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National standard of gravitational acceleration

Name of standard: National Standard of Gravity Acceleration

Code designation: ECM 120-3/08-040

Year of publication: 2019

Department: Research Institute of Geodesy, Topography and Cartography

                   Ústecká 98, 250 66 Zdiby

Guarantor: Ing. Vojtech Pálinkáš, Ph.D., Ing. Jakub Kostelecký, Ph.D.

Number of CMCs: 2

Rozsah měření9,75 m×s-2 až 9,85 m×s-2
Opakovatelnost měření1,2×10-8 m×s-2
Standardní nejistota měření2,2×10-8 m×s-2

The national standard of gravity acceleration is composed by two absolute gravimeters of FG5 [1] and FG5X [2] type, which determine the free fall acceleration from the functional relationship between length and time samples measured during the free fall of a test mass (consisting a corner cube retroreflector) in a high vacuum environment.  The free fall is repeatedly realized at a distance of about 0.2 m / 0.3 m (in case of FG5 / FG5X) and detected by a laser interferometer. The generated interferometric signal with a wavelength determined by the laser calibration (iodine-stabilized He-Ne laser) for its so-called "zero-crossings" (600 000 / 900 000 samples) is associated by time samples (controlled by a rubidium oscillator). Absolute gravity measurements are thus traceable to SI units of time and distance through repeated calibrations of the laser and rubidium oscillator with relative uncertainties better than 2·10-10.

The determined values of the free-fall acceleration are corrected to the conventional quantity of the gravity acceleration by including instantaneous corrections from the vertical component of the tidal acceleration, from the change in centrifugal acceleration due to polar motion, and from the variable loading effect of anomalous atmospheric masses in accordance with IERS conventions [3].

The FG5 No. 215 absolute ballistic gravimeter was declared as the national standard of gravity acceleration in 2008. In 2019, the national standard was updated due to improvements of this gravimeter and due to the extension of the standard by the FG5X No. 251 gravimeter. Both gravimeters were manufactured by Micro-g LaCoste, USA, and technologically and methodologically improved and innovated on the basis of intensive research [4-11] carried out in a cooperation between ČMI and VÚGTK. Significant systematic errors and contributions to the measurement uncertainty were detected, estimated or refined. The gravimeters were equipped with a new measurement system and are newly labelled as FG5-215/HS5 and FG5X-251/HS5, which currently form the national standard of gravity acceleration (see Fig. 1).

Fig. 1. Absolute gravimeters FG5-215/HS5 (left) and FG5X-251/HS5 (right) comprising the national standard of gravity acceleration.

 

Fig. 2. Deviations of the national standard of gravity acceleration from the reference values of international comparisons. The error bars for the Degree of Equivalence (DoE) represent the expanded (k=2) uncertainty of this parameter.

 

 

References:

 

  1. Niebauer T M, Sasagawa G S, Faller J E, Hilt R and Klopping F. A new generation of absolute gravimeters. Metrologia 32:159–180, 1995. https://doi.org/10.1088/0026-1394/32/3/004
  2. Niebauer T M, Billson R, Ellis B, Mason B van Westrum D and Klopping F. Simultaneous gravity and gradient measurements from a recoil-compensated absolute gravimeter. Metrologia 48:154‑163, 2011. https://doi.org/10.1088/0026-1394/48/3/009
  3. Petit G, Luzum B. IERS Conventions 2010, IERS Technical Note 36, https://www.iers.org/IERS/EN/Publications/TechnicalNotes/tn36.html
  4. Křen P, Pálinkáš V, Mašika P. On the effect of distortion and dispersion in fringe signal of the FG5 absolute gravimeters. Metrologia 53:27-40, 2016. https://doi.org/10.1088/0026-1394/53/1/27
  5. Křen P, Pálinkáš V, Mašika P, Vaľko M. FFT swept filtering: a bias-free method for processing fringe signals in absolute gravimeters. Journal of Geodesy 93:219-227, 2018. https://doi.org/10.1007/s00190-018-1154-y
  6. Křen P, Pálinkáš V, Mašika P, Vaľko M. Effects of impedance mismatch and coaxial cable length on absolute gravimeters. Metrologia 54:161, 2017. https://doi.org/10.1088/1681-7575/aa5ba1. https://doi.org/10.1088/1681-7575/aa5ba1
  7. Křen P, Pálinkáš V, Mašika P. On the determination of verticality and Eötvös effects in absolute gravimetry. Metrologia 55:451-459, 2018. https://doi.org/10.1088/1681-7575/aac522
  8. Pálinkáš V, Křen P, Vaľko M and Mašika P. On the determination of vertical gravity gradients by corner-cube absolute gravimeters. Metrologia 56:055006, 2019. https://doi.org/10.1088/1681-7575/ab32fb
  9. Křen P, Pálinkáš V, Vaľko M, Mašika P. Improved measurement model for FG5/X gravimeters. Measurement 171:108739, 2020. https://doi.org/10.1016/j.measurement.2020.108739
  10. Křen P and Pálinkáš V. Estimation of the effective wavenumber for a collimated beam in an interferometer, case study for FG5/X absolute gravimeters, Appl. Opt. 61:1811-1817, 2022. https://doi.org/10.1364/AO.451498
  11. Křen P, Pálinkáš V. Effect of the air-vacuum interface translation on the FG5/X absolute gravimeters. Journal of Geodesy 97:26, 2023. https://doi.org/10.1007/s00190-023-01713-5