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

Report (2012)

The 8th International Comparison of Absolute Gravimeters 2009: the first Key Comparison (CCM.G-K1) in the field of absolute gravimetry

in Metrologia (2012), 49(6), 666

The 8th International Comparison of Absolute Gravimeters (ICAG2009) took place at the headquarters of the International Bureau of Weights and Measures (BIPM) from September to October 2009. It was the ... [more ▼]

The 8th International Comparison of Absolute Gravimeters (ICAG2009) took place at the headquarters of the International Bureau of Weights and Measures (BIPM) from September to October 2009. It was the first ICAG organized as a key comparison in the framework of the CIPM Mutual Recognition Arrangement of the International Committee for Weights and Measures (CIPM MRA) (CIPM 1999). ICAG2009 was composed of a Key Comparison (KC) as defined by the CIPM MRA, organized by the Consultative Committee for Mass and Related Quantities (CCM) and designated as CCM.G-K1. Participating gravimeters and their operators came from national metrology institutes (NMIs) or their designated institutes (DIs) as defined by the CIPM MRA. A Pilot Study (PS) was run in parallel in order to include gravimeters and their operators from other institutes which, while not signatories of the CIPM MRA, nevertheless play important roles in international gravimetry measurements. The aim of the CIPM MRA is to have international acceptance of the measurement capabilities of the participating institutes in various fields of metrology. The results of CCM.G-K1 thus constitute an accurate and consistent gravity reference traceable to the SI (International System of Units), which can be used as the global basis for geodetic, geophysical and metrological observations of gravity. The measurements performed afterwards by the KC participants can be referred to the international metrological reference, i.e. they are SI-traceable. The ICAG2009 was complemented by a number of associated measurements: the Relative Gravity Campaign (RGC2009), high-precision levelling and an accurate gravity survey in support of the BIPM watt balance project. The major measurements took place at the BIPM between July and October 2009. Altogether 24 institutes with 22 absolute gravimeters (one of the 22 AGs was ultimately withdrawn) and nine relative gravimeters participated in the ICAG/RGC campaign. This paper is focused on the absolute gravity campaign. We review the history of the ICAGs and present the organization, data processing and the final results of the ICAG2009. After almost thirty years of hosting eight successive ICAGs, the CIPM decided to transfer the responsibility for piloting the future ICAGs to NMIs, although maintaining a supervisory role through its Consultative Committee for Mass and Related Quantities. [less ▲]

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

in Metrologia (2012), 49(1), 95

The 8th International Comparison of Absolute Gravimeters (ICAG-2009) and the associated Relative Gravity Campaign (RGC2009) took place at the Bureau International des Poids et Mesures (BIPM) between July ... [more ▼]

The 8th International Comparison of Absolute Gravimeters (ICAG-2009) and the associated Relative Gravity Campaign (RGC2009) took place at the Bureau International des Poids et Mesures (BIPM) between July and October 2009. Altogether 24 institutes with 22 absolute gravimeters and 9 relative gravimeters participated in the ICAG/RGC campaign. Accurate absolute and relative gravity measurements as well as precision levelling measurements were performed on the micro-gravity 3D-grid at the BIPM. The 2009 comparison was the first to be organized as a Comité International des Poids et Mesures (CIPM) metrological Key Comparison under the CIPM MRA (Mutual Recognition Arrangement), which means that the result will be officially recognized by the governmental organizations responsible. As a consequence, the relative gravimeters employed were carefully selected and the measurement schedules were rigorously enforced compared with earlier campaigns. Thus the quality of the RGC2009 and the determination of the BIPM local gravity network were improved. After 30 years and eight successive ICAGs, the BIPM has decided to transfer its role to the national metrological institutes, although the CIPM will continue to organize the key comparison as ICAGs. The background to the RGC2009, and the organization, data processing and final results of the gravity and vertical gravity gradients, are presented in this paper. This report is more detailed than previous final reports of the RGCs. [less ▲]

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

Final report on the Seventh International Comparison of Absolute Gravimeters (ICAG 2005)

in Metrologia (2011), 48

Monitoring Earthquakes with gravity meters

in Geodesy and Geodynamics (2011), 2(3), 71-75

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 ▲]

Absolute Gravity Measurements in Yellowstone in September 2009

Report (2010)

On the influence of the rotation of a corner cube reflector in absolute gravimetry

in Metrologia (2010), 47(5), 567

Test masses of absolute gravimeters contain prism or hollow retroreflectors. A rotation of such a retroreflector during free-fall can cause a bias in the measured g -value. In particular, prism ... [more ▼]

Test masses of absolute gravimeters contain prism or hollow retroreflectors. A rotation of such a retroreflector during free-fall can cause a bias in the measured g -value. In particular, prism retroreflectors produce phase shifts, which cannot be eliminated. Such an error is small if the rotation occurs about the optical centre of the retroreflector; however, under certain initial conditions the error can reach the microgal level. The contribution from these rotation-induced accelerations is calculated. [less ▲]