Research On Underwater Terrain Subsidence Monitoring Mechanism And Monitoring System Based On MEMS Nine-axis Sensor Array

Underwater terrain monitoring is one of the important tasks of marine exploration and development.Monitoring the subsidence or uplift of underwater terrain has an early warning effect on the occurrence of underwater geological disasters.For example,during the exploration and production of submarine gas hydrates,the decomposition of hydrates will destroy the sediment structure,causing land subsidence,which may lead to geological disasters such as collapse,landslides and even earthquakes,threatening the safety of gas hydrate exploration.Due to the characteristics of small size,light weight,low cost,low power consumption and high reliability,MEMS(Micro-Electro-Mechanical System)9-axis sensor can be used for long-term,in-situ and multi-point underwater terrain monitoring.In this respect,this article carried out theoretical research,prototype development and experimental verification.The theoretical research guides systematic research and prototype development,while the experiments verify the correct of theoretical research and the feasibility application of prototype.In the theoretical research,the data of underwater terrain is obtained by three methods:field investigation of Zhairuoshan island,terrain deformation simulation platform and sand bed.The amplitude distribution of different terrains is obtained by one-dimensional and two-dimensional Fourier transform,then the spatial frequency components are analyzed.On this basis,the one-dimensional and two-dimensional nonuniform sampling conditions based on MEMS 9-axis sensor array are derived by the framework theory.The condition is that when the interval between sensors is less than Nyquist sampling interval,the underwater terrain can be reconstructed without distortion.In the prototype development,the multi-data synchronous acquisition and long-distance transmission scheme are studied.According to the characteristics of the sensor interface,a long-distance,multi data acquisition and transmission scheme based on the IIC(Inter-Integrated Circuit)bus and the CAN(Controller Area Network)bus are designed.On this basis,a relative time synchronization scheme of multi-microcontrollers is proposed.Through the combination of CAN bus(data transmission)and I/O(Input/Output)port(time synchronization signal),the problem of data confusion caused by the time synchronization of the multi-microcontrollers is solved.Then,solving the bending torsion angle of the underwater terrain(rotation angle around the axes,attitude angle)is studied.Based on the preprocessing and calibration of the data,the accelerometer,gyroscope and magnetometer are integrated by Kalman filter algorithm.Finally,the reconstruction model and precision analysis of underwater subsidence and uplift are studied.For the two-dimensional model,two models of linear and arc are established for the accelerometer sensor data,and some experiment are designed to verify the monitoring accuracy.For the three-dimensional model,the spatial bend and twist angles are transformed into the coordinates at the key points,then the surface interpolation algorithm is applied.The seafloor subsidence and uplift between different time and different points can be calculated after obtaining the time sequence of underwater terrain.Based on the above theoretical analysis and technology,a prototype of terrain subsidence monitoring based on MEMS 9-axis sensor array is developed.The experimental platform for terrain subsidence is set up,making laboratory experiments carried out.Moreover,the experiments including down slope deformation monitoring of sand dike(large physical model),the subsidence and uplift monitoring of intertidal zone in Zhairuoshan Island,and deep-water environment simulation and displacement monitoring are performed.The feasibility of the prototype in shallow water and deep water environment is verified by the above tests.This article can provide technical support for the subsidence monitoring of submarine gas hydrate test-mining areas and deformation monitoring of underwater curved structures.