It is well known that the self-contained deep-water stations (ADS) are widely accepted in the tasks of the World Ocean monitoring. Various information about physical fields is collected via the ADS network, distributed throughout the ocean floor. The information from each ADS is clocked with its internal clock having a relative temporary instability in the best case at a level of 10-8. The absolute daily deviation on time 10 msec corresponds to it, and is accumulated in conditions of the long-term self-contained work of the station. Naturally, this is the reason of deviation of the internal clock of the ADS in relation to the global (world) time. In this connection, there is a problem of synchronization of the internal clock by signals from outside. The complexity of solution of the task thus consists in the fact that the conventional ways of transferring synchronization signals from outside with the help of electromagnetic oscillations are unacceptable because of their rapid damping in water with depth.
The usage of hydroacoustic waves is possible. The distance of their propagation, except for the cases of their propagation in the underwater sound channel, is limited by occurrence of refraction of waves resulting in appearance of shadow zones, which in turn, brings about failures in reception of signals. In addition, the state of the medium affects the characteristics of the trajectory of of hydroacoustic wave propagation causing additional errors in time synchronization of the ADS.
In the given work, an approach to solving the problem employing seismic oscillations excited in the ground by powerful vibrational sources (vibrators) as synchronization signals from outside is considered. Due to precision of controllability of signals of the global time such sources can be used as synchronization signals sources. Moreover, due to time invariance of the characteristics of a medium of seismic waves propagation and, also, due to the fixed position of the ADS, seismic signals at reception points have high recurrence of time parameters. This circumstance is prerequisite for possibilities of precision time synchronization on the basis of using seismic oscillations.
The vibrators can excite two types of signals: harmonic and frequency-modulated (sweep-signals), when propagating in the ground the harmonic signal has higher noise immunity by an order as compared to sweep-signals . In view of this fact, the application of harmonic signals for the solution of the ADS synchronization problem is considered in the present paper.