Seismo-Acoustic Analysis for Accurate Clock-Drift Correction of Autonomous Long-Term Hydrophones

Accurate timing is crucial for precise seismic event localization from trilateration, particularly in long-term hydrophone monitoring, which assumes that all instruments are synchronized. This study addresses the challenge of estimating clock drift in autonomous underwater hydrophones deployed in the southern Indian Ocean as part of the OHA-SIS-BIO array. When GPS synchronization is impossible upon recovery due to battery failure, alternative methods to estimate clock drift become essential. We apply an approach based on weighted least-squares, which compares arrival-times of teleseismic P-waves recorded on a hydrophone station with arrival-times predicted by a propagation model in the Earth. By leveraging the International Seismological Center's EHB earthquake catalog and selecting events with large magnitude, we were able to infer clock drift with improved precision. This approach is effective, as demonstrated by the good match between calculated and directly measured clock drift, and thus provides reliable drift estimates for hydrophones that cannot be synchronised upon recovery.