A Simulation Modeling Method for the Two-Way Doppler Signal of an Active Sonar

Abstract

The present invention relates to the technical field of underwater acoustic engineering, and provides an active sonar two-way Doppler signal simulation and modeling method, including: according to the propagation of underwater acoustic signals, the movement of targets, and the movement of transceiver platforms, dividing the Doppler calculation process from the transmission of active signals to the reception of echoes into two segments of "transmission-target" and "target-reception" for Doppler calculation respectively. The present invention solves the problems of large model errors and significant impacts on echo waveform signals caused by taking twice the one-way propagation Doppler shift as the Doppler effect of the round-trip two-way; the calculation problems of the time when the transmitted signal reaches the target, the target echo returns to the receiving point, and the target position; the problem that due to the attitude changes of the target and the transmitting platform at the two moments of the transmission moment and the echo reception moment, the different radial velocities cause inaccurate simulation of Doppler signals; and enables the Doppler characteristics of the echo signals reaching the receiving point to more truly reflect the actual situation at sea and improves the accuracy of the characteristics of target echo signals.

Description

Technical Field

[0001] The present invention relates to the technical field of underwater acoustic engineering, and particularly relates to a method for simulating and modeling the two-way Doppler signal of an active sonar. Background Art

[0002] The relative motion of a marine platform will cause Doppler frequency shift of the platform radiation noise signal or the actively transmitted signal. For the simulation of the active sonar array signal, the simulation of the Doppler frequency shift characteristic modeling is of great significance. Because it is an important basis for the active sonar signal processing to estimate the target motion speed and target discrimination, and it is also a signal characteristic that some active sonar clutter rejection and reverberation rejection signal processing algorithms must have. Therefore, the Doppler characteristic modeling of the active sonar is an important part of the active sonar echo signal simulation.

[0003] In the prior art, one type of active sonar mainly uses narrowband, short pulse, medium and high frequency signals. The Doppler characteristic modeling of the active signal usually adopts the frequency domain processing of the center frequency, and the Doppler effect caused by the two-way propagation process of the active signal "transmission - target - reception" is simply doubled the one-way propagation Doppler frequency shift at the receiving end as the two-way Doppler frequency shift of the round trip. Another type of active sonar signal adopts low frequency, wide width, long pulse signals, and the detection range is getting farther and farther. Using the original Doppler simulation and modeling method, it is impossible to achieve the accurate modeling required under the new type of active sonar signal system. The above two types of prior art mainly have the following problems:

[0004] 1. The Doppler of the active broadband signal will generate Doppler for all frequencies within the signal bandwidth. It is impossible to perform Doppler simulation and modeling of arbitrarily (continuously varying) frequency signals using the frequency domain processing method, and a time domain method needs to be adopted.

[0005] 2. For long-distance detection, the time for the transmitted signal to reach the target or to be reflected from the target and reach the receiving point becomes very long. For example, the one-way time for 30 kilometers is about 20 seconds, and the round trip is 40 seconds. During such a long propagation time, in the case of different targets and transmitting platforms, the relative postures at the transmission moment and the echo reception moment will change greatly, resulting in significant differences in the radial velocities at these two moments. Using a simple doubling process will affect the accuracy of the Doppler model.

[0006] 3. The transmitted signal reaches the target through the ocean channel. Besides the distortion of the actively transmitted signal caused by the channel influence, there is also the stretching or compression of the transmitted signal caused by the moving Doppler effect. Thus, in fact, when the transmitted signal reaches the target, there are dual influences of "channel" and "Doppler". If following the existing method and only uniformly processing according to 2 times the one-way Doppler at the echo receiving point, actually when modeling the target reflection (echo) signal after the transmitted signal reaches the target, the waveform change of the active signal already caused by the Doppler influence in the "transmission section" is not considered, resulting in the echo signal reaching the receiving point not truly reflecting the actual situation at sea and seriously affecting the accuracy of the echo signal characteristics. Summary of the Invention

[0007] The present invention mainly solves the problem of the Doppler calculation method caused by the movement of the transceiver platform after transmitting an active signal in the prior art. Without considering in detail the channel propagation and the generation of the target reflection echo signal, the three problems in the above-mentioned background art are caused. A method for simulating and modeling the two-way Doppler signal of an active sonar is proposed to achieve the purpose that the echo signal reaching the receiving point can truly reflect the actual situation at sea and improve the accuracy of the echo signal characteristics.

[0008] The present invention provides a method for simulating and modeling the two-way Doppler signal of an active sonar, including:

[0009] Establish an encounter triangle for the sound wave to reach the target, and calculate the transmission lead angle and the transmission sound propagation delay when the transmitted sound signal reaches the target;

[0010] Calculate the coordinates of the transceiver platform and the target platform and the transmission relative beam angle and the transmission deviation angle between the two when the transmitted sound signal reaches the target according to the transmission lead angle and the transmission sound propagation delay;

[0011] Calculate the Doppler factor in the transmission section when the transmitted sound signal reaches the target according to the transmission lead angle, the transmission relative beam angle and the transmission deviation angle; calculate the signal affected by the Doppler effect during the propagation section from the transmission point to the target point of the transmitted sound signal according to the Doppler factor in the transmission section;

[0012] Establish an encounter triangle for the target echo to reach, and calculate the echo lead angle and the echo sound propagation delay when the target echo sound signal reaches the transceiver platform;

[0013] Calculate the coordinates of the transceiver platform and the target platform and the echo relative beam angle and the echo deviation angle between the two when the echo signal reaches the receiving point according to the echo lead angle and the echo sound propagation delay;

[0014] Calculate the Doppler factor of the echo sound signal in the echo band when it arrives at the transceiver platform based on the echo lead angle, echo relative beam angle, and echo deflection angle; calculate the signal affected by Doppler in the propagation section of the echo sound signal from the target point to the emission point according to the Doppler factor of the echo band.

[0015] Further, the steps of establishing the triangle of sound wave arrival at the target and calculating the emission lead angle and emission sound propagation delay when the emitted sound signal reaches the target include:

[0016] Assume that the active emission signal is omnidirectional or fan-shaped in the horizontal direction. After the emission platform emits a signal at point S 0 , the sound wave meets the target at point T 1 . At this time, the emission platform reaches point S 1 ; the target reflection signal generated at point T 1 propagates in the reverse direction to the emission platform and is received by the array at point S 2 .

[0017] Assume that the propagation delay of the sound wave from emission to reaching the position of T 1 is τ 1 . Then, we have:

[0018] cτ 1 sinγ 1 = v T τ 1 sinβ 0 (1)

[0019] Assume that the emission signal time is t 0 . The sound wave in this direction and the platform-target connection line at the emission moment are advanced by an angle called the lead angle γ 1 in the target movement direction. Then, the lead angle when reaching T 1 is:

[0020]

[0021] Since,

[0022] cτ 1 cosγ 1 + v T τ 1 cosβ 0 = R 0 (3)

[0023] Then, the propagation delay τ 0 from point S 1 to point T 1 is:

[0024]

[0025] In the formula, the initial distance R0 Calculated according to the initial coordinates of S 0 and T 0 .

[0026] Further, the transceiver platform, the target platform coordinates, the relative launch beam angle and the launch deviation angle between the two for calculating the arrival time of the launch sound signal at the target according to the launch lead angle and the launch sound propagation time delay include:

[0027] The coordinates of the transceiver platform are:

[0028] x s1 = x s0 + v s τ 1 sinθ s (5-1)

[0029] y s1 = y s0 + v s τ 1 cosθ s (5-2)

[0030] The coordinates of the target platform are:

[0031] x T1 = x T0 + v T τ 1 sinθ T (6-1)

[0032] y T1 = y T0 + v T τ 1 cosθ T (6-2)

[0033] The distance between the coordinates of the transceiver platform and the target platform is:

[0034]

[0035] The relative launch beam angle between the transceiver platform and the target platform coordinates is:

[0036]

[0037] β 1 = α 1 ±180 (9)

[0038] The launch deviation angle between the transceiver platform and the target platform coordinates is:

[0039]

[0040] Further, calculating the Doppler factor in the transmission section of the transmitted acoustic signal arriving at the target based on the transmission lead angle, transmission relative beam angle, and transmission deviation angle includes:

[0041] Assume the radial velocities of the transceiver platform and the target platform are v 1 and v 0 respectively. Then, the time-domain Doppler factor Δ d of the transmitted acoustic signal received by the target platform can be expressed as:

[0042]

[0043] During the signal propagation stage, the radial velocity of the transceiver platform is:

[0044] v 1 = v s cos(α 0 -γ 1 ) (12)

[0045] Since the target platform is the receiver of the transmitted acoustic signal, thus

[0046] v 0 = v T cos(β 1 +λ 1 ) (13)

[0047] Then, the Doppler factor in the transmission section is expressed as:

[0048]

[0049] Further, calculating the signal affected by Doppler in the propagation section of the transmitted acoustic signal from the transmission point to the target point based on the Doppler factor in the transmission section includes:

[0050] The distance r 0 from S 1 to T 1 can be calculated by the following formula:

[0051]

[0052] If the influence of channel propagation is not considered, the signal when the transmitted acoustic signal arrives at the target is expressed as:

[0053]

[0054] If ocean channel propagation is considered and the impulse response function of this section of the channel is h 1 (t), then the signal when the transmitted acoustic signal arrives at the target is expressed as:

[0055]

[0056] Therefore, the Doppler-affected signal is transformed into:

[0057] s 1d (t) = s 1 [(1 + △ d1 )t] (16).

[0058] Furthermore, establishing the target echo arrival encounter triangle and calculating the echo lead angle and echo sound propagation delay of the target echo sound signal arriving at the transceiver platform includes:

[0059] The target echo sound signal is emitted from point T 1 , the receiving (transmitting) platform is located at S 1 , the distance between the target platform and the transceiver platform is R 1 , and the relative beam angles are α 1 and β 1 respectively; the target echo sound signal propagates along the T 1 -S 2 direction through the channel and arrives at the transceiver platform at point S 2 . The echo lead angle is:

[0060]

[0061] Then, the propagation delay τ 1 from point T 2 to point S 2 is:

[0062]

[0063] Furthermore, calculating the coordinates of the transceiver platform and the target platform at the moment when the echo signal arrives at the receiving point, as well as the echo relative beam angle and echo deviation angle between the two, includes:

[0064] Coordinates of the transceiver platform:

[0065] x s2 = x s1 + v s τ 2 sinθ s (19 - 1)

[0066] y s2 = y s1 + v s τ 2 cosθ s (19 - 2)

[0067] Coordinates of the target platform:

[0068] x T2= x T1 + v T τ 2 sinθ T (20 - 1)

[0069] y T2 = y T2 + v T τ 2 cosθ T (20 - 2)

[0070] The distance between the target platform coordinates and the transceiver platform coordinates is:

[0071]

[0072] The relative echo beam angle between the target platform coordinates and the transceiver platform coordinates is:

[0073]

[0074] β 2 = α 2 ±180 (23)

[0075] The echo deflection angle is:

[0076]

[0077] Furthermore, calculating the Doppler factor of the echo band when the echo signal arrives at the transceiver platform according to the echo lead angle, the relative echo beam angle, and the echo deflection angle includes:

[0078] The moment when the echo signal arrives at the receiving point of the transceiver platform, the target platform reaches point T 2 The relative beam angles between the transceiver platform and the target platform are α 2 , β 2 , and at this time v 1 , v 0 are respectively:

[0079] v 1 = v T cos(β 1 - γ 2 ) (25)

[0080] v 0 = v s cos(α 2 + λ 2 ) (26)

[0081] The corresponding Doppler factor of the echo band is:

[0082]

[0083] Further, calculating the signal affected by Doppler in the propagation section from the target point to the transmitting point of the echo acoustic signal according to the echo band Doppler factor includes:

[0084] The distance r from the echo acoustic signal to the receiving point of the transceiver platform 2 is:

[0085]

[0086] If the influence of channel propagation is not considered, the signal when the echo acoustic signal reaches the receiving point of the transceiver platform is expressed as:

[0087]

[0088] If the ocean channel propagation is considered and the impulse response function of this section of the channel is assumed to be h 2 (t), then the signal when the echo acoustic signal reaches the receiving point of the transceiver platform is expressed as:

[0089]

[0090] Considering the Doppler influence in this stage, the signal affected by double - way propagation and double - stage Doppler is obtained:

[0091] r(t) = s 2 [(1 + △ d2 )t] (30).

[0092] An active sonar two - way Doppler signal simulation and modeling method provided by the present invention divides the Doppler calculation process from the active signal transmission to the echo reception into two processes of "transmission - target" and "target - reception" according to the underwater acoustic signal propagation, target movement, and transceiver platform movement, and calculates the Doppler respectively, solving the problems of large model error and large echo waveform signal caused by using twice the one - way propagation Doppler shift as the Doppler influence of the round - trip two - way in the original method;

[0093] The present invention proposes a method for solving the encounter of the arrival point of acoustic wave propagation, and solves the problems of calculating the time when the transmitted signal reaches the target, the target echo returns to the receiving point, and the target position in the case where the transceiver platform and the target move in a uniform straight line;

[0094] The present invention adopts time-domain signal processing means and can be used for calculating the Doppler frequency shift signals of any broadband continuous-spectrum signals. It solves the problem that the Doppler frequency shift in the frequency domain is limited to discrete frequency points and it is impossible to calculate the Doppler signals of any (continuously changing) frequency signals. The essence of the Doppler frequency shift is to stretch or compress the transmitted signal, which is determined by the Doppler factor in the time domain, that is, the degree of stretching or compression of this signal. By calculating the Doppler factor for each point of the time-domain discrete sampling signal, a time-domain discrete signal containing the Doppler effect is obtained;

[0095] The two-stage Doppler calculation method of the present invention solves the problem that the radial model of the Doppler signal is not accurate enough due to the large changes in the attitude (radial velocity) or Doppler factor of the target and the transmitting platform at the two moments of the transmitting moment and the echo receiving moment;

[0096] The two-stage Doppler calculation method of the present invention can, when simulating and modeling the echo signals of active sonar targets, consider that the signals reaching the target already contain the Doppler effect of the motion in the "transmit-target" segment. When subsequent methods such as the sampling bright point model are used to simulate the echo signals, the Doppler signals of the motion in the "transmit-target" segment are adopted. As a result, the echo signals reaching the receiving point fail to truly reflect the actual situation at sea, seriously affecting the accuracy of the characteristics of the echo signals. Description of the Drawings

[0097] Figure 1 is the flowchart of the method for simulating and modeling the two-way Doppler signals of an active sonar provided by the present invention;

[0098] Figure 2 is the waveform and spectrogram of the transmitted LFM signal in the embodiment;

[0099] Figure 3 is the signal reaching the target via "transmit-target" and its spectrogram in the embodiment;

[0100] Figure 4 is the signal affected by the Doppler effect of "transmit-target" reaching the target and its spectrogram in the embodiment;

[0101] Figure 5 is the echo signal reaching the receiving point via "target-receive" and its spectrogram in the embodiment;

[0102] Figure 6 is the signal affected by the Doppler effect of "target-receive" reaching the receiving point and its spectrogram in the embodiment;

[0103] Figure 7 is the received signal calculated according to twice the one-way Doppler and its spectrogram in the embodiment;

[0104] Figure 8It is a comparison diagram of the waveform of the transmitted signal and the Doppler - affected signal in the "transmission - target" section in the embodiment;

[0105] Figure 9 It is a comparison diagram of the spectrum of the transmitted signal and the Doppler - affected signal in the "transmission - target" section in the embodiment;

[0106] Figure 10 It is a comparison diagram of the waveform of the transmitted signal and the Doppler - affected signal in the "target - reception" section in the embodiment;

[0107] Figure 11 It is a comparison diagram of the spectrum of the transmitted signal and the Doppler - affected signal in the "target - reception" section in the embodiment;

[0108] Figure 12 It is a comparison diagram of the spectrum of the transmitted signal and the spectrum of the two - way Doppler - affected signal in the embodiment;

[0109] Figure 13 It is a schematic diagram of the platform movement and the sound signal propagation in the embodiment;

[0110] Figure 14 It is a flow chart of the simulation modeling method for the two - way Doppler signal of an active sonar in the embodiment. Detailed implementation manners

[0111] To make the technical problems solved by the present invention, the technical solutions adopted and the achieved technical effects clearer, the present invention will be further described in detail below with reference to the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the present invention, rather than limiting the present invention. Additionally, it should be noted that for the sake of description, only parts related to the present invention are shown in the drawings, not all of the content.

[0112] Assume that the pulse length of the actively transmitted pulse signal is T, the signal is s(t), the transmitting source level is SL, and the transmitted signal can be a single - frequency CW signal, or an LFM, HFM, or any other form of broadband pulse signal. The moment when the active sonar transmits the signal: The transmitting platform is located at S 0 , with a heading of θ s and a speed of v s ; The target is located at T 0 with a heading of θ T and a speed of v T ; The initial distance between the transmitting platform and the target is R 0 , and the initial relative beam angles are α 0 and β 0 ; Assume that the sound speed in seawater is a constant c.

[0113] Assume that the coordinates of the transceiver platform S 0 are (x s0 ,y s0) Then, the coordinates (x 0 , y T0 ) of the target platform T can be calculated based on the initial parameters: T0 )

[0114] x T0 = x s0 + R 0 sin(θ s + α 0 ) (0 - 1)

[0115] y T0 = y s0 + R 0 cos(θ s + α 0 ) (0 - 2)

[0116] During the two-way propagation process of the "transmitted signal - target - received signal", the positional relationship between the transceiver platform and the target is as Figure 13 shown.

[0117] The focus of the present invention is to solve the Doppler calculation method problem caused by the movement of the transceiver platform after transmitting an active signal, without overly considering details such as channel propagation and the generation of target echo signals. However, the method of this patent is still applicable to the complete active sonar target echo signals considering ocean channel propagation, target highlight model echoes, etc.

[0118] As Figure 1 , Figure 14 shown, the active sonar two-way Doppler signal simulation and modeling method provided by the embodiment of the present invention includes:

[0119] 101. Establish an acoustic wave arrival target encounter triangle, and calculate the transmission lead angle and acoustic wave propagation delay at the moment when the transmitted acoustic signal reaches the target;

[0120] Specifically, assuming an omnidirectional or fan-shaped horizontal transmission of the active transmitted signal, after the transmitting platform emits a signal at point S 0 , the acoustic wave encounters the target at point T 1 , and at this time, the transmitting platform reaches point S 1 ; the target reflection signal generated at point T 1 propagates in the reverse direction towards the transmitting platform and is received by the array at point S 2 . Thus, the signal propagation of one transmission cycle is completed.

[0121] The core of Doppler calculation is to calculate the relative velocity at the receiving moment, and the prerequisite is to determine the relative position.

[0122] As can be seen from Figure 13 , the signal emitted from point S 0 travels along S 0 - T1 The sound wave propagating in a certain direction meets the target at point T 1 to generate a target echo. Assume that the transmission signal time is t 0 . The sound wave in this direction is advanced by an angle (referred to as the lead angle) γ with respect to the platform-target connection line at the transmission time, in the direction of the target's movement 1 . γ 1 can be obtained by solving the meeting triangle ΔS 0 T 0 T 1 .

[0123] Assume that the propagation time delay of the sound wave from transmission to reaching point T 1 is τ 1 . Then there is:

[0124] cτ 1 sinγ 1 = v T τ 1 sinβ 0 (1)

[0125] Assume that the transmission signal time is t 0 . The sound wave in this direction is advanced by an angle called the lead angle γ with respect to the platform-target connection line at the transmission time 1 . Then the lead angle reaching T 1 is:

[0126]

[0127] Since

[0128] cτ 1 cosγ 1 + v T τ 1 cosβ 0 = R 0 (3)

[0129] Then, the propagation time delay τ 0 from point S 1 to point T 1 is:

[0130]

[0131] In the formula, the initial distance R 0 is calculated according to the initial coordinates of S 0 and T 0 .

[0132] 102. Calculate the coordinates of the transceiver platform and the target platform at the moment when the transmitted sound signal reaches the target, as well as the relative bearing angle and deviation angle of transmission between the two, based on the transmission lead angle and the propagation time delay of the transmitted sound

[0133] Specifically, the coordinates of the transceiver platform are:

[0134] x s1 = x s0 + v s τ 1 sinθ s (5-1)

[0135] y s1 = y s0 + v s τ 1 cosθ s (5-2)

[0136] The coordinates of the target platform are:

[0137] x T1 = x T0 + v T τ 1 sinθ T (6-1)

[0138] y T1 = y T0 + v T τ 1 cosθ T (6-2)

[0139] The distance between the coordinates of the transceiver platform and the target platform is:

[0140]

[0141] The relative launch angle between the transceiver platform and the target platform coordinates is:

[0142]

[0143] β 1 = α 1 ±180 (9)

[0144] The launch deviation angle between the transceiver platform and the target platform coordinates is:

[0145]

[0146] 103. Calculate the Doppler factor in the launch section when the launch sound signal reaches the target moment based on the launch lead angle, relative launch angle, and launch deviation angle; calculate the signal affected by Doppler during the propagation section from the launch point to the target point of the launch sound signal according to the Doppler factor in the launch section;

[0147] Specifically, assume that the radial velocities of the transceiver platform and the target platform are v respectively1 and v 0 then the time-domain Doppler factor Δ of the transmitted acoustic signal received by the target platform d can be expressed as:

[0148]

[0149] During the signal propagation stage, the radial velocity of the transceiver platform is:

[0150] v 1 = v s cos(α 0 -γ 1 )(12)

[0151] Since the target platform is the receiver of the transmitted acoustic signal, thus

[0152] v 0 = v T cos(β 1 +λ 1 )(13)

[0153] Then the Doppler factor in the transmission section is expressed as:

[0154]

[0155] S 0 to T 1 The distance r 1 can be calculated by the following formula:

[0156]

[0157] If the influence of channel propagation is not considered, then the signal when the transmitted acoustic signal arrives at the target is expressed as:

[0158]

[0159] If ocean channel propagation is considered, assuming the channel impulse response function for this section is h 1 (t), then the signal when the transmitted acoustic signal arrives at the target is expressed as:

[0160]

[0161] Therefore, the Doppler-affected signal is transformed into:

[0162] s 1d (t) = s 1 [(1 + △ d1 )t](16).

[0163] 104. Establish the target echo arrival encounter triangle, and calculate the echo lead angle and echo sound propagation delay of the target echo sound signal arriving at the transceiver platform;

[0164] Specifically, the target echo sound signal is emitted from point T 1 , and the receiving (transmitting) platform is located at S 1 . The distance between the target platform and the transceiver platform is R 1 , and the relative beam angles are α 1 and β 1 respectively; the target echo sound signal propagates along the T 1 -S 2 direction through the channel and arrives at the transceiver platform at point S 2 . The echo lead angle is:

[0165]

[0166] Then, the propagation delay τ 1 from point T 2 to point S 2 is:

[0167]

[0168] 105. Calculate the coordinates of the transceiver platform and the target platform at the moment when the echo signal arrives at the receiving point, as well as the echo relative beam angle and echo deflection angle between the two according to the echo lead angle and echo sound propagation delay;

[0169] Specifically, the coordinates of the transceiver platform:

[0170] x s2 = x s1 + v s τ 2 sinθ s (19 - 1)

[0171] y s2 = y s1 + v s τ 2 cosθ s (19 - 2)

[0172] The coordinates of the target platform:

[0173] x T2 = x T1 + v T τ 2 sinθ T (20 - 1)

[0174] y T2 = y T2 + v T τ 2 cosθT (20 - 2)

[0175] The distance between the target platform coordinates and the transceiver platform coordinates is:

[0176]

[0177] The relative echo bearing angle between the target platform coordinates and the transceiver platform coordinates is:

[0178]

[0179] β 2 = α 2 ±180 (23)

[0180] The echo deflection angle is:

[0181]

[0182] 106. Calculate the Doppler factor of the echo sound signal in the echo band when it reaches the transceiver platform according to the echo lead angle, the relative echo bearing angle, and the echo deflection angle; calculate the signal affected by Doppler in the propagation section of the echo sound signal from the target point to the emission point according to the Doppler factor of the echo band.

[0183] Specifically, at the moment when the echo signal reaches the receiving point of the transceiver platform, the target platform reaches point T 2 The relative bearing angles between the transceiver platform and the target platform are α 2 , β 2 , and at this time v 1 , v 0 are respectively:

[0184] v 1 = v T cos(β 1 - γ 2 ) (25)

[0185] v 0 = v s cos(α 2 + λ 2 ) (26)

[0186] The corresponding Doppler factor of the echo band is:

[0187]

[0188] The distance r when the echo sound signal reaches the receiving point of the transceiver platform 2 is:

[0189]

[0190] If the influence of channel propagation is not considered, the signal when the echo sound signal arrives at the receiving point of the transceiver platform is expressed as:

[0191]

[0192] If the ocean channel propagation is considered and the impulse response function of this section of the channel is assumed to be h 2 (t), then the signal when the echo sound signal arrives at the receiving point of the transceiver platform is expressed as:

[0193]

[0194] Considering the Doppler influence in this stage, the signal after two-way propagation and two-stage Doppler influence is obtained:

[0195] r(t) = s 2 [(1 + △ d2 )t] (30).

[0196] This embodiment is a monostatic active sonar, and the implementation process is as follows:

[0197] 1. Set and calculate the active sonar parameters, the motion posture parameters of the transceiver platform and the target

[0198] (1) Calculate the active sonar transmission signal

[0199] An LFM signal is adopted and generated by the following formula:

[0200]

[0201] Where: the pulse length T (seconds), the center frequency f 0 (Hz), the frequency modulation width F (Hz), then the frequency modulation slope k = F / T (Hz / s).

[0202] The source level SL of the transmission signal is 200 dB, then the sound pressure amplitude A of the signal is:

[0203]

[0204] (2) The initial distance R of the target platform from the transceiver platform 0 = 15 km, the initial aspect angle α 0 = 50°; the course of the transceiver platform is θ s = 45°, the speed v s = 8 knots; the course of the target platform is θ T = 335°, the speed v T = 18 knots, the aspect angle β of the transceiver platform relative to the target platform 0 = 60°;

[0205] (3) The seawater sound speed c = 1500 m / s;

[0206] (4) Set the initial coordinates of the transceiver platform as: x s0 = 0, y s0 = 0; Calculate the initial coordinates of the target platform:

[0207] x T0 = R 0 sin(θ s + α 0 )

[0208] y T0 = R 0 cos(θ s + α 0 )

[0209] 2 Solve the encounter triangle of the "transmission - target" section of the transmitted acoustic signal

[0210] (1) Calculate the lead angle according to Equation (2):

[0211]

[0212] (2) Calculate the propagation delay τ from point S 0 to point T 1 as: 1

[0213]

[0214] 3 Calculate the coordinates, distances, and relative beam angles of the transceiver platform and the target platform at the moment when the transmitted signal reaches the target

[0215] (1) Calculate the coordinates of the transmitting platform:

[0216] x s1 = x s0 + v s τ 1 sinθ s

[0217] y s1 = y s0 + v s τ 1 cosθ s

[0218] (2) Calculate the coordinates of the target platform:

[0219] x T1 = x T0 + v T τ 1 sinθ T

[0220] y T1 = y T0 + v​T τ 1 cosθ T

[0221] (3) Calculate the distance between the target platform and the transceiver platform:

[0222]

[0223] (4) Calculate the relative beam angle between the target platform and the transceiver platform:

[0224]

[0225] β 1 = α 1 ± 180

[0226] (5) Calculate the deflection angle λ 1 :

[0227]

[0228] 4 Calculate the Doppler factor at the moment when the sound wave reaches the target

[0229]

[0230] 5 Calculate the Doppler effect signal propagated in the "transmission - target" section

[0231] (1) Calculate the distance r from S 0 to T 1 : 1 :

[0232]

[0233] (2) Calculate the signal when the transmitted signal reaches the target:

[0234]

[0235] (3) Calculate the signal affected by Doppler:

[0236] s 1d s(t) = s 1 [(1 + △ d1 )t]

[0237] 6 Solve the encounter triangle in the "target - reception" section

[0238] At this time, the target reflected echo is emitted from point T 1 , and the receiving (transmitting) platform is located at S 1 , the distance between the target platform and the transceiver platform is R 1 , and the relative beam angles are α 1 , β 1 .

[0239] (1) Calculate the lead angle of the target echo signal propagating along the T 1 -S 2 direction through the channel to the receiving platform S 2 point:

[0240]

[0241] (2) Calculate the time delay τ 1 from point T 2 to point S 2 :

[0242]

[0243] 7 Calculate the coordinates, distance, relative beam angle, and deflection angle of the transmitting and receiving platforms and the target platform at the moment when the target echo signal arrives at the receiving point

[0244] (1) Calculate the coordinates of the transmitting platform:

[0245] x s2 = x s1 + v s τ 2 sinθ s

[0246] y s2 = y s1 + v s τ 2 cosθ s

[0247] (2) Calculate the coordinates of the target platform:

[0248] x T2 = x T1 + v T τ 2 sinθ T

[0249] y T2 = y T2 + v T τ 2 cosθ T

[0250] (3) Calculate the relative beam angle:

[0251]

[0252] β 2 = α 2 ±180

[0253] (4) Calculate the deflection angle λ 2 :

[0254]

[0255] 8 Calculate the Doppler factor of the target echo signal arriving at the receiving platform

[0256]

[0257] 9 Calculate the signal propagation in the second stage with Doppler effect

[0258] (1) Calculate the distance r from the target echo to the receiving point 2 :

[0259]

[0260] (2) Calculate the signal of the target echo arriving at the receiving point:

[0261]

[0262] (3) Calculate the received signal after two-way propagation and two-stage Doppler effect:

[0263] r(t) = s 2 [(1 + △ d2 )t]

[0264] 10 Calculate the effect diagram

[0265] 10.1 Simulation calculation background one

[0266] (1) Background parameters

[0267] The relative motion situation of the target is set the same as before.

[0268] The pulse length T = 2 seconds, the center frequency f 0 = 1000Hz, the frequency modulation width F = 400Hz, then the frequency modulation slope k = F / T = 200Hz / s.

[0269] In this embodiment, under the relative motion situation and calculation parameters, the Doppler factor of the "transmitter - target" segment is -0.004817 (negative indicates frequency increase); the Doppler factors of the "target - receiver" segment are -0.004837 respectively.

[0270] The frequency modulation width of the transmitted signal is 800Hz - 1200Hz. Based on the two-way Doppler calculation, the Doppler frequency shift of the finally received echo signal is 7.7Hz to the right at the 800Hz frequency point and 11.6Hz to the right at the 1200Hz frequency point. According to the traditional two - fold one - way Doppler frequency shift, it is 9.6Hz, and the Doppler frequency shift amounts at the low - frequency end and the high - frequency end are the same. Obviously, this is inaccurate.

[0271] (2) Calculation effect

[0272] Figure 2 : It is the waveform and spectrum of the transmitted LFM signal

[0273] Figure 3 : It is the waveform and spectrum of the signal that reaches the target after passing through "transmission - target"

[0274] Figure 4 : It is the signal and spectrum affected by Doppler of "transmission - target" reaching the target. It can be seen from the figure that for the signal after the transmitted signal reaches the target, its broadband Doppler frequency shift is different at different frequency points. The lower the frequency, the smaller the frequency shift; the higher the frequency, the larger the frequency shift. For example: at the low - frequency end of 813 Hz of the transmitted signal, the frequency after Doppler frequency shift is 817.1 Hz, with a frequency shift of 4.1 Hz (the theoretical value is 3.92 Hz); at the high - frequency end of 1188 Hz of the transmitted signal, the frequency after Doppler frequency shift is 1194 Hz, with a frequency shift of 6 Hz (the theoretical value is 5.77 Hz). The calculation results at the two frequency points are in agreement with the theoretical values. The error between the theoretical value and the calculated value is mainly caused by the insufficient frequency resolution of the analyzed signal length.

[0275] Figure 5 : It is the echo signal and spectrum that reach the receiving point after passing through "target - reception"

[0276] Figure 6 : It is the signal and spectrum affected by Doppler of "target - reception" reaching the receiving point. It can be seen from the figure that for the signal after the target echo signal reaches the receiving point, its broadband Doppler frequency shift is different at different frequency points. The lower the frequency, the smaller the frequency shift; the higher the frequency, the larger the frequency shift. For example: at the low - frequency end of 813 Hz of the transmitted signal, the frequency after Doppler frequency shift is 820.7 Hz, with a frequency shift of 7.7 Hz (the theoretical value is 7.85 Hz); at the high - frequency end of 1188 Hz of the transmitted signal, the frequency after Doppler frequency shift is 1200 Hz, with a frequency shift of 12 Hz (the theoretical value is 11.47 Hz). The calculation results at the two frequency points are in agreement with the theoretical values.

[0277] Figure 7 : It is the received signal and spectrum calculated according to 2 - fold one - way Doppler. It can be seen from the spectrum diagram that for the broadband echo signal calculated according to the traditional double one - way Doppler, its Doppler frequency shift is the same at both the low - frequency end and the high - frequency end, and it shows 10 Hz in the figure (the theoretical value is 9.6 Hz), which is obviously quite different from the method of this patent.

[0278] 10.2 Simulation calculation background two

[0279] (1) Background parameters

[0280] The relative motion state of the target is the same as before, only changing the frequency band parameters of the transmitted signal. Therefore, the Doppler factors of the "transmission - target" segment and the "target - reception" segment are the same as before, which are: - 0.004817 and - 0.004837 respectively.

[0281] The pulse length T = 2 seconds, and the center frequency f 0 = 2000 Hz, the frequency modulation width F = 1000 Hz, then the frequency modulation slope k = F / T = 500 Hz / s.

[0282] The frequency modulation width of the transmitted signal is 1500 Hz to 2500 Hz. Based on the two-way Doppler calculation, the Doppler frequency shift of the finally received echo signal is 14.4 Hz to the right at the 1500 Hz frequency point and 24 Hz to the right at the 2500 Hz frequency point.

[0283] (2) Calculation effect

[0284] Figure 8 : Waveform comparison between the "transmitted signal" and the Doppler-influenced signal in the "transmit-target" section. For easy comparison, the transmitted signal and the Doppler-influenced signal reaching the target are normalized, and only the waveforms of 500 sampling points are shown.

[0285] Figure 9 : Spectrum comparison between the transmitted signal and the Doppler-influenced signal in the "transmit-target" section. At the low-frequency end of 1520 Hz, the frequency of the signal after being influenced by Doppler in the "transmit-target" section is 1527 Hz, and the Doppler frequency shift value is 7 Hz (theoretical value 7.3 Hz); at the high-frequency end of 2481 Hz, the frequency of the signal after being influenced by Doppler is 2493 Hz, and the Doppler frequency shift value is 12 Hz (theoretical value 11.95 Hz). The Doppler frequency shift values calculated from the signal at the two frequency points are in agreement with the theoretical values.

[0286] Figure 10 : Waveform comparison between the transmitted signal and the Doppler-influenced signal in the "target-receive" section. For easy comparison, the transmitted signal and the Doppler-influenced signal reaching the target are normalized, and only the waveforms of 500 sampling points are shown.

[0287] Figure 11 : Spectrum comparison between the transmitted signal and the Doppler-influenced signal spectrum in the "target-receive" section. At the low-frequency end of 1520 Hz, the frequency of the transmitted signal after being influenced by Doppler in the "target-receive" section is 1534 Hz, and the Doppler frequency shift value is 14 Hz (theoretical value 14.67 Hz); at the high-frequency end of 2481 Hz, the frequency of the signal after being influenced by Doppler is 2505 Hz, and the Doppler frequency shift value is 24 Hz (theoretical value 23.95 Hz). The Doppler frequency shift values calculated from the signal at the two frequency points are in agreement with the theoretical values.

[0288] Figure 12: Comparison between the spectrum of the transmitted signal and the spectrum of the signal affected by twice the one-way Doppler effect. As can be seen from the figure, for the traditional calculation method of the signal affected by twice the one-way Doppler effect, the Doppler frequency shift is the same at all frequency points. In this example, it is 20 Hz (the theoretical value is 19.27 Hz).

[0289] It can be seen that the higher the frequency of the transmitted broadband signal, the greater the Doppler frequency shift error of the signal affected by the Doppler effect calculated by the traditional sampling method; while for the signal affected by the Doppler effect calculated by the method of this patent, accurate estimation of the Doppler frequency shift can be obtained for all frequency points within the transmitted signal frequency band.

[0290] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: making modifications to the technical solutions recorded in the foregoing embodiments, or performing equivalent replacements on some or all of the technical features therein, does not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An active sonar two-way Doppler signal simulation and modeling method, characterized in that, the method includes: Establish an encounter triangle for the sound wave to reach the target, and calculate the transmission lead angle and the transmission sound propagation delay at the moment when the transmitted sound signal reaches the target; Calculate the coordinates of the transmitting and receiving platform and the target platform at the moment when the transmitted sound signal reaches the target, as well as the transmission relative beam angle and the transmission deviation angle between the two according to the transmission lead angle and the transmission sound propagation delay; Calculate the Doppler factor in the transmission section at the moment when the transmitted sound signal reaches the target according to the transmission lead angle, the transmission relative beam angle and the transmission deviation angle; Calculate the signal affected by Doppler during the propagation section of the transmitted sound signal from the transmission point to the target point according to the Doppler factor in the transmission section; Establish an encounter triangle for the target echo to reach, and calculate the echo lead angle and the echo sound propagation delay when the target echo sound signal reaches the receiving and transmitting platform; Calculate the coordinates of the receiving and transmitting platform and the target platform at the moment when the echo signal reaches the receiving point, as well as the echo relative beam angle and the echo deviation angle between the two according to the echo lead angle and the echo sound propagation delay; Calculate the Doppler factor in the echo section when the echo sound signal reaches the receiving and transmitting platform according to the echo lead angle, the echo relative beam angle and the echo deviation angle; Calculate the signal affected by Doppler during the propagation section of the echo sound signal from the target point to the transmission point according to the Doppler factor in the echo section.

2. The active sonar two-way Doppler signal simulation and modeling method according to claim 1, characterized in that, the establishment of the encounter triangle for the sound wave to reach the target and the calculation of the transmission lead angle and the transmission sound propagation delay at the moment when the transmitted sound signal reaches the target include: Assume that the active emission signal is omnidirectional or sectorial emission in the horizontal direction. After the transceiver platform emits the signal at point S 0 , the acoustic wave meets the target at point T 1 . At this time, the transceiver platform reaches point S 1 . The target reflection signal generated by the acoustic wave at point T 1 propagates back towards the transceiver platform and is received by the array at point S 2 . The moment when the active sonar emits the signal: the transceiver platform is located at S 0 , with a heading of θ s and a speed of v s ; the target is located at T 0 , with a heading of θ T and a speed of v T ; the initial distance between the transceiver platform and the target is R 0 , and the initial relative beam angles are α 0 and β 0 respectively; assume that the sound speed of seawater is a constant c; Assume the transceiver platform S 0 has coordinates (x s0 , y s0 ). Then, the coordinates (x 0 , y T0 , y T0 ) of the target platform T 0 ) can be calculated based on the initial parameters; Assume that the propagation delay of the acoustic wave from transmission to arrival at position T 1 is τ 1 , then we have: cτ 1 sinγ 1 =v T τ 1 sinβ 0 (1) Assume that the transmission signal time is t 0 , the direction of the acoustic wave reaching the target is the line connecting the transceiver platform and the target at the transmission moment, and it is advanced by an angle called the lead angle γ in the direction of the target's movement 1 , then the lead angle reaching T 1 is: Since, cτ 1 cosγ 1 +v T τ 1 cosβ 0 =R 0 (3) Then, S 0 The propagation delay τ 1 from point S to point T 1 is as follows: In the formula, the initial distance R 0 is calculated according to the initial coordinates of S 0 and T 0 .

3. The active sonar two-way Doppler signal simulation and modeling method according to claim 2, characterized in that, the calculation of the coordinates of the transmitting and receiving platform and the target platform at the moment when the transmitted sound signal reaches the target, as well as the transmission relative beam angle and the transmission deviation angle between the two according to the transmission lead angle and the transmission sound propagation delay includes: The coordinates of the transmitting and receiving platform are: x s1 = x s0 + v s τ 1 sin θ s (5 - 1) y s1 = y s0 + v s τ 1 cos θ s (5 - 2) The coordinates of the target platform are: x T1 = x T0 + v T τ 1 sin θ T (6 - 1) y T1 = y T0 + v T τ 1 cos θ T (6 - 2) The distance between the coordinates of the transmitting and receiving platform and the target platform is: The transmission relative beam angle between the coordinates of the transmitting and receiving platform and the target platform is: β 1 ＝α 1 ±180 (9) The transmission deviation angle between the coordinates of the transmitting and receiving platform and the target platform is:

4. The active sonar two-way Doppler signal simulation and modeling method according to claim 3, characterized in that, the calculation of the Doppler factor in the transmission section at the moment when the transmitted sound signal reaches the target according to the transmission lead angle, the transmission relative beam angle and the transmission deviation angle includes: Suppose the radial velocities of the transceiver platform and the target platform are \(v\) 1 and \(v\) 0 , respectively. Then the time-domain Doppler factor \(\Delta\) d of the transmitted acoustic signal received by the target platform can be expressed as: During the signal propagation stage, the radial velocity of the transmitting and receiving platform is: v 1 = v s cos(α 0 - γ 1 ) (12) Since the target platform is the receiving party of the transmitted sound signal, v 0 = v T cos(β 1 + λ 1 ) (13) then the Doppler factor in the transmission section is expressed as:

5. The active sonar two-way Doppler signal simulation and modeling method according to claim 4, characterized in that, the calculation of the signal affected by Doppler during the propagation section of the transmitted sound signal from the transmission point to the target point according to the Doppler factor in the transmission section, includes: S 0 to T 1 The distance r 1 can be calculated by the following formula: If the influence of channel propagation is not considered, then the signal when the transmitted sound signal reaches the target is expressed as: If the ocean channel propagation is considered and the impulse response function of this section of the channel is assumed to be h 1 (t), then the signal representation when the transmitted acoustic signal reaches the target is: Therefore, the signal affected by Doppler is transformed into: s 1d s(t) = s 1 [(1 + Δ d1 )t](16).

6. The active sonar two-way Doppler signal simulation and modeling method according to claim 5, characterized in that, Establishing the target echo arrival encounter triangle and calculating the echo advance angle and echo sound propagation time delay of the target echo acoustic signal arriving at the transceiver platform, including: The target echo acoustic signal is emitted from point T 1 and the transceiver platform is located at point S 1 . The distance between the target platform and the transceiver platform is R 1 . The relative launch angles between the coordinates of the transceiver platform and the target platform are α 1 and β 1 respectively. The target echo acoustic signal propagates along the T 1 -S 2 connection direction through the channel and the echo advance angle when it reaches the transceiver platform at point S 2 is: Then, T 1 The propagation delay τ from the point to S 2 is: 2 as follows 7. The active sonar two-way Doppler signal simulation modeling method according to claim 6, characterized in that calculating the coordinates of the transceiver platform and the target platform at the moment when the echo signal arrives at the receiving point, as well as the echo relative beam angle and echo deflection angle between the two according to the echo advance angle and echo sound propagation time delay, including: Coordinates of the transceiver platform: x s2 = x s1 + v s τ 2 sin θ s (19 - 1) y s2 = y s1 + v s τ 2 cos θ s (19 - 2) Coordinates of the target platform: x T2 = x T1 + v T τ 2 sin θ T (20 - 1) y T2 = y T2 + v T τ 2 cos θ T (20 - 2) The distance between the coordinates of the target platform and the transceiver platform is: The echo relative beam angle between the coordinates of the target platform and the transceiver platform is: β 2 ＝α 2 ±180 (23) The echo deflection angle is:

8. The active sonar two-way Doppler signal simulation modeling method according to claim 7, characterized in that calculating the Doppler factor of the echo band of the echo acoustic signal arriving at the transceiver platform according to the echo advance angle, echo relative beam angle and echo deflection angle, including: The time when the echo signal arrives at the receiving point of the transceiver platform, and the target platform arrives at point T 2 The relative echo beam angles between the coordinates of the target platform and the transceiver platform are α 2 , β 2 respectively. At this time, v 1 , v 0 are respectively: v 1 = v T cos(β 1 - γ 2 ) (25) v 0 = v s cos(α 2 + λ 2 ) (26) The corresponding Doppler factor of the echo band is:

9. The active sonar two-way Doppler signal simulation modeling method according to claim 8, characterized in that calculating the signal affected by Doppler in the propagation section of the echo acoustic signal from the target point to the receiving point according to the Doppler factor of the echo band, including: The distance r from the echo sound signal to the receiving point of the transceiver platform 2 is as follows: If the influence of channel propagation is not considered, the signal when the echo acoustic signal arrives at the receiving point of the transceiver platform is expressed as: If the ocean channel propagation is considered and the impulse response function of this section of the channel is assumed to be h 2 (t), then the signal when the echo sound signal arrives at the receiving point of the transceiver platform is expressed as: Considering the Doppler influence in this stage, the signal after two-way propagation and two-stage Doppler influence is obtained: r(t) = s 2 [(1 + Δ d2 )t] (30).

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