A method for underwater target depth estimation based on broadband interference fringe structure of deep-sea vector acoustic field

Abstract

The present invention belongs to the technical field of underwater acoustic signal processing, and specifically relates to a method for estimating the depth of underwater targets based on the broadband interference fringe structure of deep-sea vector sound fields. The present invention receives the sound field information composed of the direct wave and the sea surface reflection wave of the target near the sea surface through a reliable sound path through a vector vertical array deployed at a critical depth, and intuitively reflects the broadband interference fringe structure and the target vertical arrival angle spatial information contained in the received noisy broadband sound pressure signal and broadband vibration velocity signal through a vector array signal processing method, and uses the relationship between the broadband interference fringe structure and frequency of the time-frequency distribution and the target vertical arrival angle to estimate the target depth. The present invention uses a vector vertical array to obtain the target excitation sound field information, and uses vector beamforming technology to map the characteristics of the sound field to the spatial domain, without the need for precise measurement and acquisition of ocean environmental parameters.

Description

Technical Field

[0001] The present invention belongs to the technical field of underwater acoustic signal processing, and in particular relates to a method for estimating the depth of an underwater target based on a broadband interference fringe structure of a deep-sea vector sound field. Background Art

[0002] In the field of underwater acoustics, target parameter estimation has always been a highly interesting research topic in underwater target detection. In deep-sea environments, due to the influence of the sound velocity gradient, sound rays exhibit curvature during propagation. Consequently, deep-sea acoustic propagation channels include various types, such as surface waveguides, convergence zones, and reliable acoustic paths. Different deep-sea acoustic propagation channels exhibit distinct characteristics in terms of temporal and spatial correlation, which are closely related to underwater target detection. Reliable acoustic paths, as channels with a relatively clear physical meaning, offer advantages in terms of propagation distance, channel stability, and low-frequency ambient noise levels. Vector vertical arrays, composed of vector hydrophones, not only receive sound pressure and velocity signals simultaneously in space and time but also offer a certain degree of suppression against isotropic noise. Furthermore, the simultaneous acquisition of sound pressure and velocity information at the same point further expands the array's signal processing capabilities, enabling further improvements in signal processing. Combining the physical characteristics of the target's excitation sound field with the advantages of vector array signal processing technology is a current focus in underwater acoustic target detection research.

[0003] Traditional matched field positioning technology is severely limited in practical use, especially due to its high requirements for the underwater acoustic environment parameters in which the receiving array resides. If these environmental parameters are mismatched, the positioning results will produce large errors. In deep-sea environments, when the array is located below the critical depth and receives broadband acoustic field information from a target near the sea surface, it can spatially present a broadband interference fringe structure, which is closely related to the depth of the target. Based on the physical characteristics of the deep-sea acoustic field, the present invention utilizes a vector vertical array to receive the physical acoustic field information, fully leveraging the advantages of the vector vertical array in noise suppression and other aspects to achieve target depth estimation. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for estimating the depth of underwater targets based on the broadband interference fringe structure of deep-sea vector sound fields. The method receives sound field information composed of direct waves and sea surface reflection waves from targets near the sea surface through reliable sound paths via a vector vertical array deployed at a critical depth. The broadband interference fringe structure and target vertical arrival angle spatial information contained in the received noisy broadband sound pressure signals and broadband vibration velocity signals are intuitively reflected through a vector array signal processing method. The target depth is estimated by utilizing the relationship between the broadband interference fringe structure and frequency of the time-frequency distribution and the target vertical arrival angle.

[0005] A method for estimating the depth of underwater targets based on a broadband interference fringe structure of a deep-sea vector sound field comprises the following steps:

[0006] Step 1: A vector vertical array deployed at a critical depth receives broadband noisy signals excited by an underwater target propagating along a reliable acoustic path; the broadband noisy signals include a broadband noisy pressure signal, a broadband noisy horizontal velocity signal, and a broadband noisy vertical velocity signal;

[0007] Step 2: Set L narrowband center frequencies and perform narrowband decomposition on the received wideband noisy signal;

[0008] Step 3: For each narrowband center frequency f l , take each broadband noisy signal and perform narrowband decomposition to the corresponding narrowband center frequency f l The narrowband signal of the sound pressure and vibration velocity is combined with beam forming to construct the interference structure B p (f l , t) and vertical arrival angle θ s (f l , t); l=1, 2,..., L;

[0009] Step 4: Set the center frequency f of each narrowband l The corresponding interference structure B p (f l , t) are arranged according to frequency to construct a broadband interference fringe structure B of the deep-sea vector sound field with time-frequency distribution p ;

[0010] B p =[B p (f1, t), B p (f2, t), ..., B p (f L , t)] T

[0011] Step 5: Set the center frequency f of each narrowband l The corresponding vertical arrival angle θ s (f l , t) are superimposed to obtain the target's vertical arrival angle information θ s (t);

[0012] Step 6: Combine the deep-sea vector broadband interference fringe structure and the target vertical arrival angle information, and estimate the broadband interference fringe structure of the time-frequency distribution along the frequency direction using the generalized Fourier transform method to obtain the depth output result map W(z); obtain the target depth estimation value z through the two bright lines symmetrically distributed along the depth of the depth output result map W(z) at 0 depth. s .

[0013]

[0014] Where z represents the search depth; k represents the wave number, k = 2πf / c, f represents the frequency of the target broadband signal, and c represents the reference sound speed.

[0015] Furthermore, the step 3 is specifically as follows:

[0016] Ignore the noise term and set the center frequency to f l The narrowband horizontal velocity signal and the narrowband vertical velocity signal are combined to obtain the narrowband combined velocity signal v c (t);

[0017] v c (t) = x(t)cos(θ-θ s (f l , t))

[0018] Where θ represents the search angle; the center frequency is f l The narrowband sound pressure signal x(t) and the narrowband combined vibration velocity signal v c (t) are added to obtain the sound pressure and vibration velocity combination:

[0019] x(t)+v c (t) = x(t)(1 + cos(θ - θ s (f l , t)))

[0020] Construct interference structure B p (f l , t) is:

[0021] B p (f l , t) = [(1 + cos (θ - θ s (f l , t)))cos(θ-θ s (f l ,t))]B(f l , t)

[0022] Among them, B(f l , t)=2|S p (f l )| 2 A 2 (1-cos(2kz s sinθ s (f l ,t)));S p (f l ) indicates that the center frequency is f l The spectrum of the narrowband signal; A represents the approximate amplitude of the direct wave and the sea surface reflected wave; zs Indicates the target depth value to be estimated.

[0023] The beneficial effects of the present invention are:

[0024] The present invention uses a vector vertical array deployed at a critical depth to receive acoustic field information consisting of direct waves and sea surface reflection waves from targets near the sea surface via reliable acoustic paths. Vector array signal processing methods are used to intuitively reflect the broadband interference fringe structure and target vertical arrival angle spatial information contained in the received noisy broadband sound pressure and broadband velocity signals. The target depth is estimated by leveraging the relationship between the broadband interference fringe structure and frequency of the time-frequency distribution and the target vertical arrival angle. The present invention utilizes the vector vertical array to acquire target excitation acoustic field information and uses vector beamforming technology to map the acoustic field characteristics into the spatial domain, eliminating the need for precise measurement and acquisition of ocean environmental parameters. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Flowchart of the present invention.

[0026] Figure 2 Schematic diagram of the vector vertical array and target space position in the present invention.

[0027] Figure 3 Schematic diagram of target motion state in the present invention.

[0028] Figure 4 SNR = 0dB, z s =100m (a) Broadband interference fringe structure of deep-sea vector sound field (b) Broadband vertical arrival angle (c) Depth estimation diagram.

[0029] Figure 5 SNR = 0dB, z s =200m (a) Broadband interference fringe structure of deep-sea vector sound field (b) Broadband vertical arrival angle (c) Depth estimation diagram.

[0030] Figure 6 SNR = 0dB, z s =300m (a) Broadband interference fringe structure of deep-sea vector sound field (b) Broadband vertical arrival angle (c) Depth estimation diagram. DETAILED DESCRIPTION

[0031] The present invention will be further described below with reference to the accompanying drawings.

[0032] The present invention has relevant depth estimation capabilities for underwater targets at depths of approximately 0 to 500 meters below the sea surface in deep-sea environments. The present invention receives acoustic field information consisting of direct waves and sea surface reflection waves from targets near the sea surface through reliable acoustic paths via a vector vertical array deployed at a critical depth. The vector array signal processing method intuitively reflects the broadband interference fringe structure and target vertical arrival angle spatial information contained in the received noisy broadband sound pressure signal and broadband velocity signal, and utilizes the relationship between the broadband interference fringe structure and frequency of the time-frequency distribution and the target vertical arrival angle to estimate the target depth. The present invention takes into account the impact of noise on the method and utilizes the uncorrelated characteristics between sound pressure and velocity to effectively suppress the noise contained in the received signal, achieving a good noise suppression effect on the presentation of the broadband interference fringe structure, and has good practical application prospects in engineering.

[0033] (1) A vector vertical array deployed at a critical depth receives a broadband noisy signal excited by an underwater target propagated via a reliable acoustic path; the broadband noisy signal includes a broadband noisy pressure signal p(t,f,z), a broadband noisy horizontal velocity signal v r (t,f,z) and broadband noisy vertical velocity signal v z (t,f,z);

[0034] For moving targets, a vector vertical array deployed at a critical depth can receive direct waves and sea surface reflected waves propagating through a reliable acoustic path. These two waves are the main components of the sound field received by the vector vertical array at medium distances. Ignoring the influence of acoustic impedance, the broadband sound pressure signal and vibration velocity signal can be expressed as:

[0035]

[0036] v r (t, f, z) = p (t, f, z)·cosθ s (t)

[0037] v z (t, f, z) = p (t, f, z) · sinθ s (t)

[0038]

[0039] Among them, S p (f) represents the spectrum of the target broadband signal, A represents the approximate amplitude of the direct wave and the sea surface reflected wave, z s represents the target depth, z represents the search depth, θ s (t) represents the vertical arrival angle during target movement, k represents the wave number, t cpa Indicates the time corresponding to the closest receiving distance, v sIndicates the target's moving speed.

[0040] (2) setting L narrowband center frequencies and performing narrowband decomposition on the received broadband noisy signal;

[0041] For a broadband signal s(t), convert it from the time domain to the frequency domain and perform narrowband division through a filter. Its frequency domain expression is S(f), which is divided into L narrowband signals. The lth narrowband signal can be expressed as S(f l ), whose center frequency is f l .

[0042] (3) For each narrowband center frequency f l , take each broadband noisy signal and perform narrowband decomposition to the corresponding narrowband center frequency f l The narrowband signal of the sound pressure and vibration velocity is combined with beam forming to construct an interference structure and vertical arrival angle θ s (f l , t);

[0043] The sound pressure signal and vibration velocity signal received by the vector vertical array composed of N array elements can be expressed as follows:

[0044] x(t)=a(θ s )s(t)+noise x (t)

[0045] x vr (t) = x(t) cosθ s =a(θ s )s(t)cosθ s +noise vr (t)

[0046] x vz (t) = x(t) sinθ s =a(θ s )s(t)sinθ s +noise vz (t)

[0047]

[0048] Ignore the noise term and set the center frequency to f l Narrowband horizontal vibration velocity signal x vr (t) and narrowband vertical velocity signal x vz (t) is combined to obtain the narrowband combined velocity signal v c (t);

[0049] v c (t) = x vr(t)cosθ+x vz (t)sinθ=x(t)cos(θ-θ s (f l , t))

[0050] Where θ represents the search angle;

[0051] Let the center frequency be f l The narrowband sound pressure signal x(t) and the narrowband combined vibration velocity signal v c (t) are added to obtain the sound pressure and vibration velocity combination:

[0052] x(t)+v c (t) = x(t)(1 + cos(θ - θ s (f l , t)))

[0053] The combined form of sound pressure and vibration velocity (x+v c )v c The obtained vector vertical array beamforming output power can be expressed as:

[0054]

[0055] Among them, P CBF (θ) represents the beam output power obtained by the sound pressure channel corresponding to the same number of array elements, which can be expressed as:

[0056]

[0057] Constructing interference structures for:

[0058]

[0059] For the convenience of description, the following Abbreviated as: B p (f l , t).

[0060] Among them, B(f l , t)=2|S p (f l )| 2 A 2 (1-cos(2kz s sinθ s (f l ,t)));S p (f l ) indicates that the center frequency is f l The spectrum of the narrowband signal; k represents the wave number, k = 2πf / c, f represents the frequency of the target broadband signal, and c represents the reference sound speed.

[0061] (4) Set each narrowband center frequency f l The corresponding interference structure B p (f l , t) are arranged according to frequency to construct a broadband interference fringe structure B of the deep-sea vector sound field with time-frequency distribution p ;

[0062] B p =[B p (f1, t), B p (f2, t), ..., B p (f L , t)] T

[0063] (5) Set each narrowband center frequency f l The corresponding vertical arrival angle θ s (f l , t) are superimposed to obtain the target's vertical arrival angle information θ s (t);

[0064] (6) Combine the deep-sea vector broadband interference fringe structure and the target vertical arrival angle information, estimate the broadband interference fringe structure of the time-frequency distribution along the frequency direction by the generalized Fourier transform method, and obtain the depth output result map W(z); obtain the target depth estimation value z through the two bright lines symmetrically distributed along the depth of the depth output result map W(z) at 0 depth. s .

[0065]

[0066] Figure 1 A flowchart of the steps involved in this invention is provided. The simulation parameters are as follows: the number of vector vertical array elements is 21, the depth of the first element is 4600m, the target center frequency is 100Hz, the frequency band distribution is 50-150Hz, and the distance between elements is set to half the wavelength of the center frequency. The target depths are 100m, 200m, and 300m, the signal sampling frequency is 100Hz, and the target motion time is 600s. Figure 2 and Figure 3 The positional relationship and motion state diagram of the target and receiving array in space are given. Gaussian white noise with a signal-to-noise ratio of 0dB is added to the sound pressure channel and vibration velocity channel of each array element. Figure 4 、 Figure 5 and Figure 6 The corresponding deep-sea vector sound field broadband interference fringe structure diagram, target vertical arrival angle, and depth estimation results are given. From the above simulation results, it can be seen that the estimation results presented by the method proposed in this invention can better reflect the true depth of the target in space.

[0067] The present invention uses a vector vertical array to obtain target excitation sound field information, and maps the characteristics of the sound field to the spatial domain through vector beamforming technology, without the need for precise measurement and acquisition of ocean environment parameters; the interference structure corresponding to the narrowband center frequency is arranged according to frequency to obtain a broadband interference fringe structure with time-frequency distribution. This interference fringe structure is obviously modulated by the target depth; and depth estimation of the broadband interference fringe structure obtained by arrangement through generalized Fourier transform along the frequency direction is given.

[0068] The present invention has the following advantages:

[0069] (1) The sound field model is simple and has clear physical meaning;

[0070] (2) Using a vector vertical array, beam output is obtained through joint processing of sound pressure and vibration velocity, which has a better noise suppression effect;

[0071] (3) The depth estimation method makes full use of the frequency correlation of the broadband interference fringe structure of the deep-sea vector sound field;

[0072] (4) The overall robustness of the method is good.

[0073] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for estimating the depth of underwater targets based on broadband interference fringe structure of deep-sea vector sound field, characterized in that: The following steps are involved: Step 1: A vector vertical array deployed at a critical depth receives broadband noisy signals excited by an underwater target propagating along a reliable acoustic path; the broadband noisy signals include a broadband noisy pressure signal, a broadband noisy horizontal velocity signal, and a broadband noisy vertical velocity signal; Step 2: Set L narrowband center frequencies and perform narrowband decomposition on the received wideband noisy signal; Step 3: For each narrowband center frequency f l , take each broadband noisy signal and perform narrowband decomposition to the corresponding narrowband center frequency f l The narrowband signal of the sound pressure and vibration velocity is combined with beamforming to construct the interference structure B p (f l ,t) and vertical arrival angle θ s (f l ,t);l=1,2,…,L; Step 4: Set the center frequency f of each narrowband l The corresponding interference structure B p (f l ,t) Arrange according to frequency to construct the time-frequency distribution of deep-sea vector sound field broadband interference fringe structure B p ; B p =[B p (f1,t),B p (f2,t),…,B p (f L ,t)] T Step 5: Set the center frequency f of each narrowband l The corresponding vertical arrival angle θ s (f l ,t) are superimposed to obtain the target’s vertical arrival angle information θ s (t); Step 6: Combine the deep-sea vector broadband interference fringe structure and the target vertical arrival angle information, and estimate the broadband interference fringe structure of the time-frequency distribution along the frequency direction using the generalized Fourier transform method to obtain the depth output result map W(z); obtain the target depth estimation value z through the two bright lines symmetrically distributed along the depth of the depth output result map W(z) at 0 depth. s； Where z represents the search depth; k represents the wave number, k = 2πf / c, f represents the frequency of the target broadband signal, and c represents the reference sound speed.

2. The method for estimating underwater target depth based on broadband interference fringe structure of deep-sea vector sound field according to claim 1, characterized in that: The step 3 is specifically as follows: Ignore the noise term and set the center frequency to f l The narrowband horizontal velocity signal and the narrowband vertical velocity signal are combined to obtain the narrowband combined velocity signal v c (t); v c (t)=x(t)cos(θ-θ s (f l ,t)) Where θ represents the search angle; the center frequency is f l The narrowband sound pressure signal x(t) and the narrowband combined vibration velocity signal v c (t) are added to obtain the sound pressure and vibration velocity combination: x(t)+v c (t)=x(t)(1+cos(θ-θ s (f l ,t))) Construct interference structure B p (f l ,t) is: B p (f l ,t)=[(1+cos(θ-θ s (f l ,t)))cos(θ-θ s (f l ,t))]B(f l ,t) Among them, B(f l ,t)=2|S p (f l )| 2 A 2 (1-cos(2kz s sinθ s (f l ,t)));S p (f l ) indicates that the center frequency is f l The spectrum of the narrowband signal; A represents the approximate amplitude of the direct wave and the sea surface reflected wave; z s Indicates the target depth value to be estimated.

Images