Background
In an actual battlefield, most of attacking objects of weapons and ammunitions are ferromagnetic targets such as helicopters, tanks and armored vehicles, the battlefield environment is complex, and the traditional laser fuze is easily influenced by the ground, trees, cloud mist, smoke dust and the like and cannot accurately identify the ferromagnetic armored targets. Therefore, if the ferromagnetic armor target can be effectively detected and identified, the detection performance of the laser fuse can be greatly improved.
The earth is a huge magnetic field, a ferromagnetic armored target in a battlefield has higher magnetic conductivity, and can cause local geomagnetic field deflection, namely the intensity and the direction of the geomagnetic field near the ferromagnetic armored target can be distorted, and according to the characteristics, the ferromagnetic metal target in a certain range around the fuze can be effectively detected and identified.
Magnetic detection is classified into strong magnetic detection and weak magnetic detection, battlefield ferromagnetic target detection is typical weak magnetic detection, and the current weak magnetic detection methods can be classified into a total magnetic field strength detection method, a magnetic field scalar gradient detection method, a magnetic field vector gradient detection method, a magnetic field gradient tensor detection method and the like.
Sheinker A et al propose a magnetic anomaly signal detection method based on the combination of a fixed AR whitening filter and an orthogonal function OBF, but the method is only suitable for the detection of magnetic anomaly signals with power density of 1/fαThe orthogonal function also needs whitening filtering processing in order to prevent signal distortion. The method is complex and cannot realize quick and efficient judgment.
Ginzburg et al propose a gradient signal processing method for constructing MAD (magnetic analog detector) signal decomposition in an orthogonalized function space based on Gram-Schmidt algorithm, and express magnetic anomaly signals by five mutually independent orthogonal functions. The magnetic signal is directly analyzed, the signal is not preprocessed, the data is complex, the calculation amount is large, and quick and efficient judgment cannot be realized.
A triaxial magnetic difference signal detection processing circuit is adopted by Wangdeli, a Nanjing university of science and technology, and comprises a multistage magnetic signal amplification hardware circuit, a low-pass filtering hardware circuit and a precise full-wave rectification hardware circuit. And extracting three target identification characteristic values of the amplitude, the local change slope and the local delay time of the magnetic signal, and judging that a real target is detected when the characteristic values of the magnetic difference signals of more than two shafts reach a threshold value. The full-wave rectification hardware circuit reversely outputs a negative value signal in the magnetic signal into a positive value signal, so that vector information of the magnetic signal is lost, the extracted magnetic signal characteristics are all characteristics in a time domain, the signal characteristics cannot be analyzed from the angle of a frequency domain, and time domain similar signals cannot be distinguished. The Zhao Cheng lean et al of northwest industry university adopts a magnetic detection fuze target identification algorithm based on target detection of dynamic threshold and fuzzy inference. The algorithm acquires magnetic signals meeting requirements through a dynamic threshold, performs denoising processing on target signals by adopting a wavelet threshold method and a moving average filtering method, extracts peak values, valley values, magnetic field change frequency and magnetic gradients of the target signals to be detected, compares real target characteristic parameters, and discriminates target characteristic quantities by adopting a fuzzy inference algorithm. The dynamic threshold acquisition can cause the loss of signals and the loss of characteristic signals of partial frequency bands due to the sliding average filtering method, wherein the complete magnetic signals cannot be acquired. Under the condition that the signal is incomplete and the characteristic signal of a part of frequency bands is lost, the extracted magnetic signal characteristic has errors, and the identification precision is not high.
Disclosure of Invention
The invention aims to provide a method for identifying a specific target by passive magnetic detection based on Discrete Meyer Wavelet (DMEy), which can accurately detect whether a ferromagnetic armor target exists in a detection range.
The technical solution for realizing the purpose of the invention is as follows: a passive magnetic detection specific target identification method based on discrete Meyer wavelet is characterized in that:
step 1, electrifying a magnetic sensor to work, detecting a ferromagnetic armored target, and outputting magnetic signals of the magnetic field intensity in the directions of three axes x, y and z of a carrier coordinate system by the magnetic sensor on a carrier;
step 2, amplifying the triaxial magnetic signals after respectively performing DC blocking treatment, respectively performing low-pass filtering treatment on the amplified triaxial magnetic signals, filtering high-frequency noise signals, and cutting off frequency fcSetting according to an empirical value; the triaxial magnetic signals after the low-pass filtering processing are subjected to pull-up processing, and triaxial sampling signals x (t), y (t) and z (t) with the reference of 1.65V and the amplitude of 0V-3.3V are output;
step 3, respectively carrying out AD sampling on the three-axis magnetic signals x (t), y (t) and z (t) to obtain digital signals x (n), y (n) and z (n), respectively, carrying out dimensionality reduction on the three-axis characteristic signals of the ferromagnetic armor target by adopting a PCA algorithm according to the three-axis characteristic signals of the ferromagnetic armor target in a typical battlefield ferromagnetic armor target database, and correspondingly obtaining a dimensionality-reduced k-dimensional data matrix
And
step 4, according to the k-dimension data matrix after dimension reduction optimization
And
correspondingly acquiring characteristic signals of k frequency bands corresponding to x, y and z axes, and respectively setting k discrete Meyer wavelet transform scale functions corresponding to the x, y and z axes according to the characteristic signals of the k frequency bands of each axis; performing discrete Meyer wavelet transformation of k multi-scale functions on AD sampling signals X (n), y (n) and z (n) of the ferromagnetic armor target to obtain a matrix X after discrete wavelet transformation of the ferromagnetic armor target
MDey、Y
MDeyAnd Z
MDey;
Step 5, according to the matrix X after the discrete wavelet change of the ferromagnetic armor target
MDey、Y
MDeyAnd Z
MDeyPerforming bilateral filtering to obtain weight index, and obtaining decision weight index of each frequency band of x, y and z axes
And
step 6, according to the decision weight index of each frequency band of the x, y and z axes
And
a multi-signal fusion model is adopted to sum the weight indexes of the characteristic signals of different frequency bands to obtain the total decision indexes of the x axis, the y axis and the z axis which are respectively e
x、e
x、e
xThen e to e
x、e
x、e
xCarrying out summation operation to obtain a total decision index e
all;
Step 7, the total judgment index eallAnd an empirical threshold UtvAnd comparing to judge whether a ferromagnetic armor target appears or not, specifically comprising the following steps:
when e isall≥UtvIn order to be in the effective detection rangeA ferromagnetic armor target is present inside; when e isall<UtvIn time, it is intended that ferromagnetic armor targets do not appear within the effective detection range.
Compared with the prior art, the invention has the remarkable advantages that:
(1) the low-pass filter circuit is adopted to process the high-frequency noise signal, the data volume required to be processed during wavelet decomposition level and discrete wavelet transformation can be reduced, a PCA (Principal Component Analysis) algorithm is adopted to obtain an adaptive scale function according to the signal characteristics of different ferromagnetic armor targets in a typical battlefield ferromagnetic armor target database, and the number of scale functions during discrete Meyer wavelet decomposition is greatly reduced, so that the rapid digital magnetic signal data processing can be realized;
(2) the fast discrete wavelet transform can be realized by adopting a discrete Meyer wavelet function, compared with the traditional wavelet transform operation, the calculation speed is higher, and similar time domain signals can be distinguished from the frequency domain;
(3) the characteristic proportion function and the characteristic distinguishing function are used as weight distribution criteria of the bilateral filtering algorithm, and the characteristics of the ferromagnetic armor target in the time domain and the frequency domain are respectively considered, so that the ferromagnetic armor target is more accurately judged;
(4) a low-pass filter circuit is adopted to process high-frequency noise signals, a PCA algorithm is adopted to perform data dimension reduction filtering processing and a discrete Meyer wavelet is adopted to distinguish ferromagnetic armor target signals and noise signals from time domains and frequencies, so that noise interference can be effectively reduced, and the signal-to-noise ratio and the limit detection distance are improved.
Detailed Description
The present invention is described in further detail below with reference to the attached drawing figures.
With reference to fig. 1 and fig. 2, the method for identifying a specific target by passive magnetic detection based on discrete meier wavelet of the present invention includes the following steps:
step 1, electrifying a magnetic sensor to work, detecting a ferromagnetic armored target, and outputting magnetic signals of the magnetic field intensity in the directions of three axes x, y and z of a carrier coordinate system by the magnetic sensor on a carrier.
Step 2, amplifying the triaxial magnetic signals after respectively performing DC blocking treatment, respectively performing low-pass filtering treatment on the amplified triaxial magnetic signals, filtering high-frequency noise signals, and cutting off frequency fcSet according to empirical values. And (3) performing pull-up processing on the triaxial magnetic signal after the low-pass filtering processing, and outputting triaxial sampling signals x (t), y (t) and z (t) with the reference of 1.65V and the amplitude of 0V-3.3V.
The low-pass filter circuit is adopted to process the high-frequency noise signal, so that the data quantity required to be processed during wavelet decomposition level and discrete wavelet transformation can be reduced, and the digital signal processing speed is improved.
Wherein, the calculation formula of the magnification G is as follows:
G=3.3/Outmax
3.3 supply Voltage, Out, for rail-to-rail amplification circuitsmaxThe maximum amplitude of the magnetic signal is output for the magnetic sensor.
Step 3, respectively carrying out AD sampling on the three-axis magnetic signals x (t), y (t) and z (t) to obtain digital signals x (n), y (n) and z (n), respectively, carrying out dimensionality reduction on the three-axis characteristic signals of the ferromagnetic armor target by adopting a PCA algorithm according to the three-axis characteristic signals of the ferromagnetic armor target in a typical battlefield ferromagnetic armor target database, and correspondingly obtaining a dimensionality-reduced k-dimensional data matrix
And
the PCA algorithm is adopted to obtain the self-adaptive scale function, so that the number of the scale functions in discrete Meyer wavelet decomposition is greatly reduced, and the rapid digital magnetic signal data processing can be realized.
Typical battlefield ferromagnetic armor targets, exemplified by the x-axisData matrix X of X-axis in databasetargetAs follows:
Xtargetthe row elements of (1) represent m data sampling time points, and the column elements represent from 0 to f at one sampling time pointcN frequencies, element xnmRepresenting the magnitude of the amplitude of the nth frequency at the mth time point.
Solving for XtargetCovariance matrix C of (a):
diagonalizing the covariance matrix C, and solving the eigenvector xi of CiAnd the feature vector xi is combinediAnd (3) sequencing according to the corresponding eigenvalues from large to small to obtain an eigenvector matrix P:
P=[ξ1,…,ξn]T
selecting a data matrix X of which the matrix formed by the first k rows of the feature vector matrix P is multiplied by the X axis
targetObtaining a k (k < n) dimensional matrix
Wherein λiFeature vector xi of C rearranged from large to smalliCorresponding characteristic value, λ1≥λ2≥…≥λk…>>λn。
The y-axis and the z-axis respectively correspond to the reduced k-dimension data matrix
The solving process is the same
Step 4, obtaining the k-dimension data matrix after dimension reduction and optimization according to the step 3
And
acquiring the characteristic signals of k frequency bands corresponding to x, y and z axes, and respectively setting k discrete Meyer wavelet transform scale functions corresponding to the x, y and z axes according to the characteristic signals of the k frequency bands of each axis. Performing discrete Meyer wavelet transformation of k multi-scale functions on AD sampling signals X (n), y (n) and z (n) of the ferromagnetic armor target to obtain a matrix X after discrete wavelet transformation of the ferromagnetic armor target
MDey、Y
MDeyAnd Z
MDey。
The discrete Meyer wavelet function is adopted to realize fast discrete wavelet transform, compared with the traditional wavelet transform operation, the calculation speed is higher, and similar time domain signals can be distinguished from the aspect of frequency domain.
Taking the X axis as an example, after discrete Meyer wavelet transformation of k multi-scale functions is carried out on sampling signals X (n) of the ferromagnetic armor target, a matrix X of the ferromagnetic armor target after discrete wavelet transformation is obtainedMDey:
ωi∈{ω1,…,ωk}
ΨM(ωi) Is a discrete Meyer wavelet function; omega1~ωkFor the frequencies of the characteristic signals of the ferromagnetic armor target corresponding to the k frequency bands after dimensionality reduction, v (x) is an auxiliary function for constructing discrete Meyer wavelets, j isA complex number symbol;
matrix X of ferromagnetic armor targets after discrete wavelet transformMDeyThe k-th line of (a) represents the amplitude of the AD sampling signal x (n) on the x-axis at each sampling time corresponding to the discrete meier wavelet transform performed on the k-th scale function.
Matrix Y after discrete wavelet change corresponding to Y-axis and z-axisMDey、ZMDeyAnd XMDeyThe solving method is the same.
A typical battlefield ferromagnetic armor target database includes target magnetic signal data of various ferromagnetic armors (e.g., tanks, infantry combat vehicles, radar vehicles, armor scouts, transport vehicles, etc.), and noise magnetic signal data under environments such as vibration of a detection device carrier (e.g., unmanned aerial vehicles, helicopters, etc.), a detection device carrier interference field, and a geomagnetic background field.
Step 5, according to the matrix X after the discrete wavelet change of the ferromagnetic armor target
MDey、Y
MDeyAnd Z
MDeyPerforming bilateral filtering to obtain weight index to obtain decision weight index of each frequency band of x, y and z axes
And
the characteristic proportion function and the characteristic distinguishing function are used as weight distribution criteria of the bilateral filtering algorithm, the characteristics of the ferromagnetic armor target in the time domain and the frequency domain are respectively considered, and the ferromagnetic armor target is more accurately judged.
Taking X-axis as an example, matrix X after discrete wavelet transformationMDeyThe weighting index is obtained by bilateral filtering:
wherein
The weight index of the ith frequency band characteristic signal (i is more than or equal to 0 and less than or equal to k) of the x-axis magnetic signal; i (x)
i) The amplitude of the characteristic signal of the ith frequency band of the input magnetic signal; t (x)
i) The characteristic signal duration of the ith frequency band of the input magnetic signal; t is
i(x) The characteristic signal duration of the ith frequency band corresponding to the specific ferromagnetic armored target and the input magnetic signal in the typical battlefield ferromagnetic armored target database; x is the number of
iIs the characteristic signal of the ith frequency band of the input magnetic signal; w
pIs a normalization factor; omega is a characteristic signal domain of the input magnetic signal; x is characteristic information of a particular ferromagnetic armor target in a typical battlefield ferromagnetic armor target database.
fr(||T(xi)-Ti(x) | | l)) is a feature proportion function, weights of proportion values are given according to different feature proportions of feature signals of different frequency bands in the whole ferromagnetic armor target magnetic signal, the larger the feature proportion is, the larger the distribution weight is, and a weight index distribution expression is as follows:
x′icharacteristic information of the ith frequency band of a specific ferromagnetic armor target in a typical battlefield ferromagnetic armor target database; sign (x'i) Is x'iThe sign function of (a); sign (x)i) Is x'iThe sign function of (2).
gs(||xi-x | |) is a characteristic distinguishing function, according to the intrinsic magnetic characteristic signal of the ferromagnetic armored target, the intrinsic invariant characteristic can distinguish the frequency band magnetic signal from the noise or time domain similar interference signal in the typical battlefield ferromagnetic armored target database, so that the frequency band signal is distributed with a larger weight, and the weight index distribution expression is as follows:
xnoisecharacteristic information of noise in a typical battlefield ferromagnetic armor target database; f (x)i) And (4) a judgment function for distinguishing the graduation of the ith frequency band signal of the ferromagnetic armored target from noise in a typical battlefield ferromagnetic armored target database.
Decision weight index of each frequency band of y and z axes
And
the solving method is the same.
6, obtaining the decision weight index of each frequency band of the x axis, the y axis and the z axis according to the step 5
And
a multi-signal fusion model is adopted to sum the weight indexes of the characteristic signals of different frequency bands to obtain the total decision indexes of the x axis, the y axis and the z axis which are respectively e
x、e
x、e
xThen e to e
x、e
x、e
xCarrying out summation operation to obtain a total decision index e
all。
Wherein, the expression of the multi-signal fusion model is as follows,
step 7, obtaining the total decision index e in the step 6allAnd an empirical threshold UtvAnd comparing to judge whether a ferromagnetic armor target appears or not, specifically comprising the following steps:
when e isall≥UtvIn order to obtain ferromagnetism in the effective detection rangeAn armor target; when e isall<UtvIn time, it is intended that ferromagnetic armor targets do not appear within the effective detection range.
Example 1
Taking a detection tank as an example, a three-axis magnetic sensor outputs a magnetic signal, performs amplification, filtering and pull-up processing, performs AD sampling, and converts an analog signal into a digital signal to obtain sampling signals x (n), y (n) and z (n). Performing dimensionality reduction on data by adopting PCA (principal component analysis) self-adaptive algorithm according to magnetic signal data of tanks in typical battlefield ferromagnetic armored target database under interference resistance to obtain k-dimensional data matrix
And
(account for 80% of the tank magnetic signal data information). k-dimensional data matrix
And
converting the corresponding frequency band into a scale function of discrete Meyer wavelet transform, and performing multi-window discrete Meyer wavelet transform on the input sampling signals X (n), y (n) and z (n) to obtain a matrix X after the discrete Meyer wavelet transform
MDey、Y
MDeyAnd Z
MDeyMatrix X after discrete Meyer wavelet transform
MDey、Y
MDeyAnd Z
MDeyAnd comparing the data with the data of the ferromagnetic armor targets and the noise in the typical battlefield ferromagnetic armor target database, and obtaining the weight index through bilateral filtering. Obtaining a total decision index e by the weight indexes of each frequency band and each axis through a multi-signal fusion model
allFinally, the total decision index e
allAnd an empirical threshold U
tvAnd comparing, and judging whether a tank appears in the effective detection range.