondence according to an embodiment of the present disclosure.
As shown in fig. 4, operation S1401 is further included before the step of determining the matched filter for focusing the ground-specific target point to the first preset pixel position in operation S140.
In operation S1401, the azimuth time-frequency correspondence of the ground specific target point is calculated according to the distance history.
The orientation time-frequency corresponding relation can be expressed as that the two-dimensional frequency point(s) of the ground specific target point is obtainedf τ ，f η )，(f τ ，f η ) Corresponding azimuth time
Can be determined according to the azimuth time-frequency corresponding relation.
The azimuth time-frequency corresponding relation is determined according to the following formula:
wherein, the first and the second end of the pipe are connected with each other,f τ 、f η respectively, range frequency and azimuth frequency;
is prepared from (a)f τ ，f η ) A corresponding azimuth time; (·)' denotes derivation;r c (η) Is a distance history;cis the speed of light;f 0 is the carrier frequency of the transmitted signal.
Based on the orientation time-frequency correspondence relationship, the matched filter in operation S140 is calculated according to the following formula:
wherein the content of the first and second substances,F c (f τ ，f η ) Is a matched filter;R c is a preset distance;H c is the azimuth zero doppler time;πis the circumferential ratio;
is the distance history of the ground specific target point at the azimuth time.
Thus, the matched filter enables ground-specific target pointsP c Focusing precisely to a first predetermined pixel positionn r ，n a ]。
Then, the baseband echo signal is processeds(τ，η) Performing two-dimensional Fourier transform to obtain two-dimensional frequency domain signalS(f τ ，f η )。
Then, the two-dimensional frequency domain signal is processedS(f τ ，f η ) By usingP c Of dotsMatched filterF c (f τ ，f η ) Matched filtering was performed and the result is noted as S 1 (f τ ，f η ). Namely:
finally, toS 1 (f τ ，f η ) Performing two-dimensional inverse Fourier transform to obtain pairsP c Focusing target image with point-accurate focusing, recorded ass 1 (τ，η)。
Fig. 5 schematically shows a flow chart of an ultra-high resolution spaceborne synthetic aperture radar imaging method according to another embodiment of the disclosure. Fig. 6 schematically illustrates an operational flow diagram of an ultra-high resolution spaceborne synthetic aperture radar imaging method according to another embodiment of the present disclosure.
With reference to fig. 5 and fig. 6, after operation S170 of the foregoing embodiment of the present disclosure, the ultrahigh resolution spaceborne synthetic aperture radar imaging method according to another embodiment of the present disclosure may further include operation S210-operation S260.
In operation S210, a first preset pixel position [ 2 ] is set according to a motion trajectory of a phase center of a satellite antennan r ，n a ]And determining four ground surrounding target points of which the zero Doppler positions are respectively positioned at four second preset pixel positions at the edges of the rectangular pixel area.
Wherein, the four second preset pixel positions are [ 2 ]n r −d r /2，n a ]、[n r +d r /2，n a ]、[n r ，n a −d a /2]、[n r ，n a +d a /2]，d r Andd a the number of pixels in the area direction and the number of pixels in the area direction are respectively.
For convenience of explanation, three-dimensional coordinates of four ground surrounding target points sequentially corresponding to the four second preset pixel positions are recorded as P r0[x r0，y r0，z r0]、P r1[x r1，y r1，z r1]、P a0[x a0，y a0，z a0]、P a1[x a1，y a1，z a1]The calculation method refers to specific operations S1301 to S1302 in the operation S130. The nearest distances of the target points around the four ground are respectively recorded asR r0 、R r1 、R a0 、R a1 And zero Doppler time is respectively recorded asH r0 、H r1 、H a0 、H a1 。
In operation S220, distance histories between each of the four ground surrounding target points and the satellite antenna phase center are calculated.
The distance history calculation method refers to the formula in operation S140, and specifically, the four distance histories obtained are:
wherein, the first and the second end of the pipe are connected with each other,r r0 (η)、r r1 (η)、r a0 (η)、r a1 (η) Respectively, the distance histories of the first, second, third and fourth ground surrounding target points.
In operation S230, the position time-frequency correspondence of the target points around the four ground surfaces is calculated according to the obtained four distance histories.
The method for calculating the orientation time-frequency correspondence is performed by referring to the formula in operation S1401, and specifically, the orientation times of the target points around the four ground are determined by the following mapping relationships:
wherein the content of the first and second substances,
four target points around the ground and (f τ ，f η ) The corresponding azimuth time.
In operation S240, the distance direction resampling is performed on the two-dimensional frequency domain signal after the matched filtering at each azimuth frequency point, so as to obtain a distance resampling signal.
Specifically, the matched filtered two-dimensional frequency domain signal pair is matched according to the following formula S 1 (f τ ，f η ) Distance direction resampling is carried out at each azimuth frequency point, and the obtained distance resampling signals are recorded asS 1 (f τ ＇，f η ) In whichf τ ＇Distance frequency after resampling for distance direction:
wherein, the first and the second end of the pipe are connected with each other,f τ 、f η respectively, range frequency and azimuth frequency; (·)' denotes derivation;cis the speed of light;f 0 a carrier frequency for the transmitted signal;R r1 、R r0 the shortest distances to the target points around the second and first ground respectively;
respectively second and first ground surrounding target points and (f τ ，f η ) A corresponding azimuth time;
at azimuth times for the second and first ground surrounding target points, respectively
The distance history of the time.
In operation S250, the distance resample signals are resampled in the azimuth direction at each distance frequency point to obtain azimuth resample signals.
In particular, the distance resampled signal is generated according to the following formulaS 1 (f τ ＇，f η ) At each distance frequency pointAzimuth resampling, and recording the obtained azimuth resampling signal asS 1 (f τ ＇，f η ＇) Whereinf η ＇The rear azimuth frequency is resampled for azimuth:
wherein the content of the first and second substances,H a1 、H a0 respectively the zero doppler time of the fourth and third ground surrounding target points;
the fourth and the third ground surrounding target points respectively and (f τ ，f η ) A corresponding azimuth time;
at azimuth time for the fourth and third ground surrounding target points, respectively 
The distance history of the time.
In operation S260, the position resampled signal is subjected to two-dimensional inverse fourier transform to obtain a focused area image of a rectangular pixel area centered on the ground specific target point.
In particular, the signal is resampled to the azimuthS 1 (f τ ＇，f η ＇) Performing two-dimensional inverse Fourier transform to obtain a focus area image of a rectangular pixel area with the ground specific target point as the center, and recording the focus area image ass 1 (τ＇，η＇) Whereinτ＇、η＇Respectively the distance time and the orientation time after the distance resampling and the orientation resampling. The focusing area image is used as an oblique distance plane SAR image after accurate focusing.
Thus, the present embodiment can realizeP c The vicinity of the pointd r ×d a Precise focusing of the region.
Fig. 7 schematically shows a flow chart of focus effect verification of a focus area image according to another embodiment of the present disclosure.
As shown in fig. 7, in another embodiment of the present disclosure, the focusing effect of the focusing area image of the rectangular pixel area centered on the ground specific target point obtained in the above operation S260 can be verified according to the following operations S310 to S320.
In operation S310, a ground verification point where the zero doppler position is at a third preset pixel position is determined according to the motion trajectory of the satellite antenna phase center.
Wherein the third preset pixel position is [ 2 ]n r +d r /2，n r +d r /2]. The ground verification point is recorded asP e [x e ，y e ，z e ]The calculation method refers to specific operations S1301 to S1302 in the operation S130.
In operation S320, a focus verification image of the ground verification point is calculated using the step of determining the focus target image of the ground specific target point.
Referring to the steps of determining the focus target image of the ground specific target point in operations S140 to S160, the ground specific target point is replaced with a ground verification point, and thus the focus verification image of the ground verification point can be obtained.
Specifically, the focusing effect of the focus area image is verified according to the waveform, resolution, peak side lobe ratio and integral side lobe ratio of the focus verification image of the ground verification point.
Therefore, after the accurate two-dimensional matched filter of the specific target position is obtained, the accurate focusing of the scene in the area range is realized in the certain area range with the specific target position as the center, and meanwhile, the method for verifying the area focusing effect is provided.
Based on the ultrahigh-resolution spaceborne synthetic aperture radar imaging method, the disclosure also provides an ultrahigh-resolution spaceborne synthetic aperture radar imaging method device, which will be described in detail below with reference to fig. 8 and 9.
Fig. 8 schematically shows a block diagram of an apparatus for an ultra-high resolution spaceborne synthetic aperture radar imaging method according to an embodiment of the present disclosure.
As shown in fig. 8, the ultrahigh resolution spaceborne synthetic aperture radar imaging method apparatus 800 of the embodiment includes a signal acquisition module 810, a motion trajectory acquisition module 820, a specific target point determination module 830, a matched filter determination module 840, a signal transformation module 850, a matched filter module 860, and a focused target image determination module 870.
The signal obtaining module 810 is configured to obtain a baseband echo signal of the space-borne SAR. In an embodiment, the signal obtaining module 810 may be configured to perform the operation S110 described above, which is not described herein again.
And the motion track acquisition module 820 is configured to acquire a motion track of a phase center of the satellite antenna in the WGS84 coordinate system. In an embodiment, the motion trajectory acquiring module 820 may be configured to perform the operation S120 described above, which is not described herein again.
A specific target point determining module 830, configured to determine, according to the motion trajectory, a ground specific target point with a zero doppler position located at a first preset pixel position, where the first preset pixel position is [, ] ] [, ]n r ，n a ]，n r Andn a the first preset distance pixel number and the first preset azimuth pixel number of the baseband echo signal are respectively. In an embodiment, the specific target point determining module 830 may be configured to perform the operation S130 described above, which is not described herein again.
And the matched filter determining module 840 is configured to calculate a distance history between the ground specific target point and the satellite antenna phase center, and determine a matched filter for focusing the ground specific target point to a first preset pixel position according to the distance history. In an embodiment, the matched filter determining module 840 may be configured to perform the operation S140 described above, which is not described herein again.
The signal transforming module 850 is configured to perform two-dimensional fourier transform on the baseband echo signal to obtain a two-dimensional frequency domain signal. In an embodiment, the signal transforming module 850 may be configured to perform the operation S150 described above, and is not described herein again.
And a matched filtering module 860, configured to perform matched filtering on the two-dimensional frequency domain signal by using a matched filter. In an embodiment, the matched filtering module 860 may be configured to perform the operation S160 described above, which is not described herein again.
And the focusing target image determining module 870 is configured to perform two-dimensional inverse fourier transform on the two-dimensional frequency domain signal after the matching filtering to obtain a focusing target image of the ground specific target point. In an embodiment, the focusing target image determining module 870 may be configured to perform the operation S170 described above, which is not described herein again.
Fig. 9 schematically shows a block diagram of an apparatus of an ultra-high resolution spaceborne synthetic aperture radar imaging method according to another embodiment of the disclosure.
As shown in fig. 9, the ultrahigh resolution satellite-borne synthetic aperture radar imaging method apparatus 900 according to this embodiment may further include, on the basis of the apparatus 800, a surrounding target point determining module 910, a distance history calculating module 920, a two-dimensional frequency point calculating module 930, a distance resampling module 940, an azimuth resampling module 950, and a focus area image determining module 960.
A peripheral target point determining module 910, configured to set a first preset pixel position [ 2 ] according to the motion trajectory of the satellite antenna phase centern r ，n a ]A rectangular pixel area as a center, and four ground surrounding target points with zero Doppler positions respectively at four second preset pixel positions are determined at the edge of the rectangular pixel area, wherein the four second preset pixel positions are sequentially set to be [ 2 ] ]n r −d r /2，n a ]、[n r +d r /2，n a ]、[n r ，n a −d a /2]、[n r ，n a +d a /2]，d r Andd a the number of pixels in the area direction and the number of pixels in the area direction are respectively. In an embodiment, the surrounding target point determining module 910 may be configured to perform the operation S210 described above, which is not described herein again.
And a distance history calculating module 920, configured to calculate distance histories between the four ground surrounding target points and the satellite antenna phase center. In an embodiment, the distance history calculating module 920 may be configured to perform the operation S220 described above, which is not described herein again.
And a two-dimensional frequency point calculating module 930, configured to calculate, according to the obtained four distance histories, an orientation time-frequency correspondence relationship between the target points around the four grounds. In an embodiment, the two-dimensional frequency point calculating module 930 may be configured to perform the operation S230 described above, which is not described herein again.
And a distance resampling module 940, configured to perform distance resampling on the two-dimensional frequency domain signals after the matched filtering at each azimuth frequency point, so as to obtain distance resampling signals. In an embodiment, the distance resampling module 940 may be configured to perform the operation S240 described above, and is not described herein again.
And the azimuth resampling module 950 is configured to perform azimuth resampling on the distance resampling signals at each distance frequency point to obtain azimuth resampling signals. In an embodiment, the azimuth resampling module 950 may be configured to perform the operation S250 described above, and is not described herein again.
A focused region image determining module 960, configured to perform two-dimensional inverse fourier transform on the azimuth resample signal to obtain a focused region image of a rectangular pixel region centered on the ground specific target point. In an embodiment, the focus area image determining module 960 may be configured to perform the operation S260 described above, which is not described herein again.
According to the embodiment of the present disclosure, any plurality of the signal acquisition module 810, the motion trajectory acquisition module 820, the specific target point determination module 830, the matched filter determination module 840, the signal transformation module 850, the matched filter module 860, the focused target image determination module 870, the surrounding target point determination module 910, the distance history calculation module 920, the two-dimensional frequency point calculation module 930, the distance direction resampling module 940, the azimuth direction resampling module 950, and the focused region image determination module 960 may be combined into one module to be implemented, or any one of them may be split into a plurality of modules. Alternatively, at least part of the functionality of one or more of these modules may be combined with at least part of the functionality of other modules and implemented in one module. According to the embodiment of the disclosure, at least one of the signal acquisition module 810, the motion trajectory acquisition module 820, the specific target point determination module 830, the matched filter determination module 840, the signal transformation module 850, the matched filter module 860, the focused target image determination module 870, the surrounding target point determination module 910, the distance history calculation module 920, the two-dimensional frequency point calculation module 930, the distance re-sampling module 940, the orientation re-sampling module 950, and the focused area image determination module 960 may be at least partially implemented as a hardware circuit, such as a Field Programmable Gate Array (FPGA), a Programmable Logic Array (PLA), a system on a chip, a system on a substrate, a system on a package, an Application Specific Integrated Circuit (ASIC), or may be implemented by hardware or firmware, such as any other reasonable manner of integrating or packaging the circuits, or implemented by any one of three implementations of software, hardware, and firmware, or by a suitable combination of any of them . Alternatively, at least one of the signal acquisition module 810, the motion trajectory acquisition module 820, the specific target point determination module 830, the matched filter determination module 840, the signal transformation module 850, the matched filter module 860, the focused target image determination module 870, the surrounding target point determination module 910, the distance history calculation module 920, the two-dimensional frequency point calculation module 930, the distance resampling module 940, the azimuth resampling module 950, and the focused region image determination module 960 may be at least partially implemented as a computer program module that, when executed, may perform corresponding functions.
It should be understood that the specific order or hierarchy of steps in the processes disclosed is an example of exemplary approaches. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the processes may be rearranged without departing from the scope of the present disclosure. The accompanying method claims present elements of the various steps in a sample order, and are not intended to be limited to the specific order or hierarchy.
Similarly, in the above description of exemplary embodiments of the disclosure, various features of the disclosure are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various disclosed aspects. Reference to the description of the terms "one embodiment," "some embodiments," "an example," "a specific example," or "some examples" or the like means that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the disclosure. In this specification, the schematic representations of the terms used above do not necessarily refer to the same embodiment or example. Furthermore, the particular features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.
Furthermore, the terms "first", "second" and "first" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or to implicitly indicate the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present disclosure, "a plurality" means at least two, e.g., two, three, etc., unless explicitly specifically limited otherwise.
The above-mentioned embodiments are intended to illustrate the objects, aspects and advantages of the present disclosure in further detail, and it should be understood that the above-mentioned embodiments are only illustrative of the present disclosure and are not intended to limit the present disclosure, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present disclosure should be included in the scope of the present disclosure.
Claims (13)
1. An ultra-high resolution spaceborne synthetic aperture radar imaging method is characterized by comprising the following steps:
acquiring a baseband echo signal of the satellite-borne SAR;
acquiring a motion track of a satellite antenna phase center under a WGS84 coordinate system;
according to the motion trail, determining a ground specific target point with a zero Doppler position at a first preset pixel position, wherein the first preset pixel position is [ [ phi ] ] [ [ alpha ] ] n r ，n a ]，n r Andn a respectively the number of pixels of a first preset distance direction and the number of pixels of a first preset direction of the baseband echo signal;
calculating a distance process between the ground specific target point and a satellite antenna phase center, and determining a matched filter which enables the ground specific target point to be focused to the first preset pixel position according to the distance process;
performing two-dimensional Fourier transform on the baseband echo signal to obtain a two-dimensional frequency domain signal;
performing matched filtering on the two-dimensional frequency domain signal by using the matched filter;
and performing two-dimensional inverse Fourier transform on the matched and filtered two-dimensional frequency domain signal to obtain a focusing target image of the ground specific target point.
2. The ultra-high resolution spaceborne synthetic aperture radar imaging method according to claim 1, wherein the baseband echo signal is obtained according to:
obtaining baseband echo data in a two-dimensional time domain after orthogonal demodulation;
and performing range compression on the baseband echo data to obtain a baseband echo signal.
3. The ultra-high resolution spaceborne synthetic aperture radar imaging method according to claim 1, wherein the determining the ground specific target point with the zero doppler position at the first preset pixel position specifically comprises:
On the ground within the beam irradiation range of the satellite antenna under the WGS84 coordinate system, enabling the nearest distance from the ground specific target point to the motion trail of the satellite antenna phase center to be a preset distance, wherein the preset distanceR c Comprises the following steps:
wherein, the first and the second end of the pipe are connected with each other,R minis the nearest slope distance of the baseband echo signal;cis the speed of light;f s is the data sampling rate;
the distance between the ground specific target point and the motion trail of the satellite antenna phase center is enabled to be the firstn a A minimum value is reached at every pulse.
4. The ultra-high resolution spaceborne synthetic aperture radar imaging method according to claim 1, wherein a distance history between the ground specific target point and a satellite antenna phase centerr c (η) Calculated according to the following formula:
wherein the content of the first and second substances,X(η)，Y(η)，Z(η) The three-dimensional coordinates of the motion trail of the satellite antenna phase center under the WGS84 coordinate system;x c ，y c ，z c are the three-dimensional coordinates of a specific target point below the WGS84 coordinate system.
5. The ultra-high resolution spaceborne synthetic aperture radar imaging method according to claim 1, wherein prior to the step of determining the matched filter that focuses the ground-specific target point to the first preset pixel location, further comprising:
according to the distance process, calculating the azimuth time-frequency corresponding relation of the ground specific target point, wherein the azimuth time-frequency corresponding relation is determined according to the following formula:
Wherein, the first and the second end of the pipe are connected with each other,f τ 、f η respectively, range frequency and azimuth frequency;
is prepared from (a)f τ ，f η ) A corresponding azimuth time; (·)' denotes derivation;r c (η) Is a distance history;cis the speed of light;f 0 is the carrier frequency of the transmitted signal.
6. The ultra-high resolution spaceborne synthetic aperture radar imaging method according to claim 5, wherein the matched filter is calculated according to the following formula:
wherein the content of the first and second substances,F c (f τ ，f η ) Is a matched filter;R c is a preset distance;H c is the azimuth zero doppler time;πis the circumferential ratio;
is the distance history of the ground specific target point at the azimuth time.
7. The ultra-high resolution spaceborne synthetic aperture radar imaging method of claim 1, further comprising:
setting a first preset pixel position according to the motion track of the phase center of the satellite antennan r ，n a ]A rectangular pixel area as a center, and four ground surrounding target points with zero Doppler positions respectively positioned at four second preset pixel positions are determined at the edge of the rectangular pixel area, wherein the four second preset pixel positions are sequentially' 2n r −d r /2，n a ]、[n r +d r /2，n a ]、[n r ，n a −d a /2]、[n r ，n a +d a /2]，d r Andd a respectively the number of pixels in the direction of the area distance and the number of pixels in the direction of the area direction;
calculating the distance history between each of the four ground surrounding target points and the phase center of the satellite antenna;
Calculating the azimuth time-frequency corresponding relation of the target points around the four grounds according to the obtained four distance processes;
performing distance direction resampling on the two-dimensional frequency domain signals subjected to matching filtering at each azimuth frequency point to obtain distance resampling signals;
carrying out azimuth resampling on the distance resampling signals at each distance frequency point to obtain azimuth resampling signals;
and performing two-dimensional inverse Fourier transform on the azimuth resampling signal to obtain a focusing area image of a rectangular pixel area with the ground specific target point as the center.
8. The ultra-high resolution spaceborne synthetic aperture radar imaging method according to claim 7, wherein the distance resampling is carried out on the matched and filtered two-dimensional frequency domain signals at each azimuth frequency point according to the following formula:
wherein, the first and the second end of the pipe are connected with each other,f τ 、f η respectively, range frequency and azimuth frequency; (·)' denotes derivation;cis the speed of light;f 0 a carrier frequency for the transmitted signal;R r1 、R r0 the shortest distances to the target points around the second and first ground respectively;
respectively second and first ground surrounding target points and (f τ ，f η ) A corresponding azimuth time;
at azimuth times for the second and first ground surrounding target points, respectively 
The distance history of the time.
9. The ultrahigh resolution spaceborne synthetic aperture radar imaging method according to claim 8, wherein the range resampling signals are subjected to azimuth resampling at each range frequency point according to the following formula:
wherein, the first and the second end of the pipe are connected with each other,H a1 、H a0 respectively the zero doppler time of the fourth and third ground surrounding target points;
the fourth and the third ground surrounding target points respectively and (f τ ，f η ) A corresponding azimuth time;
at azimuth time for the fourth and third ground surrounding target points, respectively
The distance history of the time.
10. The ultra-high resolution spaceborne synthetic aperture radar imaging method according to claim 7, wherein the focusing effect of the focusing area image of the rectangular pixel area centered on the ground specific target point is verified according to the following manner:
according to the motion track of the phase center of the satellite antenna, determining a ground verification point with a zero Doppler position at a third preset pixel position, wherein the third preset pixel position is [ [ solution ] ]n r +d r /2，n r +d r /2]；
And calculating to obtain a focusing verification image of the ground verification point by using the step of determining the focusing target image of the ground specific target point.
11. The ultra-high resolution spaceborne synthetic aperture radar imaging method according to claim 10, wherein the focusing effect of the focus area image is verified according to the waveform, resolution, peak sidelobe ratio and integral sidelobe ratio of the focus verification image of the ground verification point.
12. An ultra-high resolution spaceborne synthetic aperture radar imaging device, comprising:
the signal acquisition module is used for acquiring a baseband echo signal of the satellite-borne SAR;
the motion track acquisition module is used for acquiring a motion track of a satellite antenna phase center under a WGS84 coordinate system;
a specific target point determining module, configured to determine, according to the motion trajectory, a ground specific target point at which a zero doppler position is located at a first preset pixel position, where the first preset pixel position is set to [ 2 ]n r ，n a ]，n r Andn a respectively the number of pixels of a first preset distance direction and the number of pixels of a first preset direction of the baseband echo signal;
the matched filter determining module is used for calculating a distance process between the ground specific target point and a satellite antenna phase center and determining a matched filter which enables the ground specific target point to be focused to the first preset pixel position according to the distance process;
the signal transformation module is used for carrying out two-dimensional Fourier transformation on the baseband echo signal to obtain a two-dimensional frequency domain signal;
the matched filtering module is used for performing matched filtering on the two-dimensional frequency domain signal by using the matched filter;
and the focusing target image determining module is used for performing two-dimensional inverse Fourier transform on the two-dimensional frequency domain signal subjected to matching filtering to obtain a focusing target image of the ground specific target point.
13. The ultra-high resolution spaceborne synthetic aperture radar imaging apparatus as claimed in claim 12, further comprising:
a peripheral target point determination module for setting a first preset pixel position according to the motion track of the satellite antenna phase centern r ，n a ]A rectangular pixel area which is a center, and four ground surrounding target points of which the zero Doppler positions are respectively positioned at four second preset pixel positions are determined at the edge of the rectangular pixel area, wherein the four second preset pixel positions are sequentially set as [ [ 2 ] ]n r −d r /2，n a ]、[n r +d r /2，n a ]、[n r ，n a −d a /2]、[n r ，n a +d a /2]，d r Andd a respectively the number of pixels in the direction of the area distance and the number of pixels in the direction of the area direction;
the distance history calculation module is used for calculating the distance histories between the four ground surrounding target points and the phase center of the satellite antenna;
the two-dimensional frequency point calculation module is used for calculating the orientation time-frequency corresponding relation of the target points around the four grounds according to the obtained four distance processes;
the distance resampling module is used for performing distance resampling on the two-dimensional frequency domain signals after the matched filtering at each azimuth frequency point to obtain distance resampling signals;
the azimuth resampling module is used for performing azimuth resampling on the distance resampling signals at each distance frequency point to obtain azimuth resampling signals;
And the focusing area image determining module is used for performing two-dimensional inverse Fourier transform on the azimuth resampling signal to obtain a focusing area image of a rectangular pixel area with the ground specific target point as the center.
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