Design Of Clock Synchronization In Large-scale Seismic Data Acquision System

Seismic exploration method is the main method used in contemporary hydrocarbonexploration. Seismic exploration system is a kind of large-scale distributed systemwhich works in the wild. The conventional seismic exploration systems rarelyconsidered the clock synchronization issues, which lead to a cumbersome explorationprocess and hardly to enhance efficiency. Based on the demand of continuing acquiring,focus on clock drift and communication delay between nodes, research work is carriedout on the clock synchronization technology of the network of seismic instrument.Firstly, this paper analyzed the network topology of a current seismic instrument,then summed up the inadequacies of the system workflow and discussed the specificneeds of seismic instrument system clock synchronization. On this basis, established afour-layer network architecture and planning of the overall system synchronizationscheme composed by a tri-level sync.Designed and implemented a high-precision master clock calibrationscheme. By using GPS timing system module as an external clock reference,detailed studied the limitations of each calibration solution. On the IXP460platform, achieved the dislocation adjustment method.On the basis of the existing of the master clock, designed thesynchronization algorithm between master and slave clocks. Considering thedifference of the network protocol, respectively proposed the correspondingsolutions. Established the principle that the timestamp capture should be asclose as possible to the physical layer. Designed the program to capture thetimestamp on the acquisition unit. The sliding window filtering is used to filterout random noise in the synchronization process. On this basis, discussed theeffects on synchronization performance caused by latency and other parameters.Design and implemented the clock synchronization on acquisition units.Based on FPGA, achieved a high-precision control of a local clock and achievedthe hardware logic to accurately capture the timestamp. By designing the SOPC,the synchronization algorithm and process control is achieved on the acquisitionunit. Based on the analysis of the factors that may affect the accuracy of thesynchronization system, put forward the corresponding solutions. By substituting sync synchronization packets by sync code, the error reduced from10~20μs to2μs.Build a simple seismograph system, on which to verify the performance ofthe clock synchronization system. Experiment results show that the calibrationaccuracy of the master clock reached60ns. The synchronization accuracy on theacquisition unit achieved2μs. The system is able to meet the application requirements.