An autonomous working method of a shallow seismic profiler based on seafloor tracking technology

Abstract

The present invention discloses a self - contained working method of a shallow - layer profiler based on seafloor tracking technology, which emits detection signals, receives feedback signals until effective feedback signals are obtained. The feedback signals of the current frame are saved while the corresponding seafloor position is tracked. The first - arrival wave energy is calculated according to the seafloor position, and the system gain is adjusted. The time - varying gain is adjusted according to the signal characteristics of two sections of signals below the seafloor calculated based on the seafloor position. The seafloor position is compared with the previous seafloor position, and the signal emission times are adjusted. The measurement range, signal period, and signal form are adjusted in real - time based on the seafloor position. Finally, the above steps are repeated. The present invention changes the traditional operation mode that requires real - time interaction during shallow - profile measurement. Once it enters the measurement state, the device will automatically adjust each measurement parameter according to the actual measurement situation without human intervention, improving the measurement effectiveness and accuracy.

Description

Technical Field

[0001] The present invention belongs to the field of marine geological exploration, and particularly relates to a self-contained working method of a shallow stratum profiler based on seabed tracking technology. Background Art

[0002] A shallow stratum profiler is a geophysical exploration instrument developed based on the acoustic principle for continuously detecting the structure and tectonics of the underwater shallow stratum. Its working principle is as follows: When sound waves propagate in a medium, reflections occur when encountering interfaces with different acoustic properties. For example, assume seawater is medium 1 with a density of ρ1, a sound velocity of V1, and an acoustic impedance of Z1 = ρ1V1. Stratum 1 is medium 2 with a density of ρ2, a sound velocity of V2, and an acoustic impedance of Z2 = ρ2V2. Stratum 2 is medium 3 with a density of ρ3, a sound velocity of V3, and an acoustic impedance of Z3 = ρ3V3. The interfaces between the three are R1, R2, and R3 respectively. When sound waves propagate in seawater and encounter these interfaces, reflections will occur, and the greater the impedance difference, the stronger the echo signal. These reflected sound waves carry a large amount of useful seabed geological information. By observing and analyzing them, stratum stratification, geological structure, geological properties of sediments, etc. can be obtained.

[0003] According to the propagation law of sound waves, the energy attenuation of the detection beam used in a shallow stratum profiler during propagation mainly comes from two aspects: on the one hand, the spherical diffusion of sound waves causes the sound wave energy to attenuate with distance; on the other hand, it is due to the absorption attenuation of the medium. Therefore, when designing the equipment, compensation for the energy losses in these two aspects will be considered. General sonar systems consider compensation from two aspects: on the one hand, overall amplification of the received signal, which is the system gain; on the other hand, adjusting the gain according to the distance (which can also be considered the order of arrival time of the echo signal). The adjustment amplitude for a short distance is small, and the adjustment amplitude for a long distance is large, which is time-varying gain. For shallow profiling equipment, since penetration information below the seabed is required and the attenuation of sound waves by seabed sediments is very strong, so shallow profiling equipment also performs seabed compensation. Various gain adjustments can be completed at the hardware end of the equipment or implemented under software algorithms, but the prerequisite for processing at the software end is to ensure a certain signal-to-noise ratio of the echo. In addition, in order to obtain the optimal measurement effect, parameters such as the signal period, signal form, and transmission frequency also need to be optimally selected according to the actual situation.

[0004] In order to reduce the requirements for the professional knowledge reserve of sonar operators and improve the convenience of sonar applications, some sonar systems will consider adding an automatic gain control method. For example, the article "Design and Implementation of the Imaging Sonar TVG / AGC Circuit" published by Yang Kang, Yang Cheng, Xia Weijie, etc. in "Electronic Measurement Technology" in 2014 disclosed a normalized TVG / ACG gain control scheme; the article "Improvement and Implementation of a High-Precision Sonar Signal Preprocessing System" published by Miao Kangle, Yang Rijie, and Yang Chengwei in "Chinese Journal of Scientific Instrument" in 2011 mainly realized automatic gain control by means of signal window comparison and width detection. Through consulting relevant materials, the current measurement control of sonar mainly focuses on automatic gain control. The methods used generally adopt the method of window comparison for the overall signal, and the application objects are generally devices such as depth sounders and image sonars with relatively high frequencies and only concerned about the detection situation above the bottom.

[0005] Under the existing technology, traditional shallow profiling equipment is generally hung on the side of the ship's hull or fixed at the bottom of the ship. During measurement, the working state of the equipment can be directly controlled manually through the display and control unit, and the measurement results can be displayed in real time. When the shallow profiling equipment is integrated with an unmanned platform, the communication, synchronization with the platform, and the operation of the equipment, etc., all need to be controlled through the platform, and in many cases, the unmanned platform cannot achieve real-time control. Especially for platforms such as AUVs and UUVs, once they start working, it is completely impossible for the equipment to interact with the operator. Therefore, reasonable control technologies and processing algorithms need to be designed for the robustness of the shallow profiling equipment during operation and the data reception and processing methods. If the system measurement parameters are not adjusted in real time according to specific mission tasks and a fixed preset parameter is used for measurement from beginning to end, it is very likely to cause measurement failure.

[0006] The commonly used automatic gain adjustment methods for current high-frequency depth sounding or image sonars cannot be fully applied to shallow profiling equipment. On the one hand, these devices only focus on the signal in the water part; on the other hand, this type of device only focuses on gain, and for other parameter settings, even including the threshold of gain adjustment, manual intervention is still required. Summary of the Invention

[0007] The technical object of the present invention is to provide a self-contained working method for a shallow layer profiler based on seabed tracking technology to solve the problems in the prior art.

[0008] To solve the above problems, the technical solution of the present invention is as follows:

[0009] A self-contained working method for a shallow layer profiler based on seabed tracking technology, configured for a shallow layer profiling device, includes the following steps:

[0010] S1: Transmit a detection signal, receive each frame of feedback signal, and determine whether the feedback signal of the current frame is valid until a valid feedback signal is obtained;

[0011] S2: Save the feedback signal of the current frame and track the seabed position corresponding to this feedback signal.

[0012] S3: Calculate the first arrival wave energy based on the tracked seabed position, and adjust the system gain according to the calculated first arrival wave energy.

[0013] Calculate the signal characteristics of two segments of the signal below the seabed based on the tracked seabed position, and adjust the time-varying gain according to the signal characteristics of the signal below the seabed.

[0014] Compare the currently tracked seabed position with the previously obtained seabed position, and adjust the number of signal transmissions.

[0015] Based on the currently tracked seabed position, adjust the measurement range, signal period, and signal form in real time.

[0016] S4: After the system gain, time-varying gain, number of signal transmissions, measurement range, signal period, and signal form are adjusted, jump back to the step S1.

[0017] Among them, in the step S1, it specifically includes the following steps:

[0018] Transmit a detection signal, receive the feedback signal of each frame, and determine whether the feedback signal of the current frame is valid. If it is judged to be invalid, the invalid count is incremented by one. When the invalid count reaches the preset threshold, it is determined that the measurement fails and the device is restarted to transmit / receive signals again.

[0019] If it is judged to be valid, the invalid count is cleared, and the measurement parameters and data of the feedback signal of the current frame are saved.

[0020] Among them, in the step S2, specifically:

[0021] S21: Cross-correlate and normalize the detection signal and the transmitted signal.

[0022] S22: Sequentially find the positions greater than 0.3 in the normalized data, and identify them as suspected seabed positions.

[0023] S23: Compare the suspected seabed position with the seabed position measured last time, and judge whether the change exceeds the seabed change threshold.

[0024] If it exceeds, the seabed tracking error count is incremented by 1. At this time, if the seabed tracking error count exceeds the preset threshold, directly use the seabed position measured last time as the current seabed position; if the seabed tracking error count does not exceed the preset threshold, return to the step S22.

[0025] If it does not exceed, the seabed tracking error count is cleared, and the suspected seabed position is used as the current seabed position.

[0026] Among them, in the step S3, the adjustment of the system gain is specifically as follows;

[0027] Calculate the energy of the first arrival wave based on the tracked seabed position, and adjust the system gain according to the calculated energy of the first arrival wave to ensure that the energy of the first arrival wave can reach between 60% and 90% of its saturation state.

[0028] Among them, in the step S3, the adjustment of the time-varying gain is specifically as follows;

[0029] Let the distance between the working range and the seabed position be L. Perform normalized envelope detection on the signal below the seabed, then find an echo position near the position of adding L / 5 to the seabed, and then find another echo position near the position of adding 4*L / 5 to the seabed. Adjust the time-varying gain according to the amplitudes of the above two echoes to make the amplitudes of the two echoes as large as possible or the difference does not exceed a preset value.

[0030] Among them, in the step S3, the adjustment of the number of signal transmissions is specifically as follows;

[0031] Adjust the number of signal transmissions according to the current and the previously measured seabed positions. If the change in the seabed positions between the two times is relatively large, increase the number of signal transmissions, and vice versa, the number of signal transmissions can be reduced.

[0032] Among them, in the step S3, the real-time adjustment of the measurement range, signal period, and signal form is specifically as follows:

[0033] Adjust the equipment range in real time according to the seabed position to ensure the effectiveness of the measurement. At the same time, the signal transmission period and the form parameters of the signal can be adjusted. If the measurement distance is far, reduce the frequency and increase the transmission period.

[0034] Due to the adoption of the above technical solutions, the present invention has the following advantages and positive effects compared with the prior art:

[0035] The self-contained working method of the shallow layer profiler based on the seabed tracking technology provided by the present invention, after correctly tracking the seabed position, focuses on the processing of the echo signal below the seabed, and designs a set of equipment parameter setting schemes according to the state of the echo signal below the seabed. This method will change the traditional operation mode that requires real-time interaction during shallow profile measurement. Once the measurement state is entered, the equipment will automatically adjust each measurement parameter according to the actual measurement situation without manual intervention, improving the measurement effectiveness and accuracy. Description of the Drawings

[0036] By reading the detailed description of the preferred embodiments below, various other advantages and benefits will become clear to those of ordinary skill in the art. The drawings are only for the purpose of showing the preferred embodiments and are not considered to be a limitation of the present invention.

[0037] Figure 1 is the working process of a shallow profiling device;

[0038] Figure 2 is the flowchart of a self - contained working method of a shallow - layer profiler based on seabed tracking technology according to the present invention;

[0039] Figure 3 is the flowchart of seabed tracking according to the present invention. Specific Embodiments

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the specific embodiments of the present invention will be described below with reference to the accompanying drawings. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings, and other embodiments can be obtained.

[0041] To make the drawings concise, only the parts related to the present invention are schematically shown in each drawing, and they do not represent their actual structures as products. In addition, to make the drawings concise and easy to understand, in some drawings, components with the same structure or function are only schematically shown as one of them, or only one of them is marked. In this article, "one" not only means "only this one", but also can mean "more than one" situation.

[0042] The following further details a self - contained working method of a shallow - layer profiler based on seabed tracking technology proposed by the present invention with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will be clearer according to the following description and the claims.

[0043] Embodiment

[0044] Refer to Figures 1 to 3 , this embodiment provides a self - contained working method of a shallow - layer profiler based on seabed tracking technology, configured in a shallow - layer profiling device. As Figure 1 shown, it is a working flowchart of a self - contained measurement method of a shallow profiling device adopting this embodiment. The whole process can be described as: before the unmanned platform is launched into the water or before the device starts working, some measurement parameters are preset according to the measurement task, such as signal form, working frequency, initial gain, initial depth, initial energy value, etc. After starting the measurement, the whole system enters the automatic test state, and all parameters can be automatically adjusted in real time according to the measurement situation. After completing the measurement task, the result data can be processed and viewed.

[0045] Further preferably, the initial parameters of this embodiment can be set according to experience before launching into the water. In practice, a series of learning methods can also be set, and after a period of environmental learning after the device starts working, they can be determined. For example, the setting of the initial depth: after starting the measurement, the device range is set to the full range, and then the full-range signal is received. In the full-range signal, the seabed is tracked according to the seabed tracking method until the seabed can be stably tracked. Then the system enters the automatic measurement state. In addition, the gain can also be adjusted and determined through the learning process. For example, the initial gain is set to the minimum and adjusted step by step until the signal energy requirement is met.

[0046] See Figure 2 , the following steps are included in this embodiment:

[0047] First of all, in step S1, the device emits a detection signal to the seabed and then receives the feedback signal of each frame. After receiving the feedback signal, it is also necessary to determine whether the feedback signal of the current frame is valid. If the feedback signal is judged to be invalid, the number of invalid times is recorded, and the invalid count is incremented by one. If the number of invalid times reaches a preset value, it is considered that there is a problem with the system, and the initial settings are restored by restarting the device to jump out of the measurement error. If the number of invalid times does not reach the predicted value, no action is taken and waiting for the arrival of the next frame of received signal. If it is judged to be valid, the invalid count is cleared, and the measurement parameters and data of the feedback signal of the current frame are saved.

[0048] Immediately afterwards, see Figure 3 , in step S2, while saving the feedback signal of the current frame, the seabed position corresponding to the feedback signal is tracked. The specific steps are as follows: the detection signal sR(t) and the transmitted signal sT(t) are cross-correlated and normalized to obtain the normalized data R0(t). Sequentially search for the normalized data R0(t), and find the first position where the value is greater than 0.3, which is recognized as the suspected seabed position Bt. Compare the suspected seabed position Bt with the previously obtained seabed position Blast to determine whether the change in the seabed position exceeds the seabed change threshold.

[0049] If it exceeds, the seabed tracking error count is incremented by 1. At this time, if the seabed tracking error count exceeds the preset threshold, the previously measured seabed position is directly used as the current seabed position. If the seabed tracking error count does not exceed the preset threshold, search for the next position where the value is greater than 0.3 and recognize it as another suspected seabed position, and traverse the above steps again.

[0050] If it does not exceed, the seabed tracking error count is cleared, and the suspected seabed position is used as the current seabed position.

[0051] Then, see Figure 2, in step S3, based on the tracked seabed position, the sum of the part of the collected echo signal starting from the seabed position with the length of the transmitted signal is regarded as the first arrival wave energy by the method of cumulative summation. Then, the system gain is adjusted according to the calculated first arrival wave energy to ensure that the first arrival wave energy can reach between 60% and 90% of its saturation state.

[0052] Assume that the distance between the working range of the device and the seabed position is L. Perform normalized envelope detection on the signal below the seabed. Then, find an echo position near the position of adding L / 5 to the seabed, and find another echo position near the position of adding 4*L / 5 to the seabed. Adjust the time-varying gain according to the amplitudes of the above two echoes. When the amplitude of the first echo is greater than that of the second, it indicates insufficient compensation, and the compensation parameter can be increased; on the contrary, it indicates excessive compensation and the parameter needs to be appropriately reduced. Finally, make the amplitudes of the two echoes as equal as possible or the difference does not exceed the preset value.

[0053] Adjust the signal transmission times according to the current and the previous measured seabed positions. If the change in the seabed positions between the two times is relatively large, it indicates that the terrain changes complexly, and the transmission times are increased to obtain a more refined detection result; otherwise, the transmission times can be appropriately reduced to save energy and storage space.

[0054] Adjust the device range in real time according to the seabed position to ensure the effectiveness of the measurement. At the same time, parameters such as the signal transmission period and the form of the signal can be adjusted. If the distance is far, the frequency is reduced and the transmission period is lengthened to ensure that there is enough energy for the measurement.

[0055] Finally, after the above adjustments of the system gain, time-varying gain, signal transmission times, measurement range, signal period, and signal form are completed, the next measurement cycle is carried out.

[0056] The embodiments of the present invention have been described in detail above in conjunction with the accompanying drawings. However, the present invention is not limited to the above embodiments. Even if various changes are made to the present invention, provided that these changes fall within the scope of the claims of the present invention and their equivalent technologies, they still fall within the protection scope of the present invention.

Claims

1. A self - contained working method of a shallow - layer profiler based on seabed tracking technology, configured for a shallow - layer profiling device, characterized in that, It includes the following steps: S1: Transmit a detection signal, receive each frame of feedback signal, and determine whether the feedback signal of the current frame is valid until a valid feedback signal is obtained; S2: Save the feedback signal of the current frame and simultaneously track the seabed position corresponding to the feedback signal; S3: Calculate the first arrival wave energy based on the tracked seabed position, and adjust the system gain according to the calculated first arrival wave energy; Calculate the signal characteristics of two segments of signals below the seabed based on the tracked seabed position, and adjust the time-varying gain according to the signal characteristics of the signals below the seabed; Compare the currently tracked seabed position with the previously obtained seabed position, and adjust the number of signal transmissions; Based on the currently tracked seabed position, adjust the measurement range, signal period, and signal form in real time; S4: After the adjustments of the system gain, time-varying gain, number of signal transmissions, measurement range, signal period, and signal form are completed, jump back to the step S1.

2. The self - contained working method of the shallow - layer profiler based on seabed tracking technology according to claim 1, characterized in that, In the step S1, it specifically includes the following steps: Transmit a detection signal, receive each frame of feedback signal, and determine whether the feedback signal of the current frame is valid. If it is judged to be invalid, the invalid count is incremented by one. When the invalid count reaches a preset threshold, it is determined that the measurement fails and the device is restarted to transmit / receive signals again; If it is judged to be valid, the invalid count is cleared, and the measurement parameters and data of the feedback signal of the current frame are saved.

3. The self - contained working method of a shallow - layer profiler based on seabed tracking technology according to claim 1, characterized in that, Specifically in the step S2, S21: Cross-correlate and normalize the detection signal and the transmitted signal; S22: Sequentially find the positions greater than 0.3 in the normalized data, and identify them as suspected seabed positions; S23: Compare the suspected seabed position with the previously measured seabed position to determine whether the change exceeds the seabed change threshold; If it exceeds, the seabed tracking error count is incremented by 1. At this time, if the seabed tracking error count exceeds the preset threshold, directly use the previously measured seabed position as the current seabed position; If the seabed tracking error count does not exceed the preset threshold, return to the step S22; If it does not exceed, the seabed tracking error count is cleared, and the suspected seabed position is used as the current seabed position.

4. The self-contained working method of a shallow sub-bottom profiler based on seabed tracking technology according to claim 1, characterized in that In the step S3, the adjustment of the system gain is specifically as follows; Calculate the first arrival wave energy based on the tracked seabed position, and adjust the system gain according to the calculated first arrival wave energy to ensure that the first arrival wave energy can reach between 60% and 90% of its saturation state.

5. The self-contained working method of a shallow sub-bottom profiler based on seabed tracking technology according to claim 1, characterized in that In the step S3, the adjustment of the time-varying gain is specifically as follows; Let the distance between the working range and the seabed position be L. Perform normalized envelope detection on the signal below the seabed, then find an echo position near the position of adding L / 5 to the seabed, and then find another echo position near the position of adding 4*L / 5 to the seabed. Adjust the time-varying gain according to the amplitudes of the above two echoes to make the amplitudes of the two echoes as large as possible or the difference does not exceed the preset value.

6. The self - contained working method of the shallow - layer profiler based on the seabed tracking technology according to claim 1, is characterized in that, In the step S3, the adjustment of the signal transmission times is specifically as follows; Adjust the signal transmission times according to the current and the previously measured seabed positions. If the change in the seabed positions between the two measurements is relatively large, then increase the signal transmission times; otherwise, reduce the signal transmission times.

7. The self - contained working method of the shallow - layer profiler based on the seabed tracking technology according to claim 1, is characterized in that, In the step S3, the real - time adjustment of the measurement range, signal period and signal form is specifically as follows: Adjust the device range in real - time according to the seabed position to ensure the effectiveness of the measurement. At the same time, the signal transmission period and the form parameters of the signal can be adjusted. If the measurement distance is far, then reduce the frequency and increase the transmission period.

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