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Geoscientific Instrumentation, Methods and Data Systems An interactive open-access journal of the European Geosciences Union

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https://doi.org/10.5194/gi-2017-13
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
17 Mar 2017
Review status
This discussion paper is a preprint. A revision of this manuscript was accepted for the journal Geoscientific Instrumentation, Methods and Data Systems (GI) and is expected to appear here in due course.
Time-stamp correction of magnetic observatory data acquired during unavailability of time-synchronization services
Pierdavide Coïsson1, Kader Telali1, Benoit Heumez1, Vincent Lesur1, Xavier Lalanne1, and Chang Jiang Xin2 1Institut de Physique du Globe de Paris, Sorbonne Paris Cité, Université Paris Diderot, CNRS, F-75005 Paris, France
2Lanzhou Geomagnetic Observatory, Lanzhou Institute of Seismology, China Earthquake Administration
Abstract. During magnetic observatory data acquisition, the data time-stamp is kept synchronized with a precise source of time. This is usually done using a GPS controlled Pulse Per Second (PPS) signal. For some observatories located in remote areas or where internet restrictions are enforced, only the magnetometer data are transmitted, limiting the capabilities of monitoring the acquisition operations. The magnetic observatory in Lanzhou (LZH), China, experienced an interruption of the GPS PPS in 2013. The data-logger clock drifted slowly in time: in 6 months a lag of 28 s was accumulated. After a reboot on 2 April 2014 the drift became faster, 2 s per day, before the GPS PPS could be restored on 8 July 2014. To estimate the time lags that LZH time-series had accumulated, we compared it with data from other observatories located in East Asia. A synchronization algorithm was developed. Natural sources providing synchronous events could be used as markers to obtain the time lag between the observatories. The analysis of slices of 15 minutes of 1-s data at arbitrary UTC allowed estimating time lags with an uncertainty smaller than ~ 10 s, revealing the correct trends of LZH time drift. A precise estimation of the time lag was obtained by comparing data from co-located instruments controlled by an independent PPS. In this case, it was possible to take advantage of spikes and local noise that constituted precise time-markers. It was therefore possible to determine a correction to apply to LZH time-stamps to correct the data files and produce reliable 1 minute averaged definitive magnetic data.

Citation: Coïsson, P., Telali, K., Heumez, B., Lesur, V., Lalanne, X., and Xin, C. J.: Time-stamp correction of magnetic observatory data acquired during unavailability of time-synchronization services, Geosci. Instrum. Method. Data Syst. Discuss., https://doi.org/10.5194/gi-2017-13, in review, 2017.
Pierdavide Coïsson et al.
Interactive discussionStatus: closed
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
Printer-friendly Version - Printer-friendly version      Supplement - Supplement
 
RC1: 'Comments', Anonymous Referee #1, 29 Mar 2017 Printer-friendly Version 
AC1: 'Response to reviewer 1', Pierdavide Coïsson, 09 Jun 2017 Printer-friendly Version 
 
RC2: 'Interactive comment', Anonymous Referee #2, 17 Apr 2017 Printer-friendly Version 
AC2: 'Response to reviewer 2', Pierdavide Coïsson, 09 Jun 2017 Printer-friendly Version 
Pierdavide Coïsson et al.
Pierdavide Coïsson et al.

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Short summary
Data loggers of magnetic observatories use GPS receivers to provide accurate time-stamping of recorded data. Typical sampling rate is 1 s. A failure of the GPS receiver can result in erroneous time-stamps. The observatory of Lanzhou, China, accumulated a lag of 28 s over one year. Using magnetic data recorded at other locations in a radius of 3000 km it was possible to estimate the diurnal lag and correct the time-stamps to produce reliable 1-minute averages of magnetic data.
Data loggers of magnetic observatories use GPS receivers to provide accurate time-stamping of...
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