CN111766583B - Human body security check instrument imaging method based on measured data - Google Patents

Human body security check instrument imaging method based on measured data Download PDF

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CN111766583B
CN111766583B CN202010737864.7A CN202010737864A CN111766583B CN 111766583 B CN111766583 B CN 111766583B CN 202010737864 A CN202010737864 A CN 202010737864A CN 111766583 B CN111766583 B CN 111766583B
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CN111766583A (en
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王勇
曹蕊
黄岩岩
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Harbin Institute of Technology
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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
    • 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
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/89—Radar or analogous systems specially adapted for specific applications for mapping or imaging
    • G01S13/90—Radar or analogous systems specially adapted for specific applications for mapping or imaging using synthetic aperture techniques, e.g. synthetic aperture radar [SAR] techniques
    • G01S13/9004—SAR image acquisition techniques
    • 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
    • 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
    • G01S13/88—Radar or analogous systems specially adapted for specific applications
    • G01S13/887—Radar or analogous systems specially adapted for specific applications for detection of concealed objects, e.g. contraband or weapons

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Abstract

A human body security check instrument imaging method based on measured data belongs to the technical field of radar imaging. The invention solves the problem that the imaging can not be carried out by utilizing initial echo data and the traditional SAR imaging method because the actual security check instrument imaging system has system errors and the coupling exists between the azimuth direction and the distance direction of the echo signal of the circular synthetic aperture radar. The invention uses the error phase after fitting and smoothing to carry out carrier frequency correction on the echo signal, thereby compensating the carrier frequency error of the signal. Echo amplitude compensation in the channel is carried out by using the amplitude characteristics of the echo signals; and (3) extracting compensation parameters by using the echo signals of the metal plate, and performing echo amplitude, frequency and constant phase compensation among channels. After the initial echo data are compensated by adopting the method, the image of the human body is obtained by using a back projection imaging algorithm. The invention can be applied to the imaging of the human body security check instrument.

Description

Human body security check instrument imaging method based on measured data
Technical Field
The invention belongs to the technical field of radar imaging, and particularly relates to a human body security check instrument imaging method based on measured data.
Background
The traditional security inspection means such as a metal detector and an X-ray security inspection instrument are not suitable for human body imaging due to respective limitations. In contrast, the millimeter waves have good safety and can penetrate through clothes and packages, so that clearer imaging of hidden dangerous goods is obtained. And the millimeter wave has lower electron energy, and compared with X-rays, the radiation quantity of the millimeter wave is almost negligible, so that the millimeter wave does not cause damage to biological tissues and has less harm to human bodies. Therefore, the microwave-based security inspection imaging gradually becomes the most mainstream human body security inspection imaging mode, and has very wide application prospect.
The millimeter wave imaging system can be divided into two types of systems according to the imaging mode, one type is a passive millimeter wave imaging system, and the passive millimeter wave imaging system performs human body imaging by detecting millimeter waves radiated by a human body; the other type is an active millimeter wave imaging system, which is based on the synthetic aperture radar imaging technology, realizes real-time three-dimensional imaging and performs foreign matter detection by actively transmitting millimeter wave signals to a human body and then processing the received reflected echo signals. The active imaging system can carry out human body imaging more clearly, and the imaging process is quick and safe, and is the mainstream technology of the security inspection imaging system.
The millimeter wave active security inspection instrument can perform three-dimensional imaging by adopting a horizontal circumferential scanning mode and a vertical radar aperture synthesis SAR scanning mode. In the security check instrument system, a strip type scanning mode is used in the vertical direction, so that high resolution in the vertical direction can be realized; the circular scanning mode is used in the horizontal direction, so that the resolution in the horizontal direction can be improved, and a three-dimensional image of a scanning target can be obtained.
The synthetic aperture radar and the ordinary radar are basically the same in terms of system structure and working principle, except that the synthetic aperture radar receives echo signals containing more information than the ordinary radar, so that two-dimensional or three-dimensional imaging of a radar scanning target can be performed by processing the information. Conventional synthetic aperture radar imaging methods include a range-doppler (R-D) algorithm, a Chirp Scaling (CS) algorithm, and the like.
However, because an actual security check instrument imaging system has a system error, and compared with a common strip scanning synthetic aperture radar, coupling exists between the azimuth direction and the range direction of an echo signal of a circumferential synthetic aperture radar, the traditional SAR imaging method is not applicable any more.
Disclosure of Invention
The invention aims to solve the problem that imaging cannot be performed by using initial echo data and a traditional SAR imaging method due to the fact that a system error exists in an actual security check instrument imaging system and coupling exists between the azimuth direction and the distance direction of an echo signal of a circumferential synthetic aperture radar, and provides a human body security check instrument imaging method based on actual measurement data.
The technical scheme adopted by the invention for solving the technical problems is as follows: a human body security check instrument imaging method based on measured data comprises the following steps:
step one, collecting a local oscillator signal transmitted by a security check instrument, and multiplying the local oscillator signal by the conjugate of an ideal LFM signal to obtain a carrier frequency error signal sΔ(t)；
Step two, carrier frequency error signal sΔThe phase psi of (t) passes through a low-pass filter, and then a polynomial function is used for fitting the carrier frequency error signal phase after low-pass filtering to obtain the carrier frequency error signal phase after smooth fitting
Figure GDA0003497427340000021
Constructing LFM signals with fitted smoothed carrier frequency error signal phase
Figure GDA0003497427340000022
LFM signal according to configuration
Figure GDA0003497427340000023
Obtaining a difference frequency signal
Figure GDA0003497427340000024
Thirdly, collecting echo signals of the metal plate vertically placed in the center of the security check instrument, and extracting compensation parameters according to the collected echo signals, wherein the compensation parameters comprise inter-channel amplitude compensation coefficients C of all channel signalsAiChannel of each channel signalInter-frequency compensation coefficient CFiAnd the inter-channel constant phase compensation coefficient C of each channel signalPiWherein, i represents the ith channel, i is 1,2, …, N represents the number of radar channels;
step four, collecting and obtaining space clutter signals s through no-load imaging of the security check instrumentk1(t) in the actual imaging of the security inspection instrument, the collected human body echo signal is s1(t) separately aligning the space clutter signals sk1(t) performing function fitting on the signal amplitude in each channel to obtain a fitting result of the signal amplitude in each channel;
respectively compensating human body echo signals s by using fitting results of signal amplitudes in all channels1(t) and space clutter signal sk1(t) amplitude error in the corresponding channel, i.e. the human echo signal s1(t) fitting the ith channel signal to the amplitude of the signal in the ith channel Ampi(t) dividing the space clutter signal s by dividing point by pointk1(t) fitting the ith channel signal to the amplitude of the signal in the ith channel Ampi(t) performing a point-by-point division:
Figure GDA0003497427340000025
wherein s is1i(t) represents the human echo signal s1(t) ith channel signal, sk1i(t) represents a space clutter signal sk1(t) the ith channel signal of (t),
Figure GDA0003497427340000026
representing the echo signal s of a human body1(t) the amplitude error compensation result of the ith channel,
Figure GDA0003497427340000027
representing signals s of spatial clutterk1(t) the amplitude error compensation result of the ith channel;
Figure GDA0003497427340000031
Figure GDA0003497427340000032
representing the human body echo signal after the amplitude error compensation in the channel,
Figure GDA0003497427340000033
representing the space clutter signals after the amplitude error compensation in the channel;
respectively to the signals
Figure GDA0003497427340000034
And
Figure GDA0003497427340000035
removing image frequency to obtain analytic human body echo signal s2(t) and resolving the space clutter signal sk2(t)；
Step five, analyzing the human body echo signal s obtained in the step four2(t) and resolving the space clutter signal sk2(t) subtracting to obtain a signal s containing the reflection information of the scanning target3(t) and using the difference frequency signal obtained in step two
Figure GDA0003497427340000036
For signal s3(t) carrying out carrier frequency correction to obtain a carrier frequency corrected signal s4(t)；
Step six, adopting the compensation coefficient extracted in the step three to correct the signal s after carrier frequency correction4(t) performing compensation to obtain a compensated signal s5(t)；
Step seven, using a three-dimensional BP algorithm to compensate the signal s5And (t) carrying out three-dimensional imaging, and carrying out two-dimensional projection on the three-dimensional imaging result to obtain a two-dimensional image of the human body.
The invention has the beneficial effects that: the invention provides a human body security check instrument imaging method based on measured data, which passes the phase of a carrier frequency error signal through a low-pass filter and uses a quintic function for fitting, thereby not only obtaining the basic characteristic of the error phase, but also eliminating the interference of noise. And then, the error phase after fitting and smoothing is used for carrying out carrier frequency correction on the echo signal, so that the carrier frequency error of the signal is compensated. Then using the characteristics of the echo signal to compensate the echo amplitude in the channel; and (3) extracting compensation parameters by using the echo signals of the metal plate, and performing echo amplitude, frequency and constant phase compensation among channels. After the initial echo data are compensated by the method, in order to finally overcome the problem that coupling exists between the azimuth direction and the distance direction of the echo signal of the circular synthetic aperture radar, the invention obtains the image of the human body by using a back projection imaging algorithm.
Drawings
FIG. 1 is a flow chart of a human body security check instrument imaging method based on measured data according to the present invention;
fig. 2 is an image obtained by performing difference processing on the original error signal phase in the first embodiment;
FIG. 3 is an image obtained by performing a difference process on the phases of the error signals after passing through the low-pass filter according to the first embodiment;
fig. 4 is an image obtained by performing difference processing on the error signal phase after quintic function fitting in the first embodiment;
FIG. 5 is a diagram illustrating the distance compression result of the original echo signal in the second embodiment;
fig. 6 is a diagram illustrating the result of distance compression performed on the signal after carrier frequency correction in the second embodiment;
fig. 7 is a result of performing distance compression on a signal obtained by subtracting a space clutter signal from an echo original signal in the second embodiment;
FIG. 8 is a diagram of a signal after passing through a band-pass filter and compensating for an amplitude error between channels according to the second embodiment;
FIG. 9 is a signal diagram after compensating for inter-channel frequency errors according to the second embodiment;
FIG. 10 is a diagram illustrating the signals after compensating for the inter-channel normal phase error according to the second embodiment;
fig. 11a) is a front view of the actual imaging result of the first group of human bodies in the third embodiment;
FIG. 11b) is a side view of the actual imaging results of the first set of human bodies in the third embodiment;
FIG. 11c) is the top view of the first set of human body real imaging results in the third embodiment;
FIG. 12a) is the front view of the second set of human body real imaging results in the third embodiment;
FIG. 12b) is a side view of the result of the second set of human body real imaging in the third embodiment;
FIG. 12c) is the top view of the second set of human body real imaging results in the third embodiment;
FIG. 13a) is the front view of the third set of human body real imaging results in the third embodiment;
FIG. 13b) is a side view of the actual imaging results of the third set of human bodies in the third embodiment;
fig. 13c) is a top view of the third set of human body real imaging results in the third embodiment.
Detailed Description
The following detailed description of embodiments of the invention refers to the accompanying drawings.
The first embodiment is as follows: this embodiment will be described with reference to fig. 1. The human body security check instrument imaging method based on the measured data in the embodiment is specifically realized by the following steps:
step one, collecting a local oscillator signal transmitted by a security check instrument, and multiplying the local oscillator signal by the conjugate of an ideal LFM signal (linear frequency modulation signal) to obtain a carrier frequency error signal sΔ(t)；
Step two, carrier frequency error signal sΔThe phase psi of (t) passes through a low-pass filter, and then a polynomial function is used for fitting the carrier frequency error signal phase after low-pass filtering to obtain the carrier frequency error signal phase after smooth fitting
Figure GDA0003497427340000041
Constructing LFM signals with fitted smoothed carrier frequency error signal phase
Figure GDA0003497427340000042
LFM signal according to configuration
Figure GDA0003497427340000043
Obtaining a difference frequency signal
Figure GDA0003497427340000044
Thirdly, collecting echo signals of the metal plate vertically placed in the center of the security check instrument, and extracting compensation parameters according to the collected echo signals, wherein the compensation parameters comprise inter-channel amplitude compensation coefficients C of all channel signalsAiInter-channel frequency compensation coefficient C of each channel signalFiAnd the inter-channel constant phase compensation coefficient C of each channel signalPiWherein, i represents the ith channel, i is 1,2, …, N represents the number of radar channels;
and step four, because the interference of the space signals exists in the imaging process of the security check instrument, the imaging quality is seriously influenced, and therefore the echo signals can be used for subsequent processing only by subtracting the space clutter signals.
Collecting and obtaining space clutter signal s through no-load imaging of security inspection instrumentk1(t) in the actual imaging of the security inspection instrument, the collected human body echo signal is s1(t) separately aligning the space clutter signals sk1(t) performing function fitting on the signal amplitude in each channel to obtain a fitting result of the signal amplitude in each channel;
respectively compensating human body echo signals s by using fitting results of signal amplitudes in all channels1(t) and space clutter signal sk1(t) amplitude error in the corresponding channel, i.e. the human echo signal s1(t) fitting the ith channel signal to the amplitude of the signal in the ith channel Ampi(t) dividing the space clutter signal s by dividing point by pointk1(t) fitting the ith channel signal to the amplitude of the signal in the ith channel Ampi(t) performing a point-by-point division:
Figure GDA0003497427340000051
wherein s is1i(t) represents the human echo signal s1(t) the first toi channel signals, sk1i(t) represents a space clutter signal sk1(t) the ith channel signal of (t),
Figure GDA0003497427340000052
representing the echo signal s of a human body1(t) the amplitude error compensation result of the ith channel,
Figure GDA0003497427340000053
representing signals s of spatial clutterk1(t) the amplitude error compensation result of the ith channel;
Figure GDA0003497427340000054
Figure GDA0003497427340000055
representing the human body echo signal after the amplitude error compensation in the channel,
Figure GDA0003497427340000056
representing the space clutter signals after the amplitude error compensation in the channel;
respectively to the signals
Figure GDA0003497427340000057
And
Figure GDA0003497427340000058
removing image frequency to obtain analytic human body echo signal s2(t) and resolving the space clutter signal sk2(t)；
Step five, analyzing the human body echo signal s obtained in the step four2(t) and resolving the space clutter signal sk2(t) subtracting to obtain a signal s containing the reflection information of the scanning target3(t) and using the difference frequency signal obtained in step two
Figure GDA0003497427340000059
For signal s3(t) carrying out carrier frequency correction to obtain carrier frequency correctionThe latter signal s4(t)；
Step six, adopting the compensation coefficient extracted in the step three to correct the signal s after carrier frequency correction4(t) performing compensation to obtain a compensated signal s5(t)；
Step seven, using a three-dimensional BP algorithm to compensate the signal s5And (t) carrying out three-dimensional imaging, and carrying out two-dimensional projection on the three-dimensional imaging result to obtain a two-dimensional image of the human body.
Because the radar actual system of the security check instrument has system errors and the linear frequency modulation signals which are not standard are transmitted by the radar actual system, carrier frequency correction needs to be carried out on the received signals of the security check instrument, and the influence of the carrier frequency errors is eliminated.
The invention firstly needs to respectively carry out compensation and correction in the channel and between the channels on the echo signals. Because the radar structure contains a nonlinear device, when a single echo signal is transmitted and received, the amplitude and the secondary phase of the signal are also changed, so that amplitude error compensation and secondary phase error compensation in a channel are required; because the system characteristics of the security inspection instrument are different among different radar channels, the signals among different channels have errors in amplitude, frequency and secondary phase, and therefore compensation and correction of the amplitude error, the frequency error and the constant phase error among the channels are needed. And then, in order to carry out imaging of the circular SAR, the invention adopts a back projection imaging algorithm to carry out three-dimensional imaging on the echo signals after compensation and correction.
The second embodiment is as follows: the first difference between the present embodiment and the specific embodiment is: the specific process of the step one is as follows:
local oscillator signal s transmitted by collecting security inspection instrumentref(t), local oscillation signal sref(t) is of the form:
sref(t)＝exp[j2π(fc+Δfr(t))t+jπγrt2]
wherein j is an imaginary unit, γrRepresenting the modulation frequency, fcAt intermediate frequency,. DELTA.fr(t) is the carrier frequency error of the local oscillator signal, t is time;
construct a sum local oscillator signalIdeal LFM signal s with uniform frequency rangeLFM(t)：
sLFM(t)＝exp(j2πfct+jπγrt2)
The local oscillator signal is compared with an ideal LFM signal sLFM(t) to obtain a carrier frequency error signal sΔ(t)：
Figure GDA0003497427340000061
Wherein the content of the first and second substances,
Figure GDA0003497427340000062
representing the ideal LFM signal sLFM(t) conjugation.
The third concrete implementation mode: the second embodiment is different from the first embodiment in that: in the second step, the smoothed carrier frequency error signal phase is fitted
Figure GDA0003497427340000063
The expression of (a) is:
Figure GDA0003497427340000064
wherein: a is0、a1、an-1、anRepresenting the phase of the fitted smoothed carrier frequency error signal
Figure GDA0003497427340000065
N represents the phase of the carrier frequency error signal after fitting smoothing
Figure GDA0003497427340000071
The degree of the highest order term.
The phase Ψ of the carrier frequency error signal is extracted and passed through a low pass filter. However, the low-pass filtered phase still contains much noise, so it is necessary to fit it with a function, extract the basic features of the phase, and reject the noise.
However, the fitting effect of the low-order function is poor, and the basic characteristics of the phase cannot be obtained; too high a number of fitting functions will result in overfitting and thus not completely free from noise. Through experiments, the fitting effect of the quintic function is the best, the basic characteristics of the phase can be obtained, and the influence of noise is small. Therefore, the quintic function is used for fitting the signal phase after the low-pass filtering to obtain the error signal phase after the fitting smoothing
Figure GDA0003497427340000072
Therefore, in the present invention, the smoothed carrier frequency error signal phase is fitted
Figure GDA0003497427340000073
The number of times n of the highest order term takes the value 5.
The fourth concrete implementation mode: the third difference between the present embodiment and the specific embodiment is that: in the second step, constructing LFM signal with carrier frequency error signal phase after fitting smoothing
Figure GDA0003497427340000074
LFM signal according to configuration
Figure GDA0003497427340000075
Obtaining a difference frequency signal
Figure GDA0003497427340000076
The specific process comprises the following steps:
constructed LFM signal with fitted smoothed carrier frequency error signal phase
Figure GDA0003497427340000077
In the form of:
Figure GDA0003497427340000078
Figure GDA0003497427340000079
an estimated value representing a carrier frequency error of the local oscillator signal;
to pair
Figure GDA00034974273400000710
Is carried out trTime delay of tr2R/c, obtaining the delayed signal
Figure GDA00034974273400000711
Figure GDA00034974273400000712
Wherein R is the radius of the security inspection instrument, and c represents the light speed;
and delaying the delayed signal
Figure GDA00034974273400000713
Conjugate of (2) and LFM signal
Figure GDA00034974273400000714
Multiplying to obtain a difference frequency signal
Figure GDA00034974273400000715
Figure GDA00034974273400000716
Wherein the content of the first and second substances,
Figure GDA00034974273400000717
representing signals after a time delay
Figure GDA00034974273400000718
Conjugation of (1).
The fifth concrete implementation mode: the fourth difference between this embodiment and the specific embodiment is that: the specific process of the third step is as follows:
firstly, the echo signals of each channel are subjected to coherent superposition according to slow time so as to eliminate the interference of random noise.
Converting the time domain echo signals of each channel acquired by the metal plate to a frequency domain to obtain frequency domain signals of each channel, and for the ith channel, superposing the frequency domain signals of the channel according to frequency to obtain an amplitude value A after the signal corresponding to the ith channel is superposediSetting the average value of the superposed signal amplitude values of each channel as AaveThe inter-channel amplitude compensation coefficient C of the ith channel signalAiComprises the following steps: cAi＝Aave/Ai；
Respectively extracting the phases of the time domain echo signals of all the channels acquired by the metal plate, and respectively solving a first derivative of the phase of the time domain echo signal of each channel to respectively obtain a first derivative result corresponding to each channel;
for the ith channel, averaging the first derivative result corresponding to the channel, and taking the averaged result as the frequency F of the channeli(ii) a Similarly, the frequency of each channel is obtained respectively, and the average value of the frequency of each channel is FaveThe inter-channel frequency compensation coefficient C of the ith channel signalFiComprises the following steps: cFi＝Fave-Fi；
Randomly selecting one channel as a reference channel, and multiplying the time domain echo signal of the ith channel by the conjugate of the time domain echo signal of the reference channel to obtain the constant phase error P of the ith channel relative to the reference channeliA 1 is to PiConstant phase compensation coefficient C between channels as ith channel signalPiI.e. CPi＝Pi。
The sixth specific implementation mode: the fifth embodiment is different from the fifth embodiment in that: in the fourth step, the expression of the fitting result of the obtained signal amplitude in each channel is as follows:
Ampi(t)＝bmtm+bm-1tm-1+…b1t+b0
wherein, Ampi(t) represents the result of fitting the amplitude of the signal in the ith channel, b0、b1、bm-1、bmCoefficients representing the result of the fitting to the amplitude of the signal in the ith channel, m representing the result of the fitting AmpiThe degree of the highest order term of (t).
The seventh embodiment: the sixth embodiment is different from the sixth embodiment in that: the concrete process of the step five is as follows:
will analyze the human body echo signal s2(t) and resolving the space clutter signal sk2(t) subtracting to obtain a signal s containing the reflection information of the scanning target3(t)：
s3(t)＝s2(t)-sk2(t)
Then the difference frequency signal obtained in the second step is used
Figure GDA0003497427340000081
And signal s3(t) to complete the conjugate multiplication of the signal s3(t) carrier frequency correction;
Figure GDA0003497427340000082
wherein the content of the first and second substances,
Figure GDA0003497427340000083
represents s3Conjugation of (t), s4(t) represents the carrier frequency corrected signal.
The specific implementation mode is eight: the seventh embodiment is different from the seventh embodiment in that: the concrete process of the sixth step is as follows:
multiplying each channel signal after carrier frequency correction by the inter-channel amplitude compensation coefficient corresponding to the channel respectively to obtain a signal after inter-channel amplitude compensation;
multiplying each channel signal after the inter-channel amplitude compensation by an inter-channel frequency compensation coefficient C of the corresponding channelFiThe formed signal exp (j2 π CFit) to obtain an interchannel frequency-compensated signal exp (j2 π C)Fit) is an inter-channel frequency compensation coefficient CFi；
Channel-to-channel frequency compensated individual channel informationThe signals are respectively multiplied by the constant phase compensation factors exp (-jC) corresponding to the channels in the time domainPi) Finally, a compensated signal s is obtained5(t)；
s4(t)＝[s41(t)，s42(t)，…，s4i(t)，…，s4N(t)]
s5i(t)＝exp(-jCPi)·[exp(j2πCFit)·(CAi·s4i(t))]
s5(t)＝[s51(t),s52(t),…,s5i(t),…s5N(t)]
Wherein s is4i(t) is s4(t) signal of the ith channel, s5i(t) is s5(t) signal of ith channel, compensated signal s5(t) the amplitude value corresponding to each channel signal is AaveThe center frequency of each channel signal is FaveThe constant phase error of each channel signal relative to the reference channel signal is 0.
The specific implementation method nine: the eighth embodiment is different from the eighth embodiment in that: the concrete process of the seventh step is as follows:
step seven one: gridding an imaging area according to the azimuth, elevation and distance resolution scanned by the security check instrument (azimuth, elevation and distance);
step seven and two: will compensate the signal s5(t) transforming to the frequency domain;
step seven and three: when the radar array is at the starting position of the circular scanning, calculating the distance R between the 1 st channel and the jth grid point by using a back projection algorithm on the radar echo signal of the 1 st channel in the vertical directionjJ is 1,2, …, J represents the total number of grid points, and the two-way delay Δ t corresponding to the jth grid point is: Δ t ═ 2RjObtaining the position of the j-th grid point double-pass time delay corresponding to the signal frequency domain coordinate axis, and finding out the frequency domain echo value corresponding to the coordinate position;
multiplying the found frequency domain echo value by a coefficient exp (j2 pi f)cDelta t), obtaining a frequency domain echo value after phase compensation;
step seven and four: repeating the operation of the seventh step and the third step for other channels of the radar array at the starting position of the circular scanning;
seventhly, steps: for the jth grid point, superposing the phase-compensated frequency domain echo values obtained by the grid point on all channels to obtain a superposed frequency domain echo value;
step seven and six: when the radar array is at other positions of the circular scanning, repeating the operations of the step seven, the step three to the step seven, and the step seven;
seventhly, overlapping the overlapped frequency domain echo values corresponding to the jth grid point at each position of the circular scanning to obtain overlapped three-dimensional data corresponding to the jth grid point;
obtaining an absolute value of the superposed three-dimensional data corresponding to the jth grid point to obtain the energy of the jth grid point, wherein the energy of all grid points forms a three-dimensional imaging result;
and respectively carrying out two-dimensional projection on the three-dimensional imaging result to a horizontal plane and two vertical planes which are vertical to each other to obtain a two-dimensional image of the human body.
The following examples demonstrate the beneficial effects of the present invention.
The first embodiment is as follows:
the present embodiment is directed to illustrating the implementation effect of the carrier frequency correction method in the present invention. Fig. 2 to 4 are images obtained by performing phase difference processing on the original error signal, difference images obtained by performing low-pass filter on the phase, and difference images obtained by performing quintic function fitting on the phase, respectively. It can be seen that after low-pass filtering and function fitting, the characteristics of the error signal phase can be extracted and the noise interference is reduced.
Example two:
this embodiment is intended to demonstrate the effect of the error compensation method of the present invention.
In an actual security checker imaging system, the scanning radius of the security checker is 0.68 m and the height is 2 m. The antenna array in the vertical direction works in a time-sharing mode to obtain echo data in the vertical direction; and meanwhile, the antenna array rotates and scans along the horizontal direction in a circumferential manner to obtain echo data at different angles.
And vertically placing a metal plate in the center of the security check instrument, collecting echo signals of the metal plate, and obtaining compensation parameters of the echo data of the security check instrument through the echo signals. And then, scanning the human body by using a security check instrument, and compensating the actual echo data by using the compensation parameters to obtain a compensated result.
Fig. 5 is a result image of distance compression of an echo original signal, fig. 6 is a result image of distance compression of a signal subjected to carrier frequency correction, fig. 7 is a result image of distance compression of a signal obtained by subtracting the echo original signal from a space clutter signal, fig. 8 is a signal diagram of a signal subjected to a band pass filter and compensated for an inter-channel frequency error, fig. 9 is a signal diagram of a signal subjected to a compensation for an inter-channel frequency error, and fig. 10 is a signal diagram of a signal subjected to a compensation for an inter-channel normal phase error;
example three:
this example is intended to demonstrate the practical imaging effect of the method of the present invention.
And carrying out three-dimensional imaging on the corrected and compensated human body echo data to obtain a human body scanning imaging result.
11a) to 11c) are the results of the first set of actual human body imaging; fig. 12a) to 12c) are the results of the second set of actual human body imaging; fig. 13a) to 13c) are the third set of actual imaging results of human body.
The above-described calculation examples of the present invention are merely to explain the calculation model and the calculation flow of the present invention in detail, and are not intended to limit the embodiments of the present invention. It will be apparent to those skilled in the art that other variations and modifications of the present invention can be made based on the above description, and it is not intended to be exhaustive or to limit the invention to the precise form disclosed, and all such modifications and variations are possible and contemplated as falling within the scope of the invention.

Claims (9)

1. A human body security check instrument imaging method based on measured data is characterized by comprising the following steps:
step one, collecting emission of a security check instrumentAnd multiplying the local oscillator signal by the conjugate of the ideal LFM signal to obtain a carrier frequency error signal sΔ(t)；
Step two, carrier frequency error signal sΔThe phase psi of (t) passes through a low-pass filter, and then the carrier frequency error signal phase after low-pass filtering is fitted to obtain the carrier frequency error signal phase after fitting smoothing
Figure FDA0003497427330000011
Constructing LFM signals with fitted smoothed carrier frequency error signal phase
Figure FDA0003497427330000012
LFM signal according to configuration
Figure FDA0003497427330000013
Obtaining a difference frequency signal
Figure FDA0003497427330000014
Thirdly, collecting echo signals of the metal plate vertically placed in the center of the security check instrument, and extracting compensation parameters according to the collected echo signals, wherein the compensation parameters comprise inter-channel amplitude compensation coefficients C of all channel signalsAiInter-channel frequency compensation coefficient C of each channel signalFiAnd the inter-channel constant phase compensation coefficient C of each channel signalPiWherein, i represents the ith channel, i is 1,2, …, N represents the number of radar channels;
step four, collecting and obtaining space clutter signals s through no-load imaging of the security check instrumentk1(t) in the actual imaging of the security inspection instrument, the collected human body echo signal is s1(t) separately aligning the space clutter signals sk1(t) performing function fitting on the signal amplitude in each channel to obtain a fitting result of the signal amplitude in each channel;
respectively compensating human body echo signals s by using fitting results of signal amplitudes in all channels1(t) and space clutter signal sk1(t) amplitude error in the corresponding channel, i.e. the human echo signal s1(t) fitting the ith channel signal to the amplitude of the signal in the ith channel Ampi(t) dividing the space clutter signal s by dividing point by pointk1(t) fitting the ith channel signal to the amplitude of the signal in the ith channel Ampi(t) performing a point-by-point division:
Figure FDA0003497427330000015
Figure FDA0003497427330000016
wherein s is1i(t) represents the human echo signal s1(t) ith channel signal, sk1i(t) represents a space clutter signal sk1(t) the ith channel signal of (t),
Figure FDA0003497427330000017
representing the echo signal s of a human body1(t) the amplitude error compensation result of the ith channel,
Figure FDA0003497427330000018
representing signals s of spatial clutterk1(t) the amplitude error compensation result of the ith channel;
Figure FDA0003497427330000021
Figure FDA0003497427330000022
Figure FDA0003497427330000023
representing amplitude errors in the channelThe human body echo signals after the difference compensation,
Figure FDA0003497427330000024
representing the space clutter signals after the amplitude error compensation in the channel;
respectively to the signals
Figure FDA0003497427330000025
And
Figure FDA0003497427330000026
removing image frequency to obtain analytic human body echo signal s2(t) and resolving the space clutter signal sk2(t)；
Step five, analyzing the human body echo signal s obtained in the step four2(t) and resolving the space clutter signal sk2(t) subtracting to obtain a signal s containing the reflection information of the scanning target3(t) and using the difference frequency signal obtained in step two
Figure FDA0003497427330000027
For signal s3(t) carrying out carrier frequency correction to obtain a carrier frequency corrected signal s4(t)；
Step six, adopting the compensation coefficient extracted in the step three to correct the signal s after carrier frequency correction4(t) performing compensation to obtain a compensated signal s5(t)；
Step seven, using a three-dimensional BP algorithm to compensate the signal s5And (t) carrying out three-dimensional imaging, and carrying out two-dimensional projection on the three-dimensional imaging result to obtain a two-dimensional image of the human body.
2. The human body security check instrument imaging method based on the measured data according to claim 1, characterized in that the specific process of the first step is as follows:
local oscillator signal s transmitted by collecting security inspection instrumentref(t), local oscillation signal sref(t) is of the form:
sref(t)＝exp[j2π(fc+Δfr(t))t+jπγrt2]
wherein j is an imaginary unit, γrRepresenting the modulation frequency, fcAt intermediate frequency,. DELTA.fr(t) is the carrier frequency error of the local oscillator signal, t is time;
constructing an ideal LFM signal s consistent with the frequency range of the local oscillator signalLFM(t)：
sLFM(t)＝exp(j2πfct+jπγrt2)
The local oscillator signal is compared with an ideal LFM signal sLFM(t) to obtain a carrier frequency error signal sΔ(t)：
Figure FDA0003497427330000028
Wherein the content of the first and second substances,
Figure FDA0003497427330000029
representing the ideal LFM signal sLFM(t) conjugation.
3. The method as claimed in claim 2, wherein in the second step, the smoothed carrier frequency error signal phase is fitted
Figure FDA0003497427330000031
The expression of (a) is:
Figure FDA0003497427330000032
wherein: a is0、a1、an-1、anRepresenting the phase of the fitted smoothed carrier frequency error signal
Figure FDA0003497427330000033
N represents the phase of the carrier frequency error signal after fitting smoothing
Figure FDA0003497427330000034
The degree of the highest order term.
4. The method as claimed in claim 3, wherein in the second step, the LFM signal with the carrier frequency error signal phase after fitting smoothing is constructed
Figure FDA0003497427330000035
LFM signal according to configuration
Figure FDA0003497427330000036
Obtaining a difference frequency signal
Figure FDA0003497427330000037
The specific process comprises the following steps:
constructed LFM signal with fitted smoothed carrier frequency error signal phase
Figure FDA0003497427330000038
In the form of:
Figure FDA0003497427330000039
Figure FDA00034974273300000310
an estimated value representing a carrier frequency error of the local oscillator signal;
to pair
Figure FDA00034974273300000311
Is carried out trTime delay of tr2R/c, obtaining the delayed signal
Figure FDA00034974273300000312
Figure FDA00034974273300000313
Wherein R is the radius of the security inspection instrument, and c represents the light speed;
and delaying the delayed signal
Figure FDA00034974273300000314
Conjugate of (2) and LFM signal
Figure FDA00034974273300000315
Multiplying to obtain a difference frequency signal
Figure FDA00034974273300000316
Figure FDA00034974273300000317
Wherein the content of the first and second substances,
Figure FDA00034974273300000318
representing signals after a time delay
Figure FDA00034974273300000319
Conjugation of (1).
5. The human body security check instrument imaging method based on the measured data according to claim 4, characterized in that the specific process of the third step is as follows:
converting the time domain echo signals of each channel acquired by the metal plate to a frequency domain to obtain frequency domain signals of each channel, and for the ith channel, superposing the frequency domain signals of the channel according to frequency to obtain an amplitude value A after the signal corresponding to the ith channel is superposediSetting the average value of the superposed signal amplitude values of each channel as AaveInter-channel amplitude of ith channel signalDegree compensation coefficient CAiComprises the following steps: cAi＝Aave/Ai；
Respectively extracting the phases of the time domain echo signals of all the channels acquired by the metal plate, and respectively solving a first derivative of the phase of the time domain echo signal of each channel to respectively obtain a first derivative result corresponding to each channel;
for the ith channel, averaging the first derivative result corresponding to the channel, and taking the averaged result as the frequency F of the channeli(ii) a Similarly, the frequency of each channel is obtained respectively, and the average value of the frequency of each channel is FaveThe inter-channel frequency compensation coefficient C of the ith channel signalFiComprises the following steps: cFi＝Fave-Fi；
Randomly selecting one channel as a reference channel, and multiplying the time domain echo signal of the ith channel by the conjugate of the time domain echo signal of the reference channel to obtain the constant phase error P of the ith channel relative to the reference channeliA 1 is to PiConstant phase compensation coefficient C between channels as ith channel signalPiI.e. CPi＝Pi。
6. The method according to claim 5, wherein in the fourth step, the obtained fitting result for the signal amplitude in each channel has an expression as follows:
Ampi(t)＝bmtm+bm-1tm-1+…b1t+b0
wherein, Ampi(t) represents the result of fitting the amplitude of the signal in the ith channel, b0、b1、bm-1、bmCoefficients representing the result of the fitting to the amplitude of the signal in the ith channel, m representing the result of the fitting AmpiThe degree of the highest order term of (t).
7. The human body security check instrument imaging method based on the measured data according to claim 6, characterized in that the concrete process of the fifth step is as follows:
will analyze the human body echo signal s2(t) and resolving the space clutter signal sk2(t) subtracting to obtain a signal s containing the reflection information of the scanning target3(t)：
s3(t)＝s2(t)-sk2(t)
Then the difference frequency signal obtained in the second step is used
Figure FDA0003497427330000041
And signal s3(t) to complete the conjugate multiplication of the signal s3(t) carrier frequency correction;
Figure FDA0003497427330000042
wherein the content of the first and second substances,
Figure FDA0003497427330000043
represents s3Conjugation of (t), s4(t) represents the carrier frequency corrected signal.
8. The human body security check instrument imaging method based on the measured data according to claim 7, characterized in that the specific process of the sixth step is as follows:
multiplying each channel signal after carrier frequency correction by the inter-channel amplitude compensation coefficient corresponding to the channel respectively to obtain a signal after inter-channel amplitude compensation;
multiplying each channel signal after the inter-channel amplitude compensation by an inter-channel frequency compensation coefficient C of the corresponding channelFiThe formed signal exp (j2 π CFit) to obtain an interchannel frequency-compensated signal exp (j2 π C)Fit) is an inter-channel frequency compensation coefficient CFi；
Each channel signal after inter-channel frequency compensation is multiplied by a constant phase compensation factor exp (-jC) corresponding to the channel on the time domainPi) Finally, a compensated signal s is obtained5(t)；
s4(t)＝[s41(t)，s42(t)，…，s4i(t)，…，s4N(t)]
s5i(t)＝exp(-jCPi)·[exp(j2πCFit)·(CAi·s4i(t))]
s5(t)＝[s51(t),s52(t),…,s5i(t),…s5N(t)]
Wherein s is4i(t) is s4(t) signal of the ith channel, s5i(t) is s5(t) signal of ith channel, compensated signal s5(t) the amplitude value corresponding to each channel signal is AaveThe center frequency of each channel signal is FaveThe constant phase error of each channel signal relative to the reference channel signal is 0.
9. The human body security check instrument imaging method based on the measured data according to claim 8, characterized in that the specific process of the seventh step is as follows:
step seven one: gridding the imaging area according to the azimuth direction, the pitching direction and the distance direction resolution scanned by the security check instrument;
step seven and two: will compensate the signal s5(t) transforming to the frequency domain;
step seven and three: when the radar array is at the starting position of the circular scanning, calculating the distance R between the 1 st channel and the jth grid point by using a back projection algorithm on the radar echo signal of the 1 st channel in the vertical directionjJ is 1,2, …, J represents the total number of grid points, and the two-way delay Δ t corresponding to the jth grid point is: Δ t ═ 2RjObtaining the position of the j-th grid point double-pass time delay corresponding to the signal frequency domain coordinate axis, and finding out the frequency domain echo value corresponding to the coordinate position;
multiplying the found frequency domain echo value by a coefficient exp (j2 pi f)cDelta t), obtaining a frequency domain echo value after phase compensation;
step seven and four: repeating the operation of the seventh step and the third step for other channels of the radar array at the starting position of the circular scanning;
seventhly, steps: for the jth grid point, superposing the phase-compensated frequency domain echo values obtained by the grid point on all channels to obtain a superposed frequency domain echo value;
step seven and six: when the radar array is at other positions of the circular scanning, repeating the operations of the step seven, the step three to the step seven, and the step seven;
seventhly, overlapping the overlapped frequency domain echo values corresponding to the jth grid point at each position of the circular scanning to obtain overlapped three-dimensional data corresponding to the jth grid point;
obtaining an absolute value of the superposed three-dimensional data corresponding to the jth grid point to obtain the energy of the jth grid point, wherein the energy of all grid points forms a three-dimensional imaging result;
and respectively carrying out two-dimensional projection on the three-dimensional imaging result to a horizontal plane and two vertical planes which are vertical to each other to obtain a two-dimensional image of the human body.
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