Underwater target distance and depth estimation method based on deep sea near-seabed very low frequency and high frequency sound field interference structure

Abstract

The application provides an underwater target distance and depth estimation method based on deep sea near seabed very low frequency and high frequency sound field interference structure. First, by assuming a sound source depth, combining the direct wave + seabed reflection wave sound field calculation formula, the array received sound pressure and propagation loss when the sound source is located at different distances under the condition of very low frequency are obtained, and then the simulation propagation loss and the actual propagation loss are matched and related to obtain the target distance information. Then, combining the direct wave + sea surface reflection wave sound field calculation formula, the array received sound pressure and propagation loss when the sound source is located at different depths under the condition of high frequency are obtained, and finally the target depth estimation is realized through the matching processing between the simulation and the actual propagation loss. The basic principle and implementation scheme of the application have been verified by computer numerical simulation, and the results show that the underwater target distance and depth estimation method based on deep sea near seabed very low frequency and high frequency sound field interference structure can realize the deep sea direct sound area near sea surface target ranging and depth determination.

Description

Technical Field

[0001] This invention relates to the field of acoustic positioning technology, specifically a method for estimating the distance and depth of underwater targets based on the interference structure of extremely low-frequency and high-frequency acoustic fields near the seabed in the deep sea. Background Technology

[0002] The deep-sea direct acoustic zone is a key area for underwater target detection, characterized by stable acoustic field interference structures and strong environmental adaptability. Therefore, conducting research on highly reliable target localization in the direct acoustic zone is of great significance for improving the accuracy and robustness of target localization.

[0003] In the direct-sound region, the multipath grazing angle is highly sensitive to target distance, and the target distance information can be obtained by estimating the signal grazing angle using a vertical array. Zheng Guangying et al. found that the acoustic field interference structure is sensitive to the sound source depth under high-frequency conditions, and proposed a depth estimation method based on this. This method first uses the signal grazing angle to achieve target ranging; then, it simulates the acoustic field interference structure based on the estimated grazing angle and distance; finally, it obtains the target depth information by matching the simulated interference structure with the measured interference structure. Theoretically, this method requires the array element spacing to be no more than half a wavelength; if this condition cannot be met, grating lobes will appear in the beamforming result, severely affecting the estimation of the grazing angle and thus reducing the estimation performance of target distance and depth. Although this paper presents good experimental results, it does not explain the grating lobe problem. Furthermore, high-frequency arrays are also highly susceptible to the effects of ocean currents such as turbulence.

[0004] The aforementioned theory posits that the acoustic field structure in the direct sound region, under high-frequency conditions, primarily originates from the interference between the direct wave and the sea surface reflected wave. However, this invention reveals that under extremely low-frequency conditions, the acoustic field structure is mainly formed by the interference between the direct wave and the seabed reflected wave, and this interference structure is sensitive to distance but insensitive to depth. In real-world navigation, the periodic motion of large mechanical equipment often generates high-frequency line spectra, while propeller shaft frequencies and their harmonics contribute to the extremely low-frequency line spectra. Therefore, this invention proposes a method for estimating the distance and depth of underwater targets based on the interference structure of extremely low-frequency and high-frequency acoustic fields near the deep seabed. Summary of the Invention

[0005] The technical problem this invention aims to solve is to provide a method for estimating the distance and depth of underwater targets based on the interference structure of extremely low-frequency and high-frequency acoustic fields near the seabed in the deep sea. First, the target distance is estimated by matching the extremely low-frequency interference structure. Finally, using the estimated distance as a known quantity, the depth is estimated by matching the high-frequency interference structure at that distance point. The method proposed in this invention does not require the array to satisfy half-wavelength constraints, nor does it require beamforming to estimate the grazing angle of the signal, thus avoiding dependence on grazing angle information. Furthermore, it is robust to disturbances in the marine environment, such as turbulence.

[0006] To address the aforementioned technical problems, embodiments of the present invention provide the following technical solution: a method for estimating the distance and depth of underwater targets based on the interference structure of extremely low-frequency and high-frequency acoustic fields near the seabed in the deep sea, comprising: For the target's extremely low frequency line spectrum, the actual array received sound pressure and propagation loss were calculated, and a calculation model for the sound pressure of the direct wave plus the seabed reflected wave was constructed. Assuming a sound source depth, the array received sound pressure and propagation loss are simulated using the direct wave + seabed reflected wave sound field calculation model at different sound source distances. The target distance is estimated by matching the simulated propagation loss with the actual propagation loss at different distances. For the target high-frequency line spectrum, the actual array received sound pressure and propagation loss are calculated, and a calculation model of the sound field of direct wave + sea surface reflected wave is constructed; Based on the target distance estimate, the sound field calculation model of the direct wave + sea surface reflected wave is used to simulate the array received sound pressure and propagation loss at different sound source depths. The target depth is estimated by matching the simulated propagation loss at different depths with the actual propagation loss.

[0007] Furthermore, the construction of the direct wave + seabed reflected wave sound pressure calculation model specifically involves: Let the true depth of the sound source be With a horizontal distance of r between the transmitter and receiver, a receiving depth of z, and transmitting an extremely low frequency narrowband signal, assuming the seabed is an absolutely hard boundary, the sound field expression can be obtained using the virtual source method model as follows: ; in, ; Among them, wave number f is the signal frequency, c is the speed of sound in the sea, and h is the sea depth; Considering the sound source is located near the sea surface, i.e. The receiving point is located near the seabed, that is ; In deep-sea environments, where the depth h is relatively large, the path distances of direct waves and reflected waves from the seabed are approximately equal. , This represents the slant distance between the receiving point and the projection of the sound source onto the sea surface. If the amplitudes are approximated as the same, the phase difference is determined by the path difference, which is calculated as follows: ; Therefore, sound pressure can be written as: ; After unfolding, we get: .

[0008] Furthermore, assuming a sound source depth, the array receives sound pressure and propagation loss at different sound source distances using a direct wave + seabed reflected wave sound field calculation model is specifically as follows: Assuming the vertical array has N elements and the element spacing is d, under extremely low frequency conditions, the received sound pressure of each element in the simulated array is calculated using the obtained expression for the sound pressure of the direct wave plus the seabed reflected wave. Specifically, it can be expressed as: ; in, This represents the depth of the i-th element. The propagation loss of the simulated array receiver can then be expressed as: .

[0009] Furthermore, the method of matching the simulated propagation loss with the actual propagation loss at different distances to achieve target distance estimation specifically involves: ; in, To simulate the propagation loss of the array receiver, The actual array reception propagation loss is expressed as: , For the actual array to receive sound pressure; in, This represents the conjugate transpose, and the distance matching coefficient. The distance corresponding to the maximum value is the estimated distance to the target. .

[0010] Furthermore, the construction of the acoustic field calculation model for the direct wave + sea surface reflected wave is specifically as follows: In the deep-sea environment, caused by the interference of direct waves and sea surface reflected waves, the sound pressure at the receiving depth z for the horizontal distance r between the transmitter and receiver can be expressed as: ; in, This represents the glancing angle from the projection of the sound source onto the sea surface to the receiving point. This represents the slant distance between the receiving point and the projection of the sound source onto the sea surface. For the true depth of the sound source, wavenumber f is the signal frequency, and c is the speed of sound of seawater; Assumption Let be the glancing angle from the projection point of the sound source on the sea surface to the first array element. Let be the glancing angle from the projection point to the i-th element, then: ; Where r is the horizontal spacing between the transmitter and receiver, and d is the spacing between array elements. The depth of the first array element. The depth of the i-th array element; , The difference between the two can be expressed as: ; The depth of the Nth array element; make The sound pressure of the i-th element can be expressed as: .

[0011] Furthermore, based on the target distance estimate, the simulation of the array-received sound pressure and propagation loss at different sound source depths using the direct wave + sea surface reflected wave sound field calculation model is as follows: The obtained distance estimation results Substituting the direct wave + sea surface reflected wave sound field calculation model, the simulated sound pressure expression for each array element at different sound source depths is as follows: ; The received sound pressure of each element in the simulation array was calculated using the obtained expression for the sound pressure of the direct wave plus the sea surface reflected wave. , represented as: ; in, This represents the depth of the i-th element. Then the kth array element The corresponding propagation loss expression is: .

[0012] Furthermore, the method of matching the simulated propagation loss at different depths with the actual propagation loss to achieve target depth estimation is specifically expressed as follows: ; in, To simulate the propagation loss of the array receiver, The actual array reception propagation loss is expressed as: , For the actual array to receive sound pressure; in, This represents the conjugate transpose, and the deep matching coefficient. The depth corresponding to the maximum value is the estimated depth of the target. .

[0013] The beneficial effects of the above-described technical solution of the present invention are as follows: This invention addresses the problem of ranging and determining the depth of near-surface sound sources in deep-sea environments using narrowband signals. It proposes an underwater target distance-depth estimation method based on an interference structure of extremely low-frequency and high-frequency sound fields near the seabed. First, by assuming a sound source depth and combining the calculation formulas for the direct wave + seabed reflected wave sound field, the array-received sound pressure and propagation loss at different distances from the sound source under extremely low-frequency conditions are obtained. Then, the simulated propagation loss is matched with the actual propagation loss to obtain the target distance information. Next, combining the calculation formulas for the direct wave + sea surface reflected wave sound field, the array-received sound pressure and propagation loss at different depths from the sound source under high-frequency conditions are obtained. Finally, the target depth is estimated by matching the simulated and actual propagation losses. Using the underwater target distance-depth estimation method based on the interference structure of extremely low-frequency and high-frequency sound fields near the seabed proposed in this invention, ranging and depth determination of near-surface targets in deep-sea direct sound zones can be achieved. Attached Figure Description

[0014] Figure 1 This is a flowchart of the method of the present invention.

[0015] Figure 2 This is a distribution diagram of near-seabed propagation loss under extremely low and high frequency conditions according to an embodiment of the present invention.

[0016] Figure 3 This is a distribution diagram of the propagation loss of direct wave + seabed reflected wave at different sound source depths according to an embodiment of the present invention.

[0017] Figure 4 This is a cross-sectional view of the speed of sound in an embodiment of the present invention.

[0018] Figure 5 This is a diagram showing the distance and depth matching results of a target at a distance of 3.7 km and a depth of 60 m according to an embodiment of the present invention.

[0019] Figure 6 This is a graph showing the distribution of estimation error of a water surface target (7m) as a function of distance in an embodiment of the present invention.

[0020] Figure 7 This is a graph showing the distribution of estimation error of an underwater target (70m) as a function of distance in an embodiment of the present invention. Detailed Implementation

[0021] To make the technical problems, technical solutions and advantages of the present invention clearer, a detailed description will be given below in conjunction with the accompanying drawings and specific embodiments.

[0022] Example 1 refer to Figure 1As shown, this invention proposes a method for estimating the distance and depth of underwater targets based on the interference structure of extremely low-frequency and high-frequency acoustic fields near the seabed in the deep sea. First, the expressions for the interference structure in the vertical direction between the direct wave and the seabed reflected wave, and between the direct wave and the sea surface reflected wave, are derived theoretically. Then, the target distance information is obtained by matching and correlating the interference structure of the direct wave + seabed reflected wave under extremely low-frequency conditions with the measured interference structure. Next, using the estimated distance as a known quantity, the interference structure of the direct wave + sea surface reflected wave at that distance point under high-frequency conditions is calculated. Finally, the target depth can be estimated by matching simulation and measured interference structures. The specific technical solution is as follows: A method for estimating the distance and depth of underwater targets based on the interference structure of extremely low-frequency and high-frequency acoustic fields near the seabed in the deep sea includes the following steps: Step 1: Simulate the near-seabed sound field structure using direct waves and seabed reflected waves. The actual depth of the sound source is... The horizontal distance between the transmitter and receiver is r, the receiving depth is z, and the transmitted signal is an extremely low frequency narrowband signal. Assuming the seabed is an absolutely hard boundary, the sound field expression can be obtained using the virtual source method model: ; in, ; Among them, wave number f is the signal frequency, c is the speed of sound in the sea, and h is the sea depth.

[0023] Considering the sound source is located near the sea surface ( The receiving point is located near the seabed. Due to the large depth h in the deep-sea environment, the path distances of direct waves and seabed reflected waves are approximately equal, i.e. , This represents the slant distance between the receiving point and the projection of the sound source onto the sea surface. Therefore, the amplitudes can be approximated as the same, while the phase difference is determined by the path difference, which is calculated as follows: ; Therefore, sound pressure can be written as: ; After unfolding, we get: ; Under extremely low frequency conditions, the sound field simulated by Krakenc is used as the actual sound field. Figure 2The propagation loss distribution near the seabed is presented under the conditions of a frequency of 100Hz, a horizontal distance of 4.5km between the transmitter and receiver, and a source depth of 50m. It can be seen that although the sound field constructed using the direct wave + seabed reflected wave differs somewhat in amplitude from the actual sound field, the positions of the peak and trough values ​​match well, indicating that this method is feasible for simulating near-seabed interference structures. Furthermore, Figure 3 The propagation loss distribution of the direct wave + seabed reflected wave sound field at different source depths is presented under the same transmitter-receiver spacing. It is easy to see that for a near-surface target, the source depth has a negligible impact on the sound field model calculation.

[0024] Step Two: Target Distance Estimation. Assuming the vertical array has N elements and the element spacing is d, under extremely low frequency conditions, the acoustic pressure received by each element of the simulated array is calculated using the direct wave + seabed reflected wave acoustic pressure expression obtained in Step One. : ; in, Let represent the depth of the i-th array element. Assume the actual array receives sound pressure level as . The propagation loss of the simulated and actual array reception can be expressed as: ; The target distance can be estimated by matching the simulated propagation loss with the actual propagation loss at different distances. The correlation matching process is as follows: ; in, This indicates taking the conjugate transpose. Distance matching coefficients. The distance corresponding to the maximum value is the estimated distance to the target. .

[0025] Step 3: Simulate the near-seabed acoustic field structure using direct waves and sea surface reflected waves. In a deep-sea environment, the sound pressure at the receiving depth z, caused by the interference of direct waves and sea surface reflected waves, can be expressed as follows: ; in, This represents the glancing angle from the projection of the sound source onto the sea surface to the receiving point. Assume... Let be the glancing angle from the projection point of the sound source on the sea surface to the first array element. Let be the glancing angle from the projection point to the i-th array element.

[0026] ; The difference between the two can be expressed as: ; Within the scope of this invention, .make The sound pressure of the i-th element can be expressed as: ; Figure 2 The distribution of near-seabed propagation loss at 3800Hz was also shown. It can be seen that the sound field constructed using the direct wave + sea surface reflected wave matches the actual sound field well in the locations of the peak and trough of propagation loss, and the difference in amplitude between the two is also small. This indicates that using this method to simulate near-seabed propagation loss is feasible. The distance estimation results obtained in step two are then used... Substituting into the above equation, we can obtain the expressions for the received sound pressure of each array element under different sound source depths in the simulation: ; The received sound pressure of each element in the simulation array was calculated using the obtained expression for the sound pressure of the direct wave plus the sea surface reflected wave. , represented as: ; in, This represents the depth of the i-th element. Then the kth array element The corresponding propagation loss expression is: .

[0027] Step 4: Achieve target depth estimation. Similar to Step 2, scan the depths of different sound sources under high-frequency conditions. The received sound pressure of the simulated array was obtained as follows: The actual sound pressure received by the array is The propagation loss of the simulated and actual array receivers can be expressed as: ; By matching the simulated propagation loss with the actual propagation loss at different depths, we can obtain the following correlation: ; Among them, the depth matching coefficient The depth corresponding to the maximum value is the estimated depth of the target. .

[0028] Finally, a distance and depth matching coefficient diagram at a specific sound source location is presented, and the distance and depth measurement errors of surface and underwater targets are given as a function of distance, to verify the effectiveness of the method of the present invention.

[0029] Example 2 The underwater target distance-depth estimation method based on the interference structure of extremely low-frequency and high-frequency sound fields near the seabed of the present invention is mainly used for distance and depth determination of targets in deep-sea direct sound zones. Specifically, it includes the following steps: Step 1: The simulation standard environment parameters are as follows: The target signal contains two line spectra with frequencies of 100Hz and 3800Hz respectively. Two sound source depths are considered: 7m and 70m, representing surface and underwater targets respectively. The vertical linear array has an element spacing of 1m, 201 elements, and element 1 has a depth of 3700m. The P-wave velocity on the seabed is 1600m / s, and the seabed density is 1.5. The attenuation of P-waves on the seabed is 0.5. Deep-sea sound speed profile, such as Figure 4 As shown. First, the measurement field is set according to standard environmental parameters, and the Krakenc model is used to calculate the actual array received sound pressure corresponding to the 100Hz line spectrum. The actual reception propagation loss can be calculated using the following formula. .

[0030] ; Step 2: Assuming the sound source depth is any value between 0 and 200m, calculate the array-received sound pressure using the following formula. and transmission loss .

[0031] ; ; in, ; Step 3: Calculate the simulation propagation loss using the following formula. Compared with actual transmission loss Perform matching correlation, distance matching coefficient The distance corresponding to the maximum value is the estimated distance to the target. .

[0032] ; Step 4: Calculate the actual array received sound pressure level corresponding to the 3800Hz line spectrum using the Bellhop model. The actual reception and propagation loss can be obtained using the following formula. .

[0033] ; Step 5: Based on the distance estimates obtained in Step 3, scan the depths of different sound sources. Computation array receives sound pressure The received sound pressure of the i-th array element can be expressed as: ; The array receiver propagation loss is calculated using the following formula. .

[0034] ; Step Six: Calculate the simulation propagation loss using the following formula. Compared with actual transmission loss Perform matching correlation, deep matching coefficient The depth corresponding to the maximum value is the estimated depth of the target. .

[0035] ; The estimation results for distance and depth are as follows: Figure 5 , Figure 6 , Figure 7 As shown. From Figure 5 As can be seen, the distance and depth estimation errors are very small, with a sharp main peak and low side lobes, which is beneficial for target localization. The estimation performance for surface targets is as follows: Figure 6 As shown, it is not difficult to see that the distance estimation performance is good, with a maximum error of no more than 0.3km, while the depth estimation error is 4m. For a target with a true depth of 7m, this error is relatively large, but it can still basically reflect that the target is a surface target. Figure 7 The performance of this method for estimating underwater targets is demonstrated. It can be seen that the maximum distance estimation error does not exceed 0.2 km, indicating that the method's distance estimation performance is good. The depth estimation error generally increases with increasing distance. When the actual target distance reaches 5.9 km, the error reaches 6 m. For an underwater target at a depth of 70 m, this error is still within an acceptable range.

[0036] Figure 2 The distribution of near-seabed propagation loss at frequencies of 100Hz and 3800Hz is shown, and the simulation results of the model of this invention are compared with those of Krakenc and Bellhop. Figure 3 This demonstrates the impact of changes in sound source depth on the calculated sound field results of direct wave + seabed reflected wave; Figure 4 A profile of deep-sea sound speed is provided. Figure 5 The distance and depth matching results for a target at a distance of 3.7km and a depth of 60m are displayed. Figure 6 This demonstrates how the estimation error of a surface target (7m) varies with distance; Figure 7 The estimation error of an underwater target (70m) varies with distance. Table 1 shows the meanings of relevant symbols in this invention: Table 1 The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for estimating the distance and depth of underwater targets based on the interference structure of extremely low-frequency and high-frequency acoustic fields near the seabed in the deep sea, characterized in that... include: For the target's extremely low frequency line spectrum, the actual array received sound pressure and propagation loss are calculated, and a calculation model of the sound field of direct wave + seabed reflected wave is constructed, specifically as follows: Let the true depth of the sound source be With a horizontal distance of r between the transmitter and receiver, a receiving depth of z, and transmitting an extremely low frequency narrowband signal, assuming the seabed is an absolutely hard boundary, the sound field expression obtained using the virtual source method model is: ； in, ； Among them, wave number f is the signal frequency, c is the speed of sound in the sea, and h is the sea depth; Considering the sound source is located near the sea surface, i.e. The receiving point is located near the seabed, that is ; In deep-sea environments, where the depth h is relatively large, the path distances of direct waves and reflected waves from the seabed are approximately equal. , This represents the slant distance between the receiving point and the projection of the sound source onto the sea surface. If the amplitudes are approximated as the same, the phase difference is determined by the path difference, which is calculated as follows: ； The sound field can then be written as: ； After unfolding, we get: ； Assuming a sound source depth, the array received sound pressure and propagation loss are simulated using the direct wave + seabed reflected wave sound field calculation model at different sound source distances. The target distance is estimated by matching the simulated propagation loss with the actual propagation loss at different distances. For the target high-frequency line spectrum, the actual array received sound pressure and propagation loss are calculated, and a calculation model of the sound field of direct wave + sea surface reflected wave is constructed, specifically as follows: In a deep-sea environment, the interference between the direct wave and the reflected wave from the sea surface causes the sound field at the receiving depth z, with a horizontal distance r between the transmitter and receiver, to be expressed as: ； in, This represents the glancing angle from the projection of the sound source onto the sea surface to the receiving point. This represents the slant distance between the receiving point and the projection of the sound source onto the sea surface. For the true depth of the sound source, wavenumber f is the signal frequency, and c is the speed of sound of seawater; Assumption Let be the glancing angle from the projection point of the sound source on the sea surface to the first array element. Let be the glancing angle from the projection point to the i-th element, then: ； Where r is the horizontal spacing between the transmitter and receiver, and d is the spacing between array elements. The depth of the first array element. The depth of the i-th array element; , The difference between the two is expressed as: ； The depth of the Nth array element; make The sound field of the i-th element is represented as: ； Based on the target distance estimate, the sound field calculation model of the direct wave + sea surface reflected wave is used to simulate the array received sound pressure and propagation loss at different sound source depths. The target depth is estimated by matching the simulated propagation loss at different depths with the actual propagation loss.

2. The underwater target distance and depth estimation method based on the interference structure of extremely low-frequency and high-frequency acoustic fields near the seabed in deep sea, as described in claim 1, is characterized in that... The sound field calculation model of the direct wave + seabed reflected wave is used to simulate the array received sound pressure and propagation loss at different sound source distances, specifically: Assuming the vertical array has N elements and the element spacing is d, under extremely low frequency conditions, the received sound pressure of each element in the simulated array is calculated using the obtained expression for the sound pressure of the direct wave plus the seabed reflected wave. Specifically, it means: ； in, This represents the depth of the i-th element. The simulated array receive propagation loss is expressed as: 。 3. The underwater target distance and depth estimation method based on the interference structure of extremely low-frequency and high-frequency acoustic fields near the seabed in deep sea, as described in claim 1, is characterized in that... The method of matching the simulated propagation loss with the actual propagation loss at different distances to achieve target distance estimation is as follows: ； in, To simulate the propagation loss of the array receiver, The actual array reception propagation loss is expressed as: , For the actual array to receive sound pressure; in, This represents the conjugate transpose, and the distance matching coefficient. The distance corresponding to the maximum value is the estimated distance to the target. .

4. The underwater target distance and depth estimation method based on the interference structure of extremely low-frequency and high-frequency acoustic fields near the seabed in deep sea, as described in claim 1, is characterized in that... The simulation of array-received sound pressure and propagation loss at different sound source depths, based on the target distance estimate and using the direct wave + sea surface reflected wave sound field calculation model, is as follows: The obtained distance estimation results Substituting the direct wave + sea surface reflected wave sound field calculation model, the simulated sound pressure expression for each array element at different sound source depths is as follows: ； The received sound pressure of each element in the simulation array was calculated using the obtained expression for the sound pressure of the direct wave plus the sea surface reflected wave. , represented as: ； in, This represents the depth of the i-th element. Then the kth array element The corresponding propagation loss expression is: 。 5. The underwater target distance-depth estimation method based on the interference structure of extremely low-frequency and high-frequency acoustic fields near the seabed in deep sea, as described in claim 1, is characterized in that... The method of matching the simulated propagation loss at different depths with the actual propagation loss to achieve target depth estimation is specifically expressed as follows: ； in, To simulate the propagation loss of the array receiver, The actual array reception propagation loss is expressed as: , For the actual array to receive sound pressure; in, This represents the conjugate transpose, and the deep matching coefficient. The depth corresponding to the maximum value is the estimated depth of the target. .

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