CN111766583B - An imaging method of human body security detector based on measured data - Google Patents

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

An imaging method of human body security detector based on measured data

technical field

The invention belongs to the technical field of radar imaging, and in particular relates to an imaging method of a human body security checker based on measured data.

Background technique

Traditional security inspection methods, such as metal detectors and X-ray security scanners, are not suitable for human imaging due to their respective limitations. In contrast, millimeter waves have good safety and can penetrate clothing and packages, resulting in clearer imaging of hidden dangerous objects. Moreover, the electron energy of millimeter wave is low, and its radiation amount is almost negligible compared with X-ray, which will not cause damage to biological tissue, and is less harmful to the human body. Therefore, microwave-based security imaging has gradually become the most mainstream human security imaging method, and has a very broad application prospect.

Millimeter wave imaging systems can be divided into two types according to the imaging method. One is passive millimeter wave imaging system, which performs human imaging by detecting millimeter waves radiated from the human body; the other is active millimeter wave imaging system, which is based on synthetic aperture. Radar imaging technology realizes real-time three-dimensional imaging and foreign object detection by actively transmitting millimeter wave signals to the human body, and then performing signal processing on the received reflected echo signals. The active imaging system can image the human body more clearly, and the imaging process is fast and safe. It is the mainstream technology of the security inspection imaging system.

The millimeter-wave active security detector can perform three-dimensional imaging by using the SAR scanning mode of horizontal circular scanning and vertical radar aperture synthesis. In the security inspection system, the strip scanning mode is used in the vertical direction, which can achieve high resolution in the vertical direction; the circular scanning mode is used in the horizontal direction, which can improve the resolution in the horizontal direction. At the same time, a three-dimensional image of the scanning target is obtained.

Synthetic aperture radar and ordinary radar are basically the same in terms of system structure and working principle. The difference is that compared with ordinary radar, the echo signal received by synthetic aperture radar contains more information, so the radar can be processed by processing this information. 2D or 3D imaging of scanned targets. Traditional synthetic aperture radar imaging methods include range-Doppler (R-D) algorithm, Chirp Scaling (CS) algorithm and so on.

However, due to the existence of systematic errors in the actual imaging system of the security detector, and compared with the ordinary strip scanning synthetic aperture radar, there is coupling between the azimuth direction and the range direction of the echo signal of the circular synthetic aperture radar, so the traditional SAR imaging method no longer works.

SUMMARY OF THE INVENTION

The purpose of the present invention is to solve the problem that due to the existence of systematic errors in the imaging system of the actual security detector and the coupling between the azimuth direction and the range direction of the echo signal of the circular synthetic aperture radar, the initial echo data and the traditional SAR imaging method are used. The problem of imaging has been unable to be carried out, and an imaging method of human security checker based on measured data is proposed.

The technical solution adopted by the present invention to solve the above-mentioned technical problems is: a method for imaging a human body security detector based on actual measured data, the method comprises the following steps:

Step 1: Collect the local oscillator signal transmitted by the security inspection instrument, and multiply the local oscillator signal with the conjugate of the ideal LFM signal to obtain the carrier frequency error signal s _Δ (t);

Step 2: Pass the phase Ψ of the carrier frequency error signal s _Δ (t) through a low-pass filter, and then use a polynomial function to fit the phase of the carrier frequency error signal after the low-pass filter, to obtain a fitted and smoothed carrier frequency Error signal phase

根据构造的LFM信号

得到差频信号

Construct LFM signal with fitted and smoothed phase of carrier frequency error signal

According to the constructed LFM signal

get the difference frequency signal

Step 3: Collect the echo signal of the metal plate vertically placed in the center of the security inspection instrument, and extract the compensation parameter according to the collected echo signal. The compensation parameter includes the inter-channel amplitude compensation coefficient C _Ai of each channel signal, and each channel signal The inter-channel frequency compensation coefficient C _Fi and the inter-channel constant phase compensation coefficient C _Pi of each channel signal, where i represents the ith channel, i=1,2,...,N,N represents the number of radar channels;

Step 4: Collect the space clutter signal s _k1 (t) through the no-load imaging of the security inspection instrument. In the actual imaging of the security inspection instrument, the collected echo signal of the human body is s ₁ (t). Perform function fitting on the signal amplitudes in each channel of s _k1 (t) to obtain the fitting results of the signal amplitudes in each channel;

Use the fitting results of the signal amplitudes in each channel to compensate the amplitude errors in the corresponding channels of the human body echo signal s ₁ (t) and the space clutter signal s _k1 (t) respectively, that is, the first time of the human echo signal s ₁ (t) The i channel signal and the fitting result Amp _i (t) of the signal amplitude in the i channel are divided point by point, and the i channel signal of the space clutter signal _sk1 (t) The fitting result Amp _i (t) of the inner signal amplitude is divided point by point:

代表对人体回波信号s₁(t)第i个通道的幅度误差补偿结果，

代表对空间杂波信号s_k1(t)第i个通道的幅度误差补偿结果；Among them, s _1i (t) represents the ith channel signal of the human body echo signal s ₁ (t), _sk1i (t) represents the ith channel signal of the space clutter signal _sk1 (t),

represents the amplitude error compensation result of the ith channel of the human body echo signal s ₁ (t),

represents the amplitude error compensation result of the ith channel of the space clutter signal _sk1 (t);

代表通道内幅度误差补偿后的人体回波信号，

代表通道内幅度误差补偿后的空间杂波信号；

represents the echo signal of the human body after the amplitude error compensation in the channel,

Represents the space clutter signal after amplitude error compensation in the channel;

和

进行去除镜频，得到解析人体回波信号s₂(t)和解析空间杂波信号s_k2(t)；signal separately

and

Remove the mirror frequency to obtain the analytical body echo signal s ₂ (t) and the analytical space clutter signal s _k2 (t);

对信号s₃(t)进行载频校正，得到载频校正后的信号s₄(t)；Step 5. Subtract the analytic body echo signal s ₂ (t) obtained in step 4 and the analytical space clutter signal s _k2 (t) to obtain a signal s 3 (t) containing the reflection information of the scanning target, and obtain the signal s ₃ (t) by using step 2 difference frequency signal

Perform carrier frequency correction on the signal s ₃ (t) to obtain a carrier frequency corrected signal s ₄ (t);

Step 6, using the compensation coefficient extracted in step 3 to compensate the carrier frequency corrected signal s ₄ (t) to obtain the compensated signal s ₅ (t);

Step 7: Use the three-dimensional BP algorithm to perform three-dimensional imaging on the compensated signal s ₅ (t), and then perform two-dimensional projection on the three-dimensional imaging result to obtain a two-dimensional image of the human body.

The beneficial effects of the present invention are as follows: the present invention proposes an imaging method of a human body security detector based on measured data, the present invention passes the phase of the carrier frequency error signal through a low-pass filter, and uses a quintic function for fitting, so that the error can be obtained. The basic characteristics of the phase, but also exclude the interference of noise. Then, the carrier frequency correction of the echo signal is performed using the error phase after fitting and smoothing to compensate the carrier frequency error of the signal. Then use the echo signal itself to compensate the echo amplitude within the channel; use the echo signal of the metal plate to extract the compensation parameters, and perform the echo amplitude, frequency and constant phase compensation between the channels. After the initial echo data is compensated by the above method, in order to overcome the coupling problem between the azimuth direction and the range direction of the echo signal of the circular synthetic aperture radar, the present invention uses the back projection imaging algorithm to obtain the image of the human body.

Description of drawings

Fig. 1 is a flow chart of a method for imaging a human body security checker based on measured data according to the present invention;

FIG. 2 is an image obtained by performing differential processing on the phase of the original error signal in the first embodiment;

3 is an image after differential processing is performed on the phase of the error signal after passing through the low-pass filter in the first embodiment;

4 is an image after differential processing is performed on the error signal phase after fifth-order function fitting in the first embodiment;

FIG. 5 is a result diagram of performing distance compression on the echo original signal in the second embodiment;

Fig. 6 is the result diagram of carrying out distance compression to the signal after carrier frequency correction in Embodiment 2;

Fig. 7 is the result of performing distance compression on the signal obtained after the echo original signal and the space clutter signal are subtracted in the second embodiment;

Fig. 8 is the signal diagram after passing through the band-pass filter and compensating the amplitude error between the channels in the second embodiment;

Fig. 9 is the signal diagram after the frequency error between the compensation channels in the second embodiment;

10 is a signal diagram after compensation of constant phase error between channels in the second embodiment;

Figure 11a) is a front view of the actual imaging results of the first group of human bodies in the third embodiment;

Figure 11b) is a side view of the actual imaging results of the first group of human bodies in the third embodiment;

Figure 11c) is a top view of the actual imaging results of the first group of human bodies in the third embodiment;

Figure 12a) is the front view of the actual imaging results of the second group of human bodies in the third embodiment;

Figure 12b) is a side view of the actual imaging results of the second group of human bodies in the third embodiment;

Figure 12c) is a top view of the actual imaging results of the second group of human bodies in the third embodiment;

Figure 13a) is the front view of the actual imaging results of the third group of human bodies in the third embodiment;

Figure 13b) is a side view of the actual imaging results of the third group of human bodies in the third embodiment;

FIG. 13 c ) is a top view of the actual imaging results of the third group of human bodies in the third embodiment.

Detailed ways

The specific implementation method of the present invention will be described in detail below with reference to the accompanying drawings.

Embodiment 1: This embodiment is described with reference to FIG. 1 . A method for imaging a human body security detector based on measured data described in this embodiment is specifically implemented through the following steps:

Step 1: Collect the local oscillator signal emitted by the security inspection instrument, and multiply the local oscillator signal with the conjugate of the ideal LFM signal (chirp signal) to obtain the carrier frequency error signal s _Δ (t);

Step 2: Pass the phase Ψ of the carrier frequency error signal s _Δ (t) through a low-pass filter, and then use a polynomial function to fit the phase of the carrier frequency error signal after the low-pass filter, to obtain a fitted and smoothed carrier frequency Error signal phase

根据构造的LFM信号

得到差频信号

Construct LFM signal with fitted and smoothed phase of carrier frequency error signal

According to the constructed LFM signal

get the difference frequency signal

Step 3: Collect the echo signal of the metal plate vertically placed in the center of the security inspection instrument, and extract the compensation parameter according to the collected echo signal. The compensation parameter includes the inter-channel amplitude compensation coefficient C _Ai of each channel signal, and each channel signal The inter-channel frequency compensation coefficient C _Fi and the inter-channel constant phase compensation coefficient C _Pi of each channel signal, where i represents the ith channel, i=1,2,...,N,N represents the number of radar channels;

Step 4. Since the interference of the space signal in the imaging process of the security detector will seriously affect the imaging quality, the echo signal needs to be subtracted from the space clutter signal before it can be used for subsequent processing.

The space _clutter signal _sk1 (t) is collected through the no-load imaging of the security detector. In the actual imaging of the security detector, the collected echo signal of the human body is s ₁ (t). Perform function fitting on the signal amplitudes in each channel of t) to obtain the fitting results of the signal amplitudes in each channel;

Use the fitting results of the signal amplitudes in each channel to compensate the amplitude errors in the corresponding channels of the human body echo signal s ₁ (t) and the space clutter signal s _k1 (t) respectively, that is, the first time of the human echo signal s ₁ (t) The i channel signal and the fitting result Amp _i (t) of the signal amplitude in the i channel are divided point by point, and the i channel signal of the space clutter signal _sk1 (t) The fitting result Amp _i (t) of the inner signal amplitude is divided point by point:

代表对人体回波信号s₁(t)第i个通道的幅度误差补偿结果，

代表对空间杂波信号s_k1(t)第i个通道的幅度误差补偿结果；Among them, s _1i (t) represents the ith channel signal of the human body echo signal s ₁ (t), _sk1i (t) represents the ith channel signal of the space clutter signal _sk1 (t),

represents the amplitude error compensation result of the ith channel of the human body echo signal s ₁ (t),

represents the amplitude error compensation result of the ith channel of the space clutter signal _sk1 (t);

代表通道内幅度误差补偿后的人体回波信号，

代表通道内幅度误差补偿后的空间杂波信号；

represents the echo signal of the human body after the amplitude error compensation in the channel,

Represents the space clutter signal after amplitude error compensation in the channel;

和

进行去除镜频，得到解析人体回波信号s₂(t)和解析空间杂波信号s_k2(t)；signal separately

and

Remove the mirror frequency to obtain the analytical body echo signal s ₂ (t) and the analytical space clutter signal s _k2 (t);

对信号s₃(t)进行载频校正，得到载频校正后的信号s₄(t)；Step 5. Subtract the analytic body echo signal s ₂ (t) obtained in step 4 and the analytical space clutter signal s _k2 (t) to obtain a signal s 3 (t) containing the reflection information of the scanning target, and obtain the signal s ₃ (t) by using step 2 difference frequency signal

Perform carrier frequency correction on the signal s ₃ (t) to obtain a carrier frequency corrected signal s ₄ (t);

Step 6, using the compensation coefficient extracted in step 3 to compensate the carrier frequency corrected signal s ₄ (t) to obtain the compensated signal s ₅ (t);

Step 7: Use the three-dimensional BP algorithm to perform three-dimensional imaging on the compensated signal s ₅ (t), and then perform two-dimensional projection on the three-dimensional imaging result to obtain a two-dimensional image of the human body.

Due to the existence of systematic errors in the actual system of the security inspection instrument radar, the transmitted signal is not a standard linear frequency modulation signal, so it is necessary to perform carrier frequency correction on the received signal of the security inspection instrument to exclude the influence of the carrier frequency error.

The present invention firstly needs to perform compensation and correction in the channel and between the channels respectively for the echo signal. Since the radar structure contains nonlinear devices, when transmitting and receiving a single echo signal, the amplitude and secondary phase of the signal will also change, so it is necessary to perform amplitude error compensation and secondary phase error compensation in the channel; The system characteristics between different radar channels are inconsistent, so the signals between different channels will also have errors in amplitude, frequency and secondary phase, so it is necessary to compensate and correct the amplitude error, frequency error and constant phase error between channels. Then, in order to be able to perform the imaging of the circular SAR, the present invention adopts the back projection imaging algorithm to perform three-dimensional imaging of the echo signal after compensation and correction.

Embodiment 2: The difference between this embodiment and Embodiment 1 is that the specific process of step 1 is:

Collect the local oscillator signal s _ref (t) emitted by the security inspection instrument, and the form of the local oscillator signal s _ref (t) is:

s _ref (t)=exp[j2π(f _c +Δf _r (t))t+jπγ _r t ² ]

Among them, j is the imaginary unit, γ _r represents the modulation frequency, f _c is the intermediate frequency, Δf _r (t) is the carrier frequency error of the local oscillator signal, and t is the time;

Construct an ideal LFM signal s _LFM (t) that coincides with the frequency range of the LO signal:

s _LFM (t)=exp(j2πf _c t+jπγ _r t ² )

Multiply the LO signal by the conjugate of the ideal LFM signal s _LFM (t) to obtain the carrier frequency error signal s _Δ (t):

代表理想的LFM信号s_LFM(t)的共轭。in,

represents the conjugate of the ideal LFM signal s _LFM (t).

的表达式为：Embodiment 3: The difference between this embodiment and Embodiment 2 is that in the second step, the phase of the smoothed carrier frequency error signal is fitted.

The expression is:

的各项系数，n代表拟合平滑后的载频误差信号相位

最高次项的次数。Among them: a ₀ , a ₁ , a _n-1 , a _n represent the phase of the carrier frequency error signal after fitting and smoothing

The coefficients of , n represents the phase of the carrier frequency error signal after fitting and smoothing

The number of highest-order items.

Take out the phase Ψ of the carrier frequency error signal and pass it through a low-pass filter. However, the low-pass filtered phase still contains a lot of noise, so it is necessary to use a function to fit it, extract the basic features of the phase, and remove the noise.

所以，在本发明中，拟合平滑后的载频误差信号相位

最高次项的次数n的取值为5。However, the fitting effect of the low-order function is poor, and the basic characteristics of the phase cannot be obtained; if the fitting function is too high, it will lead to over-fitting, so it cannot completely get rid of the influence of noise. After experiments, the fitting effect of the quintic function is the best, which can obtain the basic characteristics of the phase, and is less affected by noise. Therefore, the quintic function is used to fit the phase of the low-pass filtered signal to obtain the phase of the error signal after fitting and smoothing.

Therefore, in the present invention, the phase of the smoothed carrier frequency error signal is fitted

The value of the number n of the highest order item is 5.

根据构造的LFM信号

得到差频信号

其具体过程为：Embodiment 4: The difference between this embodiment and Embodiment 3 is that in the second step, an LFM signal with the phase of the carrier frequency error signal after fitting and smoothing is constructed.

According to the constructed LFM signal

get the difference frequency signal

The specific process is:

的形式为：Constructed LFM signal with fitted smoothed carrier frequency error signal phase

of the form:

代表本振信号的载频误差的估计值；

represents the estimated value of the carrier frequency error of the local oscillator signal;

进行t_r的时延，t_r＝2R/c，得到时延后的信号

right

Carry out the time delay of t _r , t _r =2R/c, and obtain the delayed signal

Among them, R is the radius of the security detector, and c is the speed of light;

的共轭与LFM信号

相乘，得到差频信号

and delay the signal

The conjugate with the LFM signal

Multiply to get the difference frequency signal

代表时延后的信号

的共轭。in,

Represents a delayed signal

the conjugate.

Embodiment 5: The difference between this embodiment and Embodiment 4 is that the specific process of the third step is:

First, the echo signals of each channel are coherently superimposed at a slow time to exclude the interference of random noise.

Transform the time domain echo signals of each channel collected by the metal plate into the frequency domain, and obtain the frequency domain signal of each channel. The amplitude value of the superimposed signals corresponding to the i channels is A _i , and the average value of the superimposed amplitude values of the signals corresponding to each channel is set to be A _ave , then the inter-channel amplitude compensation coefficient C _Ai of the i-th channel signal is: C _Ai =A _ave /A _i ;

Extract the phase of the time-domain echo signals of each channel collected by the metal plate, and obtain the first-order derivative of the phase of the time-domain echo signal of each channel, respectively, and obtain the corresponding first-order derivative results of each channel. ;

For the i-th channel, the first derivative results corresponding to the channel are averaged, and the averaged result is taken as the frequency F _i of the channel; in the same way, the frequency of each channel is obtained separately, and the average of the frequencies of each channel is F _ave , then the inter-channel frequency compensation coefficient C _Fi of the _i -th channel signal is: C _Fi =F _ave -Fi ;

Randomly select a channel as the reference channel, and then multiply the conjugate of the time domain echo signal of the ith channel and the time domain echo signal of the reference channel to obtain the constant phase error P of the ith channel relative to the reference channel _i , take Pi as the inter-channel constant phase compensation coefficient C _Pi of the _i -th channel signal, that is, C _Pi =P _i .

Embodiment 6: The difference between this embodiment and Embodiment 5 is that in the step 4, the obtained expression for the fitting result of the signal amplitude in each channel is:

Amp _i (t)=b _m t ^m +b _m-1 t ^m-1 +...b ₁ t+b ₀

Among them, Amp _i (t) represents the fitting result of the signal amplitude in the ith channel, and b ₀ , b ₁ , b _m-1 , and b _m represent the fitting results of the signal amplitude in the ith channel. Coefficient, m represents the degree of the highest order term of the fitting result Amp _i (t).

Embodiment 7: The difference between this embodiment and Embodiment 6 is that the specific process of the fifth step is:

The analytical body echo signal s ₂ (t) and the analytical space clutter signal s _k2 (t) are subtracted to obtain the signal s ₃ (t) containing the reflection information of the scanning target:

s ₃ (t)=s ₂ (t)-s _k2 (t)

与信号s₃(t)的共轭相乘，完成对信号s₃(t)的载频校正；Then the difference frequency signal obtained in step 2

Multiply with the conjugate of the signal s ₃ (t) to complete the carrier frequency correction of the signal s ₃ (t);

代表s₃(t)的共轭，s₄(t)代表载频校正后的信号。in,

represents the conjugate of s ₃ (t), and s ₄ (t) represents the carrier frequency corrected signal.

Embodiment 8: The difference between this embodiment and Embodiment 7 is that the specific process of the step 6 is:

Each channel signal after carrier frequency correction is multiplied by the inter-channel amplitude compensation coefficient corresponding to the channel to obtain the signal after inter-channel amplitude compensation;

Each channel signal after amplitude compensation between channels is multiplied by the signal exp(j2πC _Fi t) composed of the inter-channel frequency compensation coefficient C _Fi of the corresponding channel to obtain the signal after frequency compensation between channels. The signal exp(j2πC _Fi t) is The frequency is the inter-channel frequency compensation coefficient C _Fi ;

Each channel signal after frequency compensation between channels is multiplied by the constant phase compensation factor exp(-jC _Pi ) corresponding to the channel in the time domain, and finally the compensated signal s ₅ (t) is obtained;

s ₄ (t) = [s ₄₁ (t), s ₄₂ (t), ..., s _4i (t), ..., s _4N (t)]

s _5i (t)=exp(-jC _Pi )·[exp(j2πC _Fi t)·(C _Ai ·s _4i (t))]

s ₅ (t)=[s ₅₁ (t),s ₅₂ (t),…,s _5i (t),…s _5N (t)]

Among them, s _4i (t) is the signal of the ith channel in s ₄ (t), s _5i (t) is the signal of the ith channel in s ₅ (t), and each signal of the compensated signal s ₅ (t) The amplitude values corresponding to the channel signals are all A _ave , the center frequency of each channel signal is F _ave , and the constant phase error of each channel signal relative to the reference channel signal is 0.

Embodiment 9: The difference between this embodiment and Embodiment 8 is that the specific process of the step 7 is:

Step 71: Gridize the imaging area according to the azimuth, elevation and range resolutions scanned by the security checker (azimuth × pitch × range);

Step 72: Transform the compensated signal s ₅ (t) into the frequency domain;

Step 73: When the radar array is at the starting position of the circular scan, use the back projection algorithm for the radar echo signal of the first channel in the vertical direction to calculate the distance between the first channel and the jth grid point R _j , j=1,2,...,J, J represents the total number of grid points, then the two-way delay Δt corresponding to the jth grid point is: Δt=2R _j /c, and the jth grid point double The process delay corresponds to the position on the signal frequency domain coordinate axis, and then find the frequency domain echo value corresponding to the coordinate position;

Multiply the found frequency domain echo value by the coefficient exp(j2πf _c Δt) to obtain the frequency domain echo value after phase compensation;

Step 74: Repeat the operation of Step 73 for every other channel of the radar array at the starting position of the circular scan;

Step 75: For the jth grid point, superimpose the frequency domain echo values after phase compensation obtained by the grid point on all channels to obtain the superimposed frequency domain echo values;

Step 76: When the radar array is in other positions of the circular scan, repeat the operations from Step 73 to Step 75;

Step 77: Superimpose the superimposed frequency domain echo values corresponding to each position of the jth grid point in the circular scan to obtain the superimposed three-dimensional data corresponding to the jth grid point;

The absolute value of the superimposed 3D data corresponding to the jth grid point is obtained, the energy of the jth grid point is obtained, and the energy of all grid points constitutes the 3D imaging result;

The three-dimensional imaging results are respectively projected onto the horizontal plane and two mutually perpendicular vertical planes to obtain a two-dimensional image of the human body.

The beneficial effects of the present invention are verified by the following examples.

Example 1:

This embodiment aims to demonstrate the implementation effect of the carrier frequency correction method in the present invention. Figures 2 to 4 are respectively the image of the original error signal after phase difference processing, the difference image after the phase is subjected to a low-pass filter, and the difference image after the phase is fitted by a quintic function. It can be seen that after low-pass filtering and function fitting, the phase characteristics of the error signal can be extracted and the interference of noise can be reduced.

Embodiment 2:

This embodiment is intended to demonstrate the implementation effect of the error compensation method in the present invention.

In the actual security scanner imaging system, the security scanner scanning radius is 0.68 meters and the height is 2 meters. The antenna array in the vertical direction works in time division to obtain echo data in the vertical direction; at the same time, the antenna array rotates and scans in a circle along the horizontal direction to obtain echo data at different angles.

A metal plate is placed vertically in the center of the security inspection device, the echo signal of the metal plate is collected, and the compensation parameters of the echo data of the security inspection device are obtained through the echo signal. Then, the human body is scanned by the security checker, and the actual echo data is compensated by the compensation parameters, and the compensated result is obtained.

Figure 5 is the result image of distance compression of the original echo signal, Figure 6 is the result image of the distance compression of the signal after carrier frequency correction, and Figure 7 is the result obtained by subtracting the original echo signal and the space clutter signal The result image of distance compression of the signal of , Figure 8 is the signal diagram after passing the band-pass filter and compensating the frequency error between channels, Figure 9 is the signal diagram after compensating the frequency error between channels, and Figure 10 is the constant phase compensation between channels Signal diagram after error;

Embodiment three:

This embodiment is intended to demonstrate the actual imaging effect of the method of the present invention.

Perform three-dimensional imaging on the corrected and compensated human body echo data to obtain a human body scanning imaging result.

Figures 11a) to 11c) are the first group of actual human imaging results; Figures 12a) to 12c) are the second group of actual human imaging results; Figures 13a) to 13c) are the third group of actual human imaging results.

The above calculation examples of the present invention are only to illustrate the calculation model and calculation process of the present invention in detail, but are not intended to limit the embodiments of the present invention. For those of ordinary skill in the art, on the basis of the above description, other different forms of changes or changes can also be made, and it is impossible to list all the embodiments here. Obvious changes or modifications are still within the scope of the present invention.

Claims (9)

1. a human body security inspection instrument imaging method based on measured data, is characterized in that, this method comprises the following steps: Step 1: Collect the local oscillator signal transmitted by the security inspection instrument, and multiply the local oscillator signal with the conjugate of the ideal LFM signal to obtain the carrier frequency error signal s _Δ (t); Step 2: Pass the phase Ψ of the carrier frequency error signal s _Δ (t) through the low-pass filter, and then fit the phase of the carrier frequency error signal after the low-pass filter to obtain the phase of the carrier frequency error signal after fitting and smoothing.

Construct LFM signal with fitted and smoothed phase of carrier frequency error signal

According to the constructed LFM signal

get the difference frequency signal

Step 3: Collect the echo signal of the metal plate vertically placed in the center of the security inspection instrument, and extract the compensation parameter according to the collected echo signal. The compensation parameter includes the inter-channel amplitude compensation coefficient C _Ai of each channel signal, and each channel signal The inter-channel frequency compensation coefficient C _Fi and the inter-channel constant phase compensation coefficient C _Pi of each channel signal, where i represents the ith channel, i=1,2,...,N,N represents the number of radar channels; Step 4: Collect the space clutter signal s _k1 (t) through the no-load imaging of the security inspection instrument. In the actual imaging of the security inspection instrument, the collected echo signal of the human body is s ₁ (t). Perform function fitting on the signal amplitudes in each channel of s _k1 (t) to obtain the fitting results of the signal amplitudes in each channel; Use the fitting results of the signal amplitudes in each channel to compensate the amplitude errors in the corresponding channels of the human body echo signal s ₁ (t) and the space clutter signal s _k1 (t) respectively, that is, the first time of the human echo signal s ₁ (t) The i channel signal and the fitting result Amp _i (t) of the signal amplitude in the i channel are divided point by point, and the i channel signal of the space clutter signal _sk1 (t) The fitting result Amp _i (t) of the inner signal amplitude is divided point by point:

Among them, s _1i (t) represents the ith channel signal of the human body echo signal s ₁ (t), _sk1i (t) represents the ith channel signal of the space clutter signal _sk1 (t),

represents the amplitude error compensation result of the ith channel of the human body echo signal s ₁ (t),

represents the amplitude error compensation result of the ith channel of the space clutter signal _sk1 (t);

represents the echo signal of the human body after the amplitude error compensation in the channel,

Represents the space clutter signal after amplitude error compensation in the channel; signal separately

and

Remove the mirror frequency to obtain the analytical body echo signal s ₂ (t) and the analytical space clutter signal s _k2 (t); Step 5. Subtract the analytic body echo signal s ₂ (t) obtained in step 4 and the analytical space clutter signal s _k2 (t) to obtain a signal s 3 (t) containing the reflection information of the scanning target, and obtain the signal s ₃ (t) by using step 2 difference frequency signal

Perform carrier frequency correction on the signal s ₃ (t) to obtain a carrier frequency corrected signal s ₄ (t); Step 6, using the compensation coefficient extracted in step 3 to compensate the carrier frequency corrected signal s ₄ (t) to obtain the compensated signal s ₅ (t); Step 7: Use the three-dimensional BP algorithm to perform three-dimensional imaging on the compensated signal s ₅ (t), and then perform two-dimensional projection on the three-dimensional imaging result to obtain a two-dimensional image of the human body. 2. a kind of human body security inspection instrument imaging method based on measured data according to claim 1, is characterized in that, the concrete process of described step 1 is: Collect the local oscillator signal s _ref (t) emitted by the security inspection instrument, and the form of the local oscillator signal s _ref (t) is: s _ref (t)=exp[j2π(f _c +Δf _r (t))t+jπγ _r t ² ] Among them, j is the imaginary unit, γ _r represents the modulation frequency, f _c is the intermediate frequency, Δf _r (t) is the carrier frequency error of the local oscillator signal, and t is the time; Construct an ideal LFM signal s _LFM (t) that coincides with the frequency range of the LO signal: s _LFM (t)=exp(j2πf _c t+jπγ _r t ² ) Multiply the LO signal by the conjugate of the ideal LFM signal s _LFM (t) to obtain the carrier frequency error signal s _Δ (t):

in,

represents the conjugate of the ideal LFM signal s _LFM (t). 3. A kind of imaging method of human body security detector based on measured data according to claim 2, it is characterized in that, in described step 2, the phase of carrier frequency error signal after fitting and smoothing is

The expression is:

Among them: a ₀ , a ₁ , a _n-1 , a _n represent the phase of the carrier frequency error signal after fitting and smoothing

The coefficients of , n represents the phase of the carrier frequency error signal after fitting and smoothing

The number of highest-order items. 4. a kind of human body security inspection instrument imaging method based on measured data according to claim 3, is characterized in that, in described step 2, construct the LFM signal with the carrier frequency error signal phase after fitting and smoothing

According to the constructed LFM signal

get the difference frequency signal

The specific process is: Constructed LFM signal with fitted smoothed carrier frequency error signal phase

of the form:

represents the estimated value of the carrier frequency error of the local oscillator signal; right

Carry out the time delay of t _r , t _r =2R/c, and obtain the delayed signal

Among them, R is the radius of the security detector, and c is the speed of light; and delay the signal

The conjugate with the LFM signal

Multiply to get the difference frequency signal

in,

Represents a delayed signal

the conjugate. 5. A kind of human body security inspection instrument imaging method based on measured data according to claim 4, is characterized in that, the concrete process of described step 3 is: Transform the time domain echo signals of each channel collected by the metal plate into the frequency domain, and obtain the frequency domain signal of each channel. The amplitude value of the superimposed signals corresponding to the i channels is A _i , and the average value of the superimposed amplitude values of the signals corresponding to each channel is set to be A _ave , then the inter-channel amplitude compensation coefficient C _Ai of the i-th channel signal is: C _Ai =A _ave /A _i ; Extract the phase of the time-domain echo signals of each channel collected by the metal plate, and obtain the first-order derivative of the phase of the time-domain echo signal of each channel, respectively, and obtain the corresponding first-order derivative results of each channel. ; For the i-th channel, the first derivative results corresponding to the channel are averaged, and the averaged result is taken as the frequency F _i of the channel; in the same way, the frequency of each channel is obtained separately, and the average of the frequencies of each channel is F _ave , then the inter-channel frequency compensation coefficient C _Fi of the _i -th channel signal is: C _Fi =F _ave -Fi ; Randomly select a channel as the reference channel, and then multiply the conjugate of the time domain echo signal of the ith channel and the time domain echo signal of the reference channel to obtain the constant phase error P of the ith channel relative to the reference channel _i , take Pi as the inter-channel constant phase compensation coefficient C _Pi of the _i -th channel signal, that is, C _Pi =P _i . 6. A kind of human body security inspection instrument imaging method based on actual measurement data according to claim 5, is characterized in that, in described step 4, the expression obtained to the fitting result of the signal amplitude in each channel is: Amp _i (t)=b _m t ^m +b _m-1 t ^m-1 +...b ₁ t+b ₀ Among them, Amp _i (t) represents the fitting result of the signal amplitude in the ith channel, and b ₀ , b ₁ , b _m-1 , and b _m represent the fitting results of the signal amplitude in the ith channel. Coefficient, m represents the degree of the highest order term of the fitting result Amp _i (t). 7. A kind of human body security inspection instrument imaging method based on measured data according to claim 6, is characterized in that, the concrete process of described step 5 is: The analytical body echo signal s ₂ (t) and the analytical space clutter signal s _k2 (t) are subtracted to obtain the signal s ₃ (t) containing the reflection information of the scanning target: s ₃ (t)=s ₂ (t)-s _k2 (t) Then the difference frequency signal obtained in step 2

Multiply with the conjugate of the signal s ₃ (t) to complete the carrier frequency correction of the signal s ₃ (t);

in,

represents the conjugate of s ₃ (t), and s ₄ (t) represents the carrier frequency corrected signal. 8. A kind of human body security inspection device imaging method based on measured data according to claim 7, is characterized in that, the concrete process of described step 6 is: Each channel signal after carrier frequency correction is multiplied by the inter-channel amplitude compensation coefficient corresponding to the channel to obtain the signal after inter-channel amplitude compensation; Each channel signal after amplitude compensation between channels is multiplied by the signal exp(j2πC _Fi t) composed of the inter-channel frequency compensation coefficient C _Fi of the corresponding channel to obtain the signal after frequency compensation between channels. The signal exp(j2πC _Fi t) is The frequency is the inter-channel frequency compensation coefficient C _Fi ; Each channel signal after frequency compensation between channels is multiplied by the constant phase compensation factor exp(-jC _Pi ) corresponding to the channel in the time domain, and finally the compensated signal s ₅ (t) is obtained; s ₄ (t) = [s ₄₁ (t), s ₄₂ (t), ..., s _4i (t), ..., s _4N (t)] s _5i (t)=exp(-jC _Pi )·[exp(j2πC _Fi t)·(C _Ai ·s _4i (t))] s ₅ (t)=[s ₅₁ (t),s ₅₂ (t),…,s _5i (t),…s _5N (t)] Among them, s _4i (t) is the signal of the ith channel in s ₄ (t), s _5i (t) is the signal of the ith channel in s ₅ (t), and each signal of the compensated signal s ₅ (t) The amplitude values corresponding to the channel signals are all A _ave , the center frequency of each channel signal is F _ave , and the constant phase error of each channel signal relative to the reference channel signal is 0. 9. A kind of human body security inspection instrument imaging method based on measured data according to claim 8, is characterized in that, the concrete process of described step 7 is: Step 71: Gridize the imaging area according to the azimuth, pitch and range resolutions scanned by the security checker; Step 72: Transform the compensated signal s ₅ (t) into the frequency domain; Step 73: When the radar array is at the starting position of the circular scan, use the back projection algorithm for the radar echo signal of the first channel in the vertical direction to calculate the distance between the first channel and the jth grid point R _j , j=1,2,...,J, J represents the total number of grid points, then the two-way delay Δt corresponding to the jth grid point is: Δt=2R _j /c, and the jth grid point double The process delay corresponds to the position on the signal frequency domain coordinate axis, and then find the frequency domain echo value corresponding to the coordinate position; Multiply the found frequency domain echo value by the coefficient exp(j2πf _c Δt) to obtain the frequency domain echo value after phase compensation; Step 74: Repeat the operation of Step 73 for every other channel of the radar array at the starting position of the circular scan; Step 75: For the jth grid point, superimpose the frequency domain echo values after phase compensation obtained by the grid point on all channels to obtain the superimposed frequency domain echo values; Step 76: When the radar array is in other positions of the circular scan, repeat the operations from Step 73 to Step 75; Step 77: Superimpose the superimposed frequency domain echo values corresponding to each position of the jth grid point in the circular scan to obtain the superimposed three-dimensional data corresponding to the jth grid point; Taking the absolute value of the superimposed 3D data corresponding to the jth grid point, the energy of the jth grid point is obtained, and the energy of all grid points constitutes the 3D imaging result; Two-dimensional projection of the three-dimensional imaging results to the horizontal plane and two mutually perpendicular vertical planes is performed to obtain a two-dimensional image of the human body.

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