CN-121994175-A - Underwater distributed shape sensing method based on small quantity of asynchronous auxiliary sound sources and distributed optical fiber sensing

CN121994175ACN 121994175 ACN121994175 ACN 121994175ACN-121994175-A

Abstract

The invention provides an underwater distributed shape sensing method and system based on a small amount of auxiliary sound sources and distributed optical fiber sensing. According to the method, a small number of unsynchronized sound sources with known positions are arranged to emit acoustic signals, a distributed optical fiber sensing system is used for acquiring distributed response of the acoustic signals along sensing optical fibers, relative time delay information of sound waves reaching each sensing unit is extracted, the space coordinates of each sensing unit are solved through a self-adaptive constraint inversion algorithm in combination with geometrical constraint conditions of the optical fibers, and two-dimensional or three-dimensional shape reconstruction of the optical fibers is achieved. According to the invention, effective shape reconstruction can be realized only by a single sound source or two sound sources without clock synchronization, and two self-adaptive inversion schemes of equation set solving and optimizing iteration are provided for different scenes such as known starting points or known two end points, so that the complexity and the layout difficulty of the system are remarkably reduced, the environmental adaptability and the practicability are improved, and the method is suitable for shape monitoring and safe operation and maintenance of underwater long-distance optical cables, pipelines and sensing arrays.

Inventors

SONG FEIFEI
WANG ZHAOYONG
YE QING

Assignees

中国科学院上海光学精密机械研究所

Dates

Publication Date: 20260508
Application Date: 20260121

Claims (11)

1. An underwater distributed shape sensing method based on a small amount of asynchronous auxiliary sound sources and distributed optical fiber sensing is characterized by comprising the following steps: S1, arranging an auxiliary sound source with a known position under water, so that the auxiliary sound source emits an acoustic detection signal; S2, acquiring distributed sound field response of a sensing optical fiber to the acoustic detection signal through a distributed optical fiber sensing system, and extracting relative time delay information distributed along the optical fiber by taking an optical fiber head end sensing unit as a reference; S3, solving the space coordinates of each sensing unit on the sensing optical fiber through a constraint self-adaptive geometric inversion algorithm based on the relative time delay information, the known position information of the auxiliary sound source and the geometric constraint condition of the sensing optical fiber; s4, reconstructing the continuous space morphology of the sensing optical fiber according to the space coordinates of each sensing unit.
2. The underwater distributed shape sensing method based on a small amount of unsynchronized auxiliary sound sources and distributed optical fiber sensing according to claim 1, wherein the extracting of the relative delay information in the step S2 is one of the following two ways: (a) When the auxiliary sound source transmits a single-frequency signal, a continuous phase distribution curve is obtained by carrying out spectrum analysis and phase unwrapping on the DAS signal, and then the continuous phase distribution curve is converted into relative time delay; (b) When the auxiliary sound source transmits the pseudo-random coded signal, the cross-correlation operation is carried out on the channel signals of each sensing unit and the reference signal, and the peak value position of the cross-correlation function is detected to determine the relative time delay.
3. The underwater distributed shape sensing method based on a small amount of unsynchronized auxiliary sound sources and distributed optical fiber sensing according to claim 1, wherein the geometric constraint condition in step S3 includes at least one or several of the following: the interval between the sensing array elements is a fixed known value; The absolute spatial coordinates of at least one array element on the sensing fiber are known; the morphological change of the sensing optical fiber is physically continuous, and the space track of the sensing optical fiber does not have non-smooth abrupt change points. .
4. The underwater distributed shape sensing method based on a small number of unsynchronized auxiliary sound sources and distributed optical fiber sensing according to claim 1, wherein the constrained adaptive geometric inversion algorithm in the step S3 comprises an adaptive inversion method based on equation set solution and a constrained inversion method based on optimization iteration, which are alternatively used according to the following conditions: When the absolute coordinates of the starting points of the sensing optical fibers are known and the spacing between the sensing units is fixed, an adaptive inversion method based on equation set solution is adopted; when the absolute coordinates of the starting point and the ending point of the sensing optical fiber are known, adopting a constraint inversion method for optimization iteration based on the initial optical fiber coordinates established by the end points.
5. The underwater distributed shape sensing method based on a small amount of unsynchronized auxiliary sound sources and distributed optical fiber sensing according to claim 4, wherein the adaptive inversion method based on equation set solution specifically comprises: establishing a distance equation from a sound source to each sensing unit according to a spherical wave model of sound wave propagation; Constructing a nonlinear equation set taking the coordinates of the sensing units as unknowns by combining the space constraint of the fixed sensing units; And when the solution is not accurate due to measurement errors, a position estimation error function is minimized through a sequence quadratic programming algorithm, and the optimal solution is approximated under the condition of meeting the interval constraint.
6. The underwater distributed shape sensing method based on a small amount of unsynchronized auxiliary sound sources and distributed optical fiber sensing according to claim 5, wherein when the adaptive inversion method based on equation system solution is adopted: for two-dimensional shape reconstruction, only a single auxiliary sound source is needed; For three-dimensional shape reconstruction, at least two auxiliary sound sources with different spatial positions are required, or a single moving sound source is measured at two different positions.
7. The underwater distributed shape sensing method based on a small amount of unsynchronized auxiliary sound sources and distributed optical fiber sensing according to claim 4, wherein the constrained inversion method based on optimization iteration specifically comprises: (i) Linear interpolation is carried out between a known starting point and a known ending point, and initial coordinate estimation of each sensing unit is generated; (ii) Constructing a multi-objective optimization function, wherein the function comprises a phase matching term based on the difference between actual time delay and theoretical time delay, a distance penalty term used for restraining the distance between adjacent units and a curvature penalty term used for ensuring the smoothness of the shape; (iii) And iteratively adjusting the coordinates of each intermediate unit by using the coordinates of the starting point and the ending point which are fixed and the unit distance which is near a fixed value as constraints through a constraint nonlinear optimization algorithm, minimizing the multi-objective optimization function, and outputting an optimal coordinate set.
8. The underwater distributed shape sensing method based on a small number of unsynchronized auxiliary sound sources and distributed optical fiber sensing according to claim 5, wherein the constrained inversion method based on optimization iteration is applicable to different numbers of auxiliary sound sources: When a single auxiliary sound source is used, the phase matching term is calculated based on that sound source only; when a plurality of auxiliary sound sources are used, the phase matching term is expanded to the sum of the corresponding phase matching terms of the respective sound sources.
9. The method of underwater distributed shape sensing based on small number of unsynchronized auxiliary sound sources and distributed fiber optic sensing according to claim 6, wherein when multiple auxiliary sound sources are used, the multiple auxiliary sound sources are spatially non-coplanar and non-collinear, remain close to orthogonal measurement modes and have different depths.
10. The underwater distributed shape sensing method based on a small number of unsynchronized auxiliary sound sources and distributed optical fiber sensing according to claim 1, wherein the method further comprises a moving measurement mode, namely, carrying out multiple measurements by moving a single auxiliary sound source to different positions, and equivalently obtaining a plurality of sound source observation data with different spatial positions for three-dimensional shape reconstruction.
11. An underwater distributed shape sensing system based on a small number of unsynchronized auxiliary sound sources and distributed optical fiber sensing, characterized in that it is adapted to implement the method of any one of claims 1-10, said system comprising: At least one auxiliary sound source of known position for emitting an acoustic detection signal; A distributed optical fiber sensing system is provided, the sensing optical fiber is deployed in an underwater area to be measured; a process control unit configured to perform the following operations: -controlling the auxiliary sound source to emit a signal; -processing the response data acquired by the DAS system, extracting relative delay information; reconstructing the shape of the sensing fiber by a constraint-adaptive geometric inversion algorithm according to geometric constraint conditions; -outputting shape information of the sensing fiber.

Description

Underwater distributed shape sensing method based on small quantity of asynchronous auxiliary sound sources and distributed optical fiber sensing Technical Field The invention relates to the technical field of underwater sensing and positioning, in particular to an underwater distributed shape sensing method based on a small amount of auxiliary sound sources and distributed optical fiber acoustic sensing (Distributed Acoustic Sensing, DAS). Background In the fields of ocean engineering, underwater communication, deep sea scientific investigation, national defense safety and the like, it is important to accurately master the real-time space morphology of underwater cables (such as communication optical cables, hydrophone arrays and the like). The existing array shape estimation technology is mainly divided into two major categories, namely a non-acoustic method and an acoustic method, but limitations exist in the two major categories. According to the non-acoustic method, auxiliary instruments such as a Depth Sensor (Depth Sensor), a magnetic Compass (Compass) or an Inertial Measurement Unit (IMU) are arranged on the array at intervals, the attitude information of local nodes of the array is measured, and then the integral shape is fitted through spline interpolation or a hydrodynamic model. Such methods do not rely on external sound sources, but their accuracy is limited by the sensor's layout density, its own accuracy, and the accuracy of the model. The acoustic method utilizes one or more sound sources with known positions (auxiliary sound sources or opportunity sound sources in the environment), and obtains the relative positions of the array elements by estimating the propagation time difference or phase difference of the acoustic signals reaching each array element and inverting iteration based on the geometrical acoustic principle. However, the method has certain application limitations, and cannot be positioned with high precision according to the application requirements of changeable actual scenes. A 【Z.Che, J. Wang, J. Zhu, B. Zhang, Y. Zhang, and Y. Wu, "Real-Time Array Shape Estimation Method of Horizontal Suspended Linear Array Based on Non-Acoustic Auxiliary Sensors," IEEE Access9, 90500–90509 (2021).】 in the prior art constructs a segmented array estimation method based on attitude depth sensor measurement data. For underwater arrays, the translational invariance of the array curves is utilized to establish and solve the underdetermined equation of the segmented curves relative to the array state functions. But is limited to a large extent by the layout density of the sensor, its own accuracy and the accuracy of the model. In the prior art two 【I.Skog, M.L.Nordenvaad, and G.Hendeby, "Signals-of-Opportunity-Based Hydrophone Array Shape and Orientation Estimation," IEEE J. Oceanic Eng.49(3), 679–691 (2024)】, a passive calibration method is proposed, sound emitted by a nearby ship is used as a opportunistic signal, the shape of a hydrophone array is estimated automatically, but the position of a point hydrophone array which needs more is used as priori knowledge, and the passive calibration method is difficult to apply in a scene of a large-scale submarine array and lack of priori knowledge. In the third 【Chen B ,Wang Z ,Yang J , et al. Distributed shape detection for an acoustic sensitive optical cable with DAS. [J]. Optics letters, 2024, 49 (12): 3384-3387.】 prior art, a distributed acoustic shape detection (ASOC) method based on DAS is proposed for the first time, so that the perceptibility of the array shape is realized, but the method needs to arrange a plurality of sound sources and relies on accurate clock synchronization, so that the system complexity is high, and the method is difficult to be suitable for a large-scale engineering scene. In the prior art, 【Q. Miao, W. Liu, R. Guo, G. Yan, L. Jiang and C. Xiao, "Shape Calibration of the Distributed Acoustic Sensing Cable by Using the Ambient Harmonic Noise,"2024 ACP and IPOC, Beijing, China, 2024, pp. 1-4】, array self-calibration is performed by using DAS and an environmental sound source (such as noise of a past ship, and the like), shape estimation is realized by measuring the phase difference of a signal at a specific frequency peak value, so that the sound source azimuth estimation precision is effectively improved, but the calibration effect of the method is not ideal in the area where the opportunity sound source is scarce or the signal to noise ratio is low. In view of the foregoing, there is a need for an underwater distributed shape sensing technology that can not only get rid of the dependence on complex synchronization systems and dense auxiliary sensors, but also ensure good adaptability and practicality in different underwater cable scenarios. Disclosure of Invention In order to solve the problems of complex system, dependence on a large amount of priori information, poor environmental adaptability and the like in the prior