CN114325710B - Squint high-orbit SAR non-stop phase modulation compensation method and device - Google Patents
Squint high-orbit SAR non-stop phase modulation compensation method and device Download PDFInfo
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Abstract
The invention provides a squint high-orbit SAR non-stop phase modulation compensation method and device, and relates to the technical field of synthetic aperture radar signal processing. The method comprises the following steps: establishing a slope distance model of radar pulses from transmitting to receiving under the continuous motion of the satellite and the ground, wherein the slope distance model is related to the change of fast time; presetting a transmitting pulse of a radar as a linear frequency modulation signal, and carrying out orthogonal demodulation on the linear frequency modulation signal according to a slant range model to obtain a base band echo signal of a point target in a two-dimensional time domain; carrying out Fourier transform on the baseband echo signal to obtain a two-dimensional frequency domain echo signal and a two-dimensional frequency domain modulation phase caused by the continuous motion of the satellite and the ground; preprocessing the two-dimensional frequency domain modulation phase to preliminarily compensate the two-dimensional frequency domain modulation phase; and sequentially carrying out imaging processing and post-processing on the preprocessed two-dimensional frequency domain echo signals to secondarily compensate the two-dimensional frequency domain modulation phase to obtain target echo signals in a range Doppler domain.
Description
Technical Field
The disclosure relates to the technical field of Synthetic Aperture Radar (SAR) signal processing, in particular to the technical field of satellite-borne SAR imaging processing, and more particularly to a squint high-orbit SAR non-stop phase modulation compensation method and device.
Background
With the development of the satellite-borne SAR technology, a remote sensor for placing the SAR load on a geosynchronous orbit satellite becomes an emerging research hotspot in the SAR field. Compared with the low orbit SAR, the geosynchronous orbit SAR has the advantages of large coverage area, short revisit period, strong anti-strike and anti-destroy capabilities and the like, and has very wide application prospects in civil and military aspects.
The SAR employs a Pulse system to transmit and receive signals at a fixed Pulse Repetition Frequency (PRF). SAR signals are transmitted at the speed of light to form a fast time axis (namely, a distance time axis), the moving speed of the platform is far less than the speed of light to form a slow time axis (namely, an azimuth time axis). The "stop-go" assumption holds that: in the process of transmitting and receiving the pulse signals, the satellite and the target are relatively static and do not change along with the change of fast time and slow time, the slope distance is always unchanged, and the actual two-way slope distance can be replaced by 2 times of the instantaneous slope distance between the radar and the target at the pulse transmitting moment.
The orbit height of the geosynchronous orbit SAR is dozens of times of that of the low orbit SAR, so that the delay time of a target echo is long, the target synthetic aperture time is long, and the classic platform uniform linear motion model and the stop-go assumption are not applicable any more. In addition, both range and azimuth geostationary orbit SAR are significantly larger than low orbit SAR. Therefore, it is difficult to achieve precise focusing of the geosynchronous orbit SAR by directly using the imaging method of the low orbit SAR.
In the aspect of squint high-orbit SAR stop-and-go phase modulation compensation, the prior art mainly has two problems: firstly, for a high orbit satellite, a stop-and-go hypothesis model is not applicable any more, and the description of a general satellite-borne SAR two-dimensional time domain echo signal model is not accurate enough; second, the intra-pulse stopping error compensation method is not simple enough. In particular, the prior art mainly has the following disadvantages:
(1) the prior art is based on the assumption of stopping, and does not consider the change of the platform motion distance and the change of the slope distance along with the fast time in a few or even dozens of pulse time intervals from the pulse transmission to the pulse reception.
(2) In the prior art, mathematical approximations such as linear partial derivatives are utilized in the derivation of the transmitting slope and the receiving slope, a unitary high-order equation is simplified into a linear equation to be solved, and although the calculation process is simple, additional errors are introduced.
(3) The prior art is often combined with a specific imaging algorithm processing flow when compensating errors caused by stop-and-go assumptions, and has no universality.
Therefore, the existing technical scheme does not consider the satellite-ground continuous motion of the squint high-orbit satellite completely, so that the squint high-orbit SAR two-dimensional time domain echo signal model is not accurate enough, and a modulation phase error is caused, and the error is aggravated along with the increase of the synthetic aperture time, the increase of the squint imaging angle and the increase of the satellite orbit height, so that the accurate focusing is influenced.
Disclosure of Invention
In view of the above technical problems in the prior art, the present disclosure provides a squint high-orbit SAR non-stop phase modulation compensation method and device.
The disclosure provides, in one aspect, a squint high-orbit SAR non-stop phase modulation compensation method, including: establishing a slope distance model of radar pulses from transmitting to receiving under the continuous motion of the satellite and the ground, wherein the slope distance model is related to the change of fast time; presetting a transmitting pulse of a radar as a linear frequency modulation signal, and carrying out orthogonal demodulation on the linear frequency modulation signal according to a slant range model to obtain a base band echo signal of a point target in a two-dimensional time domain; carrying out Fourier transform on the baseband echo signal to obtain a two-dimensional frequency domain echo signal and a two-dimensional frequency domain modulation phase caused by the continuous motion of the satellite and the ground; preprocessing the two-dimensional frequency domain modulation phase to preliminarily compensate the two-dimensional frequency domain modulation phase; and sequentially carrying out imaging processing and post-processing on the preprocessed two-dimensional frequency domain echo signals to secondarily compensate the two-dimensional frequency domain modulation phase to obtain target echo signals in a range Doppler domain.
The present disclosure provides in another aspect a squint high-orbit SAR non-stop phase modulation compensation apparatus, including: the system comprises a slope model establishing module, a data processing module and a data processing module, wherein the slope model establishing module is used for establishing a slope model from transmitting to receiving of radar pulses under the continuous motion of the satellite and the ground, and the slope model is related to the change of fast time; the base band echo signal determining module is used for presetting a transmitting pulse of the radar as a linear frequency modulation signal, and carrying out orthogonal demodulation on the linear frequency modulation signal according to the slant range model to obtain a base band echo signal of a point target in a two-dimensional time domain; the modulation phase determining module is used for performing Fourier transform on the baseband echo signal to obtain a two-dimensional frequency domain echo signal and a two-dimensional frequency domain modulation phase caused by continuous motion of the satellite and the ground; the primary compensation module is used for preprocessing the two-dimensional frequency domain modulation phase so as to compensate the two-dimensional frequency domain modulation phase primarily; and the secondary compensation module is used for sequentially carrying out imaging processing and post-processing on the preprocessed two-dimensional frequency domain echo signals so as to secondarily compensate the two-dimensional frequency domain modulation phase and obtain target echo signals in a range Doppler domain.
Compared with the prior art, the squint high-orbit SAR non-stop phase modulation compensation method and device provided by the disclosure at least have the following beneficial effects:
(1) the present disclosure utilizes the star-to-ground continuous motion relationship to more fully account for the change in the relative star-to-ground position over fast and slow times during the transmission of the pulse to the reception, and the resulting change in the slope distance over fast time, relative to the intra-pulse stopping assumption.
(2) The method for accurately calculating the pulse transmitting slant range and the receiving slant range of the squint high-orbit SAR by using the satellite and the target position and speed at each pulse transmitting moment is provided based on the slant range model, so that the obtained transmitting slant range and receiving slant range are accurate solutions of a binary quadratic equation set, mathematical approximation is not used, the calculation result precision is higher, and additional errors are not introduced.
(3) In the process of compensating the non-stop phase modulation, the compensation is firstly carried out in the preprocessing, then the imaging operation is carried out, and finally the fine compensation is carried out in the imaging post-processing without changing into the imaging process.
Drawings
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 chart of a squint high orbit SAR non-stop phase modulation compensation method according to an embodiment of the present disclosure;
FIG. 2 schematically illustrates a geometric relationship of a model of the slant range of a radar pulse from transmission to reception in accordance with an embodiment of the present disclosure;
fig. 3 schematically illustrates a flow chart for determining a two-dimensional frequency domain modulation phase according to an embodiment of the disclosure;
FIG. 4 schematically illustrates a flow diagram of pre-processing according to an embodiment of the present disclosure;
FIG. 5 schematically shows a flow diagram of an imaging process according to an embodiment of the disclosure;
FIG. 6 schematically shows a flow diagram of a post-process according to an embodiment of the disclosure;
fig. 7 schematically shows a block diagram of a squint high-orbit SAR non-stop-go phase modulation compensation apparatus according to an embodiment of the present 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 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 flow diagrams are shown in the figures. It will be understood that some blocks of the block diagrams and/or flowchart illustrations, or combinations thereof, 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.
Fig. 1 schematically illustrates a flowchart of a squint high-track SAR non-stop phase modulation compensation method according to an embodiment of the present disclosure.
As shown in fig. 1, the squint high-track SAR non-stop phase modulation compensation method of the embodiment includes operations S110 to S150.
In operation S110, a pitch model of radar pulses from transmission to reception is established under the continuous movement of the earth, wherein the pitch model is associated with a change in fast time.
In operation S120, it is preset that a transmitting pulse of the radar is a chirp signal, and the chirp signal is orthogonally demodulated according to the slant range model to obtain a baseband echo signal of the point target in the two-dimensional time domain.
In operation S130, a fourier transform is performed on the baseband echo signal to obtain a two-dimensional frequency domain echo signal and a two-dimensional frequency domain modulation phase caused by the continuous motion of the satellite and the ground.
In operation S140, the two-dimensional frequency domain modulation phase is preprocessed to preliminarily compensate the two-dimensional frequency domain modulation phase.
In operation S150, the two-dimensional frequency domain echo signal after the preprocessing is sequentially subjected to imaging processing and post-processing to secondarily compensate the two-dimensional frequency domain modulation phase, so as to obtain a target echo signal in the range-doppler domain.
Therefore, in the embodiment, under the condition of the continuous movement of the satellite and the ground, a slant range model is established and a baseband echo signal is obtained, a two-dimensional frequency domain modulation phase caused by the continuous movement of the satellite and the ground is obtained based on the baseband echo signal, and the two-step compensation non-stop phase modulation including imaging preprocessing and post-processing is adopted, so that the method is not changed into an imaging process, can be applied to any imaging algorithm, and has universality.
The squint high-track SAR non-stop-go phase modulation compensation method according to the embodiment of the disclosure outlined in fig. 1 is described in detail below with reference to fig. 2 to 6.
Fig. 2 schematically illustrates a geometric relationship of a model of the slant range of a radar pulse from transmission to reception according to an embodiment of the disclosure.
As shown in fig. 2, according to the geometric relationship and cosine theorem in the figure, the model of the slant range of the radar pulse from the transmission to the reception in operation S110 can be established according to the following formula:
wherein, the first and the second end of the pipe are connected with each other,R 0 the nearest slant distance from the point target to the SAR antenna;R Tr is the transmit slant range from the SAR antenna to the point target, related to both the fast time and the slow time;αthe direction angle of the radar pulse at the transmitting moment is shown;R Re is the receive slant range from the point target to the SAR antenna, related to both the fast time and the slow time;Vis the radar motion speed; ΔτFor time and fast time of radar pulse from transmission to receptionτIs related to the change in (c);R n and (3) a slope distance model of each radar pulse under the continuous movement of the satellite and the ground.
Is preset withτIn order to be a fast time,ηin slow time, the transmitting slant distanceR Tr Can also be expressed asR Tr (η+τ) Receiving slant distanceR Re Can also be expressed asR Re (η+τ). That is, inη+τ) The radar pulse signal received at the moment experiences the transmitting slant distance from the SAR antenna to the point target R Tr (η+τ) Receiving slant distance from point target to SAR antennaR Re (η+τ) The transmit and receive ramps can be solved for fast time variation according to the above formula.
Therefore, for each radar pulse signal, the slope distance model under the continuous movement of the satellite and the ground can be accurately calculated.
According to the established slant range model, under the condition of continuous movement of the satellite and the ground, a satellite-borne SAR original echo signal model based on the assumption of intra-pulse stop is corrected to obtain a signal model with generality, namely a baseband echo signal.
In the embodiment of the present disclosure, the baseband echo signal of the point target in the two-dimensional time domain in operation S120 may be calculated according to the following formula:
wherein, the first and the second end of the pipe are connected with each other,s(τ,η) A baseband echo signal that is a point target;rect(. to) a unit rectangular window;k r 、Wrespectively transmitting the frequency modulation and the pulse width of a linear frequency modulation signal;w a (η) Is the signal azimuth amplitude;cis the speed of light;f c is the carrier center frequency of the radar, namely the carrier frequency;R(η+τ) For transmitting the slant range in the slant range modelR Tr (η+τ) And receiving the skew distanceR Re (η+τ) I.e. the average slope distance.
Is provided withλAndf c for radar wavelength and carrier frequency, there is c =λf c So that the baseband echo signal of the point target can be obtaineds(τ,η) The finishing method comprises the following steps:
wherein the content of the first and second substances,R(η) For transmitting the slant range in the slant range model R Tr (η) And receiving the skew distanceR Re (η) Average value of (d); Δf c 、∆k r 、∆W、∆RRespectively, the carrier frequency, the modulation frequency, the pulse width, and the change amount of the average slope distance, and all depend on the azimuth moment.
Fig. 3 schematically illustrates a flow chart for determining a two-dimensional frequency domain modulation phase according to an embodiment of the disclosure.
As shown in fig. 3, the operation S130 may specifically include operations S1301 to S1302.
In operation S1301, a distance-to-fourier transform is performed on the baseband echo signal to obtain a distance frequency domain signal related to an azimuth time domain.
In particular, the distance frequency domain signals(f,η) Calculated according to the following formula:
wherein the content of the first and second substances,fis the distance frequency axis; Φ (f,η) The base range frequency domain phase is the same as the phase based on the intra-pulse stopping hypothesis; Δ Φ1(f,η) Frequency-domain modulation of the phase at the first distance2(f,η) And the first distance frequency domain modulation phase and the second distance frequency domain modulation phase jointly form phase modulation in a distance frequency domain caused by the satellite-ground continuous motion.
In operation S1302, an azimuth fourier transform is performed on the range frequency domain signal, and a two-dimensional frequency domain echo signal and a two-dimensional frequency domain modulation phase caused by the satellite-ground continuous motion are obtained by using a stationary phase principle, where the two-dimensional frequency domain modulation phase includes a range signal modulation phase and an azimuth signal modulation phase.
The obtained distance frequency domain signal is subjected to azimuth Fourier transform, and the first distance frequency domain modulates the phase phi1(f,η) And the second distance frequency domain modulation phase phi2(f,η) Much smaller than the fundamental distance frequency domain phase Φ: (f,η) Ignoring the effect of both on solving the stationary phase expression, one can obtain:
wherein the content of the first and second substances,ξis the azimuth frequency axis;f d (η) Is the instantaneous Doppler frequency;V(η) The radar motion speed in a slow time axis.
Next, the azimuth frequency axis is setξAnd distance frequency axisfSubstituting the relation into the distance frequency domain signals(f,η) In the relation of (a), a two-dimensional frequency domain echo signal can be obtaineds(f,ξ) The expression of (c) is:
wherein Φ: (f,ξ) A basic two-dimensional frequency domain phase; Δ Φ1(f,ξ) Modulating a phase for the range signal; Δ Φ2(f,ξ) The phase is modulated for the azimuth signal.
Therefore, compared with the existing signal two-dimensional frequency domain model based on the intra-pulse stopping assumption, the two-dimensional frequency domain modulation phase caused by the continuous motion of the satellite mainly comprises the following two parts:
firstly, the distance signal modulation phase is irrelevant to the target distance and relevant to the distance frequency and the azimuth frequency;
secondly, the modulation phase of the azimuth signal is related to the target distance, the distance frequency and the azimuth frequency.
FIG. 4 schematically shows a flow diagram of pre-processing according to an embodiment of the disclosure.
As shown in fig. 4, the preprocessing of the two-dimensional frequency domain modulation phase in operation S140 may specifically include operations S1401 to S1402.
In operation S1401, a distance signal modulation phase is compensated.
In operation S1402, the azimuth signal modulation phase at the reference point is compensated, so that the preprocessed two-dimensional frequency domain echo signal generates a residual modulation phase.
Operations S1401 and S1402 may be simultaneously performed to simultaneously compensate for the distance signal modulation phase and the azimuth signal modulation phase at the reference point. Specifically, according to the obtained range signal modulation phase and azimuth signal modulation phase, the phase factor of the preliminary compensation is set as:
wherein is2.0(f,ξ) Modulating a phase for the azimuth signal at the reference point;R 0 (η(ξ) Is the slope distance at the reference point;H 1 is the phase factor of the initial compensation.
Thus, the preprocessed two-dimensional frequency domain echo signal is determined according to the following formula:
wherein the content of the first and second substances,s 2 (f,ξ) The two-dimensional frequency domain echo signals are preprocessed; Δ Φ3(f,ξ) Modulating the phase for the residual;R(η(ξ) Is the average of the transmit and receive ramps in the ramp model; ΔR(η(ξ) Is the amount of change in the average slope.
Fig. 5 schematically shows a flow chart of an imaging process according to an embodiment of the present disclosure.
As shown in fig. 5, the imaging processing on the preprocessed two-dimensional frequency domain echo signal in the operation S150 may be described by taking a cs (cs scaling) algorithm as an example, and specifically may include operations S1501 to S1503.
In operation S1501, a Chirp Scaling operation in the complementary range migration correction is performed by the first phase multiplication in the range-doppler domain.
In operation S1502, distance compression, quadratic distance compression (SRC), and coherent range migration rectification are completed by multiplying with a reference function in a two-dimensional frequency domain.
In operation S1503, the second phase multiplication is performed in the range-doppler domain to complete azimuth compression and residual phase compensation, and an SAR image is obtained in the two-dimensional time domain.
Specifically, the two-dimensional frequency domain echo signal after the preprocessing is subjected to imaging processing and calculated according to the following formula:
wherein the content of the first and second substances,H 2,1 a phase factor for the first multiplication in operation S1501;H 2,2 is the reference function in operation S1502;H 2,3 a phase factor that is the second multiplication in operation S1503;s 3 (τ,ξ) After the first multiplicationEcho signals in the range-doppler domain;s 4 (τ,ξ) The echo signal in the two-dimensional frequency domain multiplied by the reference function is obtained;s 5 (τ,ξ) The echo signals in the range-doppler domain after imaging processing, that is, the echo signals in the two-dimensional frequency domain after imaging processing.
FIG. 6 schematically shows a flow diagram of post-processing according to an embodiment of the disclosure.
As shown in fig. 6, the post-processing of the two-dimensional frequency domain echo signal after the imaging processing in operation S150 may specifically include operation S1504.
In operation S1504, the residual modulation phase is compensated in the range-doppler domain for each radar pulse in the range gate in turn to secondarily compensate the two-dimensional frequency domain modulation phase, resulting in a target echo signal in the range-doppler domain.
Specifically, the post-processing is performed on the two-dimensional frequency domain echo signal after the imaging processing according to the following formula:
wherein the content of the first and second substances,xfor each radar pulse within the range gate,x=1,2,…… ,Nr；Nrthe total number of radar pulses;R x (η(ξ) Is a distance door insidexThe average slope distance of the radar pulses in the slope distance model;R 0 (η(ξ) Is a reference pointThe skew distance of (a); ΔR x (η(ξ) Is a firstxAn amount of change in the pitch of individual radar pulses; Δ Φ3,x(f,ξ) Is as followsxA residual modulation phase of each radar pulse;H 3,x to be aligned withxThe phase factor of secondary compensation is carried out on each radar pulse;s 5 (τ,ξ) Echo signals in the range-Doppler domain after imaging processing;s 6 (τ,ξ) Is the target echo signal after being processed in the range-doppler domain.
Therefore, the post-processing can compensate the modulation phase of the residual azimuth signals of different range gates, and accurately compensate the signals in each range gate.
Based on the squint high-orbit SAR non-stop phase modulation compensation method, the disclosure also provides a squint high-orbit SAR non-stop phase modulation compensation device, which will be described in detail below with reference to fig. 7.
Fig. 7 schematically shows a block diagram of a squint high-orbit SAR non-stop-go phase modulation compensation apparatus according to an embodiment of the present disclosure.
As shown in fig. 7, the squint high-orbit SAR non-stop-and-go phase modulation compensation apparatus 700 of the embodiment includes a skew model establishing module 710, a baseband echo signal determining module 720, a modulation phase determining module 730, a primary compensation module 740, and a secondary compensation module 750.
And a slope model establishing module 710 for establishing a slope model of radar pulse from transmitting to receiving under the continuous movement of the satellite and the ground, wherein the slope model is related to the change of fast time. In an embodiment, the slant-distance model building module 710 may be configured to perform the operation S110 described above, which is not described herein again.
And the baseband echo signal determining module 720 is configured to preset a transmitting pulse of the radar as a chirp signal, and perform quadrature demodulation on the chirp signal according to the slant range model to obtain a baseband echo signal of the point target in the two-dimensional time domain. In an embodiment, the baseband echo signal determination module 720 may be configured to perform the operation S120 described above, which is not described herein again.
And the modulation phase determining module 730 is configured to perform fourier transform on the baseband echo signal to obtain a two-dimensional frequency domain echo signal and a two-dimensional frequency domain modulation phase caused by the continuous motion of the satellite and the ground. In an embodiment, the modulation phase determining module 730 may be configured to perform the operation S130 described above, which is not described herein again.
And a preliminary compensation module 740, configured to pre-process the two-dimensional frequency domain modulation phase to preliminarily compensate the two-dimensional frequency domain modulation phase. In an embodiment, the preliminary compensation module 740 may be configured to perform the operation S140 described above, which is not described herein again.
And a secondary compensation module 750, configured to perform imaging processing and post-processing on the preprocessed two-dimensional frequency domain echo signal in sequence, so as to perform secondary compensation on the two-dimensional frequency domain modulation phase, and obtain a target echo signal in a range-doppler domain. In an embodiment, the secondary compensation module 750 may be configured to perform the operation S150 described above, and is not described herein again.
According to the embodiment of the disclosure, under the condition of continuous movement of the satellite and the ground, a slant range model is established and a baseband echo signal is obtained, a two-dimensional frequency domain modulation phase caused by the continuous movement of the satellite and the ground is obtained based on the baseband echo signal, and the two-step compensation non-stop phase modulation including imaging preprocessing and post-processing is adopted, so that the imaging process is not changed, the method is applicable to any imaging algorithm, and is more universal.
According to the embodiment of the present disclosure, any plurality of the module of the slope distance model building module 710, the baseband echo signal determination module 720, the modulation phase determination module 730, the preliminary compensation module 740, and the secondary compensation module 750 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 the other modules and implemented in one module. According to an embodiment of the present disclosure, at least one of the slant range model building module 710, the baseband echo signal determination module 720, the modulation phase determination module 730, the preliminary compensation module 740, and the secondary compensation module 750 may be implemented at least partially 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 in any other reasonable manner of integrating or packaging a circuit, or implemented by any one of three implementations of software, hardware, and firmware, or by a suitable combination of any several of them. Alternatively, at least one of the ramp model establishing module 710, the baseband echo signal determination module 720, the modulation phase determination module 730, the preliminary compensation module 740 and the quadratic compensation module 750 may be at least partially implemented as a computer program module, which when executed, may perform a corresponding function.
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," etc., 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 (9)
1. A squint high-orbit SAR non-stop-run phase modulation compensation method is characterized by comprising the following steps:
establishing a slope distance model of radar pulses from transmission to reception under the continuous movement of the satellite and the ground, wherein the slope distance model is related to the change of fast time;
presetting the transmitting pulse of the radar as a linear frequency modulation signal, and carrying out orthogonal demodulation on the linear frequency modulation signal according to the slope distance model to obtain a base band echo signal of a point target in a two-dimensional time domain;
Performing Fourier transform on the baseband echo signal to obtain a two-dimensional frequency domain echo signal and a two-dimensional frequency domain modulation phase caused by the continuous motion of the satellite and the ground;
preprocessing the two-dimensional frequency domain modulation phase to preliminarily compensate the two-dimensional frequency domain modulation phase;
sequentially carrying out imaging processing and post-processing on the preprocessed two-dimensional frequency domain echo signals to secondarily compensate the two-dimensional frequency domain modulation phase to obtain target echo signals in a range-Doppler domain;
the post-processing is carried out on the two-dimensional frequency domain echo signal after the imaging processing according to the following formula:
wherein, the first and the second end of the pipe are connected with each other,xfor each radar pulse within the range gate,x=1,2,…… ,Nr；Nrthe total number of radar pulses;R x (η(ξ) Is a distance door insidexThe average slope distance of the radar pulses in the slope distance model;R 0 (η(ξ) Is the slope distance at the reference point; ΔR x (η(ξ) Is a firstxAn amount of change in the pitch of individual radar pulses;fis the distance frequency axis;ξis the azimuth frequency axis;cis the speed of light;f c is the carrier center frequency of the radar; Δ Φ3,x(f,ξ) Is as followsxA residual modulation phase of each radar pulse;H 3,x to be aligned withxThe phase factor of secondary compensation is carried out on each radar pulse;s 5 (τ,ξ) Echo signals in the range-Doppler domain after imaging processing; s 6 (τ,ξ) Is the target echo signal after being processed in the range-doppler domain.
2. The squint high-orbit SAR non-stop-go phase modulation compensation method according to claim 1, wherein the slope distance model is established according to the following formula:
wherein, the first and the second end of the pipe are connected with each other,R 0 the nearest slant distance from the point target to the SAR antenna;R Tr is the transmit slant range from the SAR antenna to the point target, related to both the fast time and the slow time;αthe direction angle of the radar pulse at the transmitting moment is shown;R Re is the receive slant range from the point target to the SAR antenna, related to both the fast time and the slow time;Vis the radar motion speed; ΔτFor time and fast time of radar pulse from transmission to receptionτIs related to the change in (c);R n and (3) a slope distance model of each radar pulse under the continuous movement of the satellite and the ground.
3. The squint altitude SAR non-stop-go phase modulation compensation method according to claim 2, wherein the baseband echo signal is determined according to the following formula:
wherein the content of the first and second substances,τthe time is fast;ηis a slow time;s(τ,η) A baseband echo signal that is a point target;rect(. to) a unit rectangular window;k r 、Wrespectively transmitting the frequency modulation and the pulse width of the linear frequency modulation signal;w a (η) Is the signal azimuth amplitude;cis the speed of light;f c is the carrier center frequency of the radar; R(η)For transmitting the slant distance in the slant distance modelR Tr (η)And receiving the skew distanceR Re (η)Average value of (d); Δf c 、∆k r 、∆W、∆RRespectively the change of carrier frequency, frequency modulation, pulse width and average slope distance.
4. The squint high-orbit SAR non-stop-go phase modulation compensation method according to claim 1, wherein the fourier transform is performed on the baseband echo signal to obtain a two-dimensional frequency domain echo signal and a two-dimensional frequency domain modulation phase caused by a satellite-ground continuous motion, specifically comprising:
carrying out range Fourier transform on the baseband echo signal to obtain a range frequency domain signal related to an azimuth time domain;
and carrying out azimuth Fourier transform on the distance frequency domain signals, and obtaining two-dimensional frequency domain echo signals and two-dimensional frequency domain modulation phases caused by the continuous motion of the satellite and the ground by using a stationary phase principle, wherein the two-dimensional frequency domain modulation phases comprise distance signal modulation phases and azimuth signal modulation phases.
5. The squint high-orbit SAR non-stop-walking phase modulation compensation method according to claim 4, wherein the preprocessing the two-dimensional frequency domain modulation phase specifically comprises:
compensating the distance signal modulation phase; and
And compensating the azimuth signal modulation phase at the reference point to enable the preprocessed two-dimensional frequency domain echo signal to generate a residual modulation phase.
6. The squint high-orbit SAR non-stop-walking phase modulation compensation method according to claim 5, characterized in that the two-dimensional frequency domain modulation phase is preprocessed according to the following formula:
wherein the content of the first and second substances,fis the distance frequency axis;ξis the azimuth frequency axis;k r a frequency modulation rate for transmitting a chirp signal;cis the speed of light;f c is the carrier center frequency of the radar; Δ Φ1(f,ξ) Modulating a phase for the range signal; Δ Φ2(f,ξ) Modulating a phase for the azimuth signal;ηis a slow time;R(. is the average of the transmit and receive ramps in the ramp model; Δ Φ2.0(f,ξ) Modulating a phase for the azimuth signal at the reference point;R 0 (η(ξ) Is the slope distance at the reference point;H 1 is the phase factor of the initial compensation.
7. The squint high-orbit SAR non-stop-walking phase modulation compensation method according to claim 1, wherein the imaging processing of the preprocessed two-dimensional frequency domain echo signal specifically comprises:
performing first phase multiplication in a range-Doppler domain to complete Chirp Scaling operation in the complementary range migration correction;
multiplying the distance compression, the secondary distance compression and the consistent distance migration correction by a reference function in a two-dimensional frequency domain; and
And performing second phase multiplication in the range-Doppler domain to complete azimuth compression and residual phase compensation, and obtaining an SAR image in a two-dimensional time domain.
8. The squint high-orbit SAR non-stop-walking phase modulation compensation method according to claim 5, wherein the post-processing of the two-dimensional frequency domain echo signal after the imaging processing specifically comprises:
and sequentially compensating the residual modulation phase in the range-Doppler domain aiming at each radar pulse in the range gate so as to compensate the two-dimensional frequency domain modulation phase for the second time and obtain a target echo signal in the range-Doppler domain.
9. A squint high orbit SAR non-stop phase modulation compensation device is characterized by comprising:
the system comprises a slope model establishing module, a slope model generating module and a slope model generating module, wherein the slope model establishing module is used for establishing a slope model from transmitting to receiving of radar pulses under the continuous motion of the earth, and the slope model is related to the change of fast time;
the baseband echo signal determination module is used for presetting the transmitting pulse of the radar as a linear frequency modulation signal, and carrying out orthogonal demodulation on the linear frequency modulation signal according to the slope distance model to obtain a baseband echo signal of a point target in a two-dimensional time domain;
the modulation phase determining module is used for carrying out Fourier transform on the baseband echo signal to obtain a two-dimensional frequency domain echo signal and a two-dimensional frequency domain modulation phase caused by the continuous motion of the satellite and the ground;
The primary compensation module is used for preprocessing the two-dimensional frequency domain modulation phase so as to compensate the two-dimensional frequency domain modulation phase primarily;
the secondary compensation module is used for sequentially carrying out imaging processing and post-processing on the preprocessed two-dimensional frequency domain echo signals so as to secondarily compensate the two-dimensional frequency domain modulation phase and obtain target echo signals in a range Doppler domain;
the secondary compensation module is further configured to perform post-processing on the two-dimensional frequency domain echo signal after the imaging processing according to the following formula:
wherein the content of the first and second substances,xfor each radar pulse within the range gate,x=1,2,…… ,Nr；Nrthe total number of radar pulses;R x (η(ξ) Is a distance door insidexThe average slope distance of the radar pulses in the slope distance model;R 0 (η(ξ) Is the slope distance at the reference point; ΔR x (η(ξ) Is a firstxAn amount of change in the pitch of individual radar pulses;fis the distance frequency axis;ξis the azimuth frequency axis;cis the speed of light;f c is the carrier center frequency of the radar; Δ Φ3,x(f,ξ) Is as followsxA residual modulation phase of each radar pulse;H 3,x to be aligned withxThe phase factor of secondary compensation is carried out on each radar pulse;s 5 (τ,ξ) Echo signals in the range-Doppler domain after imaging processing;s 6 (τ,ξ) Is the target echo signal after being processed in the range-doppler domain.
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