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Using Teleseismic P‐Wave Arrivals to Calibrate the Clock Drift of Autonomous Underwater Hydrophones
Bulletin of the Seismological Society of America ( IF 3 ) Pub Date : 2021-02-01 , DOI: 10.1785/0120200217
Alexey Sukhovich 1 , Julie Perrot 1 , Jean-Yves Royer 1
Affiliation  

Networks of autonomous underwater hydrophones (AUHs) are successfully employed for monitoring the low‐level seismicity of mid‐oceanic ridges by detecting hydroacoustic phases known as T waves. For a precise localization of a seismic event from T‐wave arrival times, all AUHs must be synchronized. To this effect, at the beginning of the experiment, all instrument clocks are set to GPS time, which serves as a common reference. However, during the experiment, the instrument clock often deviates from GPS time, and, because the amount of deviation differs from one instrument to another, the synchronization of the AUHs deteriorates, as the experiment progresses in time. Just after the instrument recovery, the time difference (called “skew”) between the instrument and the GPS clocks is measured. Assuming that the skew varies linearly with time, the correction of a time series for the clock drift is a straightforward procedure. When the final skew cannot be determined, correcting for the clock drift is not possible, and any event localization becomes problematic. In this article, we demonstrate that the clock‐drift rate (assumed to be time‐independent) can be successfully estimated from arrival times of teleseismic P waves, commonly recorded by AUHs. Using a ray‐tracing code, and accounting for the uncertainties in event hypocenter locations, origin times, and the Earth seismic‐velocity model, confidence intervals of the estimated drift rates are deduced. The validity of the approach is tested on data from two AUHs with known clock drifts. Our results show that a reliable estimation is possible for skews as small as 4 s per two years (corresponding to a drift rate of about 5.5 ms·day−1⁠). This method can also be applied to correct data of other recording instruments subject to internal‐clock drift, such as ocean‐bottom seismometers, when the skew is unknown.

中文翻译:

使用远震P波到达来校准自主水下水听器的时钟漂移

自主水下水听器(AUH)网络通过检测称为T波的水声相,成功地用于监测中洋海脊的低层地震活动。为了从T波到达时间精确定位地震事件,必须同步所有AUH。为此,在实验开始时,将所有仪器时钟设置为GPS时间,以作为通用参考。但是,在实验过程中,仪器时钟通常会偏离GPS时间,并且由于偏差量因一台仪器而异,因此随着时间的推移,AUH的同步性会恶化。仪器恢复后,即会测量仪器与GPS时钟之间的时间差(称为“偏斜”)。假设时滞随时间线性变化,校正时钟漂移的时间序列是一个简单的过程。当无法确定最终偏差时,就无法校正时钟漂移,并且任何事件定位都会成为问题。在本文中,我们证明了可以从AUH通常记录的远震P波的到达时间成功估算出时钟漂移速率(假定与时间无关)。使用射线追踪代码,并考虑事件震源位置,起源时间和地球地震速度模型中的不确定性,可以得出估计漂移率的置信区间。该方法的有效性在来自两个具有已知时钟漂移的AUH的数据上进行了测试。我们的结果表明,对于每两年仅4 s的时滞,可以进行可靠的估算(对应于约5.5 ms·day-1?⁠的漂移率)。
更新日期:2021-01-31
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