CN102121990B - Space-time analysis-based target rotation speed estimating method for inverse synthetic aperture radar - Google Patents

Abstract

The invention discloses a space-time analysis-based target rotation speed estimating method for an inverse synthetic aperture radar. The method comprises the following steps of: compensating a translation component of a target relative to the radar according to received echo data; performing space-time analysis on a target scattering center according to the echo data represented by a basis function constructed in a wave number domain space; and fitting a target rotation speed according to extracted scattering center space position and space position change rate information. In the method, the scattering center is not required to be extracted in an image domain and a high-order phase coefficient of the scattering center is also not extracted in a pulse pressure data domain; and the phase coefficient of the scattering center is extracted through the space-time analysis of the wave number domain, so the method is more stable and reliable and is particularly suitable for target parameter estimation of the high-resolution inverse synthetic aperture radar.

Description

The method for estimating rotating speed of target of the inverse synthetic aperture radar (ISAR) of analyzing during based on sky

Technical field

The present invention relates to the Radar Technology field, more specifically, the rotating speed of target that the present invention relates to a kind of inverse synthetic aperture radar (ISAR) of analyzing during based on sky is estimated and the image calibration method.

Background technology

Inverse synthetic aperture radar (ISAR) (ISAR) is a kind of microwave Imaging Technique, and two dimension even the 3-D view on non-cooperative moving targets (for example aircraft, naval vessel) can be provided, thereby strengthens follow-up recognition capability to target.ISAR provides along the high resolution capacity of radar line of sight direction (distance to) by the emission broadband signal, obtains span descriscent resolution characteristic by the echo of coherent accumulation target under difference observation visual angle.When the aspect of one-tenth's image accumulation changes hour, adopt efficient FFT to process and to obtain target at the image in distance-Doppler (RD) territory.

Because ISAR is usually for the noncooperative target imaging, therefore, the estimation that target Equivalent is rotated (being the relatively variation at visual angle between radar and the target) is extremely important, and this is because there is the demand of following two aspects: at first, and the needs of ISAR image calibration; Although the range resolution of image that ISAR becomes depends on the bandwidth (it is a known quantity normally) of radar emission signal, but the lateral resolution of image depends in the coherent accumulation time the relatively variable quantity at visual angle, and it is normally unknown for the noncooperative target imaging.Only have this visual angle change amount is estimated accurately, can laterally calibrate the ISAR image, obtain the image of distance-span delocalization, promote succeeding target identification.Secondly, the needs of high resolving power ISAR imaging.When ISAR resolution is higher, when the visual angle change that accumulates was larger, resolution element migration (MTRC) problem may appear striding, cause the image defocus problem, therefore need to carry out rotation compensation according to the rotation information of target, improve image quality.

Existing ISAR rotates that the typical method of estimating mainly contains track fitting method, picture quality method and the method for analyzing based on the high-order phase term and the method for analyzing based on image sequence.The target tracking data that the track fitting method provides by Narrow-band Radar, the visual angle change of the relative radar of calculating moving target, estimated accuracy is usually lower.The picture quality method adopts the picture appraisal function to optimize unknown corner parameter, when this picture appraisal function obtains extreme value (this moment, the focusing effect of image was best), obtaining corresponding corner estimates, because these class methods need to be searched in solution space repeatedly, each time search all needs complicated imaging processing, for example polar coordinates format image-forming, the contrary projection imaging of convolution, calculated amount is larger.

Typically the method based on the high-order phase term is that special aobvious point is processed the method for (PPP), the method is approximately linear FM signal (LFM) with the echoed signal on the target, by estimating initial frequency and the frequency modulation rate of LFM, and in conjunction with the distance at three scattering point places to positional information, thereby finish translation compensation, rotation compensation and corner and estimate that the subject matter of these class methods is to be difficult to find reliable and stable high-quality to isolate scattering point in actual conditions.For the target that lacks special aobvious point, can introduce the method for time frequency analysis (TFA) and extract the high-order phase term, but the TFA class methods all are to carry out for the echo in the range unit to the analysis of target echo signal, and the scattering point echo resides in the limited time (particularly for high resolution radar) in the same range unit.Thereby the high-order phase coefficient of signal is usually very little, the parameter extraction difficulty, and the calculated amount of parameter extraction is larger, and precision is lower, and simultaneously, its calculated amount is also larger.

In addition, there is target scattering feature extraction hard problem in the method for estimating rotating speed of target based on feature extraction in the image sequence more at present, and mainly is applicable to the with great visual angle occasion of variable quantity based on the relevant method of image sequence rotation, and their limitation is arranged.

Summary of the invention

For overcoming the horizontal calibrating method low precision of existing ISAR image, realize hard problem, the present invention proposes a kind of method for estimating rotating speed of target of the inverse synthetic aperture radar (ISAR) of analyzing during based on sky.

In one aspect, the present invention proposes a kind of method for estimating rotating speed of target of inverse synthetic aperture radar (ISAR), comprising:

Step 10), according to the echo data that receives, Compensation Objectives is with respect to the translation component of radar;

Step 20), according at the represented echo data of the basis function of wavenumber domain spatial configuration, analyze when target scattering center is carried out sky;

Analyze scattering center locus and the spatial position change rate information of extracting, match rotating speed of target during step 30), according to described sky;

Step 40), according to the rotating speed of target of institute's match, inverse synthetic aperture radar (ISAR) distance-Doppler image is calibrated or is carried out polar coordinates format image-forming.

Wherein, step 10) in, for the echo data that receives, the data of the easy motion section of select target compensate the translation component that removes the relative radar of target by translation, and described translation compensation comprises echo envelope alignment and the correction of translation first phase.

Step 20) also comprise: at first target echo is transformed in the range-Dopler domain, to scattering center apart from r _pAnd frequencies omega _pCarry out according to a preliminary estimate.

Wherein, step 20) in, at wavenumber domain spatial configuration basis function, echo data after the translation compensation is transformed to the wavenumber domain space also to be represented with described basis function, analyze when the described echo data that uses basis function to represent carries out sky to target scattering center, the distance of extracting scattering center to the position, Doppler frequency, locus rate information over time.

Wherein, in step 30) in, according to scattering center parameter estimation and spatial position change rate information, adopt least square method match target scattering center migration amount with the variation of scattering center distance to the position, estimating target rotating speed.

Wherein, step 30) in, according to a plurality of scattering center parameter estimation in the wavenumber domain, pass through expression formula

The rotating speed of match target, wherein, (r _Pn, α _Pn) be the parameter of estimated n scattering center, (r _Po, α _Po) be the parameter of estimated reference scattering center.

By using the present invention, the echo data that can directly receive according to the ISAR system obtains the estimation of target Equivalent rotating speed, does not need extra system hardware; By at the correlation space of wavenumber domain space search scattering center, the change information of frequency, obtain the rotating speed estimation of target, can guarantee the reliability that rotating speed of target is estimated.

In addition, method of the present invention is owing to be in wavenumber domain space search scattering center parameter, need to not extract scattering center at image area, also do not extract the high-order phase coefficient of scattering center at the pulse pressure data field, so that the method is more reliable and stable, and being specially adapted to the estimation of high resolving power inverse synthetic aperture radar (ISAR) target component, range of application is wider.

Description of drawings

Fig. 1 is Aircraft Targets model according to an embodiment of the invention;

Fig. 2 is for carrying out the process flow diagram of rotating speed of target estimation and formation method according to embodiments of the invention;

Fig. 3 is the inverse synthetic aperture radar imaging synoptic diagram based on the rotary body model;

Fig. 4 is for obtaining the process flow diagram of multiple scattering Center Parameter Estimation by process of iteration;

Fig. 5 is for adopting sliding window mode to select strong scattering center synoptic diagram at the distance-Doppler image area;

Fig. 6 is rotating speed of target fitting result synoptic diagram;

Fig. 7 is for adopting the not scaled distance doppler image synoptic diagram of 1024 pulses;

Fig. 8 is for adopting the scaled distance doppler image synoptic diagram of 1024 pulses; With

Fig. 9 is for adopting the polar format calibration image synoptic diagram of 1024 pulses.

Embodiment

Below in conjunction with accompanying drawing and example, the method for estimating rotating speed of target of a kind of inverse synthetic aperture radar (ISAR) provided by the invention is described further.

In one embodiment of the invention, method of the present invention is processed for the data that China experiment ISAR system provides, and the Aircraft Targets model that Fig. 1 provides is as the object of calibrating in the present embodiment.Usually, those skilled in the art can recognize that method of the present invention is not limited to the Aircraft Targets among the figure, can also be used for comprising such as other noncooperative targets such as naval vessels.For described experiment ISAR system, the radar carrier frequency is 5.52GHz; The bandwidth 400MHz of emission linear FM signal; Adopt the Dechirp mode to obtain pulse compression signal, and through the sampling of quadrature I/Q binary channels, sample frequency 10MHz; Equivalent pulse repetition frequency 200Hz (having passed through the pulse extraction); Obtaining 1024 pulses processes.

Fig. 2 illustrates the overall procedure of the method for according to an embodiment of the invention rotating speed of target estimation and imaging, as shown in Figure 2, in step 10, for the echo data that receives, compensates the translation component of relative radar.In one embodiment, the data of the easy motion section of select target compensate the translation component that removes the relative radar of target by translation, obtain turntable target movement model shown in Figure 3.Wherein, the translation compensation of target is carried out usually in two steps: echo envelope alignment and translation first phase are proofreaied and correct.More sane envelope alignment method mainly contains echo correlation method, the overall minimum entropy method based on the adjacent pulse accumulation.More sane translation first phase bearing calibration mainly contains Doppler's centroid tracking method and improves algorithm, such as the Doppler's centroid tracking method based on the circle shifting processing.

In step 20, at wavenumber domain spatial configuration basis function, echo data after the translation compensation is transformed to the wavenumber domain space also to be represented with described basis function, analyze when the described echo data that represents by basis function carries out sky to target scattering center, the distance of extracting scattering center to the position, Doppler frequency (striding distance and position), the locus information such as rate over time.

Under plane wave illumination, the wideband echoes by processing target obtains along the high-resolution of radar line of sight direction (distance to); By the echo coherent accumulation being processed the Doppler frequency information of echo, form span descriscent high-resolution.In rotary body imaging model shown in Figure 3, after the process translation compensates in the short observation time section, but hypothetical target is with ω _oUniform rotation, then 1 P (x on the target _n, y _n) arrive the distance of radar antenna phase center with burst length t _mBe changed to:

$r_n\left(t_m\right)={[r_{\mathrm{no}}^2+r_a^2-2r_{\mathrm{no}}{r}_a\cos ({\mathrm{\θ}}_{\mathrm{no}}+{\mathrm{\ω}}_o{t}_m)]}^{1/2}\≈r_a-[x_n\cos \left({\mathrm{\ω}}_o{t}_m\right)-y_n\sin \left({\mathrm{\ω}}_o{t}_m\right)]---\left(1\right)$

Wherein, (r _No, θ _No) be the polar coordinates of this scattering center, r _aBe the distance of radar and target rotation center, ω _oBe the target Equivalent rotating speed.

In limited observation time, above-mentioned distance can further be approximately:

$r_n\left(t_m\right)\≈(r_a-x_n)+y_n{\mathrm{\ω}}_o{t}_m+0.5x_n{\mathrm{\ω}}_o^2{t}_m^2=r_{\mathrm{no}}+{\mathrm{\ω}}_n{t}_m+0.5{\mathrm{\α}}_n{t}_m^2---\left(2\right)$

Wherein, r _NoFor the distance of scattering center to the position, ω _nBe scattering center Doppler frequency (position, span descriscent), α _nFor the scattering center locus with burst length t _mVariation.

Suppose that the emission linear FM signal is:

s(t)＝rect(t/T _p)exp(jπ(2f _ct+γt ²)) (3)

Wherein, rect () is the unit gate signal, T _pBe pulse width, f _cBe carrier frequency, γ is signal frequency modulation rate.

After coherent demodulation, the echoed signal that obtains from above-mentioned scattering center can be expressed as:

$s_r(t,t_m)=\mathrm{rect}\left(\frac{t-2r_n\left(t_m\right)/c}{T_p}\right)\exp \left(\mathrm{j\π\γ}{(t-\frac{2r_n\left(t_m\right)}{c})}^2\right)\exp (-j4\mathrm{\π}{f}_c\frac{r_n\left(t_m\right)}{c})---\left(4\right)$

Consider that target has N scattering center, then target echo signal can be expressed as in wavenumber domain:

$s_r(f,t_m)\≈\underset{n=1}{\overset{N}{\mathrm{\Σ}}}{\mathrm{\σ}}_n\exp (-j2\mathrm{\πf}\frac{(2r_{\mathrm{no}}+2{\mathrm{\ω}}_n{t}_m+{\mathrm{\α}}_n{t}_m^2)}{c})---\left(5\right)$

Wherein, σ _nBe scattering center intensity, f=f _b+ f _c, f _bBe base-band signal frequency, | f _b|＜B/2, B are signal bandwidth, and c is propagation velocity of electromagnetic wave, usually is approximately 300000000 meter per seconds.

And then, at wavenumber domain spatial configuration basis function:

$h_p(f,t_m)=\exp (-j2\mathrm{\π}\frac{f}{c}(2r_p+2{\mathrm{\ω}}_p{t}_m+{\mathrm{\α}}_p{t}_m^2))---\left(6\right)$

Wherein, (r _p, ω _p, α _p) the three-dimensional parameter space of expression, r _pFor the distance of scattering center to the position, ω _pBe the Doppler frequency of scattering center, α _pFor the scattering center locus with burst length t _mVariation.

Then target echo available above-mentioned basis function in wavenumber domain is expressed as:

$s_r(f,t_m)\≈\underset{p=1}{\overset{N}{\mathrm{\Σ}}}{B}_p{h}_p(f,t_m)---\left(7\right)$

The intensity of scattering center and corresponding phase parameter thereof can obtain by following process search:

${\left|B_p\right|}^2=\underset{r_p,{\mathrm{\ω}}_p,{\mathrm{\α}}_p}{\max }{|\∫s_{r(p-1)}(f,t_m)h_p^{*}(f,t_m)|}^2---\left(8\right)$

In the above-mentioned expression formula,

$\left\{\begin{array}{cc}{s}_{r0}(f,t_m)=s_r(f,t_m),& p=0\\ s_{\mathrm{rp}}=s_{r(p-1)}(f,t_m)-B_p{h}_p(f,t_m),& p>1\end{array}\right.---\left(9\right)$

That is to say, as mentioned above, can by iterative manner as shown in Figure 4, obtain the parameter estimation of a plurality of scattering centers.

The above-mentioned parameter estimation procedure needs three-dimensional search, in the practical operation, in order to improve search speed, can at first echo data be transformed in the distance-Doppler image area, and search for therein coarse distance and the frequency information at strong scattering center, as shown in Figure 4, close echo number field space then, according to the method for expression formula (8) to scattering center parameter fine search.

In the practical operation, for guaranteeing to rotate the effect of estimating, the scattering center that needs to extract is distributed in the broad as far as possible range unit scope in a plurality of distances.In the present embodiment, adopt sliding window as shown in Figure 5, in different range unit scopes, select stronger scattering center to carry out parameter extraction.Sliding window width is generally selected 2-4 range unit.In the present embodiment, slide window width and select 4 range units.

In step 30, according to scattering center parameter estimation result and spatial position change rate information, adopt least square method match target scattering center migration amount with the Changing Pattern of scattering center distance to the position, estimating target rotating speed.

According to a plurality of scattering center parameter estimation results in the wavenumber domain, can pass through following expression match rotating speed of target:

${\mathrm{\α}}_{\mathrm{pn}}-{\mathrm{\α}}_{\mathrm{po}}=-(r_{\mathrm{pn}}-r_{\mathrm{po}}){\mathrm{\ω}}_o^2---\left(10\right)$

Wherein, (r _Pn, α _Pn) be the parameter of estimated n scattering center; (r _Po, α _Po) be the correlation parameter of estimated reference scattering center.In the present embodiment, the rotating speed of target fitting result as shown in Figure 6, the rotating speed of target estimated result is 0.0099 radian per second.

In step 40, according to the rotating speed of target estimated result, to the distance-Doppler image span descriscent calibration that echo data becomes, perhaps carry out polar coordinates format image-forming.

According to the rotating speed of target estimated result, mode realizes if matched filtering is adopted in the pulse compression of inverse synthetic aperture radar (ISAR) system, this moment distance to being respectively with span descriscent scale factor,

${\mathrm{\η}}_r=\frac{c}{2f_s},{\mathrm{\η}}_a=\frac{\mathrm{\λ}{f}_r}{2M{\mathrm{\ω}}_o}---\left(11\right)$

Wherein, f _sBe the signal sampling frequency, λ is wavelength, and M is the pulse number that imaging accumulates, f _rBe pulse repetition rate.

When adopting the De-chirp processing to carry out pulse compression, the distance of distance-Doppler image is to being respectively with span descriscent scale factor:

${\mathrm{\η}}_r=\frac{f_s}{N}\frac{c}{2\mathrm{\γ}}=\frac{c{f}_s{T}_p}{2\mathrm{NB}},{\mathrm{\η}}_a=\frac{\mathrm{\λ}{f}_r}{2M{\mathrm{\ω}}_o}---\left(12\right)$

Wherein, N is the sampling number of pulsatile once.

According to estimated rotating speed of target, adopt polar coordinates format image-forming algorithm to suppress the overstepping the bounds of propriety unit migration phenomenon of distinguishing that may occur, obtain ISAR two dimensional image output well focussed, calibration.In an embodiment, Fig. 7 is when not having the target rotation information, adopts the uncertain target image of Range-Doppler imaging algorithm acquisition, obviously can't know the definite two-dimensional shape information of target.Fig. 8 is according to estimated rotating speed of target, adjust the distance-the horizontal the calibration results of Dopplergram image, Fig. 9 is the target ISAR image that has the well focussed effect and calibrated that adopts the PFA imaging to provide according to estimated rotating speed, comparison diagram 7, the image of process calibration can more accurately reflect the shape information of target.

It should be noted that at last, above embodiment is only in order to illustrate that technical scheme of the present invention is not intended to limit, and on using, can extend to other modification, variation, application and embodiment, think that simultaneously all such modifications, variation, application, embodiment are within the spirit and scope of the present invention.

Claims (7)

1. the method for estimating rotating speed of target of an inverse synthetic aperture radar (ISAR) comprises:

The echo data that step 10), basis receive, Compensation Objectives is with respect to the translation component of radar;

Step 20), at first target echo is transformed in the range-Dopler domain, to scattering center apart from r _pAnd frequencies omega _pCarry out according to a preliminary estimate; Then at wavenumber domain spatial configuration basis function, echo data after the translation compensation is transformed to the wavenumber domain space also to be represented with described basis function, analyze when the described echo data that uses basis function to represent carries out sky to target scattering center, the distance of extracting scattering center to the position, Doppler frequency, locus rate information over time;

Analyze scattering center locus and the spatial position change rate information of extracting, match rotating speed of target during step 30), according to described sky;

Step 40), according to the rotating speed of target of institute's match, inverse synthetic aperture radar (ISAR) distance-Doppler image is calibrated or is carried out polar coordinates format image-forming.

2. the method for estimating rotating speed of target of inverse synthetic aperture radar (ISAR) according to claim 1, wherein, in the step 10), for the echo data that receives, the data of the easy motion section of select target, compensate the translation component that removes the relative radar of target by translation, described translation compensation comprises echo envelope alignment and the correction of translation first phase.

3. the method for estimating rotating speed of target of inverse synthetic aperture radar (ISAR) according to claim 1, wherein, step 20) comprising:

Step 210), at wavenumber domain structure basis function $h_p(f,t_m)=\exp (-j2\mathrm{\π}\frac{f}{c}({2r}_p+2{\mathrm{\ω}}_p{t}_m+{\mathrm{\α}}_p{t}_m^2)),$ Wherein, (r _p, ω _p, α _p) the three-dimensional parameter space of expression, r _pFor the distance of scattering center to the position, ω _pBe the Doppler frequency of scattering center, α _pFor the scattering center locus with burst length t _mVariation;

Step 220), according to described basis function with the target echo signal that represents in the wavenumber domain $s_r(f,t_m)\≈\underset{n=1}{\overset{N}{\mathrm{\Σ}}}{\mathrm{\σ}}_n\exp (-j2\mathrm{\πf}\frac{(2r_{\mathrm{no}}+2{\mathrm{\ω}}_n{t}_m+{\mathrm{\α}}_n{t}_m^2)}{c})$ Be expressed as $s_r(f,t_m)\≈\underset{p=1}{\overset{N}{\mathrm{\Σ}}}{B}_p{h}_p(f,t_m),$ Wherein, σ _nBe scattering center intensity, f=f _b+ f _c, f _bBe base-band signal frequency, | f _b|＜B/2, B are signal bandwidth, and c is propagation velocity of electromagnetic wave, and N is the scattering center number, f _cBe carrier frequency;

Step 230), obtain intensity and the phase parameter of scattering center by following formula iteration:

${\left|B_p\right|}^2=\underset{r_p,{\mathrm{\ω}}_p,{\mathrm{\α}}_p}{\max }{\left|{\∫s}_{r(p-1)}(f,t_m)h_p^{*}(f,t_m)\right|}^2,$ Wherein, $\left\{\begin{array}{c}{s}_{r0}(f,t_m)=s_r(f,t_m),p=0\\ s_{\mathrm{rp}}=s_{r(p-1)}(f,t_m)-B_p{h}_p(f,t_m),p>1\end{array}\right.,$ T _pBe pulse width, f _cBe carrier frequency, γ is signal frequency modulation rate, (r _No, θ _No) be the polar coordinates of this scattering center, r _aBe the distance of radar and target rotation center, ω _oBe the target Equivalent rotating speed.

4. the method for estimating rotating speed of target of inverse synthetic aperture radar (ISAR) according to claim 1, wherein, in step 30) in, according to scattering center parameter estimation and spatial position change rate information, adopt least square method match target scattering center migration amount with the variation of scattering center distance to the position, estimating target rotating speed.

5. the method for estimating rotating speed of target of inverse synthetic aperture radar (ISAR) according to claim 4, wherein, step 30) in, according to a plurality of scattering center parameter estimation in the wavenumber domain, pass through expression formula

The rotating speed of match target, wherein, (r _Pn, α _Pn) be the parameter of estimated n scattering center, (r _Po, α _Po) be the parameter of estimated reference scattering center.

6. the method for estimating rotating speed of target of inverse synthetic aperture radar (ISAR) according to claim 1, wherein, in step 40) in, if the matched filtering mode is adopted in the pulse compression of inverse synthetic aperture radar (ISAR) system, then distance is to being respectively η with span descriscent scale factor _r=c/ (2f _s) and η _a=λ f _r/ (2M ω _o), wherein, f _sBe the signal sampling frequency, λ is wavelength, and M is the pulse number that imaging accumulates, f _rBe pulse repetition rate.

7. the method for estimating rotating speed of target of inverse synthetic aperture radar (ISAR) according to claim 6, wherein, in step 40) in, if adopt De-chirp to process when carrying out pulse compression, the distance of distance-Doppler image is to being respectively η with span descriscent scale factor _r=cf _s/ (2N γ) and η _a=λ f _r/ (2M ω _o), wherein, γ is linear FM signal frequency modulation rate, f _sBe the signal sampling frequency, λ is wavelength, and M is the pulse number that imaging accumulates, f _rBe pulse repetition rate, N is the sampling number of pulsatile once.

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