CN112114310B - Microwave millimeter wave holographic image reconstruction method based on three-dimensional decomposition - Google Patents
Microwave millimeter wave holographic image reconstruction method based on three-dimensional decomposition Download PDFInfo
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Abstract
The invention provides a microwave millimeter wave holographic image reconstruction method based on three-dimensional decomposition, which sequentially comprises the following steps: carrying out image focusing processing on the backscattering echo signal in a two-dimensional dimension, wherein the two-dimensional dimension is a two-dimensional dimension perpendicular to the arrangement direction of the microwave millimeter wave antenna elements; and carrying out secondary image focusing on the backscattered echo signals subjected to the image focusing, wherein the secondary image focusing is carried out on the dimension of the array direction of the microwave and millimeter wave antenna elements. The image reconstruction method of the invention carries out three-dimensional decomposition on the three-dimensional echo signal, and the three-dimensional echo signal is decomposed into a two-dimensional dimension and a one-dimensional dimension for image reconstruction respectively, thereby simplifying the computational complexity.
Description
Technical Field
The invention relates to the field of microwave and millimeter wave holographic imaging, in particular to a microwave and millimeter wave holographic image reconstruction method based on three-dimensional decomposition.
Background
A microwave millimeter wave three-dimensional holographic imaging security inspection system is an important technical means for realizing active microwave millimeter wave human body security inspection. The imaging security inspection system can comprise a planar mechanical scanning type imaging system, a cylindrical surface mechanical scanning type imaging system or a two-dimensional sparse array electronic scanning type imaging system. The microwave millimeter wave frequency electromagnetic wave can penetrate through clothes, so that three-dimensional holographic images obtained through microwave millimeter wave three-dimensional holographic imaging can represent body surface information of a human body more abundantly, and the microwave millimeter wave three-dimensional holographic imaging security inspection system can effectively detect dangerous goods hidden under the clothes of the human body through the three-dimensional holographic images, so that the microwave millimeter wave three-dimensional holographic imaging security inspection system is an effective new means for human body security inspection and is widely applied to the field of human body security inspection.
At present, a microwave millimeter wave three-dimensional holographic image reconstruction method mainly comprises a time domain type image reconstruction algorithm and a frequency domain type image reconstruction algorithm.
Time-domain class image reconstruction algorithms are known to include time-domain correlation algorithms and backprojection reconstruction algorithms. The time domain algorithm does not need any approximation in the derivation process, the implementation process of the algorithm is simple and easy to understand, and the implementation technology threshold is low, but the time domain algorithm directly processes the three-dimensional echo data to enable the three dimensions to be cross-coupled together, so that the calculation of one pixel point in an image needs to be traversed for all echo data at one time, the calculation amount is large, and the traversal processing needs to access the storage space of the three-dimensional echo data when a hardware platform is implemented, so that the real-time performance of image reconstruction calculation is delayed, meanwhile, high requirements are provided for resources of the hardware platform, and the method is difficult to be applied to an imaging system with high real-time requirements.
In mainstream frequency domain algorithms, a wavenumber domain algorithm is mainly known, but due to different data acquisition modes of a planar mechanical scanning type imaging system and a cylindrical surface mechanical scanning type imaging system, the derivation processes of the corresponding wavenumber domain algorithms have great difference, source codes need to be developed and a hardware platform needs to be implemented respectively, and thus, higher requirements on labor, time and cost are provided. Therefore, it is necessary to develop an image reconstruction method suitable for the two imaging systems to greatly reduce the labor, time and cost in the system engineering implementation process.
Disclosure of Invention
Aiming at the problems, the invention provides a microwave millimeter wave holographic image reconstruction method based on three-dimensional decomposition.
The invention relates to a microwave millimeter wave holographic image reconstruction method based on three-dimensional decomposition, which is used for processing a backscattering echo signal obtained by scanning a target by transmitting a microwave millimeter wave beam by a microwave millimeter wave antenna array element, wherein the target is positioned in an imaging target area, and the microwave millimeter wave antenna array element is an antenna array element of a one-dimensional antenna array in a mechanical scanning type imaging system, and is characterized by comprising the following steps of:
A. discretizing the imaging target area and the mechanical scanning position of the one-dimensional antenna array in a two-dimensional dimension, wherein the two-dimensional dimension is a two-dimensional dimension perpendicular to the arrangement direction of the microwave millimeter wave antenna array elements;
B. performing image focusing processing on the two-dimensional dimension on the backscatter echo signal;
C. performing interpolation processing on the backscatter echo signals processed in the step B, wherein the interpolation processing is performed on a distance dimension in the two-dimensional dimension;
D. performing second discretization processing on the imaging target area, wherein the second discretization processing is performed on the dimension of the arrangement direction of the microwave millimeter wave antenna elements;
E. and carrying out secondary image focusing on the backscattered echo signals subjected to the image focusing, wherein the secondary image focusing is carried out on the dimension of the array direction of the microwave and millimeter wave antenna elements.
Further, in the present invention,
the microwave millimeter wave holographic image reconstruction method further comprises the following steps: a rectangular coordinate system of a three-dimensional space is established,
wherein the content of the first and second substances,
taking the arrangement direction of the microwave millimeter wave antenna array elements as the Y-axis direction of the three-dimensional space rectangular coordinate system;
when the mechanical scanning type imaging system is a one-dimensional antenna array plane mechanical scanning type imaging system, the scanning moving direction of the microwave millimeter wave antenna array elements is taken as the X-axis direction of the three-dimensional space rectangular coordinate system, and the Z-axis direction of the three-dimensional space rectangular coordinate system is established according to the relation of the directions of three coordinate axes of the three-dimensional space rectangular coordinate system;
when the mechanical scanning type imaging system is a one-dimensional antenna array cylindrical surface mechanical scanning type imaging system, the Y-axis direction and the Z-axis direction of a three-dimensional space rectangular coordinate system are determined according to the relation of the directions of three coordinate axes of the three-dimensional space rectangular coordinate system;
the dimension corresponding to the Z axis is the distance dimension.
Further, in the present invention,
and recording Y-axis coordinates of the microwave millimeter wave antenna array elements' k ，k∈[1,N ant ]，N ant The number of the microwave millimeter wave antenna elements in the one-dimensional antenna array is an integer which is more than 1,
L a is the length of the one-dimensional antenna array;
traverse the coordinate y' k At each coordinate y' k And C, executing the step B and the step C.
Further, in the present invention,
in the step a, the two-dimensional dimensions are (x, z) dimensions, that is, x dimension and z dimension, and the coordinates of the divided imaging target region at the discrete grid points in the two-dimensional dimensions are (x, z) i ,z j ) Wherein i ∈ [0, N ∈ ] x ]，j∈[0,N z ]，N x A number of meshes, N, of discrete meshes divided along the x-dimension for the imaging target region z A number of meshes, N, of discrete meshes of the imaging target region divided along the z-dimension x And N z Are all integers greater than 1;
the grid obtained by discretization satisfies the following conditions: grid size divided along the x dimension
Number of said grids
Grid size divided along the z dimension
Number of said grids
Meaning that the rounding is done down,
wherein λ is 0 Is the central wavelength, theta, of the radio frequency signal of the mechanically scanned imaging system x Antenna beam width, L, of x dimension x The spatial range covered by the scanning in the dimension x, B is the bandwidth of the microwave millimeter wave signal of the mechanical scanning type imaging system, c is the speed of light in vacuum, and L is z A range covered in the z dimension for the imaging target area;
obtaining discretized mechanical scanning positions of the divided one-dimensional antenna array
Wherein the content of the first and second substances,
a grid number of discrete grids divided along an x-dimension for the discretized mechanical scan location,
a grid number divided into discrete grids divided along the z-dimension by the discretized mechanical scan location,
and
are all integers greater than 1;
the discretized mechanical scan location satisfies: adopt the oneWhen the dimension antenna array plane mechanical scanning type imaging system is used,
L s the grid size divided by the x dimension of the mechanical scanning position is the scanning distance of the microwave millimeter wave antenna array element
Taking a certain value; when the one-dimensional antenna array cylindrical surface mechanical scanning type imaging system is adopted,
and satisfy
R is the radius of the cylindrical surface scanning track of the microwave millimeter wave antenna array element,
the scanned angle of the microwave millimeter wave antenna array element,
discrete interval of
r s For scanning the radius of the object, k is the microwave and millimeter wave frequency wave number, k z The number of spatial waves in the arrangement direction of the microwave millimeter wave antenna elements is shown.
Further, L a Is 0.5 to 3 m, L x Is 0.3-2 m, L z Is 0.1 to 1.5 m, L s Is 0.1 to 2 m in length,
further, L a Is 2 m, L x Is 1 m, L z Is 0.2-0.8 m, L s 2 m, R0.6 m,
is composed of
Further, in the present invention,
the backscatter echo signal is S (x, y, z, f), where f is the microwave millimeter wave frequency dimension, then in step B, at each discrete grid point coordinate (x, z) in the (x, z) dimension i ,z j ) The following steps are carried out:
calculating the discrete grid point coordinates (x) i ,z j ) Discretized mechanical scanning position to the microwave and millimeter wave antenna elements
Angular distance of
Then obtaining the matched filtering signal in the z dimension
Matching the filtered signal
And the mechanical scanning position
To echo signals
Is/are as follows
Carrying out matched filtering processing after dimensionality multiplication to obtain a signal
Will be at all of said mechanical scanning positions
The signal of
All are calculated and accumulated to obtain a signal S D (x i ,y' k ,z j )。
Further, in the present invention,
in the step C, the interpolation processing employs any one of linear interpolation, SINC interpolation, spline interpolation, or cubic interpolation methods;
obtaining an up-sampled signal S by the interpolation processing F (x i ,y' k ,z p1 )，
Wherein p1 is an integer, p1 epsilon [0, N' z ]And N' z ＞N z And N' z ＝N 0 ·N z And the pixel interval of the up-sampling signal in the z dimension is set to be Δ z
And z in the z dimension p1 Coverage and z j The coverage is consistent.
Further, in the present invention,
in the step D, the coordinates of the discrete grid points in the y-dimension are y after the second discretization process q ，q∈[0,N y ]，N y A number of meshes of a discrete mesh divided along the y-dimension and is an integer greater than 1.
Further, in the present invention,
in said step E, said second image focusing comprises at each discrete grid point coordinate (x) i ,y q ,z j ) The following steps are carried out:
calculating the discrete grid point coordinates (x) i ,y q ,z j ) To all sampling positions of the microwave millimeter wave antenna array element
I.e. the slope in the y and z dimensions
And acquiring a distance matching point signal S at the sampling position in the z dimension G (x i ,y' k ,z L )＝S F (x i ,y' k ,z L ) Wherein, in the step (A),
taor＝c/(2·B)/N 0 ；
calculating all sampling positions y 'of y dimension of microwave millimeter wave antenna array element' k Matched filtered signal
Wherein f is 0 The central frequency of the microwave millimeter wave radio frequency signal in the imaging target area is obtained;
all sampling positions y 'of y dimension of microwave millimeter wave antenna array element' k Matched filtered signal
Are all equal to the sampling position y' k The distance matching point signal S of G (x i ,y' k ,z L ) Y' k All sampling positions y 'of the y dimension of the microwave millimeter wave antenna array element are obtained through corresponding multiplication of the dimensions' k Signal of
All sampling positions y 'of y dimension of microwave millimeter wave antenna array element' k Signal of
Performing complex number accumulation calculation to obtain signal S (x) i ,y q ,z j )。
The microwave millimeter wave holographic image reconstruction method based on three-dimensional decomposition integrates the characteristics of a time domain reconstruction algorithm, respectively processes three dimensions of echo data, is more suitable for high-speed parallel realization of hardware signal processing platforms such as an FPGA (field programmable gate array), a DSP (digital signal processor), a GPU (graphic processing unit) and the like, is not limited by any scanning mode of scanning dimensions, is suitable for both a planar mechanical scanning type imaging system and a cylindrical mechanical scanning type imaging system, and is a universal three-dimensional image reconstruction method.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below, and it is obvious that the drawings in the following description are some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to these drawings without creative efforts.
Fig. 1 shows a diagram of an operation (scanning) mode of a microwave millimeter wave holographic reconstruction system 1 (one-dimensional antenna array planar mechanical scanning type imaging system) according to an embodiment of the present invention;
fig. 2 is a diagram showing an operation (scanning) mode of a microwave millimeter wave holographic reconstruction system 2 (one-dimensional antenna array cylindrical surface mechanical scanning type imaging system) according to an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be obtained by a person skilled in the art without making any creative effort based on the embodiments in the present invention, belong to the protection scope of the present invention.
Fig. 1 is a scanning mode diagram of a one-dimensional antenna array planar mechanical scanning imaging system, and fig. 2 is a scanning mode diagram of a one-dimensional antenna array cylindrical surface mechanical scanning imaging system. In fig. 1 and 2, 1 is a microwave millimeter wave antenna array element in the one-dimensional antenna array, 2 is a horizontal scanning direction of the one-dimensional antenna array, 3 is an imaging target area, and a plurality of microwave millimeter wave antenna array elements 1 are arranged along the same direction to form the one-dimensional antenna array. As can be seen from fig. 1, if the center of the imaging target region 3 is taken as the origin of coordinates, the arrangement direction of the microwave millimeter wave antenna array elements 1 of the one-dimensional antenna array plane mechanical scanning type imaging system is the Y-axis direction, the plane scanning moving direction of the microwave millimeter wave antenna array elements 1 is the X-axis direction, and a three-dimensional rectangular spatial coordinate system can be established, where the imaging target region 3 is located on one side of the plane track through which the microwave millimeter wave antenna array elements 1 scan. As can be seen from fig. 2, if the center of the imaging target region 3 is taken as the origin of coordinates, a three-dimensional space rectangular coordinate system can be established with the arrangement direction of the microwave millimeter wave antenna array elements 1 of the one-dimensional antenna array cylindrical surface mechanical scanning type imaging system as the Y-axis direction, wherein the imaging target region 3 is located in the cylindrical surface track through which the microwave millimeter wave antenna array elements 1 scan.
In the two scanning type imaging systems, the beam of the transmitting antenna and the beam of the receiving antenna of the imaging system realize vertical (i.e. Y-axis direction) moving scanning by switching the radio frequency switch of the microwave millimeter wave antenna array element 1; the one-dimensional antenna array is driven by a high-precision mechanical scanning control device to realize horizontal scanning (scanning along the X-axis direction in figure 1 and scanning along the cylindrical surface in figure 2), and finally, the discrete distribution of antenna beams (including the beams of a transmitting antenna and a receiving antenna) on an (X, z) two-dimensional space plane is obtained.
The microwave millimeter wave holographic image reconstruction method comprises the following steps of:
first, a backscatter echo signal S (x, y, z, f) (referred to as echo signal) of the target is acquired.
By performing the scanning, the microwave millimeter wave transceiving front ends in the two scanning type imaging systems can detect and obtain three-dimensional echo signals S (x, y, z, f) of the imaging target region 3, wherein the y dimension is a microwave millimeter wave antenna array element switch scanning dimension, the f is a microwave millimeter wave frequency dimension, the echo signals S (x, y, z, f) are complex signals and contain amplitude and phase information, and the signal system of the transceiving front ends is a frequency modulation continuous wave signal or a frequency stepping continuous wave signal. For a one-dimensional antenna array plane mechanical scanning type imaging system, if the microwave millimeter wave antenna array element 1 scans along the X axis, the scanning coordinate on the (X, z) two-dimensional space or the (X, z) dimension (namely the X dimension and the z dimension) is (X, z) 10 ) Wherein z is 10 The coordinate of the Z axis of the microwave millimeter wave antenna array element 1 is a fixed value; for a one-dimensional antenna array cylindrical surface mechanical scanning type imaging system, setting the Y axis as the central axis of the cylindrical surface, and then scanning coordinates of the two-dimensional space
Wherein R is the radius of the cylindrical surface scanning track,
is the angle mechanically scanned by the one-dimensional antenna array.
It is to be noted that Y 'is the Y-axis coordinate of the microwave millimeter wave antenna array element 1' k ，k∈[1,N ant ]，N ant Is the number of the antenna elements 1 in the one-dimensional antenna array and is an integer greater than 1
L a Is the length, L, of the one-dimensional antenna array a It may be desirable to be from 0.5 to 3 meters, preferably 2 meters.
Secondly, traversing the coordinate y 'of the microwave millimeter wave antenna array element 1' k At each coordinate y' k Then, the following steps 2a and 2b are performed:
2a discretizing the imaged target area 3 and the mechanical scanning position of the one-dimensional antenna array in (x, z) dimensions, i.e. x and z dimensions.
Through the discretization, the coordinates of the discrete grid points of the divided imaging target area 3 are obtained as (x) i ,z j ) I is an integer and i belongs to [0, N ] x ]J is an integer and j is an element [0, N ] z ]，N x Number of discrete grids divided along x-dimension for imaging target area 3, N z The number of meshes, N, of the discrete grid divided along the z-dimension (also referred to as the distance dimension) for the imaging target region 3 x And N z Are all integers greater than 1. The mesh subjected to the discretization satisfies: mesh size for x dimension partitioning
Number of grids
Represents rounding down; grid size for z-dimension partitioning
Number of grids
Wherein λ is 0 Is the central wavelength theta of the radio frequency signals of the two scanning type imaging systems x Antenna beam width, L, of x dimension x The spatial range covered by the scanning of the imaging target region 3 in the x dimension, B ═ f max -f min For the bandwidth (f) of the microwave millimeter wave signal in the imaging target region 3 max And f min Respectively the highest frequency and the lowest frequency of the microwave millimeter wave signal), c is the speed of light in vacuum, L z Is the extent covered in the z-dimension by the imaging target area 3. L is x Generally, the particle size is 0.3 to 2 m, preferably 1 m,is the human body transverse coverage, L z Generally 0.1-1.5 m, preferably 0.2-0.8 m, which is the span of the human body in the z dimension. The smaller the values of the grid sizes delta x and delta z are, the finer the divided grid is, and the higher the fineness of the image reconstruction result is.
Obtaining the discretized mechanical scanning position (hereinafter referred to as mechanical scanning position) of the divided one-dimensional antenna array by the discretization
When a one-dimensional antenna array planar mechanical scanning type imaging system is adopted,
l is an integer and
L s l is the scanning distance of the microwave millimeter wave antenna array element 1 according to specific application scenes s Can be 0.1-2 m, preferably 2 m,
the number of grids of the discrete grid divided along the x-dimension for the mechanical scan position,
can be-2 to-0.1 meter, preferably-0.4 meter; when a one-dimensional antenna array cylindrical surface mechanical scanning type imaging system is adopted,
and
m is an integer of
And
a grid number divided into discrete grids of mechanical scan positions divided along the x-dimension and z-dimension,
r is preferably 0.6 m and has
Preferably, it is
The discretization condition of the mechanical scanning position is different from the discretization condition A in that when the one-dimensional antenna array plane mechanical scanning type imaging system is adopted, the number of grids is increased
In this embodiment, the size Δ x of the grid divided in the x dimension of the imaging target region 3 and the size Δ x of the grid divided in the x dimension of the mechanical scanning position
The values can be the same or different according to different working conditions in specific application; when one-dimensional antenna array cylindrical surface mechanical scanning type imaging system is adopted, the number of grids
Discrete interval of
r s Is the radius of the scanned object (i.e. the radius of the scanned object can be the largest radius of the scanned objectRadius of the small cylinder), k is the microwave millimeter wave frequency wavenumber (i.e., the wavenumber of the microwave millimeter wave in the microwave millimeter wave frequency dimension), k is z The number of spatial waves in the arrangement direction of the microwave millimeter wave antenna elements.
2b, carrying out (x, z) dimensional image focusing processing on the backscatter echo signal S (x, y, z, f) at each discrete grid point coordinate (x, y, z, f) i ,z j ) The following steps 2ba to 2bc are performed:
2ba, in the (x, z) dimension, the coordinates (x) of the discrete grid points are first calculated i ,z j ) Mechanical scanning position to microwave millimeter wave antenna element 1 in one-dimensional antenna array
Angular distance of
Then obtaining matched filtering signal in z dimension
Wherein the mechanical scanning position of the one-dimensional antenna array of the planar mechanical scanning type imaging system
The mechanical scanning position of the one-dimensional antenna array of the cylindrical surface mechanical scanning type imaging system
Angle mechanically scanned for one-dimensional antenna array
Discretized coordinates of (a);
2bb, filtering the matched filter signal
And the mechanical scanningPosition of
To echo signals
Is/are as follows
Carrying out matched filtering processing after dimensionality multiplication to obtain a signal
2bc, will be at all said mechanical scanning positions
The signal of
All are calculated and accumulated to obtain a signal S D (x i ,y' k ,z j )。
Obtaining all the microwave millimeter wave antenna array elements 1 at the position y 'through the step two' k Signal S of D (x i ,y' k ,z j ) So far the image in (x, z) dimension is fully focused.
Three, two signals S D (x i ,y' k ,z j ) Z of (a) j And carrying out interpolation processing on the dimension.
Obtaining an up-sampled signal S by the interpolation processing F (x i ,y' k ,z p1 ) Wherein p1 is an integer, p1 ∈ [0, N' z ]And N' z ＞N z And N' z ＝N 0 ·N z . Since the grid size divided in the z dimension is Δ z, and the pixel interval of the up-sampled signal in the z dimension is Δ z', then
And z in the z dimension p1 Coverage and z j The coverage range is consistent; the interpolation processing may adopt interpolation methods such as linear interpolation, SINC interpolation, spline interpolation, cubic interpolation and the like.
And fourthly, discretizing the y dimension in the imaging scene.
Through the discretization processing, the coordinates of the discrete grid points in the y dimension are y q ，q∈[0,N y ]，N y The number of meshes of the discrete mesh divided along the y-dimension and is an integer greater than 1. Setting y q The position coordinate range of the antenna array element 1 in the one-dimensional antenna array is consistent, and the coordinate of the discrete grid point of the z dimension is still z j 。
Fifthly, final image focusing processing
At each discrete grid point coordinate (x) i ,y q ,z j ) The following steps 5a to 5d are performed:
5a, calculating discrete grid point coordinates (y) in the (y, z) dimensions, i.e. the y and z dimensions q ,z j ) To all sampling positions of said antenna element 1 in the one-dimensional antenna array (i.e. the coordinate position of the antenna element 1 during scanning)
Is inclined distance
And acquiring a distance matching point signal S at the sampling position in the z dimension G (x i ,y' k ,z L )＝S F (x i ,y' k ,z L ) The selection criterion of the location of the distance dimension is
taor＝c/(2·B)/N 0 B is the bandwidth of the microwave millimeter wave signal;
5b, calculating all y-dimension sampling positions y 'of the microwave millimeter wave antenna array element 1' k Matched filtered signal
Wherein f is 0 The central frequency of the microwave millimeter wave radio frequency signal in the imaging target area 3;
5c, sampling all y-dimensional sampling positions y 'of the microwave millimeter wave antenna array element 1' k Matched filtered signal
Are all equal to the sampling position y' k Distance matching point signal S G (x i ,y' k ,z L1 ) The y dimension of the microwave millimeter wave antenna array element 1 is obtained by corresponding multiplication q All sample locations in dimension y' k Signal of
5d, sampling all y-dimensional sampling positions y 'of the microwave millimeter wave antenna array element 1' k Signal of
Are calculated and subjected to complex accumulation to obtain a signal S (x) i ,y q ,z j )。
Obtaining all discrete grid point coordinates (x) through step five i ,y q ,z j ) Signal S (x) of i ,y q ,z j ) Completing the focusing of the image in the y dimension to obtain the final three-dimensional complex image O (x) i ,y q ,z j )。
Finally, the three-dimensional complex image O (x) obtained is obtained i ,y q ,z j ) And transmitting the data to a display end for displaying, target detecting, target classifying and identifying and the like.
The method is particularly suitable for high-speed parallel processing of a hardware platform, and is a universal image reconstruction method because the time domain type algorithm is adopted, the mechanical scanning mode of a microwave millimeter wave imaging system is not limited, and the method achieves the purpose that the image reconstruction method is suitable for two one-dimensional antenna array mechanical scanning imaging modes.
Although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the corresponding technical solutions of the embodiments of the present invention.
Claims (9)
1. A microwave millimeter wave holographic image reconstruction method based on three-dimensional decomposition is used for processing a backscattering echo signal obtained by scanning a target by transmitting a microwave millimeter wave beam by a microwave millimeter wave antenna array element, wherein the target is positioned in an imaging target area, and the microwave millimeter wave antenna array element is an antenna array element of a one-dimensional antenna array in a mechanical scanning type imaging system, and is characterized by comprising the following steps of:
s1, discretizing the imaging target area and the mechanical scanning position of the one-dimensional antenna array in a two-dimensional dimension, wherein the two-dimensional dimension is a two-dimensional dimension perpendicular to the arrangement direction of the microwave millimeter wave antenna array elements;
s2, carrying out image focusing processing on the two-dimensional dimension on the backscatter echo signal;
s3, performing interpolation processing on the backscatter echo signals processed in the step S2, wherein the interpolation processing is performed on a distance dimension of the two-dimensional dimensions;
s4, performing second discretization processing on the imaging target area, wherein the second discretization processing is performed on the dimension of the arrangement direction of the microwave millimeter wave antenna elements;
and S5, carrying out secondary image focusing on the backscattered echo signals subjected to the image focusing processing in the two-dimensional dimension, wherein the secondary image focusing is carried out in the dimension of the arrangement direction of the microwave millimeter wave antenna elements.
2. The three-dimensional decomposition-based microwave and millimeter wave holographic image reconstruction method according to claim 1,
the microwave millimeter wave holographic image reconstruction method further comprises the following steps: a three-dimensional rectangular coordinate system is established,
wherein the content of the first and second substances,
taking the arrangement direction of the microwave millimeter wave antenna array elements as the Y-axis direction of the three-dimensional space rectangular coordinate system;
when the mechanical scanning type imaging system is a one-dimensional antenna array plane mechanical scanning type imaging system, the scanning moving direction of the microwave millimeter wave antenna array elements is taken as the X-axis direction of the three-dimensional space rectangular coordinate system, and the Z-axis direction of the three-dimensional space rectangular coordinate system is established according to the relation of the directions of three coordinate axes of the three-dimensional space rectangular coordinate system;
when the mechanical scanning type imaging system is a one-dimensional antenna array cylindrical surface mechanical scanning type imaging system, the Y-axis direction and the Z-axis direction of a three-dimensional space rectangular coordinate system are determined according to the relation of the directions of three coordinate axes of the three-dimensional space rectangular coordinate system;
and the dimension corresponding to the Z axis is the distance dimension.
3. The three-dimensional decomposition-based microwave and millimeter wave holographic image reconstruction method according to claim 2,
and recording Y-axis coordinates of the microwave millimeter wave antenna array elements' k ，k∈[1,N ant ]，N ant The number of the microwave millimeter wave antenna elements in the one-dimensional antenna array is an integer which is more than 1,
L a is the length of the one-dimensional antenna array;
traverse the coordinate y' k At each coordinate y' k Here, the steps S2 and S3 are performed.
4. The three-dimensional decomposition-based microwave and millimeter wave holographic image reconstruction method according to claim 3,
in step S1, the two-dimensional dimensions are (x, z) dimensions, that is, x dimension and z dimension, and the coordinates of the divided imaging target region at the discrete grid points in the two-dimensional dimensions are (x, z) i ,z j ) Wherein i ∈ [0, N ∈ ] x ]，j∈[0,N z ]，N x A number of meshes, N, of discrete meshes divided along the x-dimension for the imaging target region z A number of meshes, N, of discrete meshes divided along the z-dimension for the imaging target region x And N z Are all integers greater than 1;
the grid obtained by discretization satisfies the following conditions: grid size divided along the x dimension
Number of said grids
Grid size divided along the z dimension
Number of said grids
Meaning that the rounding is done down,
wherein λ is 0 Is the central wavelength, theta, of the radio frequency signal of the mechanically scanned imaging system x Antenna beam width, L, of x dimension x The spatial range covered by the scanning in the x dimension, B being the mechanical scanning typeBandwidth of microwave and millimeter wave signals of the image system, c is speed of light in vacuum, L z A range covered in the z dimension for the imaging target area;
obtaining discretized mechanical scanning positions of the divided one-dimensional antenna array
Wherein the content of the first and second substances,
a grid number of discrete grids divided along an x-dimension for the discretized mechanical scan location,
a grid number of discrete grids divided along a z-dimension for the discretized mechanical scan location,
and
are all integers greater than 1;
the discretized mechanical scan location satisfies: when the one-dimensional antenna array plane mechanical scanning type imaging system is adopted,
L s the grid size divided by the x dimension of the mechanical scanning position is the scanning distance of the microwave millimeter wave antenna array element
Taking a certain value;when the one-dimensional antenna array cylindrical surface mechanical scanning type imaging system is adopted,
and satisfy
R is the radius of the cylindrical surface scanning track of the microwave millimeter wave antenna array element,
the scanned angle of the microwave millimeter wave antenna array element,
discrete interval of
r s For scanning the radius of the object, k' is the frequency wave number of the microwave millimeter wave, k z The number of spatial waves in the arrangement direction of the microwave millimeter wave antenna elements is;
wherein L is a Is 0.5 to 3 m, L x Is 0.3-2 m, L z Is 0.1 to 1.5 m, L s Is 0.1 to 2 m in length,
the weight of the rice is reduced,
5. the three-dimensional decomposition-based microwave and millimeter wave holographic image reconstruction method according to claim 4, wherein L is a Is 2 m, L x Is 1 m, L z Is 0.2-0.8 m, L s 2 m, R0.6 m,
is composed of
6. The three-dimensional decomposition-based microwave and millimeter wave holographic image reconstruction method according to any one of claims 4 to 5,
the backscattered echo signals are S (x, y, z, f), where f is the microwave millimeter wave frequency dimension, then in step S2, at each discrete grid point coordinate (x, z) in the (x, z) dimension i ，z j ) The following steps are carried out:
calculating the discrete grid point coordinates (x) i ，z j ) Discretized mechanical scanning position to the microwave and millimeter wave antenna elements
Angular distance of
Then obtaining the matched filtering signal in the z dimension
Matching the filtered signal
And the mechanical scanning position
To echo signals
Is/are as follows
Carrying out matched filtering processing after dimensionality multiplication to obtain a signal
Will be at all of said mechanical scanning positions
The signal of
All are calculated and accumulated to obtain a signal S D (x i ，y′ k ，z j )。
7. The three-dimensional decomposition-based microwave and millimeter wave holographic image reconstruction method according to claim 6,
in the step S3, the interpolation processing employs any one of linear interpolation, SINC interpolation, spline interpolation, or cubic interpolation methods;
obtaining an up-sampled signal S by the interpolation processing F (x i ，y′ k ，z p1 )，
Wherein p1 is an integer, pl ∈ [0, N' z ]And N' z ＞N z And N' z ＝N 0 ·N z Let the pixel spacing of the up-sampled signal in the z-dimension be Δ z', then
And z in the z dimension p1 Coverage and z j The coverage is consistent.
8. The three-dimensional decomposition-based microwave and millimeter wave holographic image reconstruction method according to claim 7,
in the step S4, the discrete grid point coordinates in the y-dimension are y-coordinates through the second discretization process q ，q∈[0，N y ]，N y For discrete grids divided along the y-dimensionAnd is an integer greater than 1.
9. The three-dimensional decomposition-based microwave and millimeter wave holographic image reconstruction method according to claim 8,
in said step S5, said second image focusing comprises at each discrete grid point coordinate (x) i ，y q ，z j ) The following steps are carried out:
calculating the discrete grid point coordinates (x) i ，y q ，z j ) To all sampling positions of the microwave millimeter wave antenna array element
I.e. the slope in the y and z dimensions
And acquiring a distance matching point signal S at the sampling position in the z dimension G (x i ，y′ k ，z L )＝S F (x i ，y′ k ，z L ) Wherein, in the step (A),
taor＝c/(2·B)/N 0 ；
calculating all sampling positions y 'of y dimension of microwave millimeter wave antenna array element' k To match the filtered signal to the filtered signal,
wherein f is 0 The central frequency of the microwave millimeter wave radio frequency signal in the imaging target area is obtained;
all sampling positions y 'of y dimension of microwave millimeter wave antenna array element' k Matched filtered signal
Are all at the distance from the sampling position y' kSignal S from the matching point G (x i ，y′ k ，z L ) Y' k All sampling positions y 'of the y dimension of the microwave millimeter wave antenna array element are obtained through corresponding multiplication of the dimensions' k Signal of
All sampling positions y 'of y dimension of microwave millimeter wave antenna array element' k Signal of
Performing complex number accumulation calculation to obtain signal S (x) i ，y q ，z j )。
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