CN103064082A - Microwave imaging method based on direction dimension random power modulation - Google Patents

Abstract

The invention discloses a microwave imaging method based on direction dimension random power modulation. The direction dimension power distribution of radar transmitting signals is modulated randomly, a compressive sensing theory is combined to an imaging radar system, and accordingly imaging time is reduced. Meanwhile, the power modulation information of a target echo and a transmit signal is used as the common input of an imaging algorithm, a super-resolution result is obtained by using the sparse reconstruction capacity of a convex optimization algorithm, and accordingly the quality of images is improved. The microwave imaging method can overcome the defects of long imaging time and low resolution ratio and the like in close distance and wide viewing angle imaging application of a narrow beam scanning radar, and the practical process of the microwave radar in the field of close distance and wide viewing angle imaging is promoted.

Description

Microwave imaging method based on the random power modulation of azimuth dimension

Technical field

The present invention relates to the microwave imaging field, be specially a kind of microwave imaging method based on the random power modulation of azimuth dimension.

Background technology

Because microwave and millimeter wave can penetrate the nonmetallic substances such as cloud and mist, vegetation, clothing, case and bag, so the microwave and millimeter wave radar not only is widely used in the remote imaging field such as military surveillance, geographical remote sensing, also can be used for the closely imaging scenes such as lossless detection.Be subject to applied environment, closely imaging radar is difficult to adopt synthetic aperture technique to improve azimuthal resolution, so such radar often adopts large aperture antenna (array), finishes imaging with the narrow beam scan mode.Yet closely the imaging angular field of view of imaging radar is usually larger, and it is longer that narrow beam scans required imaging time, is difficult to satisfy the practical application request of current fast detecting or even real time imagery.Except imaging time is long, microwave closely imaging radar to be difficult to promote another practical major reason be that imaging resolution and practical application request still have certain gap, therefore super-resolution is processed for microwave imaging radar closely and is seemed particularly important, it can improve actual imaging resolution under the prerequisite that does not increase system antenna (array) bore, restoring image detail improves picture quality.Constantly surging along with closely microwave imaging demands such as safety detection, lossless detections needed a kind of imaging new method that not only can reduce sweep time but also take into account hyperresolution at present badly.

Summary of the invention

The object of the invention provides a kind of microwave imaging method based on the random power modulation of azimuth dimension, and is long to solve microwave radar imaging technique imaging time, the problem of image resolution rate variance.

In order to achieve the above object, the technical solution adopted in the present invention is:

Microwave imaging method based on the random power modulation of azimuth dimension, it is characterized in that: to the radar emission signal in the spatial power of the azimuth dimension in addition Stochastic Modulation that distributes, distribute with irradiation order random variation at the power of azimuth dimension so that transmit, transmit all not identical in the power distribution of azimuth dimension, each time transmits and do not have regularity or relevance between the distribution of azimuth dimension power at every turn; As common input quantity, utilize protruding optimization process algorithm to obtain last image the power modulation information of the radar observation result that obtains of irradiation repeatedly and radar emission signal.

Described microwave imaging method based on the random power modulation of azimuth dimension is characterized in that: utilize reconfigurable antenna technology or phased-array technique, change the transmitter pattern function, realize transmitting in the power modulation of azimuth dimension.

Described microwave imaging method based on the random power modulation of azimuth dimension is characterized in that: the power distribution that transmits in the space does not have obvious main beam, and its emittance covers whole observation area.

Described microwave imaging method based on the random power modulation of azimuth dimension is characterized in that: l is adopted in protruding optimization process ₁The norm optimization algorithm, preferred BP algorithm, OMP algorithm.

Described microwave imaging method based on the random power modulation of azimuth dimension is characterized in that: the observed result that each radar emission signal irradiation obtains has comprised the information of all targets in the whole observation area.

Described microwave imaging method based on the random power modulation of azimuth dimension, it is characterized in that: be used for closely, wide visual angle imaging system, utilize the random power modulation of the described azimuth dimension that transmits, take radar observation result and the protruding optimization process of Stochastic Modulation content as common input quantity that transmit.

The present invention is fused to compressive sensing theory in the imaging radar system by the in addition Stochastic Modulation that distributes of the azimuth dimension power to the radar emission signal, consists of a kind of compression sampling system, thereby reduces imaging time.Simultaneously, with radar observation result and the common input quantity of the power modulation information that transmits as imaging algorithm, utilize the sparse re-configurability of convex optimized algorithm to obtain the super-resolution imaging result, thereby improve picture quality.

Description of drawings

Fig. 1 is traditional wave beam scanning imagery principle schematic.

Fig. 2 is image-forming principle schematic diagram of the present invention.

Fig. 3 tradition scanning imagery simulation result figure.

Fig. 4 the invention process Case Simulation imaging results figure.

Embodiment

Microwave imaging method based on the random power modulation of azimuth dimension, to the radar emission signal in the spatial power of the azimuth dimension in addition Stochastic Modulation that distributes, distribute with irradiation order random variation at the power of azimuth dimension so that transmit, transmit all not identical in the power distribution of azimuth dimension, each time transmits and do not have regularity or relevance between the distribution of azimuth dimension power at every turn; As common input quantity, utilize protruding optimization process algorithm to obtain last image the power modulation information of repeatedly the radar observation result that obtains of irradiation and radar emission signal.

Utilize reconfigurable antenna technology or phased-array technique, change the transmitter pattern function, realize transmitting in the power modulation of azimuth dimension.

The power distribution that transmits in the space does not have obvious main beam, and its emittance covers whole observation area.

L is adopted in protruding optimization process ₁The norm optimization algorithm, preferred BP algorithm, OMP algorithm.

The observed result that each radar emission signal irradiation obtains has comprised the information of all targets in the whole observation area.

Be used for closely, wide visual angle imaging system, utilize the random power modulation of the described azimuth dimension that transmits, take the radar observation result with transmit the protruding optimization process of Stochastic Modulation content as common input quantity.

Compressed sensing is a kind of information acquisition and signal processing theory framework of novelty, this theory can be briefly described below: length is the signal x of N, it is expressed as x=Ψ Θ on orthogonal basis Ψ, wherein Ψ is N * N orthogonal dimension basis matrix, and Θ is that the ordered series of numbers vector is maintained in N * 1.If the nonzero term number K in the coefficient, claims then that the expression of x in the Ψ territory is that the K item is sparse less than N.Use and the incoherent measurement matrix of Ψ Φ _{M * N}Coefficient is carried out conversion, can obtain the M * 1 dimension (observed result of M＜N)

y=ΦΘ=ΦΨ ^Tx=A ^CSx

A wherein ^CS=Φ Ψ ^T, be called as sensing matrix, if A ^CSSatisfied constraint isometry condition (when Φ is taken as stochastic matrix, A ^CSGenerally can satisfy the RIP condition), and M 〉=Klog (N/K), can adopt so protruding optimization method (often to be l ₁Norm optimization, specific algorithm comprise orthogonal matching pursuit OMP, and base is followed the trail of BP etc.), from observed result y, recover original signal x with very high probability, rejuvenation is formulated as

min||Ψ ^Tx|| _l?s.t.?y=ΦΨ ^Tx

An important application of compressed sensing is compression sampling, namely finishing the sampling of sparse signal far below the speed of coming Qwest's frequency, and intactly carries the contained information of original signal.Take this theory as the basis, can be by loading time domain or spatial domain Stochastic Modulation (the random sensing matrix in the corresponding compressed sensing) at receiving end, structure compression sampling system.Microwave radar is a kind of active imaging system, so its Stochastic Modulation process not only can be placed in receiving end and also can be fused to and transmit, so that the compression sampling mode of radar is more flexible.

The present invention has been fused to compressive sensing theory in the imaging system by the Stochastic Modulation that radar emission aspect dimension power distributes, and proposes a kind of new target information compression sampling scheme and super-resolution imaging method.The method and traditional beam scanning are imaged on very large difference on basic thought and the specific implementation, Fig. 1 and Fig. 2 have illustrated respectively both imaging process.The narrow beam of tradition scanning imagery radar emission concentration of energy carries out point by point scanning with narrow beam to the observed object zone, and scanning result is stitched together can obtains the observation area image.Also illustrated the mathematics implication that traditional scanning imagery process is corresponding among Fig. 1, if the target scattering information in the observation area represents with N * 1 dimensional vector x, each irradiation only can obtain the scattered information in the narrow beam scope in the scanning process, therefore radar directional diagram Jacobian matrix Φ can think a unit matrix, scanning result is the vectorial y identical with the x dimension, at last scanning result y is reset the two dimensional image that splicing just can obtain N pixel.The different introducings that are the random power modulation of azimuth dimension of the present invention and traditional scanning imagery maximum, as shown in Figure 2, because the introducing of Stochastic Modulation, so that radar distributes with irradiation order random variation at the power of azimuth dimension, the power of each time irradiation distributes all not identical, and irradiation energy no longer concentrates in the narrow beam scope, but in whole observation area distribution arranged all.In radar system, the power of azimuth dimension distributes and is expressed by the antenna radiation pattern function, therefore pattern function of the present invention and traditional scanning radar have very large difference: each direction of illumination figure does not have clear and definite main beam, and does not have any regularity or relevance between the pattern function of each time irradiation yet.The difference of new method and traditional scanning imagery not only is embodied on the pattern function, also show the reception ﹠ disposal aspect: image and the information that not merely relies on the reception observed result to provide obtain, but reception observed result and pattern function information co-treatment obtain.Fig. 2 has illustrated the mathematics implication that imaging process of the present invention is corresponding equally, the corresponding sensing matrix A of the radar directional diagram function of each irradiation ^CSIn a row vector because the different Stochastic Modulation of each time irradiation employing, so A ^CSCapable vector between be uncorrelated, guaranteed A ^CSSatisfy the desired constraint isometry of compressed sensing condition.Because each irradiation energy has covered whole observation area, so the observed result that each irradiation obtains has comprised the information of all targets in the whole observation area, and unlike scanning imagery, only comprise the information of narrow beam range of exposures internal object.According to compressive sensing theory, as long as target information is sparse in the expression of certain transform domain, so with dimension much smaller than target information (M＜＜N) measurement result y and pattern function matrix A ^CSBe initial conditions, utilize l ₁The norm optimization method just can reconstruct the image of N pixel.The present invention incorporates compressive sensing theory in the imaging system design dexterously by the random power modulation in the orientation that transmits, and compression sampling that not only can realize target information significantly reduces imaging time, and can obtain the super-resolution imaging effect.

The below describes embodiments of the invention in detail, and the example of described embodiment is shown in the drawings.Be exemplary below by the embodiment that is described with reference to the drawings, only be used for explaining the present invention, and can not be interpreted as limitation of the present invention.

For simplifying the analysis, at first consider one-dimensional case, the research conclusion of one dimension is easy to be generalized to two dimension.If the target scattering strength function in the observation area is σ (θ) (θ is the position angle), only have K target in the irradiation area, namely target scattering function σ (θ) itself just has very strong sparse property.If the radar directional diagram function is s (θ), the echoed signal power that receives so is

$p=\∫{\left|s\left(\mathrm{\θ}\right)\right|}^2\mathrm{\σ}\left(\mathrm{\θ}\right)\mathrm{d\θ}---\left(3\right)$

With σ (θ) and s (θ) discretize, discrete counting is N, and then formula can be expressed as follows

$p=\underset{n=1}{\overset{N}{\mathrm{\Σ}}}{\left|s\left({\mathrm{\θ}}_n\right)\right|}^2\mathrm{\σ}\left({\mathrm{\θ}}_n\right)---\left(4\right)$

If shine M time, can obtain M time so observed result, the observed result of establishing the m time irradiation is p (m), pattern function is s _m(θ _n), consist of the matrix of a M * N as the capable row vector of m take the pattern function of the m time irradiation.According to formula, M time irradiation process can be used following matrix representation

$\left[\begin{array}{c}p\left(1\right)\\ p\left(2\right)\\ .\\ .\\ .\\ p\left(M\right)\end{array}\right]=\left[\begin{array}{cccc}{\left|s_1\left({\mathrm{\θ}}_1\right)\right|}^2& {\left|s_1\left({\mathrm{\θ}}_2\right)\right|}^2& ...& {\left|s_1\left({\mathrm{\θ}}_N\right)\right|}^2\\ {\left|s_2\left({\mathrm{\θ}}_1\right)\right|}^2& {\left|s_2\left({\mathrm{\θ}}_2\right)\right|}^2& ...& {\left|s_2\left({\mathrm{\θ}}_N\right)\right|}^2\\ & .& & \\ & .& & \\ & .& & \\ {\left|s_M\left({\mathrm{\θ}}_1\right)\right|}^2& {\left|s_M\left({\mathrm{\θ}}_2\right)\right|}^2& ...& {\left|s_M\left({\mathrm{\θ}}_N\right)\right|}^2\end{array}\right]\left[\begin{array}{c}\mathrm{\σ}\left({\mathrm{\θ}}_1\right)\\ \mathrm{\σ}\left({\mathrm{\θ}}_2\right)\\ .\\ .\\ .\\ \mathrm{\σ}\left({\mathrm{\θ}}_N\right)\end{array}\right]---\left(5\right)$

The contrast formula as can be known, this matrix just and the compressed sensing process that represents of formula (1) corresponding, therefore, if the pattern function matrix [| s _m(θ _n) | ²] _{M * N}Satisfy the equidistant condition of the desired constraint of compressive sensing theory, and shine number of times M 〉=Klog (N/K), so just can from measurement result few in number, reconstruct by protruding optimization method the super resolution image of target.

Below in conjunction with the imaging scene; come principle of the present invention is described in detail by accompanying drawing and specific embodiments; because the imaging scene that the present invention relates to is wider; the below is only take a comparatively classical embodiment as example; provide the specific embodiment of the present invention; but, should not limit practical application of the present invention and protection domain with this.

Analogue system adopts 16 * 16 aerial array, and array element is omnidirectional's point source antenna, and evenly arranges.The beam scanning imaging is regulated the array element first phase in the phased array mode, and point by point scanning is carried out in the imaging observation zone, and imaging process needs 1530 irradiations altogether, and Fig. 3 is the imaging results that traditional beam sweeping method obtains.Utilize new method that the present invention puies forward, adopt the mode of randomly changing first phase to realize the Stochastic Modulation that azimuth dimension power distributes, general needs more than 400 irradiation can finish imaging, sometimes in addition more than 100 irradiation just can imaging, and the resolution of institute of the present invention extracting method is significantly better than the beam scanning imaging, the imaging effect at (for example trigger place) is better at some details places, and Fig. 4 is the imaging results that institute of the present invention extracting method obtains.The formation method that the present invention carries not only can reduce scanning times than traditional scan imaging method, shorten imaging time, and imaging resolution also is better than the latter.

Claims (6)

1. based on the microwave imaging method of the random power modulation of azimuth dimension, it is characterized in that: to the radar emission signal in the spatial power of the azimuth dimension in addition Stochastic Modulation that distributes, distribute with irradiation order random variation at the power of azimuth dimension so that transmit, transmit all not identical in the power distribution of azimuth dimension, each time transmits and do not have regularity or relevance between the distribution of azimuth dimension power at every turn; As common input quantity, utilize protruding optimization process algorithm to obtain last image the power modulation information of the observed result that obtains of irradiation repeatedly and radar emission signal.

2. the microwave imaging method based on the random power modulation of azimuth dimension according to claim 1 is characterized in that: utilize reconfigurable antenna technology or phased-array technique, change the transmitter pattern function, realize transmitting in the power modulation of azimuth dimension.

3. the microwave imaging method based on the random power modulation of azimuth dimension according to claim 1 is characterized in that: the power in the space of transmitting distributes and does not have obvious main beam, and its emittance covers whole observation area.

4. the microwave imaging method based on the random power modulation of azimuth dimension according to claim 1 is characterized in that: protruding optimization process employing l ₁The norm optimization algorithm, preferred BP algorithm, OMP algorithm.

5. the microwave imaging method based on the random power modulation of azimuth dimension according to claim 1 is characterized in that: the observed result that each radar emission signal irradiation obtains has comprised the information of all targets in the whole observation area.

6. the microwave imaging method based on the random power modulation of azimuth dimension according to claim 1, it is characterized in that: be used for closely, wide visual angle imaging system, utilize the random power modulation of the described azimuth dimension that transmits, take radar observation result and the protruding optimization process of Stochastic Modulation content as common input quantity that transmit.

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