CN106597442A - Orientation multi-channel intra-pulse bunching SAR imaging method - Google Patents

Abstract

The invention relates to the synthetic aperture radar imaging technology field and particularly relates to an orientation multi-channel intra-pulse bunching SAR imaging method. The imaging method comprises steps that a long pulse signal is decomposed into multiple sub pulse signals, and phase modulation is further carried out; the sub pulse signals are emitted to different orientation sub scenes; a full aperture antenna is decomposed in an azimuth into multiple sub aperture antennas for receiving echo signals; APC phase demodulation and separation for the echo signals received by each sub aperture are respectively carried out; residual constant phases in a phase demodulation process are compensated; the sub pulse echo signals after processing are aligned in a distance direction; sub Doppler frequency band synthesis for the sub pulse echo signals after processing is carried out to acquire a main Doppler frequency band; focusing imaging is carried out. The method is advantaged in that all the echos of an irradiated scene can be received, moreover, signal separation is carried out through employing the azimuth spatial domain filtering technology, and performance is not influenced by fluctuation of a ground scene.

Description

A kind of orientation multichannel arteries and veins internal bunching SAR imaging method

Technical field

The present invention relates to synthetic aperture radar image-forming technical field, more particularly to a kind of orientation multichannel arteries and veins internal bunching SAR Imaging method.

Background technology

When synthetic aperture radar (SAR) is loaded into hypersonic platform (such as Hypersonic Aircraft, satellite etc.), due to flat The high-speed motion of platform, the dopplerbroadening of ground scene echo is very serious, is to meet nyquist sampling law, it is ensured that orientation Signal is not obscured, and system needs to adopt very high pulse recurrence frequency (PRF).High PRF will cause distance dimension sample window long Degree reduces, and when the coverage that wave beam is tieed up in radar pitching is very wide or needs to be imaged very wide scene, can not keep away Range ambiguity or blind range zone occurs with exempting from.Therefore, for hypersonic platform carry SAR system, distance dimension wide swath with Azimuth dimension high-resolution constitutes conflict.Current conventional imaging pattern only speciality in one aspect, Spotlight SAR Imaging and cunning The azimuth resolution of dynamic Spotlight SAR Imaging can be very high, but limited apart from mapping swath width, and orientation mapping band is also discontinuous； Scan and TOPS patterns it is very wide apart from observation scope, be but to sacrifice azimuth resolution as cost；Stripmap SAR only can be obtained To medium resolution and mapping swath width.

In order to solve the contradiction between high-resolution and wide swath, Chinese scholars propose multi-channel system system, Pitching dimension multichannel and azimuth dimension multichannel can be divided into.Pitching dimension multi-channel system ensures orientation echo letter using high PRF Number without fuzzy, and system receives scene echoes simultaneously in pitching dimension using multiple passages, and by pitching spatial domain wave beam shape is tieed up Suppress distance to blurred signal into technology, then complete imaging processing.Azimuth dimension multi-channel system is then received and dispatched using relatively low PRF Signal, it is ensured that distance is fuzzy to occurring without, and simultaneously scene echoes are received using multiple passages in azimuth dimension, with spatial sampling generation For the deficiency of time sampling, then obtained without fuzzy 2D signal by azimuth dimension spatial domain beam-forming technology, finally completed Imaging processing.

At present, Chinese scholars have made substantial amounts of research work to both multi-channel systems, and in channel error The aspect such as estimation and compensation technique, spatial domain beam-forming technology, system optimization technology achieves substantial amounts of achievement in research.However, Conventional multi-channel system generally launches wideband correlation using sub-aperture, and all passages receive scene echoes simultaneously. Transmitting antenna area is less, and gain is little, and this can cause scene echoes signal to noise ratio low, possibly cannot meet imaging demand.

In order to take into account distance dimension mapping bandwidth, azimuth dimension resolution and echo signal to noise ratio problem simultaneously, scientific research personnel proposes Multi-dimensional waveform coding techniques, has than more typical：

(1), Gerhard Krieger et al. are in " Multidimensional Waveform Encoding:A New Digital Beamforming Technique for Synthetic Aperture Radar Remote Sensing, [J], IEEE Transactions on GRS, 2008,46 (1):The pitching dimension multi-dimensional waveform coding techniques that 32-46. " is proposed, Full aperture antenna transmission signal is adopted during transmission signal, and long pulse signal is divided into into multiple subpulses, control antenna beam Make different subpulse irradiation different distance dimension sub-swathses；Multiple passages are tieed up when receiving echo using pitching to receive simultaneously, then The spatial domain degree of freedom provided by multi-channel system isolates the echo of each sub-swaths；Complete the imaging of each sub-swathses Afterwards, wide swath imaging results are obtained to splicing along distance.However, the program is separated using pitching dimension airspace filter technology Signal, its performance is easily risen and fallen by ground scene to be affected.

(2), Wu Qisong et al. " arteries and veins internal bunching SAR orientation high resolution wide swath be imaged [J]. Xi'an electronics technology College journal (natural science edition), 2010,37 (4):676-682. " proposes a kind of Working mould for being referred to as arteries and veins internal bunching SAR Formula, by long pulse multiple subpulse signals are divided into, and scan position scene obtains long synthesis hole within the different subpulse times Footpath is so as to realizing orientation high-resolution, and scene footprint similar to band pattern；Obtained using low pulse repetition frequency (PRF) simultaneously Obtain wide swath.However, 2 points of method presence is not enough in text：1) orientation receives signal using full aperture, and wave beam is narrower, may All echoes of illuminated scene cannot be received；2) echo is received using pitching dimension multichannel simultaneously and ties up spatial domain using pitching Filtering separates signal, and its ambiguity solution performance is easily affected by image scene hypsography.

The content of the invention

It is an object of the invention to provide a kind of orientation multichannel arteries and veins internal bunching SAR imaging method, existing at least to solve A technical problem present in SAR imaging methods.

The technical scheme is that：

A kind of orientation multichannel arteries and veins internal bunching SAR imaging method, comprises the steps：

Step one, long pulse signal is decomposed into into multiple subpulse signals, and using APC technologies to subpulse each described The phase-modulation of signal；

Step 2, will be carried out using full aperture antenna each the described subpulse signal after the phase-modulation carry out send out Penetrate, and to schedule Separation control antenna beam is pointed to so that each described subpulse signal is transmitted into different orientation Sub-scene；

Step 3, the full aperture antenna is decomposed into into multiple sub-aperture antennas along orientation, each described sub-aperture day Line receives the echo-signal of all subpulses, wherein, the sub-aperture number is more than or equal to the subpulse signal number；

Step 4, APC phase demodulatings are carried out to the echo-signal that each sub-aperture is received according to equation below (1)：

Wherein, k is transmitting umber of pulse, and N is orientation frequency-shifting operator, and L is sub-aperture antenna number；

Step 5, the echo-signal that each described sub-aperture after demodulated is received is separated, obtained each institute State the echo-signal of subpulse；

Remaining constant phase during APC phase demodulatings in step 6, compensation process four；

Step 7, according to the predetermined time interval, by the subpulse echo-signal processed through the step 6 away from Align descriscent；

Step 8, the synthesis that the subpulse echo-signal processed through the step 7 is carried out sub- Doppler frequency band, obtain To total Doppler frequency band；

Step 9, total Doppler frequency band data are focused into imaging.

Optionally, in the step 5, optiaml ciriterion is constructed using following relational expression (2)：

Wherein, W_lThe weighing vector for separating l-th subpulse signal is represented, H represents vectorial conjugate transpose；f_aFor Doppler Frequency cells；R(f_a) it is f_aCorresponding statistics covariance matrix, R (f_a)=Ε [S (f_a)·S^H(f_a)], E represents statistical expection, S (f_a) for orientation multichannel SAR system output vector, S (f_a)=[S₁(f_a) S₂(f_a) … S_M(f_a)]^T, T represent vector turn Put, M is sub-aperture antenna number；Q be L × 1 dimensional vector, Q=[h₁ h₂ … h_L]^T；Wherein h_l=1, h_i≠l=0, l take 1～ L；

Further, C is that M × L ties up matrix, can be expressed as formula：

C(f_a)=[a₁(f_a) a₂(f_a) … a_L(f_a)]；

Wherein,

Wherein, d is each sub-aperture central point and the half with reference to the distance between sub-aperture central point, and v is that platform flies Scanning frequency degree, j is

Further,

Wherein, f_PRFIt is the pulse recurrence frequency of radar emission signal；

Further, the optimal solution of optimization problem is shown in relational expression (2)：

Further, after obtaining optimum weight vector, for Doppler frequency unit f_a, from the echo-signal that sub-aperture is received Extracting the process of l-th orientation sub-scene component of signal can be expressed as：

Invention effect：

The orientation multichannel arteries and veins internal bunching SAR imaging method of the present invention, using orientation sub-aperture scene echoes are received, and are received Wave beam width, can receive all echoes of illuminated scene；In addition, signal is separated using orientation airspace filter technology, its Performance will not be risen and fallen by ground scene to be affected；Further, it is also possible to apply the invention to following hypersonic platform carries SAR systems System, realizes remote high resolution wide swath earth observation.

Description of the drawings

Fig. 1 is orientation multichannel arteries and veins internal bunching SAR imaging method transmission signal illustraton of model of the present invention；

Fig. 2 is orientation multichannel arteries and veins internal bunching SAR imaging method receipt signal model figure of the present invention；

Fig. 3 a, Fig. 3 b are in orientation multichannel arteries and veins internal bunching SAR imaging method of the present invention, to be demodulated using APC phase-modulations The relationship between frequency and time of different azimuth sub-scene echo-signal in front and back；

Fig. 4 is in orientation multichannel arteries and veins internal bunching SAR imaging method of the present invention, to introduce the Signal Compression result figure after APC；

Fig. 5 is that in orientation multichannel arteries and veins internal bunching SAR imaging method of the present invention, sub-scene 1 adopts orientation multichannel certainly Adapt to the result figure that beam-forming technology separates echo-signal；

Fig. 6 is that in orientation multichannel arteries and veins internal bunching SAR imaging method of the present invention, sub-scene 2 adopts orientation multichannel certainly Adapt to the result figure that beam-forming technology separates echo-signal；

Fig. 7 is that in orientation multichannel arteries and veins internal bunching SAR imaging method of the present invention, sub-scene 3 adopts orientation multichannel certainly Adapt to the result figure that beam-forming technology separates echo-signal；

Fig. 8 is the sub- Doppler frequency band composite result of point target in orientation multichannel arteries and veins internal bunching SAR imaging method of the present invention Figure；

Fig. 9 is point target imaging results in orientation multichannel arteries and veins internal bunching SAR imaging method of the present invention.

Specific embodiment

To make purpose, technical scheme and the advantage of present invention enforcement clearer, below in conjunction with the embodiment of the present invention Accompanying drawing, the technical scheme in the embodiment of the present invention is further described in more detail.In the accompanying drawings, identical from start to finish or class As label represent same or similar element or the element with same or like function.Described embodiment is the present invention A part of embodiment, rather than the embodiment of whole.It is exemplary below with reference to the embodiment of Description of Drawings, it is intended to use It is of the invention in explaining, and be not considered as limiting the invention.Based on the embodiment in the present invention, ordinary skill people The every other embodiment that member is obtained under the premise of creative work is not made, belongs to the scope of protection of the invention.Under Face combines accompanying drawing and embodiments of the invention is described in detail.

In describing the invention, it is to be understood that term " " center ", " longitudinal direction ", " horizontal ", "front", "rear", The orientation or position relationship of the instruction such as "left", "right", " vertical ", " level ", " top ", " bottom ", " interior ", " outward " is based on accompanying drawing institute The orientation for showing or position relationship, are for only for ease of the description present invention and simplify description, rather than indicate or imply the dress of indication Put or element with specific orientation, with specific azimuth configuration and operation, therefore it is not intended that must be protected to the present invention The restriction of scope.

Below in conjunction with the accompanying drawings 1 to Fig. 5 does further specifically to orientation multichannel arteries and veins internal bunching SAR imaging method of the present invention It is bright.

The invention provides a kind of orientation multichannel arteries and veins internal bunching SAR imaging method, comprises the steps：

The transmission signal model of step one, reference Fig. 1, multiple subpulses letters are decomposed into during transmission signal by long pulse signal Number, and the phase-modulation using APC technologies to subpulse signal each described.

Specifically, it is assumed that system launches altogether L sub- pulse signal, and assumes L for odd number, then l-th subpulse signal Corresponding APC phase modulations can be expressed as：

Wherein k is transmitting umber of pulse, and N is orientation frequency-shifting operator, and the span of N is Wherein f_PRFFor system pulses repetition rate, f_dcOffset for the Doppler center between adjacent subpulse, B_a For full aperture orientation doppler bandwidth.Therefore, l-th subpulse signal transmitted waveform be：

In formulaFor the transmitted waveform of conventional SAR system.

Step 2, will be phase modulated using full aperture antenna after each subpulse signal launched, and according to Predetermined time interval (i.e. the time of each subpulse) control antenna beam is pointed to so that each subpulse signal transmitting (i.e. edge Launch in aircraft flight direction) to different orientation sub-scenes.

Step 3, as shown in Fig. 2 when receiving scene echoes, by full aperture antenna along orientation (the i.e. side of aircraft flight To) multiple sub-aperture antennas are decomposed into while receiving signal, each sub-aperture antenna receives the echo-signal of all subpulses； Wherein, sub-aperture number M is more than or equal to subpulse signal number L；

Step 4, APC phase demodulatings, energy are carried out to the echo-signal that each sub-aperture is received according to equation below (1) Enough echo-signals for ensureing sub-scene in the middle of after demodulation will not produce additional Doppler frequency shift：

Wherein, k is transmitting umber of pulse, and N is orientation frequency-shifting operator, and L is subpulse signal number

After phase-modulation with demodulation, the remaining phase modulation of l-th sub-scene echo-signal can be expressed as：

Section 1 is the slow time t in orientation in relation (5) formula_aFirst order, this cause through orientation phase-modulation with demodulation Afterwards, there is Doppler frequency shift phenomenon in echo-signal, and the Doppler frequency shift of l-th sub-scene echo is 2nd is constant phase item, needs to compensate when sub- Doppler frequency spectrum splices.APC phase codes and decoding (phase-modulation Demodulation) front and back position signal relationship between frequency and time such as Fig. 3 a (APC phase-modulations demodulation before) and 3b (after APC phase-modulations are demodulated) institute Show.

Step 5, the echo-signal for receiving demodulated rear each sub-aperture, using azimuth dimension multi-channel adaptive Beam-forming technology is separated, and obtains the echo-signal of each subpulse.

Specifically, in order in order to extract the echo of l-th sub-scene, in the step 5, using following relational expression (2) optiaml ciriterion is constructed：

Wherein, W_lThe weighing vector for separating l-th subpulse signal is represented, H represents vectorial conjugate transpose；f_aFor Doppler Frequency cells；R(f_a) it is f_aCorresponding statistics covariance matrix, can estimate to obtain, R (f from sampled data_a)=Ε [S (f_a)·S^H(f_a)]；E represents statistical expection, S (f_a) for orientation multichannel SAR system output vector, S (f_a)=[S₁(f_a) S₂ (f_a) … S_M(f_a)]^T, T represents vectorial transposition, and M is sub-aperture antenna number；Q be L × 1 dimensional vector, Q=[h₁ h₂ … h_L]^T；Wherein h_l=1, h_i≠l=0, l take 1～L；

Further, C is that M × L ties up matrix, can be expressed as formula：

C(f_a)=[a₁(f_a) a₂(f_a) … a_L(f_a)]；

Wherein,

Wherein, d is each sub-aperture central point and the half with reference to the distance between sub-aperture central point, and v is that platform flies Scanning frequency degree, j is

Further,

Wherein, f_PRFIt is the pulse recurrence frequency of radar emission signal；

Further, the optimal solution of optimization problem is shown in relational expression (2)：

Further, after obtaining optimum weight vector, for Doppler frequency unit f_a, from the echo-signal that sub-aperture is received Extracting the process of l-th orientation sub-scene component of signal can be expressed as：

With reference to APC technologies, Signal Compression result figure is as shown in Figure 4；And using orientation multi-channel adaptive Wave beam forming Shown in the result such as Fig. 5-Fig. 7 of technology separation echo-signal.

Remaining constant phase (known technology, equivalent to general during APC phase demodulatings in step 6, compensation process four Tell somebody what one's real intentions are in material formula (5)Compensate into zero).

Step 7, according to predetermined time interval (or transmitting subpulse signal between delay), will be at step 6 The subpulse echo-signal of reason is alignd in distance to (the signal direction of the launch).

Step 8, the synthesis that the subpulse echo-signal processed through step 7 is carried out sub- Doppler frequency band, obtain total Doppler frequency band (and then according to each corresponding Doppler center of subpulse signal carry out azimuth spectrum up-sampling, translation, it is complete Into the synthesis of sub- Doppler frequency band, total Doppler frequency band is obtained)；Obtain Fig. 8 such as and provide the sub- Doppler frequency band synthesis of point target As a result.

Step 9, total Doppler frequency band data are focused imaging (conventional frequency domain algorithm)；Obtain Fig. 9 such as to be given a little Target imaging result.

The orientation multichannel arteries and veins internal bunching SAR imaging method of the present invention, using orientation sub-aperture scene echoes are received, and are received Wave beam width, can receive all echoes of illuminated scene；In addition, signal is separated using orientation airspace filter technology, its Performance will not be risen and fallen by ground scene to be affected.The present invention is taking into account SAR image scene fabric widths, imaging resolution and echo While signal to noise ratio, solve the problems, such as that existing method ambiguity solution performance is easily affected by image scene hypsography, improve in arteries and veins The imaging performance of Spotlight SAR Imaging system, is that necessary theoretical basiss are established in Future Projects application.Further, the present invention can also be answered SAR system is carried for following hypersonic platform, remote high resolution wide swath earth observation is realized.

The above, the only specific embodiment of the present invention, but protection scope of the present invention is not limited thereto, any Those familiar with the art the invention discloses technical scope in, the change or replacement that can be readily occurred in, all should It is included within the scope of the present invention.Therefore, protection scope of the present invention should be with the scope of the claims It is accurate.

Claims (2)

1. a kind of orientation multichannel arteries and veins internal bunching SAR imaging method, it is characterised in that comprise the steps：

Step one, long pulse signal is decomposed into into multiple subpulse signals, and using APC technologies to subpulse signal each described Phase-modulation；

Step 2, launched each the described subpulse signal after the phase-modulation is carried out using full aperture antenna, and To schedule Separation control antenna beam is pointed to so that each described subpulse signal is transmitted into different orientation subfields Scape；

Step 3, the full aperture antenna is decomposed into into multiple sub-aperture antennas along orientation, each described sub-aperture antenna is equal The echo-signal of all subpulses is received, wherein, the sub-aperture number is more than or equal to the subpulse signal number；

Step 4, APC phase demodulatings are carried out to the echo-signal that each sub-aperture is received according to equation below (1)：

Wherein, k is transmitting umber of pulse, and N is orientation frequency-shifting operator, and L is sub-aperture antenna number；

Step 5, the echo-signal that each described sub-aperture after demodulated is received is separated, obtained each son The echo-signal of pulse；

Remaining constant phase during APC phase demodulatings in step 6, compensation process four；

Step 7, according to the predetermined time interval, by the subpulse echo-signal processed through the step 6 distance to Alignment；

Step 8, the synthesis that the subpulse echo-signal processed through the step 7 is carried out sub- Doppler frequency band, obtain total Doppler frequency band；

Step 9, total Doppler frequency band data are focused into imaging.

2. orientation multichannel arteries and veins internal bunching SAR imaging method according to claim 1, it is characterised in that in the step In five, optiaml ciriterion is constructed using following relational expression (2)：

$\left\{\begin{array}{c}\underset{W_l}{min}{W}_l^H\left(f_a\right)R\left(f_a\right)W_l\left(f_a\right)\\ \begin{array}{cc}s.t.& W_l^H\left(f_a\right)C\left(f_a\right)=Q^H\end{array}\end{array}\right.......\left(2\right);$

Wherein, W_lThe weighing vector for separating l-th subpulse signal is represented, H represents vectorial conjugate transpose；f_aFor Doppler frequency Unit；R(f_a) it is f_aCorresponding statistics covariance matrix, R (f_a)=E [S (f_a)·S^H(f_a)], E represents statistical expection, S (f_a) For the output vector of orientation multichannel SAR system, S (f_a)=[S₁(f_a) S₂(f_a) … S_M(f_a)]^T, T represents vectorial transposition, M It is sub-aperture antenna number；Q be L × 1 dimensional vector, Q=[h₁ h₂ … h_L]^T；Wherein h_l=1, h_i≠l=0, l take 1～L；

Further, C is that M × L ties up matrix, can be expressed as formula：

C(f_a)=[a₁(f_a) a₂(f_a) … a_L(f_a)]；

Wherein,

$a_l\left(f_a\right)={\left[\begin{array}{cccc}\exp \left(j2\mathrm{\π}\frac{d_1}{v}{f}_a^l\right)& \exp \left(j2\mathrm{\π}\frac{d_2}{v}{f}_a^l\right)& ...& \exp \left(j2\mathrm{\π}\frac{d_M}{v}{f}_a^l\right)\end{array}\right]}^T;$

Wherein, d is each sub-aperture central point and the half with reference to the distance between sub-aperture central point, and v is platform flight speed Spend, j is

Further,

$f_a^l=f_a+l\·(f_{PRF}-\frac{f_{PRF}}{N});$

$-\frac{f_{PRF}}{2}\≤f_a\≤\frac{f_{PRF}}{2};$

Wherein, f_PRFIt is the pulse recurrence frequency of radar emission signal；

Further, the optimal solution of optimization problem is shown in relational expression (2)：

$W_l^{opt}\left(f_a\right)=R^{-1}\left(f_a\right)C\left(f_a\right){\left(C^H\right(f_a\left)R^{-1}\right(f_a\left)C\right(f_a\left)\right)}^{-1}Q;$

Further, after obtaining optimum weight vector, for Doppler frequency unit f_a, from the echo-signal extraction that sub-aperture is received The process of l-th orientation sub-scene component of signal can be expressed as：

$S_l\left(f_a\right)={\[W_l^{opt}\left(f_a\right)\]}^H\·S\left(f_a\right).$