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IGFS 2014 pp 45-51 | Cite as

The Effect of Helium Emissions by a Superconducting Gravimeter on the Rubidium Frequency Standards of Absolute Gravimeters

  • Jaakko MäkinenEmail author
  • Heikki Virtanen
  • Mirjam Bilker-Koivula
  • Hannu Ruotsalainen
  • Jyri Näränen
  • Arttu Raja-Halli
Part of the International Association of Geodesy Symposia book series (IAG SYMPOSIA, volume 144)

Abstract

Recently, large offsets in the frequency of rubidium oscillators of absolute gravimeters have been reported, due to contamination by helium from a superconducting gravimeter that shares the same laboratory space. Such offsets can cause large errors in measured gravity if they go unnoticed and are not corrected for in the data processing. We give an account of the calibration histories of the rubidium oscillators of the FG5-221 (2003–2012) and of the FG5X-221 (2013–2014) of the FGI from the viewpoint of helium contamination. These gravimeters have been stationed (when not in field work) in the Metsähovi gravity laboratory, about 5 m from the superconducting gravimeter GWR TT020, in a separate room. The drift of the oscillator of the FG5-221 during the 10 years has been larger than specifications but reasonably linear. Evidence for possible helium effects is indirect: when the gravimeter is away from the laboratory some relaxation of the frequency offset is seen. This could be an indication that contamination by helium contributed to the large drift. The drift of the oscillator of the FG5X-221 has been much larger and correlates with known episodic helium emissions. During the installation of a new superconducting gravimeter GWR Dual OSG 073 in January-February 2014 and the ensuing large helium emissions we monitored the response of the FG5X-221 oscillator continuously. In 5 days, the clock frequency increased by 4.7 × 10−9. Such an offset, if not corrected for in the data processing would cause an offset of −9.2 μGal in observed gravity.

Keywords

Absolute gravimeter Helium contamination Rubidium oscillator 

Notes

Acknowledgment

The opportunity to use the reference frequency from the hydrogen maser of the Metsähovi Radio Observatory of Aalto University (formerly of Helsinki University of Technology) is gratefully acknowledged.

References

  1. Faller JE, Guo YG, Gschwind J, Niebauer TM, Rinker RL, Xue J (1983) The JILA portable absolute gravity apparatus. BGI Bull Inf 53:87–97Google Scholar
  2. Goldberg S, Lynch TJ, Riley WJ (1985) Further test results for prototype GPS rubidium clock. In: Proceedings of the 17th annual precise time and time interval (PTTI) application and planning meeting, Dec 1985. NASA, Washington DC, pp 145–155. http://tycho.usno.navy.mil/ptti/1985papers/Vol%2017_14.pdf
  3. Hinderer J, Florsch N, Mäkinen J, Legros H, Faller JE (1991) On the calibration of a superconducting gravimeter using absolute gravity measurements. Geophys J Int 106:491–497CrossRefGoogle Scholar
  4. Niebauer TM, Hoskins JK, Faller JE (1986) Absolute gravity: a reconnaissance tool for studying vertical crustal motion. J Geophys Res 91:9145–9149CrossRefGoogle Scholar
  5. Niebauer TM, Sasagawa GS, Faller JE, Hilt R, Klopping F (1995) A new generation of absolute gravimeters. Metrologia 32:159–180CrossRefGoogle Scholar
  6. Niebauer M, Billson R, Ellis B, van Westrum D, Klopping F (2011) Simultaneous gravity and gradient measurements from a recoil-compensated absolute gravimeter. Metrologia 48:154–163CrossRefGoogle Scholar
  7. van Westrum D, Bianchi T, Billson R, Ellis B, Niebauer TM, Rohner H (2014) The effect of helium contamination on rubidium clock references in absolute gravity meters. In: Peshekhonov VG (ed) Proceedings of the IAG symposium on terrestrial gravimetry: static and mobile measurements (TG-SMM2013), Saint Petersburg, Russia, 17–20 Sept 2013. State Research Center of Russia Elektropribor, St Petersburg, pp 125–130Google Scholar
  8. Virtanen H (2006) Studies of earth dynamics with the superconducting gravimeter, vol 133. Finnish Geodetic Institute, Kirkkonummi, 130 pGoogle Scholar

Copyright information

© Springer International Publishing Switzerland 2015

Authors and Affiliations

  • Jaakko Mäkinen
    • 1
    Email author
  • Heikki Virtanen
    • 1
  • Mirjam Bilker-Koivula
    • 1
  • Hannu Ruotsalainen
    • 1
  • Jyri Näränen
    • 1
  • Arttu Raja-Halli
    • 1
  1. 1.Finnish Geospatial Research Institute FGIMasalaFinland

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