CN112213721B - Millimeter wave three-dimensional imaging method for scanning external or internal cylindrical scene facing security inspection - Google Patents
Millimeter wave three-dimensional imaging method for scanning external or internal cylindrical scene facing security inspection Download PDFInfo
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- G—PHYSICS
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
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- G01S7/41—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00 using analysis of echo signal for target characterisation; Target signature; Target cross-section
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Abstract
The invention discloses a millimeter wave three-dimensional imaging method for scanning a scene outside or inside a cylinder for security inspection, which comprises the following steps: n antennas of a linear array antenna are utilized to transmit N step frequency signals to a target, and the N antennas of the linear array antenna receive (2N-1) one-dimensional echo signals generated after the step frequency signals transmitted by the N antennas are transmitted to the target; obtaining a three-dimensional target echo signal based on the (2N-1) one-dimensional echo signals; obtaining a target echo signal after decoupling in the height direction and the distance direction according to the three-dimensional target echo signal; and performing distance and azimuth two-dimensional coherent processing on the target echo signals after the altitude direction and the distance direction are decoupled to obtain a target three-dimensional image. The three-dimensional high-resolution imaging of the target is realized by scanning outside the cylinder and then carefully scanning in the cylinder and combining omega-k and BP algorithms. Compared with the existing three-dimensional millimeter wave imaging method of the cylindrical security inspection instrument, the method can greatly improve the security inspection efficiency and improve the security inspection work intensity.
Description
Technical Field
The invention belongs to the technical field of radar signal processing, and particularly relates to a millimeter wave three-dimensional imaging method for scanning a scene outside or inside a cylinder for security inspection.
Background
In recent years, security inspection of public safety places such as railway stations, airports and subways is particularly important due to the severity of international and domestic public safety situations. Traditional security inspection means such as metal detectors and X-ray security inspection machines are unsuitable or cannot be efficiently used for human security inspection due to respective limitations. Millimeter waves have the congenital advantages of strong penetrating power, small radiation to human bodies, high resolution and the like, and are particularly suitable for hidden object detection, so that millimeter wave imaging provides a new choice for human body security inspection and has wide application prospect.
The active millimeter wave radar 3-dimensional imaging is based on a synthetic aperture radar (Synthetic Aperture Radar, SAR) imaging technology, so that the human body is rapidly imaged in 3 dimensions and the foreign matter is detected, and the millimeter wave 3-dimensional imaging security inspection system is widely valued at home and abroad. The millimeter wave 3-dimensional imaging system has various implementation modes, is deeply studied at home and abroad, has practical engineering application capability, mainly comprises plane scanning imaging and cylindrical scanning imaging, and has 3-dimensional resolution capability, but is limited by a beam scanning range, so that omnidirectional observation angle imaging cannot be realized through one-time scanning. The circular scanning imaging system adopts a method of combining array SAR and circular SAR, so that the 3-dimensional resolution problem of the millimeter wave imaging system is solved theoretically, the defect of a plane scanning mode is overcome, and high-performance 3-dimensional imaging is realized under the condition of low system cost. At present, the domestic research focus is mainly focused on a circumferential scanning imaging system, wen Xin, huang Pei-kang, nian Feng et al in the document Active millimeter-wave near-field cylindrical scanning three-dimensional imaging system [ J ] ((Systems Engineering and Electronics) 2014,36 (6): 1044-1049.DOI:10.3969/J. Issn.1001-506 X.2014.06.05), an active millimeter wave circumferential scanning 3-dimensional imaging system model and a reconstruction algorithm are provided, and an actual imaging system based on the model is established. In the literature Millimer-wave human security imaging based on frequency-domain sparsity and rapid imaging sparse array architecture [ J ] (Journal of Radars, in press, DOI:10.12000/JR17082 ]) Tian He, li Dao-jin, qi Chun-chao, a Millimeter wave human body security inspection 3-dimensional imaging method based on cylindrical surface scanning and based on Baker sparse sampling and frequency domain compressed sensing is provided, a corresponding sparse planar array based on Baker codes and receiving-transmitting division modes is designed, and a better 3-dimensional imaging real-time processing effect is obtained.
Although the 3-dimensional millimeter wave imaging method can realize three-dimensional scene imaging and realize security inspection tasks, when the number of scene grid points is large, the operation amount is greatly increased by utilizing a BP (Back Projection) algorithm to perform 3-dimensional imaging, and real-time human body security inspection is difficult to meet.
Disclosure of Invention
In order to solve the problems in the prior art, the invention provides a millimeter wave three-dimensional imaging method for scanning a scene outside or inside a cylinder for security inspection. The technical problems to be solved by the invention are realized by the following technical scheme:
a millimeter wave three-dimensional imaging method for scanning a scene outside or inside a cylinder facing security inspection comprises the following steps:
n antennas of a linear array antenna are utilized to transmit N stepping frequency signals to a target, the N antennas of the linear array antenna receive (2N-1) one-dimensional echo signals generated after the stepping frequency signals transmitted by the N antennas are transmitted to the target, wherein the x-th antenna and the (x+1) -th antenna receive one-dimensional echo signals generated after the stepping frequency signals transmitted by the x-th antenna are transmitted to the target, x is more than or equal to 1 and less than or equal to N, and the target is positioned in or outside a cylinder;
obtaining a three-dimensional target echo signal based on the (2N-1) one-dimensional echo signals;
obtaining a target echo signal after decoupling in the height direction and the distance direction according to the three-dimensional target echo signal;
and performing distance and azimuth two-dimensional coherent processing on the target echo signals after the altitude direction and the distance direction are decoupled to obtain a target three-dimensional image.
In one embodiment of the present invention, N stepped frequency signals are transmitted to a target by using N antennas of a linear array antenna, where the N antennas of the linear array antenna receive (2N-1) one-dimensional echo signals generated after the stepped frequency signals transmitted by the N antennas are transmitted to the target, and the method includes:
transmitting N step frequency signals to a target by utilizing N antennas of the linear array antenna;
obtaining an echo signal of the nth frequency point received by the mth antenna according to the signal of the nth frequency point of the step frequency signal, wherein m is more than or equal to 1 and less than or equal to N;
and carrying out line-splitting frequency modulation processing on the echo signals of all the frequency points corresponding to the mth antenna to obtain one-dimensional echo signals of the mth antenna.
In one embodiment of the present invention, the one-dimensional echo signal is:
wherein s is if (t, m) is the one-dimensional echo signal of the mth antenna, t is the time of signal transmission of a single antenna, delta i As a shock function, a a (m) is the window function of the mth antenna, j is the imaginary part, c is the speed of light, f c Where t is the time at which the signal is transmitted by a single antenna, γ is the frequency modulation, γ=Δf/τ, t=nτ, Δf is the frequency interval, τ is the duration of the signal transmitted by a single frequency, R i (m) is the tilt history of the mth antenna, R ref Is the reference distance.
In one embodiment of the present invention, obtaining a three-dimensional target echo signal based on the (2N-1) one-dimensional echo signals includes:
and acquiring a plurality of one-dimensional echo signals to a cylindrical inner or cylindrical outer ring scanning target by using N antennas of the linear array antenna so as to obtain the three-dimensional target echo signals.
In one embodiment of the present invention, obtaining the target echo signal after decoupling in the altitude direction and the distance direction according to the three-dimensional target echo signal includes:
obtaining a two-dimensional echo signal of a distance wave number domain according to the one-dimensional echo signals, wherein the set of all the one-dimensional echo signals is the three-dimensional target echo signal;
based on a stationary phase principle, carrying out Fourier transform on the two-dimensional echo signals of the distance wave number domain along the height direction to obtain frequency spectrum signals;
performing center matched filtering processing on the spectrum signals to obtain matched spectrum signals;
based on an interpolation method, decoupling the matched spectrum signals by using variable substitution of an omega-k algorithm to obtain decoupled signals;
compensating the decoupled signal to obtain a compensated signal;
and performing distance-dimensional inverse Fourier transform and height-dimensional inverse Fourier transform on the compensated signal to obtain a target echo signal after decoupling in the height direction and the distance direction.
In one embodiment of the present invention, the target echo signals after the altitude direction and the distance direction are decoupled are:
wherein S (t, Z) is the target echo signal after decoupling the altitude direction and the distance direction, t is the time of signal transmission of a single antenna, Δt=2Δr/c, c is the speed of light, Δr=r Bi -R S ，R Bi For the linear distance from the ith point target to the antenna, Z is the height-wise variable, Z i For the height of the ith point target, j is the imaginary part, K Rc At a center frequency f c Corresponding wave vector, Δr=r Bi -R S ，R S Is the closest distance from the origin of coordinates to the vertical array antenna.
In one embodiment of the present invention, performing distance and azimuth two-dimensional coherent processing on the altitude direction and the distance direction decoupled target echo signals to obtain a target three-dimensional image, including:
dividing a 3-dimensional imaging scene into P two-dimensional imaging sections along the height direction, wherein the two-dimensional imaging sections comprise a grid pattern, and the grid pattern is used for defining a target area;
obtaining a two-dimensional signal after linear interpolation and phase compensation of the two-dimensional imaging section according to the target echo signals after the height direction and the distance direction decoupling;
for the linearityThe two-dimensional signals after interpolation and phase compensation are coherently overlapped in the azimuth direction to obtain a target point (x) i ,y i ) Is a scattering function of (2);
according to the target point (x i ,y i ) And obtaining a three-dimensional image of the target.
In one embodiment of the invention, the target point (x i ,y i ) The scattering function of (2) to obtain a three-dimensional image of the target, comprising:
according to the target point (x i ,y i ) Obtaining a plurality of target two-dimensional images by the scattering function of the (a);
and superposing all the target two-dimensional images to obtain the target three-dimensional image.
In one embodiment of the invention, the target point (x i ,y i ) The scattering function of (2) is:
wherein S (t) is a two-dimensional signal after linear interpolation and phase compensation, K Rc At a center frequency f c Corresponding wave vector R ij Is the distance of the antenna to the grid in the grid pattern.
The invention has the beneficial effects that:
the three-dimensional high-resolution imaging of the target is realized by scanning outside the cylinder and then carefully scanning in the cylinder and combining omega-k and BP algorithms. Compared with the existing three-dimensional millimeter wave imaging method of the cylindrical security inspection instrument, the method can greatly improve the security inspection efficiency and improve the security inspection work intensity.
The present invention will be described in further detail with reference to the accompanying drawings and examples.
Drawings
Fig. 1 is a schematic flow diagram of a millimeter wave three-dimensional imaging method for scanning a scene outside or inside a cylinder for security inspection, which is provided by the embodiment of the invention;
fig. 2 is a schematic flow chart of another security inspection-oriented millimeter wave three-dimensional imaging method for scanning a scene outside or inside a cylinder according to an embodiment of the present invention;
fig. 3a to 3c are schematic diagrams of target scanning in a cylindrical external simulation scene of a millimeter wave three-dimensional imaging method for scanning a cylindrical external scene, which is provided by the embodiment of the invention and is oriented to security inspection;
fig. 4a to 4c are schematic diagrams of target scanning in a cylindrical simulation scene of a millimeter wave three-dimensional imaging method for scanning a cylindrical scene facing security inspection, which is provided by the embodiment of the invention;
fig. 5a to 5d are schematic diagrams of three-dimensional imaging experiments of a mannequin by a millimeter wave three-dimensional imaging method for scanning a scene outside and inside a cylinder for security inspection, which are provided by the embodiment of the invention.
Detailed Description
The present invention will be described in further detail with reference to specific examples, but embodiments of the present invention are not limited thereto.
Example 1
At present, the 3-dimensional imaging mode with more research results and engineering applications of the three-dimensional scanning system comprises two types of planar SAR and cylindrical SAR. The planar SAR scanning imaging has three-dimensional resolution, but because the planar scanning is limited by the beam width, the object to be detected cannot be subjected to omnibearing examination, and the omnibearing image of the object to be detected can be acquired only by scanning for a plurality of times, so that the time consumption is long. The single cylindrical scanning adopts vertical array scanning, solves the 3-dimensional resolution problem of plane scanning, but also takes a long time.
Based on the above-mentioned problems, please refer to fig. 1 and fig. 2, fig. 1 is a schematic flow chart of a millimeter wave three-dimensional imaging method for scanning a scene outside or inside a cylinder for security inspection provided in an embodiment of the present invention, and fig. 2 is a schematic flow chart of another millimeter wave three-dimensional imaging method for scanning a scene outside or inside a cylinder for security inspection provided in an embodiment of the present invention, where the present invention provides a millimeter wave three-dimensional imaging method for scanning a scene outside or inside a cylinder for security inspection, and the millimeter wave three-dimensional imaging method includes steps 1 to 4, where:
step 1, generating (2N-1) one-dimensional echo signals after N antennas of the linear array antenna receive step frequency signals transmitted by the N antennas to a target, wherein the x-th antenna and the (x+1) -th antenna receive the one-dimensional echo signals generated after the step frequency signals transmitted by the x-th antenna to the target, x is more than or equal to 1 and less than N, and the target is positioned in or outside the cylinder.
The target of this embodiment can image in the cylinder, also can image outside the cylinder, through installing the linear array antenna on the cylinder along the direction of height of cylinder to the target transmission signal, wherein, the linear array antenna is total including N antenna, and every antenna transmission is step frequency signal, and this embodiment adopts transmission step frequency signal to replace LFM (linear frequency modulation) signal to realize the distance to high resolution. After the target receives the N step-frequency signals, the N antennas of the linear array antenna receive (2N-1) one-dimensional echo signals generated by the N antennas after the step-frequency signals are transmitted to the target, wherein the 1 st antenna and the 2 nd antenna simultaneously receive the one-dimensional echo signals generated by the 1 st antenna after the step-frequency signals are transmitted to the target, the 2 nd antenna and the 3 rd antenna simultaneously receive the one-dimensional echo signals generated by the 2 nd antenna after the step-frequency signals are transmitted to the target, and so on, the x antenna and the (x+1) antenna receive the one-dimensional echo signals generated by the x antenna after the step-frequency signals are transmitted to the target, wherein the one-dimensional echo signals generated by the N antenna after the step-frequency signals are received by the N antenna are only the N antenna, so that the embodiment inserts a new sampling point between every two adjacent antennas, and can be equivalently (2N-1) antennas automatically receive and can generate (2N-1) one-dimensional echo signals altogether.
In a specific embodiment, step 1 may specifically include:
step 1.1, N step frequency signals are transmitted to a target by utilizing N antennas of the linear array antenna.
Step 1.2, obtaining an echo signal of the nth frequency point received by the mth antenna according to the signal of the nth frequency point of the step frequency signal, wherein m is more than or equal to 1 and less than or equal to N.
Specifically, the signal of the nth frequency point of the step frequency signal is expressed as:
wherein s is n (t,f cn ) For the signal of the nth frequency point, t is the time of transmitting the signal by a single antenna, τ is the duration of transmitting the signal by the single frequency point, f cn The frequency of the nth frequency point is represented by j, and the imaginary part is represented by j.
In this embodiment, the attenuation of the signal along with the distance and the interaction between the targets are not considered in the short-distance range, so that the echo signal of the nth frequency point received by the mth antenna can be obtained according to the signal of the nth frequency point of the step frequency signal, and the echo signal is expressed as:
wherein r (t, f) cn M) is the echo signal of the nth frequency point, a a (m) is the window function of the mth antenna, R i (m) is the pitch history of the mth antenna, c is the speed of light, and Δf is the frequency interval.
In order to perform echo signal simulation, the embodiment needs to calculate the slope distance history, and for the ith target point on the target, the height is Z i The nearest slant distance is R Bi The corresponding pitch history is deduced as follows:
wherein Deltaz is the linear array channel interval, R Bi Selecting a reference distance R for the linear distance between the ith point target and the antenna ref To construct a reference signal, the reference distance R is typically chosen for ease of computation ref Set to 0.
And 1.3, performing line-splitting frequency modulation processing on echo signals of all frequency points corresponding to the mth antenna to obtain one-dimensional echo signals of the mth antenna.
Specifically, in this embodiment, since step frequency signals are used, the echo signals are converted into single frequency signals by using the de-chirping process, the frequency of the single frequency signals is proportional to the distance difference between the echo signals and the reference signals, after sampling, the acquired data corresponding to each frequency point of each step frequency signal are arranged according to the frequency points, so the one-dimensional echo signal of the mth antenna can be expressed as:
wherein s is if (t, m) is the one-dimensional echo signal of the mth antenna, t is the time of signal transmission of a single antenna, delta i As a shock function, a a (m) is the window function of the mth antenna, j is the imaginary part, c is the speed of light, f c Let t be the time of signal transmission of a single antenna, gamma be the frequency modulation rate, gamma=Δf/τ, t=nτ, n be the number of frequency points of the stepped frequency signal, Δf be the frequency interval, τ be the duration of signal transmission of a single frequency point, R i (m) is the tilt history of the mth antenna, R ref Is the reference distance.
And 2, obtaining a three-dimensional target echo signal based on the (2N-1) one-dimensional echo signals.
Specifically, N antennas of a linear array antenna are utilized to scan a target to the inside or outside of a cylinder to acquire a plurality of one-dimensional echo signals so as to obtain three-dimensional target echo signals, the scanning mode is a synthetic aperture mode, and the scanning is repeated from top to bottom by switching angles from top to bottom so as to obtain the three-dimensional target echo signals. Scanning in the height direction resembles a stripe synthetic aperture radar imaging observation mode; the linear array rotates along the turntable to form an azimuth scanning mode similar to a beam-focusing synthetic aperture radar observation mode.
And step 3, obtaining the target echo signals after decoupling in the height direction and the distance direction according to the three-dimensional target echo signals.
Specifically, in this embodiment, because the full focusing without approximate conditions is implemented for the whole three-dimensional scene, for this purpose, step 3 of this embodiment performs the two-dimensional decoupling and focusing for the height and distance of the three-dimensional target echo signal, so as to obtain the target echo signal after the decoupling for the height direction and the distance direction. Specifically comprises the steps 3.1 to 3.6, wherein:
and 3.1, obtaining a two-dimensional echo signal of a distance wave number domain according to the one-dimensional echo signals, wherein the set of all the one-dimensional echo signals is a three-dimensional target echo signal.
Specifically, in this embodiment, a two-dimensional echo signal is obtained according to a one-dimensional echo signal, that is, a set of all the one-dimensional echo signals in a height direction is a two-dimensional echo signal, and then the two-dimensional echo signal is converted into a two-dimensional echo signal in a distance wave number domain, and then the two-dimensional echo signal in the distance wave number domain is expressed as:
S(K R ,m)＝∑ i δ i a a (m)exp(-jK R (R i (m)-R ref ))；
wherein S (K) R M) is a two-dimensional echo signal of a distance wave number domain,representing the wave number, f, corresponding to the distance frequency c Is the center frequency, gamma is the tuning frequency, delta i As a function of the impact.
And 3.2, carrying out Fourier transformation on the two-dimensional echo signals of the distance wave number domain along the height direction based on the principle of stationary phase to obtain a frequency spectrum signal.
Specifically, the present embodiment requires fourier transformation of the obtained two-dimensional echo signal of the range wave number domain along the height direction, so that it can be obtained using the principle of stationary phase:
wherein S (K) R ,K Z ) Is a frequency spectrum signal, K Z For the corresponding quantity of the height position after the Fourier transform, namely the corresponding frequency of the height position after the Fourier transform, A i Is the corresponding quantity of the impact function after fourier transformation.
And 3.3, performing center matched filtering processing on the spectrum signals to obtain matched spectrum signals.
Specifically, the present embodiment needs to perform pulse compression on the signal for the next step, so after the first phase compensation of the spectrum signal is completed, two-dimensional spectrum phases only remain, namely:
the first term is RCM (Range Cell Migration) resulting from the coupling of distance and Z direction, representing the change in skew of the target. Center matched filtering is carried out on the frequency spectrum signals, and the center point matching function is as follows: />At this time, a matched spectrum signal is obtained, and the matched spectrum signal is expressed as:
wherein R is S For the closest distance of the origin of coordinates to the vertical array antenna, Δr=r Bi -R S 。
And 3.4, based on an interpolation method, decoupling the matched spectrum signals by using variable substitution of an omega-k algorithm to obtain decoupled signals.
Specifically, the present embodiment needs to obtain a decoupled signal for the next step, where the first term of the matched spectrum signal is RCM generated by distance and altitude coupling, and the linear phase of the second term is the position of the target altitude. The present embodiment uses a variable substitution pair in ω -k algorithm (wavenumber domain algorithm), and the first term coupling phase of the matched spectrum signal is decoupled:
the above formula is called Stolt mapping and is usually implemented by interpolation. The interpolated wavenumber spectrum is:
wherein the method comprises the steps ofK Rc At a center frequency f c Corresponding wave vectors.
And 3.5, compensating the decoupled signal to obtain a compensated signal.
Specifically, in this embodiment, the decoupled signal needs to be compensated to remove the redundant phase, so the second phase of the decoupled signal is compensated to obtain a compensated signal, where the compensated signal is expressed as:
wherein S (DeltaR, K) Z ) To compensate for the signal.
And 3.6, performing distance dimension inverse Fourier transform and altitude dimension inverse Fourier transform on the compensated signal to obtain an altitude-direction and distance-direction decoupled target echo signal.
Specifically, in this embodiment, two-dimensional tangent plane imaging of the signal is completed, and two-dimensional inverse fourier transform is required for restoring the time domain, so that the compensated signal is subjected to distance-dimensional inverse fourier transform and altitude-dimensional inverse fourier transform to obtain an altitude-direction and distance-direction decoupled target echo signal, where the target echo signal is expressed as:
wherein S (t, Z) is the target echo signal after decoupling the altitude direction and the distance direction, t is the time of signal transmission of a single antenna, Δt=2Δr/c, c is the speed of light, Δr=r Bi -R S ，R Bi Straight line distance from the antenna for the ith point targetZ is a height direction variable, Z i For the height of the ith point target, j is the imaginary part, K Rc For the wave vector corresponding to the center frequency fc, Δr=r Bi -R S ，R S Is the closest distance from the origin of coordinates to the vertical array antenna. As a result, it does not distinguish scattering points in azimuth dimension, i.e. azimuth has no resolution, and the residual phase is exp (-jK) Rc Δr) that is compensated during the BP imaging process.
And 4, performing distance and azimuth two-dimensional coherent processing on the target echo signals after the decoupling of the altitude direction and the distance direction to obtain a target three-dimensional image.
In particular, this embodiment is because after its height and distance decoupling is accomplished with the ω -k algorithm, the 3-dimensional focusing problem of imaging at this time can be regarded as a projection problem in each XOY plane along the vertical direction. For this reason, step 4 of the present embodiment performs distance and azimuth two-dimensional coherent processing on the target echo signal after the altitude direction and the distance direction are decoupled, so as to obtain a target three-dimensional image. Specifically comprises the steps 4.1 to 4.4, wherein:
and 4.1, dividing the 3-dimensional imaging scene into P two-dimensional imaging sections along the height direction, wherein the two-dimensional imaging sections comprise a grid pattern, and the grid pattern is used for limiting a target area.
Specifically, in this embodiment, since the BP algorithm is required, the 3-dimensional imaging scene is divided into P XOY imaging slices (i.e., two-dimensional imaging slices) along the Z axis, and a grid pattern is set with the center as a base point, and the grid pattern is divided into a plurality of grids.
And 4.2, obtaining a two-dimensional signal after linear interpolation and phase compensation of the two-dimensional imaging section according to the target echo signal after the decoupling of the height direction and the distance direction.
First, the distance R from each grid to the echo receiving position on the grid pattern is calculated ij 。
Specifically, the present embodiment requires the BP algorithm to be used, so the distance from the antenna to the mesh divided in the mesh pattern is calculated first, and this distance is:
wherein, atn r For antenna position distance coordinates, ann a The position and orientation coordinates of the antenna; n is n r-bp Distance coordinates, n, for a grid divided in a grid pattern a-bp Azimuth coordinates of the grid divided in the grid pattern.
In this embodiment, BP algorithm is required, so that linear interpolation and phase compensation are required for two-dimensional imaging sections, and for each two-dimensional imaging section perpendicular to the Z axis, the height direction and the distance direction in the target echo signal after decoupling have been processed, so that the two-dimensional signal after linear interpolation and phase compensation for the two-dimensional imaging section can be abbreviated as:
wherein S (t) is a two-dimensional imaging slice.
Step 4.3, performing coherent superposition on the two-dimensional signals subjected to linear interpolation and phase compensation in the azimuth direction to obtain a target point (x) i ,y i ) Is a scattering function of (a).
Let the scattering function of each pixel point (x, y) on the two-dimensional signal be u (x, y), and the two-dimensional signal is coherently superimposed in azimuth direction to derive the position coordinate as (x i ,y i ) The scatter function of the target point of (c) is:
the description position coordinates are (x i ,y i ) R ij Is the position coordinates (x i ,y i ) A slant distance to the antenna.
Step 4.4, according to the target point (x i ,y i ) And obtaining a three-dimensional image of the target.
Step 4.41, according to the target point (x i ,y i ) Obtaining a plurality of target two-dimensional images by the scattering function of the (a);
and 4.42, superposing all the target two-dimensional images to obtain a target three-dimensional image.
Specifically, for each two-dimensional imaging slice, the BP algorithm is applied to the obtained target point (x i ,y i ) The scattering function of the two-dimensional imaging section is subjected to azimuth coherence, namely a 2-dimensional image of the two-dimensional imaging section, namely a target two-dimensional image, and then each target two-dimensional image is overlapped along the Z-axis direction, and a 3-dimensional image can be reconstructed, namely a target three-dimensional image is obtained.
In summary, according to the millimeter wave three-dimensional imaging method for scanning a scene outside or inside a cylinder for security inspection provided by the embodiment, security inspection is performed by adopting a mode of scanning a scene outside the cylinder and scanning a scene inside the cylinder, firstly, people outside the cylinder are detected and become a low-resolution image, if suspicious people are found in the image, the suspicious people are led to enter a cylindrical security inspection instrument to be detected and become a high-resolution image, and the implementation thinking is that firstly, the omega-k algorithm is adopted to realize the two-dimensional decoupling and focusing of the height direction and the distance direction of a signal, and then the BP algorithm is adopted to perform the coherent superposition processing of the azimuth direction of the signal. The simulation experiment realizes the three-dimensional reconstruction of the three-dimensional lattice target scene. Compared with the traditional algorithm, the method saves the calculated amount in the processing process, overcomes the limitation of the imaging angle, can be suitable for a non-ideal cylindrical scanning system, and has higher feasibility and engineering applicability.
In order to verify the effectiveness of the millimeter wave three-dimensional imaging method for scanning the cylindrical external scene, which is provided by the invention, the effectiveness is further illustrated by the following simulation experiment:
please refer to fig. 3a to 3c, and fig. 3a to 3c are schematic diagrams of target scanning in a cylindrical external simulation scene and schematic diagrams of target point distribution in the simulation scene of the millimeter wave three-dimensional imaging method for scanning a cylindrical external scene for security inspection provided by the embodiment of the invention. Setting up 27 target points in total in a three-dimensional coordinate system, namely, 27 target points in one group, two groups, one group for cylindrical internal simulation and one group for cylindrical external simulation; the antenna scans outwards from the cylinder, and the transmitted continuous wave signal with the step frequency interval of 150MHz and the bandwidth of 15GHz; the pitch beam angle is 45 degrees, and the azimuth beam angle is 45 degrees; azimuth pitch Δx=7 mm, and elevation pitch Δz=5 mm; the distance delta y=7mm, the angle range of the linear array rotating along the cylindrical axis is 180 degrees, and the three-dimensional resolutions of azimuth (X), distance (Y) and height (Z) are 0.021m, 0.012m and 0.007m respectively. The sampling points of the three axes of the azimuth (X), the distance (Y) and the height (Z) are 100, 210 and 512 respectively.
The specific simulation parameters of this embodiment are shown in table 1.
TABLE 1 simulation parameters
Referring to fig. 4a to 4c, fig. 4a to 4c are schematic diagrams of target scanning in a cylindrical simulation scene of a millimeter wave three-dimensional imaging method for scanning a cylindrical scene, which is provided by the embodiment of the invention and is oriented to security inspection. Setting up 27 target points in total in 3 multiplied by 3 in a three-dimensional coordinate system, and setting up two groups; the antenna scans the cylinder, the transmitted continuous wave signal with the step frequency interval of 150MHz and the bandwidth of 15GHz; the pitch beam angle is 45 degrees, and the azimuth beam angle is 45 degrees; azimuth pitch Δx=5 mm, and elevation pitch Δz=5 mm; the distance delta y=5mm, the angle range of the linear array rotating along the cylindrical axis is 90 degrees, and the three-dimensional resolutions of azimuth (X), distance (Y) and height (Z) are respectively 0.017m, 0.008m and 0.007m. The sampling points of the three axes of the azimuth (X), the distance (Y) and the height (Z) are 40, 210 and 512 respectively.
The specific simulation parameters of this embodiment are shown in table 2.
TABLE 2 simulation parameters
Referring to fig. 5a to 5d, fig. 5a to 5d are schematic diagrams of a three-dimensional imaging experiment of a mannequin by a millimeter wave three-dimensional imaging method for scanning a scene outside and inside a cylinder for security inspection according to an embodiment of the present invention. Fig. 5a to 5b show the results of scanning imaging outside the cylinder, and fig. 5c to 5d show the results of scanning imaging inside the cylinder. Three-dimensional imaging experiments for a mannequin were conducted in a microwave dark room, the size of the mannequin was approximately 0.44m (Y width) by 0.26 (X thickness) by 1.77m (Z height). The front and the back of the mannequin are respectively scanned by fans, and the relative positions of the mannequin and the scanning cylindrical surface are changed, so that the full coverage of the human body target is realized. In the experiment, the frequency range of the transmitted signal is 25-35GHz, the rotation radius of the linear array is 0.8m, the rotation range is 75 degrees, and the scanning distance in the Z direction is 2m. The number of signal sampling points of the whole three-dimensional scene is 40 multiplied by 200 multiplied by 512 points.
The specific simulation parameters of this embodiment are shown in table 3.
TABLE 3 simulation parameters
The embodiment of the invention provides a millimeter wave three-dimensional imaging method for cylindrical scanning, which is used for carrying out 3-D reconstruction on a target, and then folding the 3-D image into a complete 2-D image of the target through maximum projection so as to display the complete 2-D image on a computer.
It should be noted that in this document relational terms such as first and second, and the like are used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Moreover, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that an article or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed. Without further limitation, an element defined by the phrase "comprising one … …" does not exclude the presence of other like elements in an article or apparatus that comprises the element. The terms "connected" or "connected," and the like, are not limited to physical or mechanical connections, but may include electrical connections, whether direct or indirect. The orientation or positional relationship indicated by "upper", "lower", "left", "right", etc. is based on the orientation or positional relationship shown in the drawings, and is merely for convenience of description and to simplify the description, and is not indicative or implying that the apparatus or elements referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention.
In the description of the present specification, a description referring to terms "one embodiment," "some embodiments," "examples," "specific examples," or "some examples," etc., means that a particular feature or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the present invention. In this specification, schematic representations of the above terms are not necessarily directed to the same embodiment or example. Furthermore, the particular features or characteristics described may be combined in any suitable manner in any one or more embodiments or examples. Further, one skilled in the art can engage and combine the different embodiments or examples described in this specification.
The foregoing is a further detailed description of the invention in connection with the preferred embodiments, and it is not intended that the invention be limited to the specific embodiments described. It will be apparent to those skilled in the art that several simple deductions or substitutions may be made without departing from the spirit of the invention, and these should be considered to be within the scope of the invention.
Claims (7)
1. The millimeter wave three-dimensional imaging method for scanning the scene outside or inside the cylinder for security inspection is characterized by comprising the following steps of:
transmitting N step frequency signals to a target by utilizing N antennas of the linear array antenna;
obtaining an echo signal of the nth frequency point received by the mth antenna according to the signal of the nth frequency point of the step frequency signal, wherein m is more than or equal to 1 and less than or equal to N;
carrying out line-splitting frequency modulation processing on echo signals of all the frequency points corresponding to the mth antenna to obtain one-dimensional echo signals of the mth antenna, wherein the x-th antenna and the (x+1) -th antenna receive one-dimensional echo signals generated after step frequency signals transmitted by the x-th antenna are transmitted to a target, x < N is more than or equal to 1, and the target is positioned in or out of a cylinder;
obtaining a three-dimensional target echo signal based on the generated (2N-1) one-dimensional echo signals;
taking the set of all the one-dimensional echo signals in the height direction as two-dimensional echo signals, and then converting the two-dimensional echo signals into two-dimensional echo signals of a distance wave number domain, wherein the two-dimensional echo signals of the distance wave number domain are expressed as: s (K) R ,m)＝∑ i δ i a a (m)exp(-jK R (R i (m)-R ref ) A) is provided; wherein S (K) R M) is a two-dimensional echo signal of a distance wave number domain,representing the wave number, f, corresponding to the distance frequency c Is the center frequency, gamma is the tuning frequency, delta i As a shock function, a a (m) is the window function of the mth antenna, j is the imaginary part, c is the speed of light, R i (m) is the tilt history of the mth antenna, R ref T is the reference distance, and t is the time for a single antenna to transmit signals;
based on a stationary phase principle, carrying out Fourier transform on the two-dimensional echo signals of the distance wave number domain along the height direction to obtain frequency spectrum signals;
performing center matched filtering processing on the spectrum signals to obtain matched spectrum signals;
based on an interpolation method, decoupling the matched spectrum signals by using variable substitution of an omega-k algorithm to obtain decoupled signals;
compensating the decoupled signal to obtain a compensated signal;
performing distance dimension inverse Fourier transform and height dimension inverse Fourier transform on the compensated signal to obtain a target echo signal after decoupling in the height direction and the distance direction;
and performing distance and azimuth two-dimensional coherent processing on the target echo signals after the altitude direction and the distance direction are decoupled to obtain a target three-dimensional image.
2. The millimeter wave three-dimensional imaging method according to claim 1, wherein the one-dimensional echo signal is:
wherein s is if (t, m) is the one-dimensional echo signal of the mth antenna, γ=Δf/τ, t=nτ, Δf is the frequency interval, τ is the duration of the single frequency transmit signal.
3. The millimeter wave three-dimensional imaging method according to claim 1, wherein obtaining a three-dimensional target echo signal based on the (2N-1) one-dimensional echo signals comprises:
and acquiring a plurality of one-dimensional echo signals to a cylindrical inner or cylindrical outer ring scanning target by using N antennas of the linear array antenna so as to obtain the three-dimensional target echo signals.
4. The millimeter wave three-dimensional imaging method according to claim 1, wherein the target echo signals after the decoupling in the height direction and the distance direction are:
wherein S (t, Z) is the target echo signal after decoupling the altitude direction and the distance direction, t is the time of signal transmission of a single antenna, Δt=2Δr/c, c is the speed of light, Δr=r Bi -R S ，R Bi For the linear distance from the ith point target to the antenna, Z is the height-wise variable, Z i For the height of the ith point target, j is the imaginary part, K Rc At a center frequency f c Corresponding wave vector, Δr=r Bi -R S ，R S Is the closest distance from the origin of coordinates to the vertical array antenna.
5. The millimeter wave three-dimensional imaging method according to claim 1, wherein performing distance and azimuth two-dimensional coherent processing on the target echo signals after the altitude direction and the distance direction are decoupled to obtain a target three-dimensional image comprises:
dividing a 3-dimensional imaging scene into P two-dimensional imaging sections along the height direction, wherein the two-dimensional imaging sections comprise a grid pattern, and the grid pattern is used for defining a target area;
obtaining a two-dimensional signal after linear interpolation and phase compensation of the two-dimensional imaging section according to the target echo signals after the height direction and the distance direction decoupling;
performing coherent superposition on the two-dimensional signal subjected to linear interpolation and phase compensation in the azimuth direction to obtain a target point (x) i ,y i ) Is a scattering function of (2);
according to the target point (x i ,y i ) And obtaining a three-dimensional image of the target.
6. The millimeter wave three-dimensional imaging method according to claim 5, characterized in that, according to the target point (x i ,y i ) The scattering function of (2) to obtain a three-dimensional image of the target, comprising:
according to the target point (x i ,y i ) Obtaining a plurality of target two-dimensional images by the scattering function of the (a);
and superposing all the target two-dimensional images to obtain the target three-dimensional image.
7. The millimeter wave three-dimensional imaging method according to claim 5, characterized in that the target point (x i ,y i ) The scattering function of (2) is:
wherein S (t) is a two-dimensional signal after linear interpolation and phase compensation, K Rc At a center frequency f c Corresponding wave vector R ij Is the distance of the antenna to the grid in the grid pattern.
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| CN113239773B (en) * | 2021-05-08 | 2022-07-22 | 重庆邮电大学 | Human body perception method based on CSAR three-dimensional imaging |
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