阅读说明：本技术 一种用于抑制墙体杂波干扰的穿墙成像方法 (Through-wall imaging method for inhibiting clutter interference of wall body ) 是由 孙永强 胡甫 杨来法 陶进 陆贝儿 叶兵 熊保春 孔荣花 闫朝耀 于 2020-06-19 设计创作，主要内容包括：本发明公开了一种用于抑制墙体杂波干扰的穿墙成像方法,包括有回波建模、抑制天线耦合干扰、回波离散化、计算回波、迭代杂波抑制处理、平滑后的数据熵值,所述回波离散化包括穿墙雷达使用多收多发天线,经收发天线组合后可以形成等效天线阵元,对于每一个天线阵元,在时间域进行离散化采样后,形成采样点,本发明中,可有效降低墙体回波对穿墙成像雷达的干扰,极大提高穿墙成像雷达的成像质量,改变以往的空域滤波方法、背景对消法和基于熵的杂波抑制法方式复杂,会导致墙体与目标的空间谱在零频附近的公共频带展宽,无法在实际情况下达到理想滤除杂波效果,影响慢速运动目标的探测,对微弱目标存在无法正确提取的问题。(The invention discloses a through-wall imaging method for inhibiting wall clutter interference, which comprises echo modeling, antenna coupling interference inhibition, echo discretization, echo calculation, iterative clutter inhibition processing and a smoothed data entropy value, wherein the echo discretization comprises that a through-wall radar uses a multi-receiving multi-transmitting antenna, an equivalent antenna array element can be formed after the transmitting antenna and the receiving antenna are combined, and each antenna array element is subjected to discretization sampling in a time domain to form a sampling point. The detection of slow moving targets is influenced, and the problem that weak targets cannot be extracted correctly exists.)

1. A through-wall imaging method for suppressing wall clutter interference comprises echo modeling, antenna coupling interference suppression, echo discretization, echo calculation, iterative clutter suppression processing and smoothed data entropy values, and is characterized in that: the echo discretization comprises the steps that a through-wall radar uses a multi-receiving multi-transmitting antenna, equivalent antenna array elements can be formed after the receiving and transmitting antennas are combined, and for each antenna array element, discretization sampling is carried out in a time domain to form sampling points.

2. The through-wall imaging method for suppressing wall clutter interference according to claim 1, wherein: the antenna coupling interference is suppressed by a space domain filtering method or a time domain high-pass filtering method, and the cut-off frequency spectrum of the filter can be selected in a self-adaptive mode according to the position of the wall body and the movement speed of the detection target.

3. The through-wall imaging method for suppressing wall clutter interference according to claim 1, wherein: and performing multiple iterations of wall clutter suppression processing, wherein the execution times are judged by the imaging result, and if the wall residual component after filtering imaging is very small, the iteration can be stopped.

4. The through-wall imaging method for suppressing wall clutter interference according to claim 1, wherein: the discretization of the echo signal needs to cut off and discretize the sampling signal when harmonic analysis is performed by adopting fast fourier transform, thereby causing spectrum leakage and barrier effect.

5. The through-wall imaging method for suppressing wall clutter interference according to claim 1, wherein: and when calculating the probability space of the echo data, performing Laplace smoothing on the echo data.

6. The through-wall imaging method for suppressing wall clutter interference according to claim 1, wherein: and calculating a proper threshold value according to the smoothed data entropy value.

7. The through-wall imaging method for suppressing wall clutter interference according to claim 1, wherein: and the iteration clutter suppression processing further filters residual wall clutter.

8. The through-wall imaging method for suppressing wall clutter interference according to claim 1, wherein: the through-wall imaging method for inhibiting the clutter interference of the wall body comprises the following specific steps;

s1, firstly, modeling is carried out through echo;

s2, antenna coupling clutter signal suppression, wherein in the scanning process of the through-wall radar, a transmitting antenna is coupled to a signal component of a receiving antenna through air;

s3, discretizing echo data, wherein the through-wall imaging radar is provided with a plurality of transmitting and receiving antennas, N equivalent antenna array elements can be formed through the combination of the transmitting and receiving antennas, and M sampling points can be formed for each antenna array element N after discretization sampling in a time domain t;

s4, calculating the probability distribution of the echo;

s5, filtering wall clutter based on entropy;

and S6, iterating the depth suppression processing.

Technical Field

The invention relates to the technical field of radars, in particular to a through-wall imaging method for inhibiting clutter interference of a wall body.

Background

The through-wall imaging radar is an important nondestructive detection technology, the penetration characteristic of low-frequency electromagnetic waves is utilized, a hidden target behind a non-metal wall body is detected by combining two technologies of an ultra-wideband and a synthetic aperture radar, in the process of detecting and imaging a target behind the wall body by the through-wall imaging radar, because the wall body influences the electromagnetic waves, the energy of signals in the propagation process of a wall body barrier is rapidly attenuated, and because the target only has weak electromagnetic scattering characteristics, required target signals can be submerged in wall clutter, echoes of wall bodies in front of and behind a building can be several orders of magnitude stronger than the target, the signal-to-noise ratio of the target is reduced, the target leakage detection or false alarm is caused, how to effectively filter out non-target echoes is avoided, the detection rate of the target signals is improved, and the detection rate of the target behind the wall body becomes one of key steps of the image.

The existing main solutions include a spatial filtering method, a background cancellation method, an entropy-based inhibition method, a singular value decomposition inhibition method and the like, but the methods have certain limitations on the inhibition effect improvement and cannot well solve the interference problem.

Disclosure of Invention

The through-wall imaging method for inhibiting the clutter interference of the wall body has the advantages that the interference of wall body echoes to the through-wall imaging radar can be effectively reduced, and the imaging quality of the through-wall imaging radar is greatly improved.

In order to achieve the purpose, the invention provides the following technical scheme: the utility model provides a wall-through imaging method for suppressing wall clutter interference, is including the echo model building, restrain antenna coupling interference, echo discretization, calculate the echo, iteration clutter suppression processing, data entropy value after the level and smooth, the echo discretization includes that the through-the-wall radar uses the multi-receiving multi-transmitting antenna, can form equivalent antenna array element after receiving and dispatching antenna combination, to each antenna array element, carries out the discretization sampling in the time domain after, forms the sampling point.

Preferably, the antenna coupling interference is suppressed by a spatial filtering method or a time domain high-pass filtering method, and the cut-off frequency spectrum of the filter can be selected in a self-adaptive manner according to the position of the wall and the movement speed of the detection target.

Preferably, the multiple iteration wall clutter suppression processing is performed, the execution times are judged according to the imaging result, and if the wall residual component after filtering imaging is very small, the iteration can be terminated.

Preferably, when harmonic analysis is performed by using fast fourier transform, the discretization of the echo signal needs to cut and discretize the sampling signal, thereby causing spectrum leakage and a barrier effect.

Preferably, when calculating the probability space of the echo data, the laplacian smoothing is performed on the echo data.

Preferably, the threshold value is calculated according to the smoothed data entropy value.

Preferably, the iterative clutter suppression process further filters residual wall clutter.

The through-wall imaging method for inhibiting the clutter interference of the wall body comprises the following specific steps:

s1, firstly, modeling is carried out through echo;

s2, antenna coupling clutter signal suppression, wherein in the scanning process of the through-wall radar, a transmitting antenna is coupled to a signal component of a receiving antenna through air;

s3, discretizing echo data, wherein the through-wall imaging radar is provided with a plurality of transmitting and receiving antennas, N equivalent antenna array elements can be formed through the combination of the transmitting and receiving antennas, and M sampling points can be formed for each antenna array element N after discretization sampling in a time domain t;

s4, calculating the probability distribution of the echo;

s5, filtering wall clutter based on entropy;

and S6, iterating the depth suppression processing.

Compared with the prior art, the invention has the beneficial effects that:

the through-wall imaging method for inhibiting the clutter interference of the wall body can effectively reduce the interference of wall body echoes on the through-wall imaging radar, greatly improve the imaging quality of the through-wall imaging radar, and change the complex modes of the conventional airspace filtering method, background cancellation method and entropy-based clutter inhibition method, which can cause the broadening of the public frequency band of the space spectrum of the wall body and the target near zero frequency, thus being incapable of achieving the ideal clutter filtering effect under the actual condition, influencing the detection of the slow-moving target and solving the problem that the weak target cannot be correctly extracted.

Drawings

The present invention will be further explained with reference to the drawings and examples;

FIG. 1 is a flow chart of the operation of the present invention.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

A through-wall imaging method for suppressing wall clutter interference comprises echo modeling, antenna coupling interference suppression, echo discretization, echo calculation, iterative clutter suppression processing and smoothed data entropy values, and is characterized in that: the echo discretization includes that the through-wall radar uses many receipts to send out the antenna more, can form a N equivalent antenna array element after receiving and dispatching antenna combination, to each antenna array element N, carries out the discretization sampling back at time domain t, forms M sampling points.

And inhibiting antenna coupling interference by a space domain filtering or time domain high-pass filtering method, wherein the cut-off frequency spectrum of the filter can be selected in a self-adaptive manner according to the position of the wall and the movement speed of the detection target.

And performing multiple iterations of wall clutter suppression processing, wherein the execution times are judged by the imaging result, and if the wall residual component after filtering imaging is very small, the iteration can be stopped.

Discretizing the echo signal.

When calculating the probability space of the echo data, laplacian smoothing is performed on the echo data.

And calculating a proper threshold value according to the smoothed data entropy value.

And (5) iteration clutter suppression processing is carried out, and residual wall clutter is further filtered.

The through-wall imaging method for inhibiting the clutter interference of the wall body comprises the following specific steps:

s1, modeling is performed by using echo, and the model of the echo signal received by the antenna is expressed as follows:

e(t，n)＝e_a(t，n)+e_w(t，n)+e_tin the formula (t, n), e_a(t, n) is an antenna coupling signal, e_wAnd (t, n) are reflection signals of the front wall and the rear wall and are target echo signals to be obtained. In order to achieve high output signal-to-noise ratio, it is necessary to filter out wall clutter e_a(t, n) and e_w(t，n)；

S2, suppressing the coupling clutter signals of the antenna, and passing through the air by the transmitting antenna in the scanning process of the through-wall radarSignal component coupled to the receiving antenna, called antenna-coupled clutter signal e_a(t), the amplitude of the echo signal sometimes even exceeds the target signal, the antenna coupling clutter has time stability and does not change along with time, the suppression can be carried out by a space domain filtering method or a time domain high-pass filtering method, and the cut-to frequency spectrum of the filter can be selected according to the wall position and the motion speed of the detection target in a self-adaptive manner;

s3, discretizing echo data; through-wall imaging radar has a plurality of transmission and receiving antenna, can form a N equivalent antenna array element through receiving and dispatching antenna combination, to each antenna array element N, after time domain t passes through the discretization sampling, can form M sampling points, then after the discretization processing, the echo signal formula becomes:

a_mnthe signal strength of the echo received by the mth sampling point of the nth antenna element is (M1, 2., M, N1, 2., N).

S4, calculating the probability distribution of the echo, at a_mnDiscrete echo data, P (a)_mn) The probability of (d) can be calculated by:

if a certain component does not have observation sampling in the training set, that is, the probability estimation value of the component is 0, and when the value of a discrete source at a certain position is equal to or approaches zero, an abnormality occurs in the calculation of the entropy value of the overall echo signal. We propose a probability calculation method for laplacian smoothing as follows:

according to the probability formula, the information entropy can be calculated as:

s5, filtering wall clutter based on entropy; because the uncertainty of wall body echo is great for the uncertainty of target signal, therefore wall body echo entropy value is great, and target signal entropy value is less, can eliminate the wall body clutter through setting for the threshold like this, promptly:

a_F1(m，n)＝F(m)×a(m，n)

wherein F₁For filter coefficients whose size is less than the entropy dependence of the information, a filter coefficient is given here:

wherein beta is a threshold regulating factor, and the value range is (0, 1)

S6, iteration deep suppression processing, in order to further improve the signal-to-noise ratio, a can be added on the basis of section 3.3_F1Removing zero values in (m, n) to obtain matrix

Dimension of the data matrix is M₂×N，(M₂M), the matrix is mostly target data, only contains a small amount of wall residual clutter, and the pair e₂Probability density was calculated according to a similar method in section 3.2:

and information entropy H_2，m(E)：

And performing filtering treatment:

a_F2(m，n)＝F₂(m)×a_F1(m，n)

wherein the filter F₂(m) is:

wherein beta is₂The value range is (0, 1) for a threshold adjustment factor (which may be the same as or different from 3.3).

The iterative wall clutter suppression processing can be repeatedly executed for multiple times, the execution times can be judged according to the final imaging result, and if the residual component of the wall after filtering imaging is very small, the iteration can be stopped;

after the wall clutter filtering processing, the imaging processing can be carried out by adopting a conventional synthetic aperture imaging method, and the adopted method comprises the following steps: a backprojection imaging algorithm, an RD imaging algorithm, a CS imaging algorithm, etc.

The working principle is as follows: firstly discretizing an echo signal, then performing Laplace smoothing on the echo signal when calculating an echo data probability space to obtain a smoothed data entropy value, setting a proper threshold value to obtain data for filtering out clutter for the first time, performing iteration clutter suppression processing to further filter out residual wall clutter and finally performing synthetic aperture imaging processing on the processed data to obtain a radar image.

Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes, modifications, substitutions and alterations can be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.