A method for modeling space-time reverberation of active sonar

Abstract

The present invention provides a method for modeling space-time reverberation of active sonar, which divides the reverberation space into grid-shaped scattering units, establishes an isochronous ellipsoidal shell model that depends on the sampling time, and then calculates the spatial azimuth of each scattering unit relative to the sonar platform, derives the linear relationship between the Doppler frequency and the spatial azimuth, and obtains the space-time distribution of the reverberation. The present invention can effectively solve the problem of reverberation modeling of active sonar platforms under complex motion conditions, especially under high-speed motion, and can accurately describe the space-time distribution of ocean reverberation under any sonar installation mode through the characterization of the space-time coupling characteristics of the reverberation, providing a model reference and data support for reverberation suppression. Starting from the reverberation formation mechanism, the present invention is targeted at reverberation suppression, taking into account the actual application background and model complexity, and filling the gap in the space-time reverberation modeling of active sonars moving at any angle.

Description

Technical Field

[0001] The invention relates to the technical field of underwater acoustic engineering, and in particular to a space-time reverberation modeling method. Background Art

[0002] In the process of active sonar detection, in addition to being disturbed by background noise such as ocean environmental noise and self-noise, it is also disturbed by reverberation signals, and to a large extent, ocean reverberation is the main background interference. Reverberation is formed by the superposition of scattered wave signals generated by a large number of irregular scatterers and irregular scattering boundaries in the ocean on the incident signal at the receiving point. It is an irregular random process and is closely related to the characteristics of the transmitted signal itself and the channel characteristics. Its spectrum is almost the same as the transmitted signal.

[0003] For a long time, the research on ocean reverberation has been mostly based on fixed-position or low-speed horizontally moving sonar platforms. However, with the development of technology and complex mission requirements, sonar platforms need faster movement speeds and more diverse movement postures. Therefore, it is necessary to conduct active sonar reverberation research under complex movement conditions to ensure detection performance. In the process of deep-sea pre-set active sonar platforms moving at any angle, strong ocean reverberation is the main interference factor. At the same time, high-speed movement will cause the reverberation to have space-time coupling characteristics, which seriously affects the normal operation of the sonar system.

[0004] Since the actual reverberation data acquisition test design is complex, costly, and difficult to implement, the use of models for research is an important means. Therefore, it is urgent to study the reverberation signal characteristics under complex motion backgrounds and establish an accurate reverberation model to provide a theoretical basis for subsequent reverberation suppression. Summary of the invention

[0005] In order to overcome the shortcomings of the prior art, the present invention provides a method for modeling space-time reverberation of active sonar. In view of the fact that previous studies on ocean reverberation when the sonar platform is fixed in position or moves horizontally at a low speed are not applicable to the situation of complex movement, the present invention provides a method for modeling space-time reverberation of active sonar, which divides the reverberation space into grid-shaped scattering units, establishes an isochronous ellipsoidal shell model that depends on the sampling time, and then calculates the spatial azimuth of each scattering unit relative to the sonar platform, derives the linear relationship between the Doppler frequency and the spatial azimuth, and obtains the space-time distribution of the reverberation. The results show that the modeling method disclosed in the present invention is applicable to active sonar platforms moving at any angle, and the space-time distribution of the reverberation can be accurately obtained.

[0006] The present invention provides an active sonar space-time reverberation modeling method, which can establish space-time reverberation models of different ocean environments, motion states and different sonar platforms.

[0007] The technical solution adopted by the present invention to solve the technical problem comprises the following steps:

[0008] Step 1: Initialize the active sonar platform parameters;

[0009] Set sonar parameters: the sonar array installation angle is δ, the horizontal receiving sector angle range is The vertical receiving sector angle range is Transmitted signal center frequency f0 and pulse width τ;

[0010] Set the motion parameters: the angle between the motion direction and the sea surface ω, the initial motion speed V0, and the acceleration Δ;

[0011] Step 2: Use the sonar platform parameters in step 1 to characterize the reverberation time characteristics and give the active sonar reverberation isochronous ellipsoid shell scale formula;

[0012] Step 3: Use the sonar platform parameters to characterize the reverberation space characteristics and give the elliptical polar coordinate equations of the longitudinal center section and the horizontal section;

[0013] Step 4: Based on the characterization formula of reverberation time and spatial characteristics, give the plane parameter z n ∈[z0,z N ] and the spatial azimuth of the scattering unit is:

[0014]

[0015] in, is the pitch angle, θ is the horizontal angle;

[0016] Step 5: Give the Doppler frequency expression of the reverberation scattering unit:

[0017] f d =f dmax cosβ

[0018] Among them, f d represents the Doppler frequency of the reverberation scattering unit, β is the angle between the scattering element and the direction of motion, and f dmax =2V / λ is the maximum Doppler frequency, λ is the wavelength of the transmitted signal frequency, and the expression is f0 is the center frequency of the transmitted signal;

[0019] Step 6: The Doppler frequency expression at any array installation angle is given as:

[0020]

[0021] Among them, α is the angle between the scattering element and the array axis, and δ is the installation angle of the sonar array;

[0022] 1) δ = 0° is a positive side-view array sonar, and the Doppler frequency of the scattering element echo is:

[0023] f d =f dmax cosα

[0024] 2) δ = 90° is the forward-looking array sonar, and the Doppler frequency of the scattering element echo is:

[0025]

[0026] 3) 0°<δ<90° is the oblique side-view array sonar, and the Doppler frequency of the scattering element echo satisfies the elliptic equation

[0027]

[0028] in,

[0029]

[0030]

[0031] Step 7: The space-time reverberation model of active sonar is established based on the Doppler frequency expression given in step 6, where the space-time distribution is determined by the azimuth cosine cosα and the Doppler frequency f d It is determined by the relationship between and is applicable to active sonar platforms that move at any angle, reflecting the distribution model formed in a two-dimensional plane in space and time.

[0032] The values ​​of ψ and φ are between 0° and 360°.

[0033] The center frequency f0 of the transmission signal is tens to hundreds of kHz.

[0034] The angle between the moving direction and the sea surface is ω∈[-90°,90°].

[0035] The active sonar reverberation isochronous ellipsoid shell scale formula is:

[0036]

[0037] Among them, d is half of the voyage, V is the speed at time t, V=V0+Δt, t is the current sampling time, V0 is the initial velocity, Δ is the acceleration, a1, b1 are the major and minor axes of the inner ellipsoid, a2, b2 are the major and minor axes of the outer ellipsoid, c is the water sound speed, and τ is the signal pulse width.

[0038] In step 3, the polar coordinate equation of the longitudinal central section ellipse is:

[0039]

[0040] Wherein, a and b are the major and minor semi-axis of the ellipsoid, respectively. The present invention takes the inner ellipsoid and uses the inner ellipsoid to calculate the ellipsoidal shell scale characteristic ellipsoid, and γ is the pitch angle between the scattering unit layer and the sonar array;

[0041] The polar coordinate equation of the ellipse of the horizontal section is:

[0042]

[0043] in,

[0044]

[0045] a, b are the major and minor axes of the ellipsoid, respectively. is the horizontal angle, the horizontal receiving sector is the range of the horizontal angle θ, and the plane parameter z n ∈[z0,z N ],and

[0046]

[0047] Among them, H is the platform movement depth at the current receiving moment, and Z is the sea depth.

[0048] The beneficial effects of the present invention are that it provides a method for modeling the space-time reverberation of active sonar, specifically combines with the complex motion background, establishes an isochronous ellipsoidal shell model that depends on the sampling time, gives the expression of the Doppler frequency and spatial azimuth of the echo of the transmitting and receiving active sonar platform, derives the linear relationship between the Doppler frequency and the spatial azimuth, and obtains the space-time distribution of the reverberation. The present invention can effectively solve the problem of reverberation modeling of active sonar platforms under complex motion conditions, especially under high-speed motion, and can accurately describe the space-time distribution of ocean reverberation under any sonar installation method through the characterization of the space-time coupling characteristics of the reverberation, providing a model reference and data support for reverberation suppression. Starting from the reverberation formation mechanism, with reverberation suppression as the goal orientation, the present invention takes the actual application background and the model complexity into consideration, and fills the gap in the space-time reverberation modeling of active sonars moving at any angle. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 A flowchart of the modeling process for the present invention is provided.

[0050] Figure 2 Schematic diagram of the ellipsoidal shell coordinate system. DETAILED DESCRIPTION

[0051] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0052] Step 1: Initialize the active sonar platform parameters;

[0053] Set sonar parameters: sonar array installation angle δ∈[0°,90°], horizontal receiving sector angle Vertical receiving sector angle The values ​​of ψ and φ are between 0° and 360°, the center frequency of the transmitted signal is f0 (generally ranging from tens to hundreds of kHz), and the pulse width is τ; motion parameters: the angle between the motion direction and the sea surface ω∈[-90°,90°], the initial velocity of the motion V0, and the acceleration Δ.

[0054] Step 2: Use the input parameters to characterize the reverberation time characteristics and give the active sonar reverberation isochronous ellipsoidal shell scale formula;

[0055] The signal transmission position remains unchanged, and the receiving position changes with the movement of the sonar platform. The sum of the distances between the scatterers that contribute to the reverberation at the current moment and the transmitting and receiving positions is equal to the length of the major axis of the ellipsoid. Its distribution is centered at the transmitting position and the receiving position, and the thickness is Each sampling moment corresponds to a unique ellipsoidal shell, and the reverberation generated by the scatterers on the ellipsoidal shell reaches the receiving end at the same time. The ellipsoidal shell is composed of the inner and outer ellipsoidal surfaces, and the scale parameters are

[0056]

[0057] Wherein, d is half of the voyage, a1, b1 are the major and minor axes of the inner ellipsoid, a2, b2 are the major and minor axes of the outer ellipsoid, V is the speed of the sonar platform, V(t) = V0 + Δt, t is the sampling time, c is the underwater sound speed, and the interface scattering between the seabed and the sea surface is generated by the isochronous elliptical ring area obtained by intersecting the interface with the isochronous ellipsoid shell.

[0058] Step 3: Use the input parameters to characterize the reverberation space characteristics and give the elliptical polar coordinate equations of the longitudinal center section and the horizontal section;

[0059] like Figure 2 As shown, the midpoint of the line between the transmitting position T and the receiving position R is O, which is also the origin of the coordinate system. The straight line through point O and parallel to the direction of movement is the X-axis, the straight line perpendicular to the direction of movement and pointing to the sea surface is the Z-axis, and the Y-axis is perpendicular to the XOZ plane and is determined by the right-hand rule. Among them, the coordinates of the transmitting position T are (-d, 0, 0), and the coordinates of the receiving position R are (d, 0, 0). The ellipsoid equation satisfied by the reverberation unit (x, y, z) on the isochronous ellipsoid shell reverberation model is:

[0060]

[0061] The intersection line l between the XOZ plane and the ellipsoid, the intersection line l is the ellipse Taking the receiving position R as the pole, the polar coordinate equation of the longitudinal center section is obtained:

[0062]

[0063] Among them, a and b are the major and minor axes of the ellipsoid respectively. is the pitch angle.

[0064] The angle between the active sonar platform and the sea surface is ω. The reverberation is equivalent to a vector rotation of the original ellipsoid surface at an angle of ω in the XOZ plane, and the oblique ellipsoid equation is obtained.

[0065]

[0066] Then, the coordinates of the transmitting position T are (-d cosω, 0, -d sinω), and the coordinates of the receiving position R are (d cosω, 0, dsinω). The scattering area that contributes to the reverberation is the part of the ellipsoidal shell illuminated by the beam fan. This part is divided into N layers, each of which is a plane z = z n ∈[z0,z N ] is formed by the intersection line of the ellipsoid and the spatial orientation is solved layer by layer.

[0067] z=z n ∈[z0,z N The intersection of the plane and the ellipsoid is an ellipse, with the point (d cosω,0,z n ) is the pole to obtain the polar coordinate equation of the horizontal section:

[0068]

[0069] in,

[0070]

[0071] a, b are the major and minor axes of the ellipsoid, d is half of the voyage, ω is the angle between the direction of motion and the sea surface, is the horizontal angle, plane parameter z n ∈[z0,z N ],and

[0072]

[0073] Among them, H is the platform movement depth at the current receiving moment, and Z is the sea depth.

[0074] Step 4: Based on the characterization formula of reverberation time and spatial characteristics, give the plane parameter z n ∈[z0,z N ] and the spatial azimuth angle of the scattering unit;

[0075]

[0076] in, is the pitch angle, θ is the horizontal angle. When ω=0, it is the expression for horizontal motion.

[0077] Step 5: Give the Doppler frequency expression of the reverberation scattering unit;

[0078] f d =f dmax cosβ

[0079] Where β is the angle between the scattering element and the direction of motion, f dmax =2V / λ is the maximum Doppler frequency, λ is the wavelength of the transmitted signal frequency, and the expression is f0 is the center frequency of the transmitted signal.

[0080] Step 6: Give the Doppler frequency expression at any array installation angle;

[0081] The space angle cosine formula Substituting the Doppler frequency expression in step 5 into the linear relationship between the Doppler frequency and the spatial azimuth angle is obtained:

[0082]

[0083] Among them, α is the angle between the scattering element and the array axis, and δ is the installation angle of the sonar array.

[0084] 1) δ = 0° is the positive side-view array sonar, and the Doppler frequency of the scattering element echo is

[0085] f d =f dmax cosα

[0086] 2) δ = 90° is the forward-looking array sonar, and the Doppler frequency of the scattering element echo is

[0087]

[0088] 3) 0°<δ<90° is the oblique side-view array sonar, and the Doppler frequency of the scattering element echo satisfies the elliptic equation

[0089]

[0090] Step 7: Complete the establishment of the space-time reverberation model of active sonar. The space-time distribution is composed of the azimuth cosine cosα and the Doppler frequency f d The relationship between is determined and it is applicable to active sonar platforms that move at any angle.

Claims

1. A method for modeling active sonar space-time reverberation, characterized in that The steps include: Step 1: Initialize the active sonar platform parameters; Set sonar parameters: the sonar array installation angle is δ, the horizontal receiving sector angle range is The vertical receiving sector angle range is Transmitted signal center frequency f0 and pulse width τ; Set the motion parameters: the angle between the motion direction and the sea surface ω, the initial motion speed V0, and the acceleration Δ; Step 2: Use the sonar platform parameters in step 1 to characterize the reverberation time characteristics and give the active sonar reverberation isochronous ellipsoid shell scale formula; Step 3: Use the sonar platform parameters to characterize the reverberation space characteristics and give the elliptical polar coordinate equations of the longitudinal center section and the horizontal section; Step 4: Based on the characterization formula of reverberation time and spatial characteristics, give the plane parameter z n ∈[z0,z N ] and the spatial azimuth of the scattering unit is: in, is the pitch angle, θ is the horizontal angle; Step 5: Give the Doppler frequency expression of the reverberation scattering unit: in d =f dmax cosβ Among them, f d represents the Doppler frequency of the reverberation scattering unit, β is the angle between the scattering element and the direction of motion, and f dmax =2V / λ is the maximum Doppler frequency, λ is the wavelength of the transmitted signal frequency, and the expression is f0 is the center frequency of the transmitted signal; Step 6: The Doppler frequency expression at any array installation angle is given as: Among them, α is the angle between the scattering element and the array axis, and δ is the installation angle of the sonar array; 1) δ = 0° is a positive side-view array sonar, and the Doppler frequency of the scattering element echo is: f d =f dmax cosα 2) δ = 90° is the forward-looking array sonar, and the Doppler frequency of the scattering element echo is: 3) 0°<δ<90° is the oblique side-view array sonar, and the Doppler frequency of the scattering element echo satisfies the elliptic equation in, Step 7: The space-time reverberation model of active sonar is established based on the Doppler frequency expression given in step 6, where the space-time distribution is determined by the azimuth cosine cosα and the Doppler frequency f d It is determined by the relationship between and is applicable to active sonar platforms that move at any angle, reflecting the distribution model formed in a two-dimensional plane in space and time.

2. The active sonar space-time reverberation modeling method according to claim 1, characterized in that: The values ​​of ψ and φ are between 0° and 360°.

3. The active sonar space-time reverberation modeling method according to claim 1, characterized in that: The center frequency f0 of the transmission signal is tens to hundreds of kHz.

4. The active sonar space-time reverberation modeling method according to claim 1, characterized in that: The angle between the moving direction and the sea surface is ω∈[-90°,90°].

5. The active sonar space-time reverberation modeling method according to claim 1, characterized in that: The active sonar reverberation isochronous ellipsoid shell scale formula is: Among them, d is half of the voyage, V is the speed at time t, V=V0+Δt, t is the current sampling time, V0 is the initial velocity, Δ is the acceleration, a1, b1 are the major and minor axes of the inner ellipsoid, a2, b2 are the major and minor axes of the outer ellipsoid, c is the water sound speed, and τ is the signal pulse width.

6. The active sonar space-time reverberation modeling method according to claim 1, characterized in that: In step 3, the polar coordinate equation of the longitudinal central section ellipse is: Wherein, a and b are the major and minor semi-axis of the ellipsoid, respectively. The present invention takes the inner ellipsoid and uses the inner ellipsoid to calculate the ellipsoidal shell scale characteristic ellipsoid, and γ is the pitch angle between the scattering unit layer and the sonar array; The polar coordinate equation of the ellipse of the horizontal section is: in, a, b are the major and minor axes of the ellipsoid, respectively. is the horizontal angle, the horizontal receiving sector is the range of the horizontal angle θ, and the plane parameter z n ∈[z0,z N ],and Among them, H is the platform movement depth at the current receiving moment, and Z is the sea depth.

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