Research On Communication And Time Synchronization Of Ocean Bottom Optical Fiber Seismometer

Optical fiber seafloor seismometer has the advantages of ultra-high sensitivity,ultra-large dynamic range and wide frequency band.It is expected to replace the traditional seismometer and become a new generation of seismic monitoring,prediction,early warning and geophysical research equipment for long-term fixed monitoring of seafloor.In practical applications,fiberoptic seafloor seismometers need to be networked to form a detection array.The time synchronization performance of each array element to obtain seismic information directly affects the detection accuracy of the source target.Aiming at the engineering application requirements of long-term bottom-sitting observation of optical fiber seafloor seismometer and optical fiber to twisted-pair communication,this paper designs the communication system and time synchronization system of optical fiber seafloor seismometer.From the two aspects of precise time synchronization protocol algorithm and master clock timing,the time synchronization method with high precision,low delay and high precision is deeply explored.The main work of this paper is as follows :Optimization of precise time synchronization protocol.According to the network topology design of the optical fiber seafloor seismometer,the high-speed digital user line technology is used to realize the information transmission and transformation between the optical fiber and the twisted pair.However,due to the difference in bandwidth,the information transmission path is asymmetric,which affects the time synchronization accuracy.The core algorithm of precise time synchronization protocol is improved,and an algorithm improvement method of precise time synchronization protocol is proposed.Based on the weighted balance and mathematical statistics method,this method adjusts the algorithm formula according to the weight of different messages in the time synchronization protocol,and weakens the error accumulation caused by the asymmetry of the round-trip transmission path delay of the time message.Then,the arithmetic mean of the time deviation value is solved by statistical method,and the time synchronization accuracy is further improved by approximating the master-slave phase deviation.Optimization of timing method of communication system.According to the improved precise time synchronization protocol and the working scene of the fiber-optic seafloor seismometer,a dual-mode timing structure with GPS as the main clock source and Beidou system as the backup main clock source is constructed.Aiming at the abnormal fluctuation of clock source caused by random white noise and jump value of GPS signal,an improved timing method of precise time synchronization system for seafloor seismometer is proposed.This method is based on the theory of innovation sequence combined with adaptive algorithm and traceless filtering algorithm,which can correct the frequency nonlinear drift caused by the main clock source,and can also suppress the jump outliers of GPS second pulse signal,reduce the influence of system noise on filtering,and finally achieve the purpose of improving the timing accuracy.Then the timing signal is further verified by the best master clock algorithm to improve the stability of the system time synchronization clock source.Experimental verification.The test link of optical fiber seafloor seismometer is built,and the practical engineering application is simulated by using GPS / Bei Dou dual-mode timing module,P68 time synchronization module and communication synchronization bridge.The optical fiber transmission network,optical fiber twisted pair asymmetric transmission network and optimized balanced optical fiber twisted pair transmission network are built.The time synchronization parameters and network communication packet loss rate of these three cases are tested.The feasibility of time synchronization algorithm optimization and GPS timing method optimization proposed in this paper is verified.