ECAG-2011: European Compariosn of Absolute Gravimeters 2011, Walferdange, Luxembourg

Report (2013)

On the gravimetric contribution to watt balance experiments

in Metrologia (2013), 50(5), 452

It has been recommended that the relative standard uncertainty of the numerical value of the Planck constant required for the redefinition of the kilogram should not exceed 2 × 10 −8 . To reach this goal ... [more ▼]

It has been recommended that the relative standard uncertainty of the numerical value of the Planck constant required for the redefinition of the kilogram should not exceed 2 × 10 −8 . To reach this goal using experiments based on a watt balance, the free-fall acceleration ( g ) traceable to the SI, at a given point and a given time, needs to be known with a sufficiently small uncertainty well below 2 × 10 −8 . Reducing the uncertainty in g allows the other uncertainties related to the watt balance to be increased. Instead of a simultaneous operation of an absolute gravimeter with a watt balance, we propose an alternative approach and demonstrate that a standard uncertainty below 5 µGal (relative uncertainty of 5 × 10 −9 ) is reachable under the conditions at BIPM. Further decreasing the uncertainty could significantly increase commitments in terms of personnel and equipment and would not significantly improve the uncertainty targeted for the BIPM watt balance experiment. A 5 µGal uncertainty might also satisfy the needs of other watt balance experiments underway or planned. In our approach we combine the following information: (1) the Key Comparison Reference Values obtained from the CCM.G-K1, a key comparison carried out in the frame of the International Comparison of Absolute Gravimeters in 2009 (ICAG2009); (2) the accurate gravity network established using the qualified absolute and relative gravimeters; (3) temporal gravity variations based on observed Earth-tide parameters and modelled effects of polar motion and atmospheric mass redistribution; (4) uncertainty estimates that account for non-modelled effects; (5) the option to carry out absolute gravity measurements once every one or two years with two or more gravimeters for monitoring the stability of the gravity field at the BIPM. [less ▲]

The European Comparison of Absolute Gravimeters 2011 (ECAG-2011) in Walferdange, Luxembourg: results and recommendations

in Metrologia (2013), 50(3), 257

We present the results of the third European Comparison of Absolute Gravimeters held in Walferdange, Grand Duchy of Luxembourg, in November 2011. Twenty-two gravimeters from both metrological and non ... [more ▼]

We present the results of the third European Comparison of Absolute Gravimeters held in Walferdange, Grand Duchy of Luxembourg, in November 2011. Twenty-two gravimeters from both metrological and non-metrological institutes are compared. For the first time, corrections for the laser beam diffraction and the self-attraction of the gravimeters are implemented. The gravity observations are also corrected for geophysical gravity changes that occurred during the comparison using the observations of a superconducting gravimeter. We show that these corrections improve the degree of equivalence between the gravimeters. We present the results for two different combinations of data. In the first one, we use only the observations from the metrological institutes. In the second solution, we include all the data from both metrological and non-metrological institutes. Those solutions are then compared with the official result of the comparison published previously and based on the observations of the metrological institutes and the gravity differences at the different sites as measured by non-metrological institutes. Overall, the absolute gravity meters agree with one another with a standard deviation of3.1 µ Gal. Finally, the results of this comparison are linked to previous ones. We conclude with some important recommendations for future comparisons. [less ▲]

Absolute Gravity Measurements ath the Geodynamics Observatory in Moxa (Germany)

Report (2012)

Final report of the regional key comparison EURAMET.M.G-K1: European Comparison of Absolute Gravimeters ECAG-2011

in Metrologia (2012), 49(1A), 07014

During November 2011 a EURAMET key comparison of absolute gravimeters was organized in the Underground Laboratory for Geodynamics in Walferdange, Luxemburg. The comparison assembled 22 participants coming ... [more ▼]

During November 2011 a EURAMET key comparison of absolute gravimeters was organized in the Underground Laboratory for Geodynamics in Walferdange, Luxemburg. The comparison assembled 22 participants coming from 16 countries and four different continents. The comparison was divided into two parts: a key comparison that included six National Metrology Institutes or Designated Institutes, and a pilot study including all participants. The global result given by the pilot study confirms that all instruments are absolutely coherent with each other. The results obtained in the key comparison confirm a good agreement between the NMI instruments. Finally, a link to ICAG-2009 [http://iopscience.iop.org/0026-1394/49/1A/07011/] shows also that the NMI gravimeters are stable in time. Main text. To reach the main text of this paper, click on Final Report [http://www.bipm.org/utils/common/pdf/final_reports/M/G-K1/EURAMET.M.G-K1.pdf] . Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/ [http://kcdb.bipm.org/] . The final report has been peer-reviewed and approved for publication by the CCM, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA). [less ▲]

Results of the first North American comparison of absolute gravimeters, NACAG-2010

in Journal of Geodesy (2012), 86

Bedrock displacements in Greenland manifest ice mass variations, climate cycles and climate change

in Proceedings of the National Academy of Sciences of the United States of America (2012), 109(30), 11944-11948

The Greenland GPS Network (GNET) uses the Global Positioning System (GPS) to measure the displacement of bedrock exposed near the margins of the Greenland ice sheet. The entire network is uplifting in ... [more ▼]

The Greenland GPS Network (GNET) uses the Global Positioning System (GPS) to measure the displacement of bedrock exposed near the margins of the Greenland ice sheet. The entire network is uplifting in response to past and present-day changes in ice mass. Crustal displacement is largely accounted for by an annual oscillation superimposed on a sustained trend. The oscillation is driven by earth’s elastic response to seasonal variations in ice mass and air mass (i.e., atmospheric pressure). Observed vertical velocities are higher and often much higher than predicted rates of postglacial rebound (PGR), implying that uplift is usually dominated by the solid earth’s instantaneous elastic response to contemporary losses in ice mass rather than PGR. Superimposed on longer-term trends, an anomalous ‘pulse’ of uplift accumulated at many GNET stations during an approximate six-month period in 2010. This anomalous uplift is spatially correlated with the 2010 melting day anomaly. [less ▲]

Comparison between the Transfer Functions of three Superconducting Gravimeters

in Marées Terrestres Bulletin d'Informations (2011), 147

Second-order Doppler-shift corrections in free-fall absolute gravimeters

in Metrologia (2011), 48(3), 187-195

In a free-fall absolute gravimeter usually a Michelson type interferometer is employed to track the trajectory of a freely falling retroreflector. The accelerated motion of the retroreflector produces a ... [more ▼]

In a free-fall absolute gravimeter usually a Michelson type interferometer is employed to track the trajectory of a freely falling retroreflector. The accelerated motion of the retroreflector produces a Doppler-shift in the laser wavelength. From the interference signal (beat signal) of the Doppler-shifted and the reference electromagnetic waves the relative motion of the freely falling retroreflector with respect to an inertial reference retroreflector is reconstructed. Considerations of second-order Doppler-shift terms lead to a correction in the acceleration due to gravity of several microgals (1 µGal = 10 nm s −2 ). This correction is commonly called speed of light correction . To date different correction formulae have been proposed, which differ by several microgals. In this paper we review several previous publications and show the reasons for the different results. [less ▲]

Preliminary results of the BIPM Relative Gravity Measurement Campaign during the 8th International Comparison of Absolute Gravimeters (2009)

in Peshekhonov, Vladimir (Ed.) Proceedings of the IAG Symposium on Terrestrial Gravimetry: Static and Mobile Measurements (2011)