A method for calculating the elevation angle of an active sonar based on a reverberation signal

Abstract

The present application relates to underwater acoustic signal processing and sonar system parameter calibration technical field, especially a kind of active sonar pitch angle calculation method based on reverberation signal, for the physical mismatch of existing attitude sensor direct measurement, matching field type method lacks the technical blank with the pitch angle of sonar itself as inversion target, unknown pitch angle is regarded as inversion variable, through the joint forward of transmission-dispersion sound field propagation model and interface scattering model under different hypothetical pitch angle Theoretical reverberation signal is matched with the normalized cross-correlation of measured reverberation signal, the absolute value of the peak value of correlation coefficient corresponding angle is extracted, and the positive and negative signs of the comparison determination of the early interface reverberation arrival order obtained by envelope detection and the geometric theoretical arrival time are combined, and finally the real working pitch angle of sonar system is obtained.The method does not need additional hardware, and the pointing error caused by installation deviation and deformation can be eliminated using conventional reverberation data, and the inversion precision is high and the engineering practicability is strong.

Description

Technical Field

[0001] This invention relates to the field of underwater acoustic signal processing and sonar system parameter calibration technology, specifically to a method for calculating the elevation angle of active sonar based on reverberation signals. Background Technology

[0002] In active sonar systems, especially bistatic sonar systems with separate transmitter and receiver, the beam elevation angle of the transmitting transducer or receiving hydrophone array is a key parameter determining the propagation path of sound waves in ocean waveguides and the incident / exit grazing angles at the interface. The accuracy of this angle directly affects the fidelity of subsequent processing models such as reverberation prediction, target intensity estimation, and matched field localization.

[0003] Currently, the main methods for obtaining sonar elevation angles include direct measurement and indirect estimation.

[0004] Direct measurement methods rely on attitude sensors integrated into the sonar platform to calculate the carrier's attitude using devices such as inertial measurement units or fiber optic gyroscopes. However, such methods suffer from significant physical mismatches: the sensors measure the attitude of the carrier platform, not the sonar array itself. Due to mechanical deviations in the installation of the sonar array, the dynamic deflection of the platform under different sea states and loads, and the relative motion between the transmitting and receiving arrays, there is a systematic error between the attitude angle output by the sensor and the true pointing of the sonar beam that is difficult to quantify and cannot be eliminated by improving sensor accuracy.

[0005] Indirect estimation methods borrow from the idea of ​​matched field processing, based on the inversion of environmental parameters such as the underwater acoustic channel transfer function or ambient noise. These systems acquire target signals or ambient noise, generate a copy field using a propagation model, and then perform correlation processing with measured data to estimate the sound source location or seabed acoustic parameters. However, existing matched field systems are limited to target or environmental information in terms of parameter dimensions, lacking forward models and dedicated processing modules that take the sonar system's own installation deviations, especially the elevation angle under separate transmitting and receiving configurations, as the inversion target. Furthermore, ocean reverberation, a carrier of information containing rich transmitting and receiving geometric relationships, is treated as interference and filtered out in traditional systems, and its value as an acoustic scale for calibrating the system's own state is not utilized. Summary of the Invention

[0006] To address the shortcomings of existing technologies for acquiring sonar elevation angles, such as physical mismatch or the inability to utilize reverberation geometry for self-parameter inversion, this invention provides a sonar elevation angle inversion method based on Bellhop reverberation simulation. This method utilizes a transmit-receive reverberation model to perform forward modeling of theoretical reverberation signals under different assumed elevation angles. The theoretical signals are then matched with the actual received reverberation signals to deduce the system's true operating elevation angle. This invention treats the unknown system parameter (elevation angle) as the variable to be inverted, and through reverberation—a "passively" received signal—it achieves active calculation of the sonar system's attitude.

[0007] To address the aforementioned technical problems, this invention proposes a method for calculating the elevation angle of active sonar based on reverberation signals, comprising the following steps:

[0008] Parameter acquisition steps: Acquire marine environmental parameters of the operating sea area and operating parameters of the active sonar system to be calibrated; wherein, the marine environmental parameters include at least sea depth, sound velocity profile, seabed sediment type and its acoustic characteristics; the operating parameters include at least the transmitting array depth, receiving array depth, center frequency of the transmitted signal, bandwidth, pulse width and signal waveform;

[0009] The measured signal acquisition steps are as follows: After the active sonar system transmits the designated signal in the actual operating sea area, the original reverberation time series data output by the receiving array is synchronously collected and stored as the measured reverberation signal.

[0010] The iterative forward modeling steps are as follows: Set a search range and search step size for pitch angles that include the true values, traverse every assumed pitch angle value within the range, and generate the corresponding theoretical reverberation signal for each assumed pitch angle value through joint forward modeling of the underwater acoustic propagation model and the interface scattering model.

[0011] Pitch angle absolute value estimation step: For each of the theoretical reverberation signals generated in the cyclic forward modeling step, perform similarity calculation with the measured reverberation signal to obtain a curve of similarity value changing with the assumed pitch angle; extract the peak value of the curve, and determine the absolute value of the assumed pitch angle corresponding to the peak value as the absolute value of the actual working pitch angle of the active sonar system;

[0012] The sign determination step is as follows: envelope detection is performed on the measured reverberation signal to detect the arrival times of the reverberations at at least two strong scattering interfaces that arrive early; simultaneously, based on the system geometry and the environmental parameters, the theoretical arrival times of the seabed primary scattering reverberation and the sea surface primary scattering reverberation are calculated; the measured early arrival times are matched and compared with the theoretical arrival times to determine the correct sign of the pitch angle, and finally the pitch angle calculation result with the correct sign is obtained.

[0013] Preferably, the process of generating a theoretical reverberation signal for each assumed pitch angle value in the cyclic forward modeling step specifically includes:

[0014] Step A: Using the currently assumed pitch angle value as the pointing angle of the sound source, and combining the marine environmental parameters and operating parameters, configure the environmental file for the underwater acoustic propagation model;

[0015] Step B: Call the ray acoustic model to perform intrinsic sound ray tracking, calculate and store the arrival information of all intrinsic sound rays, the arrival information including at least the arrival amplitude, propagation delay, incident grazing angle and exit grazing angle;

[0016] Step C: Traverse all possible two-way sound path combinations of "emitter → scatterer" and "scatterer → receiver", introduce the interface scattering model, and calculate the interface reverberation impact response;

[0017] Step D: Convolve the calculated reverberant impact response with the transmitted signal copy to generate the theoretical reverberant signal under the current assumed pitch angle.

[0018] Preferably, the underwater acoustic propagation model adopts the Bellhop ray acoustic model, and the interface scattering model adopts the Lambert scattering law. For the transmit-receive separate system, step A requires configuring four independent environmental files: "transmit-seabed", "transmit-sea surface", "receive-seabed", and "receive-sea surface".

[0019] Preferably, in the pitch angle absolute value estimation step, the similarity calculation adopts the normalized cross-correlation algorithm, and its calculation formula is as follows:

[0020]

[0021] Preferably, in the symbol discrimination step, envelope detection is achieved by performing a Hilbert transform on the measured reverberation signal and calculating the modulus. The theoretical arrival time can be calculated using a geometric formula under the perpendicular incidence approximation:

[0022]

[0023]

[0024] Where tb is the theoretical arrival time of the seabed first-scatter reverberation, ts is the theoretical arrival time of the sea surface first-scatter reverberation, H is the sea depth, dt is the transmission depth, dr is the reception depth, R is the horizontal distance between transmission and reception, and c is the average speed of sound in water. Alternatively, the local maxima of the seabed and sea surface reverberation envelopes can be directly extracted from the Bellhop simulation arrival structure in the cyclic forward modeling step as the theoretical arrival time.

[0025] Preferably, the marine environmental parameters include at least sea depth, sound velocity profile, seabed sediment type and its acoustic characteristics; the operating parameters include at least the depth of the transmitting array, the depth of the receiving array, the center frequency of the transmitted signal, bandwidth, pulse width and signal waveform; the pitch angle search range is set according to prior knowledge or engineering experience and is a symmetrical angle range.

[0026] Compared with the prior art, the beneficial effects of the present invention are:

[0027] 1. By transforming the pitch angle from a preset known quantity into a variable to be inverted, the true direction of the sonar beam can be directly deduced from the reverberation signal. The obtained pitch angle has automatically compensated for all physical mismatch factors such as installation deviation angle and carrier deformation, which can provide accurate system parameters for subsequent detection and processing, thereby improving the target detection probability and parameter estimation accuracy from the source.

[0028] 2. The reverberation signal, which is considered interference in traditional processing, is used as the calibration source of the system's own attitude. There is no need to add external calibration equipment or emit special test signals. The system has a compact structure and strong engineering practicality.

[0029] 3. The reverberation impact response was calculated using a two-way acoustic ray combined elliptical scattering model under separate transmitting and receiving conditions. This model realistically simulated the complete physical process of "incident-scattering-out," avoiding model errors caused by the monostatic circular ring approximation and ensuring the accuracy of the theoretical copy field. Attached Figure Description

[0030] Figure 1 This is the overall algorithm flowchart of the method of the present invention;

[0031] Figure 2 This is a schematic diagram of the reverberation simulation principle of the separate transceiver in this invention;

[0032] Figure 3 This is a measured sound velocity profile used in a specific embodiment;

[0033] Figure 4 The figure shows the simulation results when the pitch angle is 0°.

[0034] Figure 5 The simulation results are shown when the pitch angle is tilted downwards by 5°.

[0035] Figure 6 The simulation results are shown when the pitch angle is tilted downwards by 10°.

[0036] Figure 7 The simulation results are shown when the pitch angle is tilted upwards by 5°.

[0037] Figure 8 The figure shows the simulation results when the pitch angle is tilted upward by 10°. Detailed Implementation

[0038] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings, so that those skilled in the art can more clearly understand how to practice the present invention. Although the present invention has been described in conjunction with its preferred embodiments, these embodiments are merely illustrative and not intended to limit the scope of the invention.

[0039] Simulation principle of this application:

[0040] This simulation, based on ray acoustics theory and Lambert's scattering law, models interface reverberation in a deep-sea environment. The core formulas are as follows:

[0041]

[0042] Assuming the transmitted pulse width is τ, the interface reverberation intensity is:

[0043]

[0044] in p inc It is the incident sound pressure transfer function. p scatt It is the sound pressure transfer function of the scattered sound. I o This represents the sound intensity per unit distance from the sound source. ΔS k It is a scattering surface element. f(θ) inc θ scatt Based on Lambert's scattering law, it is related to the incident and exit grazing angles, and the calculation method is as follows:

[0045] f(θ) inc θ scatt =μsinθ inc sinθ scatt

[0046] Where, μ The scattering coefficients are determined empirically based on the type of seabed sediment. In reverberation simulations of softer muddy and sandy seabeds, the following values ​​are satisfied: 10log 10 With μ = -27 dB and μ ≈ 0.002, the scattering intensity at the sea surface is stronger than that at most seabed reverberation points in the simulation. Therefore, the upper limit of seabed scattering is taken. 10log 10 μ = -24dB, μ ≈ 0.004.

[0047] The incident grazing angle θ can be obtained through Bellhop simulation. incWith the exit glancing angle θ scatt Incident sound pressure transfer function p inc With the scattered sound pressure transfer function p scatt These correspond to Arr.Rcvrangle and Arr.A in the BellhopA runtime file, respectively.

[0048] Example 1

[0049] See Figure 1-8 This embodiment provides a method for forward modeling and pitch angle inversion of seabed / sea surface reverberation based on the Bellhop ray acoustic model and Lambert scattering law, applied to the calibration of the transmission pitch angle of a deep-sea active sonar system with separate transmitter and receiver locations. (Refer to...) Figure 1 The algorithm flowchart shows that the entire process includes six main steps.

[0050] Step 1: Obtain the acoustic environment parameters required for the simulation. Obtain the required marine environmental parameters for the simulation using historical oceanographic survey databases, on-site disposable probe measurements, or empirical formulas. This embodiment uses a deep-sea environment as an example, with the sea depth set as a preset value, denoted as H (unit: meters). The sound velocity profile uses measured data, such as... Figure 3 As shown, typical deep-sea surface acoustic channels and deep-sea acoustic axis characteristics are presented. The seabed sediment type was determined through sampling and analysis, and its acoustic parameters, including density, P-wave velocity, and absorption coefficient, were obtained. The sea surface scattering coefficient was empirically chosen to be higher than that of most seabeds. These parameters form the basis for constructing the Bellhop simulation environment file (.env).

[0051] Step 2: Obtain the transmission parameters, i.e., input the operating parameters of the transmit-receive active sonar system to be calibrated. These mainly include: the deployment depth of the transmitting and receiving arrays, the center frequency, bandwidth, pulse width, waveform (e.g., LFM, CW), and transmission power of the transmitted signal. These parameters will be used to generate the simulated transmission signal and configure the source and receiver properties in the Bellhop simulation. The transmitting transducer is deployed at a set depth dt=100 meters, and the receiving hydrophone array is deployed at a set depth dr=100 meters. The transmitted signal uses a linear frequency modulated (LFM) signal; here, a LFM signal with a center frequency of 1500 Hz, bandwidth of 500 Hz, and pulse width of 6 seconds is used for the simulation example. The elevation angle is horizontal by default, Δα=5°, α=10°. The horizontal transmit-receive distance R of the simulation system is 300 meters, and the sea depth is 5000 meters.

[0052] Step 3: Acquire the received actual reverberation signal. In the actual operating sea area, operate the sonar system to transmit the specified signal according to the above parameters, and simultaneously start the data acquisition and storage program of the receiving array. After the received signal is pre-amplified, bandpass filtered, and analog-to-digital converted, the original reverberation time series data is obtained, denoted as r[n]. The sampling rate is set according to the signal bandwidth based on the Nyquist theorem. This data contains the superposition of surface reverberation, seabed reverberation, and volumetric reverberation, and is the target vector for subsequent matching and inversion.

[0053] Step 4: Determine the pitch angle search range and perform iterative simulation. Let the sonar pitch angle to be inverted be θ. Based on the coarse measurement data from the platform's attitude sensors and historical installation records, set a search range [θ-α, θ+α] that includes the true value. Within this range, iterate through the range with a fixed step size Δα according to the required accuracy. For each assumed pitch angle value θ... i Perform the following simulation operations in sequence:

[0054] Step A: Configure the Bellhop environment file. Set the currently assumed pitch angle θ. i The vertical directional deflection of the emitted sound source. Since it's a separate transmit and receive system, the complete sound field of the scattering process is jointly determined by the sound field along the incident path ("emission → scattering element") and the sound field along the exit path ("scattering element → receiver"), requiring separate propagation models to be constructed. (Refer to...) Figure 2 The simulation principle shown requires configuring four sets of .env environment files: File 1, used to calculate the incident path to the seabed: describes the sound propagation from "emission → seabed scattering element", with the sound source located at depth dt. In File 1, the sound source pointing angle is configured to face the seabed, i.e., the angle with the horizontal plane is θ. i The receiver array is discretely deployed along the seabed interface; File 2 is used to calculate the incident path to the sea surface: describing the sound propagation from "emission → sea surface scattering element", with the sound source located at depth dt. In File 2, the sound source pointing angle is configured to face the sea surface, i.e., the angle with the horizontal plane is θ. i File 1, 2, and 3 are used to calculate the sound pressure transmission path from the seabed: Based on the acoustic reciprocity theorem, the actual receiving array position is set as an equivalent sound source at a depth of dr. A virtual receiver array is discretized at spatial intervals on the seabed interface. Bellhop is used to extract the sound pressure amplitude and grazing angle from the equivalent sound source to each virtual receiver. This result is numerically equivalent to the sound pressure transfer function from each seabed scattering element to the receiving array. File 4 is used to calculate the sound pressure transmission path from the sea surface: Based on the acoustic reciprocity theorem, the actual receiving array position is set as an equivalent sound source at a depth of dr. A virtual receiver array is discretized at spatial intervals on the sea surface interface. Similarly, the sound pressure transfer function of the sea surface transmission path is obtained. All four sets of files must contain complete sound velocity profiles, sea depths, seabed acoustic parameters, and corresponding geometric configurations.

[0055] Step B: Run the ray acoustic simulation. Call the Bellhop model, run mode A (amplitude and delay) and run the above four sets of environment files to calculate and store the arrival information (amplitude, delay, grazing angle) of all intrinsic sound rays.

[0056] Step C: Calculate the reverberant impact response. Based on ray acoustics theory and Lambert's scattering law, for the seabed (and similarly for the sea surface), the seabed interface is discretized along the distance direction into a series of tiny scattering elements, each element having an area of... ΔS k For any surface element, traverse all intrinsic acoustic rays emitted to that surface element and all intrinsic acoustic rays connected to that surface element and received in sub-step B, combining them pairwise to form an "incident-scattering-emission" link. Its core calculation follows the formula below:

[0057]

[0058] f(θ) inc θ scatt =μsinθ inc sinθ scatt

[0059] By superimposing the intensity contributions of all surface elements and all ray combinations according to time delay, θ can be obtained. i The reverberative impact response at the seabed and the reverberative impact response at the sea surface are added together to form the total reverberative impact response.

[0060] Step D: Generate the theoretical reverberation signal. The total reverberation impulse response obtained in Step C is linearly convolved with the transmitted signal copy of this embodiment to obtain the theoretical reverberation signal at the current assumed pitch angle θ. i The theoretical reverberation signal below.

[0061] After the above traversal, a set (2α / Δα in total) of theoretical reverberation signals corresponding to different assumed pitch angles will be obtained. Figures 4 to 8 Examples of theoretical reverberation signal envelopes under five assumed pitch angles are presented in turn. It can be intuitively observed that as the absolute value of the pitch angle increases, the arrival time interval between the sea surface and seabed reverberation gradually decreases; and when the launch pitch angle is deflected upward or downward by the same angle, there are subtle differences in the initial arrival structure of the seabed reverberation, which provides a physical basis for subsequent symbol discrimination.

[0062] Step 5: Similarity Calculation and Pitch Angle Estimation. Each of the theoretical reverberation signals generated in Step 4 is compared with the actual reverberation signals obtained in Step 3 to calculate their similarity. This invention uses Normalized Cross-Correlation (NCC) as the quantification of similarity. NCC, by normalizing the mean and variance of the signals, can effectively measure the similarity of two signals in waveform structure. Its value range is [-1, 1], with values ​​closer to 1 indicating higher similarity. The specific calculation formula is as follows:

[0063]

[0064] Where, r i Let s be the instantaneous amplitude of the actual signal at the i-th sampling point. i Let be the instantaneous amplitude of the simulated signal at the i-th sampling point. This represents the mean of the signal. In MATLAB, the NCC is calculated using the xcorr function.

[0065] Traverse all θ i Then, the curve of NCC value changing with pitch angle is obtained. Due to the symmetry of the beam's vertical pointing, this curve usually shows two similar peaks near θ = +θ0 and θ = -θ0, and the two values ​​are very close, corresponding to the case where the absolute values ​​of the pitch angles are the same but the directions are opposite. At this point, further sign determination is required.

[0066] Step 6: Pitch Angle Sign Determination. First, perform a Hilbert transform on the measured reverberation signal r[n] to obtain the modulus of its analytic signal, i.e., the envelope Er[n]. At the leading edge of the envelope Er[n], detect the two earliest significant local maxima and record their corresponding times t1 and t2. These times t1 and t2 represent the reverberation at the strong scattering interface that first reaches the receiver. Then, based on the known sea depth H, transmission depth dt, reception depth dr, and measured average sound velocity c, calculate the theoretical arrival times t of the seabed reverberation and sea surface reverberation under the vertical incidence approximation. b and t s :

[0067]

[0068]

[0069] Where the average sound velocity *c* is taken as the average value across the entire ocean depth, and *R* is the horizontal distance between the transmitter and receiver. This step can also utilize Bellhop simulation results, extracting local maxima points from the simulation results to obtain the theoretical arrival times *t* for seabed and surface reverberation. b and t sCompare the elevation angles with t1 and t2, and select the one that most closely matches the theoretical time as the correct estimate; if t1 is closer to t2, the elevation angle is lower. b This indicates that the transmitted beam first reaches the seabed, therefore the elevation angle should be negative (downward); conversely, it should be positive (upward). The final output shows the calculated elevation angle with the correct sign. This result can be cross-validated with prior knowledge of installation deviations.

[0070] Example 2

[0071] This embodiment is basically the same as Embodiment 1, except that the propagation model is replaced and the similarity index is changed, so as to demonstrate that the technical solution of the present invention has multiple implementation paths and is not limited to a specific model and index.

[0072] In steps 1, 2, and 3, the environmental parameters, system parameters, and the method for obtaining the measured reverberation signal remain unchanged. In the cyclic forward modeling of step 4, the Bellhop ray acoustic model is replaced with a parabolic equation model to adapt to scenarios with lower frequencies or strong horizontal refraction variations. The parabolic equation model obtains the amplitude and phase distribution of the sound field across the entire field by iteratively solving the parabolic equation, allowing the extraction of complex sound pressure on each scattering surface element, and then combining the contributions of the incident and scattering paths. The scattering model still uses Lambert's law. The generation process of the theoretical reverberation signal remains unchanged.

[0073] In the similarity calculation in step 5, the normalized cross-correlation is replaced with a frequency-domain-based similarity index, such as the cross-spectral density phase-weighted coherence coefficient. The zero-delay cross-spectral coefficients of the measured signal and each theoretical signal are selected as the matching metric, and the curves varying with the elevation angle are obtained, and the absolute peak value is extracted. The subsequent symbol discrimination steps still use the envelope detection and geometric theoretical time-of-arrival comparison method from Example 1.

[0074] Furthermore, in another variant, the transmitted signal can be a hyperbolic frequency-modulated signal, whose Doppler invariance improves the matching robustness to the reverberation of the moving platform. The scattering model can also be replaced, depending on the actual seabed conditions, with a perturbation method or Kirchhoff approximation model that considers the roughness spectrum, to more accurately characterize the backscattering intensity at high frequencies.

[0075] These alternative solutions are all conventional variations within the scope of the inventive concept of this invention and do not affect the overall process framework or the core inventive points. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the protection scope of this invention.

[0076] Explanation of relevant technical terms in the above embodiments:

[0077] Separate transmission and reception: refers to an underwater acoustic detection mode in which the transmitting and receiving points of the sound waves are located at different locations.

[0078] Pitch angle: In the vertical plane, the angle between the beam direction of the sonar array and the horizontal plane.

[0079] Ray acoustics: a high-frequency approximation method for propagating sound wave energy along a specific path (sound ray).

[0080] Bellhop model: A widely used underwater acoustic propagation loss and arrival structure calculation model based on ray acoustics.

[0081] Lambert's scattering law is an empirical physical law that describes the scattering intensity at a rough interface as being proportional to the product of the sine values ​​of the incident angle and the scattering angle.

[0082] Intrinsic ray: A ray that, given the locations of the sound source and receiver, can connect the two points and satisfy Snell's law.

[0083] Grazing angle: The angle between the direction of sound ray propagation and the interface (sea surface or seabed).

[0084] Reverberant impulse response: describes the response of a reverberant channel to a unit impulse excitation, and includes the time delay and amplitude information of all multipath scattering paths.

[0085] Matching field processing: A technique that uses a propagation model to generate a copy field and performs correlation matching with the measured field to achieve target localization or environmental parameter inversion.

[0086] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for calculating the elevation angle of active sonar based on reverberation signals, characterized in that, Includes the following steps: Parameter acquisition steps: Acquire marine environmental parameters of the operating area and operating parameters of the active sonar system to be calibrated; The measured signal acquisition steps are as follows: After the active sonar system transmits the designated signal in the actual operating sea area, the original reverberation time series data output by the receiving array is synchronously collected and stored as the measured reverberation signal. The iterative forward modeling steps are as follows: Set a search range and a search step size for pitch angles, traverse each assumed pitch angle value within the range, and generate the corresponding theoretical reverberation signal for each assumed pitch angle value through joint forward modeling of the underwater acoustic propagation model and the interface scattering model. Pitch angle absolute value estimation step: For all theoretical reverberation signals generated in the cyclic forward modeling step, perform similarity calculation with the measured reverberation signals one by one, and extract the absolute value of the assumed pitch angle corresponding to the similarity peak as the absolute value of the actual working pitch angle of the active sonar system; Symbol discrimination step: The measured reverberation signal is envelope detected to detect the arrival time of its early strong interface scattering reverberation, and matched with the theoretical arrival times of seabed and sea surface reverberation calculated based on the system geometry to determine the correct sign of the pitch angle, thereby obtaining the final pitch angle calculation result.

2. The method for calculating the elevation angle of active sonar based on reverberation signals according to claim 1, characterized in that, The process of generating a theoretical reverberation signal for each assumed pitch angle value in the cyclic forward modeling step specifically includes: Step A: Using the currently assumed pitch angle value as the sound source pointing angle, and combining the marine environmental parameters and operating parameters, configure the environmental file for the underwater acoustic propagation model; Step B: Call the ray acoustic model to perform intrinsic sound ray tracking, calculate and store the arrival information of all intrinsic sound rays, the arrival information including at least the arrival amplitude, propagation delay, incident grazing angle and exit grazing angle; Step C: Traverse all possible two-way sound path combinations of "emitter → scatterer" and "scatterer → receiver", introduce the interface scattering model, and calculate the interface reverberation impact response; Step D: Convolve the calculated reverberant impact response with the transmitted signal copy to generate the theoretical reverberant signal under the current assumed pitch angle.

3. The method for calculating the elevation angle of active sonar based on reverberation signals according to claim 2, characterized in that: The underwater acoustic propagation model is the Bellhop ray acoustic model, and the interface scattering model is the Lambert scattering law.

4. The method for calculating the elevation angle of active sonar based on reverberation signals according to claim 3, characterized in that, In step C, the calculation of the reverberant impact response based on Lambert's scattering law specifically involves the following: for any scattering surface element, its contribution to the reverberation intensity is proportional to the square of the modulus of the incident sound pressure transfer function, the square of the modulus of the scattered sound pressure transfer function, the scattering coefficient, the product of the sine of the incident grazing angle and the sine of the outgoing grazing angle, and the product of the area of ​​the scattering surface element.

5. The method for calculating the elevation angle of active sonar based on reverberation signals according to claim 4, characterized in that: For a separate transmit and receive system, step A requires configuring four independent environment files, corresponding to the incident path simulations for transmitting to the seabed and transmitting to the sea surface, and the outgoing path simulations for receiving from the seabed and receiving from the sea surface, based on the acoustic reciprocity theorem and setting the receiver position as an equivalent sound source.

6. The method for calculating the elevation angle of active sonar based on reverberation signals according to claim 1, characterized in that: In the pitch angle absolute value estimation step, the similarity calculation adopts the normalized cross-correlation algorithm, the mathematical expression of which is: Where, r i Let s be the instantaneous amplitude of the actual signal at the i-th sampling point. i Let be the instantaneous amplitude of the simulated signal at the i-th sampling point. This is the mean of the signal.

7. The method for calculating the elevation angle of active sonar based on reverberation signals according to claim 1, characterized in that: In the symbol discrimination step, envelope detection is achieved by performing a Hilbert transform on the measured reverberation signal and calculating the modulus.

8. The method for calculating the elevation angle of active sonar based on reverberation signals according to claim 1 or 7, characterized in that: The arrival time t of the reverberation theory of the seabed and sea surface b and t s Calculation based on approximate geometric relationships of perpendicular incidence: Among them, t b t is the theoretical arrival time of the first-order scattering reverberation from the seabed. s Let H be the theoretical arrival time of the first-order scattering reverberation from the sea surface, and d be the sea depth. t For launch depth, d r R is the receiving depth, R is the horizontal distance between transmission and reception, and c is the average speed of sound in water; or the local maxima of the reverberation envelopes of the seabed and sea surface can be extracted directly from the ray acoustic simulation results in the cyclic forward modeling step as the theoretical arrival time.

9. The method for calculating the elevation angle of active sonar based on reverberation signals according to claim 1, characterized in that: The marine environmental parameters include at least sea depth, sound velocity profile, seabed sediment type and its acoustic characteristics; the operating parameters include at least the depth of the transmitting array, the depth of the receiving array, the center frequency of the transmitted signal, bandwidth, pulse width and signal waveform; the pitch angle search range is set according to prior knowledge or engineering experience and is a symmetrical angle interval.

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