CN108957461B - Phase matching beam forming method suitable for underwater long linear array - Google Patents

Phase matching beam forming method suitable for underwater long linear array Download PDF

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CN108957461B
CN108957461B CN201810379424.1A CN201810379424A CN108957461B CN 108957461 B CN108957461 B CN 108957461B CN 201810379424 A CN201810379424 A CN 201810379424A CN 108957461 B CN108957461 B CN 108957461B
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孙超
谢磊
刘雄厚
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Northwestern Polytechnical University
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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
    • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/66—Sonar tracking systems
    • 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
    • G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
    • G01S15/02—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems using reflection of acoustic waves
    • G01S15/06—Systems determining the position data of a target
    • G01S15/08—Systems for measuring distance only
    • 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
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
    • G01S7/52017—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 particularly adapted to short-range imaging
    • G01S7/52023—Details of receivers
    • G01S7/52033—Gain control of receivers

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Physics & Mathematics (AREA)
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  • General Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Measurement Of Velocity Or Position Using Acoustic Or Ultrasonic Waves (AREA)

Abstract

The invention provides a phase matching beam forming method, which utilizes array frequency domain data to design a weighting coefficient matrix, overcomes the problem that the gain of a beam forming array is reduced due to the attenuation of the acoustic field correlation caused by the fluctuation of an underwater sound channel when an underwater long linear array is used in an actual sea area, and can still obtain higher array gain when the spatial correlation of a received signal is reduced. Firstly, converting time domain receiving data of an underwater long linear array into a frequency domain, then obtaining a weighting coefficient matrix according to the frequency domain data matrix, and finally, carrying out beam forming. The method does not need to carry out mode extraction and signal correlation estimation, does not need to invert the covariance matrix of the received data, and can still obtain higher array gain than the conventional beam forming, the minimum variance distortionless response beam forming and the eigenvalue beam forming under the complex marine waveguide environment.

Description

Phase matching beam forming method suitable for underwater long linear array
Technical Field
The invention belongs to the technical field of sonar array signal processing, and particularly relates to a phase matching beam forming method suitable for an underwater long linear array.
Background
The method has unique advantages by utilizing the large-aperture linear array to detect the underwater target. However, due to the influence of the ocean waveguide environment, the spatial correlation of the received signals among the array elements is weakened, which will cause the array gain of the traditional beamforming algorithm to decrease, such as Conventional Beamforming (CBF), Minimum Variance Distortionless Response beamforming (MVDR), Eigenvalue Beamforming (EBF), and the like, thereby affecting the detection performance of the sonar. To address this problem, L Xie et al have analyzed in detail the relationship between the gain of a horizontal array conventional beamforming array and an underwater acoustic field in a terrestrial slope marine waveguide environment in the document "L Xie, C Sun, X H Liu, G Y jiang, the array gain of a relational beam former infected by the structure of an underwater field in a relational slope marine waveguide system.sin, 2016,65(14)144303. The document "t.c. yang, modular beamforming array gain.j.acoust.soc.am.,1989,85(1), 146-. H Cox proposes a molecular array method in the documents H Cox. line array performance, when the correlation is seriously reduced, the array gain higher than that of the full array processing can be obtained, but the signal correlation needs to be estimated in advance in the sub-array division, and the signal correlation needs to be estimated at the expense of the full array processing performance, so that the detection advantage of the underwater long line array is weakened.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a Phase matching beam forming Method (MPBF), which designs a weighting coefficient matrix by using matrix frequency domain data, solves the problem that the gain of a beam forming array is reduced due to the attenuation of sound field correlation caused by the fluctuation of an underwater sound channel when an underwater long linear array is used in an actual sea area, and can still obtain higher array gain when the spatial correlation of a received signal is reduced. Firstly, converting time domain receiving data of an underwater long linear array into a frequency domain, and then obtaining a weighting coefficient matrix W according to a frequency domain data matrixMPAnd finally, performing beam forming. The method does not need to carry out modal extraction and signal correlation estimation, does not need to carry out steps such as inversion on the covariance matrix of the received data, and can still obtain higher array gain than the conventional beam forming, the minimum variance distortionless response beam forming and the eigenvalue beam forming under the complex marine waveguide environment (such as a landing-rack slope sea area with the waveguide environment changing along with the distance).
A phase matching beam forming method suitable for an underwater long linear array is characterized by comprising the following steps:
step 1: carrying out FFT (fast Fourier transform) on the received data of each array element to obtain a frequency domain received data matrix X;
step 2: selecting the 1 st array element as a reference array element, wherein the received data corresponds to a first row vector X in a matrix X1Let the weighting coefficient vector of the reference array element be the weighting coefficient matrix WMPThe elements of the first row vector in (1) are all 1; for the ith array element, i is more than or equal to 2 and less than or equal to M, M is the total number of the array elements, and the received data corresponds to the ith row vector X in the matrix XiIs mixing XiThe data of each frequency point of the frequency band of the middle signal is conjugated and then is matched with the first line vector X1Multiplying corresponding elements in the array element, taking the phase of the multiplication result as the weighted phase of each frequency point of the frequency band of the ith array element receiving signal, setting the weighted phase of each frequency point of the non-signal frequency band as 0, setting the amplitude of all the weighted coefficients as 1, and thus obtaining the weighted coefficient vector of the ith array element, namely the weighted coefficient matrix WMPThe ith row vector of (1);the weighting coefficient vectors of all array elements form a weighting coefficient matrix WMP；
And step 3: computing the matrix WMPAnd Hadamard product of matrix X as weighted frequency domain data matrix XMPAnd to XMPThe data of each array element are accumulated and summed to obtain beam output yMPBF。
The invention has the beneficial effects that: the wave beam forming method only needs to use the frequency domain receiving data matrix for multiplication and conjugate operation, has low algorithm complexity, is convenient for engineering realization, and can obtain gains higher than the traditional CBF, MVDR and EBF matrix. The method solves the problem of gain reduction of the array formed by the array beam caused by the attenuation of the sound field correlation caused by the fluctuation of an ocean sound channel, is particularly suitable for detecting underwater targets by the underwater long linear array in a waveguide environment with complex ocean environment change, can greatly improve the gain of the array formed by the array beam and increase the detection distance.
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FIG. 1 is a flow chart of a phase matching beam forming method suitable for an underwater long linear array according to the present invention
FIG. 2 is a schematic block diagram of a weighting coefficient matrix obtained from underwater long linear array received data according to the present invention
FIG. 3 is a schematic diagram of the parameters of the present invention applied to the sea area of the slope of land frame and various ocean environments
FIG. 4 is a diagram of the change of sound velocity profile of the wave guide environment of the sea at the uphill side of the land-frame slope sea area
FIG. 5 is a graph showing the array gain of four wave beam forming algorithms of CBF, MVDR, EBF and MPBF varying with the number of array elements when the underwater long linear array is 30km away from the sound source
FIG. 6 is a graph showing the array gain of four wave beam forming algorithms of CBF, MVDR, EBF and MPBF varying with the number of array elements when the underwater long linear array is 50km away from the sound source
Detailed Description
The present invention will be further described with reference to the following drawings and examples, which include, but are not limited to, the following examples.
The invention provides a Phase matching beam forming Method (MPBF) for constructing a beam forming weighting coefficient matrix according to a horizontal array received data matrix, which improves the performance of a horizontal array for detecting an underwater target in a complex marine environment.
Setting the sound source radiation signal as narrow band signal, the ith array element receiving signal of M element uniform horizontal linear array as siReception noise of ni. From the Pasteur law, the output signal power and the noise power can be calculated separately in the frequency domain. Are respectively paired with siAnd niFFT to obtain received signal and noise frequency domain data SiAnd NiThen, the received data of the ith array element can be represented as:
Xi＝Si+Ni (1)
array Gain (AG) is defined as the ratio of the output signal-to-noise ratio of the Array to the signal-to-noise ratio of the individual elements:
Figure GDA0003436617930000031
in the formula (2), SNRarrayRepresenting the output signal-to-noise ratio, SNR of the matrixhypRepresenting the signal-to-noise ratio of the output of a single array element. For three conventional beamforming algorithms (CBF, MVDR, and EBF), the array gain can be expressed as:
Figure GDA0003436617930000032
in the formula (3), wiThe weighting coefficients of the ith array element are shown, and the three beam formers respectively correspond to three different weighting modes.
For MPBF, the weighting of the ith array element is an AND XiWith the same dimension vector, the matrix gain of MPBF can be expressed as:
Figure GDA0003436617930000033
s in formula (4)MP,iAnd NMP,iRespectively representing the output signal and output after weighting of the ith array elementOut of noise, i.e.
Figure GDA0003436617930000034
In the formula (5), symbol
Figure GDA0003436617930000041
Denotes the Hadamard product, WMP,iRepresents a weighting coefficient matrix WMPRow i element of (1).
As shown in fig. 1, the MPBF algorithm of the present invention has the following calculation flow:
1. and performing FFT (fast Fourier transform) on the received data of each array element of the horizontal array to obtain a frequency domain received data matrix X.
Setting the bandwidth of the narrow-band signal as fL,fH]. And performing FFT (fast Fourier transform) on the time domain data of each array element to obtain corresponding frequency domain data, and further forming a frequency domain receiving data matrix X, wherein each row of elements in the X respectively corresponds to one array element receiving frequency domain data in the horizontal array.
2. As shown in FIG. 2, a weighting coefficient matrix W of MPBF is obtained according to the frequency domain received data matrix XMP。
Selecting the 1 st array element of the horizontal array as a reference array element corresponding to the first row element X in X1And corresponding WMPMiddle first row element (i.e. weighting coefficient vector W of reference array element)MP,1) Are all set to 1.
Taking [ f ] in X first row elementL,fH]The data of each frequency point (the data of the frequency band of the signal) in the range is marked as X1_sf. W was obtained by the following method, respectivelyMPOther row elements in (1): taking [ f ] in the ith row of X (i is more than or equal to 2 and less than or equal to M, and M is the total number of array elements)L,fH]Recording the data of each frequency point in the range as Xi_sf. Then W isMP,iThe numerical values of the elements of the frequency band of the signal are as follows:
Figure GDA0003436617930000042
in the formula (6), "anglee "indicates taking the phase and" + "indicates taking the conjugate. And WMP,iSetting the data of the frequency band of the intermediate non-signal to be 1 so as to obtain WMPRow i element of (1). The weighting coefficient matrix W can be obtained according to the above processMP。
3. Matrix W is solvedMPAnd Hadamard product of matrix X as weighted frequency domain data matrix XMPAnd to XMPAnd accumulating and summing the array element data to obtain beam output.
Namely, using the frequency domain received data matrix X obtained in step 1 and the weighting matrix W calculated in step 2MPCalculating the beam output y of the MPBFMPBFComprises the following steps:
Figure GDA0003436617930000043
the MPBF algorithm proposed in the present invention was examined by computer numerical simulation and compared with Conventional Beamforming (CBF), Minimum Variance Distortionless Response beamforming (MVDR) and Eigenvalue Beamforming (EBF) algorithms. The simulation example was implemented in a typical bench-slope sea area upslope waveguide environment, and the water sound field data was calculated using RAM-PE sound field calculation software. The examples consider a marine environment spanning three types of sea areas, deep sea, sloped and shallow sea. Wherein the depth of the deep sea area is 5000m, and the deep sea area extends for 2km from the position of the sound source to reach a slope sea area; the slope sea area inclination is 3.5 degrees, the distance of 78km is spanned, and the water depth is changed from 5000m to 229 m; the water depth of the shallow sea area is 229m and extends for a distance of 20 km. The sound velocity c of seawater is 1749m/s, and the density rho of seawater is 1941kg/m3The sound absorption coefficients of the three sea areas and the sea bottom are all 0.5 dB/lambda. Fig. 3 shows simulated sea area of the land-frame slope and various marine environmental parameters. In a land-frame slope sea area with the span of 100km, the sea water sound velocity profile is greatly changed, the shallow flat sea-bottom sea area is assumed to be a typical shallow negative gradient sound velocity profile, the deep flat sea-bottom sound velocity profile is a standard Munk curve, and the sound channel axis depth is 1300 m. Shelf slope crossingThe sound velocity profile of the transition region is obtained by: in the simulation, a deep sea sound velocity profile and a shallow sea sound velocity profile are given firstly, then sound velocity profiles of middle distance sections are sequentially generated through interpolation by utilizing RAM-PE software, the step length of the difference is 10km, and the sound velocity profiles are shown in FIG. 4. A sound source is arranged at the depth of 550m, and a narrow-band signal with the center frequency of 190Hz and the bandwidth of 10Hz is emitted. The array comprises 100 array elements, the array element spacing is 4m, the array length is 400m, the laying depth is 120m, the horizontal array receiving noise is assumed to be isotropic noise, and the array element average signal-to-noise ratio is-10 dB. And calculating the array gains of the CBF, the MVDR and the EBF of the three traditional beam forming algorithms according to the formula (3), and calculating the array gain of the MPBF according to the formula (4).
When the horizontal array is arranged at a horizontal distance of 30km from the sound source, the variation curve of the array gain formed by four wave beams along with the number of array elements is shown in fig. 5. The solid line in the figure gives the array gain in the ideal case. It can be seen that when the number of the array elements is small, the array gain is increased along with the increase of the number of the array elements, the array gains of the four beam formers are basically the same, but the increasing speed of the MPBF array gain is obviously higher than that of the gain of the other three traditional beam formers. When the number of the array elements exceeds 44, the array gains of the CBF and the MVDR are not increased along with the increase of the number of the array elements, the array gains of the EBF and the MPBF are continuously increased along with the increase of the number of the array elements, and the array gain of the MPBF is obviously greater than the array gains formed by other three wave beams.
When the horizontal array is arranged at a horizontal distance of 50km from the sound source, the variation curve of the array gain formed by four wave beams along with the number of array elements is shown in fig. 6. The solid line in the figure gives the array gain in the ideal case. It can be seen that when the number of array elements is small, the array gain increases with the increase of the number of array elements, and the array gains of the four beamformers are basically the same. However, the gain increase speed of the MPBF array is obviously higher than the gain increase speed of the other three traditional wave beam forming arrays. When the number of the array elements exceeds 44, the array gains of the CBF and the MVDR are not increased along with the increase of the number of the array elements, the array gains of the EBF and the MPBF are continuously increased along with the increase of the number of the array elements, and the array gain of the MPBF is obviously greater than the array gains formed by other three wave beams.

Claims (1)

1. A phase matching beam forming method suitable for an underwater long linear array is characterized by comprising the following steps:
step 1: carrying out FFT (fast Fourier transform) on the received data of each array element to obtain a frequency domain received data matrix X;
step 2: selecting the 1 st array element as a reference array element, wherein the frequency domain received data of the reference array element corresponds to a first row vector X in a matrix X1Let the weighting coefficient vector of the reference array element be the weighting coefficient matrix WMPThe elements of the first row vector in (1) are all 1; for the ith array element, i is more than or equal to 2 and less than or equal to M, M is the total number of the array elements, and the frequency domain received data of the array elements correspond to the ith row vector X in the matrix XiIs mixing XiThe data of each frequency point of the frequency band of the middle signal is conjugated and then is matched with the first line vector X1Multiplying corresponding elements in the array element, taking the phase of the multiplication result as the weighted phase of each frequency point of the frequency band of the ith array element receiving signal, setting the weighted phase of each frequency point of the non-signal frequency band as 0, setting the amplitude of all the weighted coefficients as 1, and thus obtaining the weighted coefficient vector of the ith array element, namely the weighted coefficient matrix WMPThe ith row vector of (1); the weighting coefficient vectors of all array elements form a weighting coefficient matrix WMP；
And step 3: computing the matrix WMPAnd Hadamard product of matrix X as weighted frequency domain data matrix XMPAnd to XMPThe data of each array element are accumulated and summed to obtain beam output yMPBF。
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