Comparison between two mobile absolute gravimeters: optical versus atomic interferometers

We report a comparison between two absolute gravimeters: the LNE-SYRTE cold atoms gravimeter and FG5#220 of Leibniz Universit\"at of Hannover. They rely on different principles of operation: atomic and optical interferometry. Both are movable which enabled them to participated to the last International Comparison of Absolute Gravimeters (ICAG'09) at BIPM. Immediately after, their bilateral comparison took place in the LNE watt balance laboratory and showed an agreement of 4.3 +/- 6.4 {\mu}Gal

Traceability of the Hannover FG5X-220 to the SI units

The absolute measurement of g is currently realized through the laser interferometric measurement of a free falling retro-reflector. The Micro-g LaCoste FG5X is a free-fall gravimeter with a laser interferometer in Mach-Zehnder configuration which uses simultaneous time and distance measurements to calculate the absolute value of g. Because the instrument itself contains the necessary working standards for precise time and length measurements, it is considered independent of external references. The timing is kept with a 10MHz rubidium oscillator with a stability of 5x10e-10. The length unit is realized by the laser interferometer. The frequency calibrated and iodine stabilized helium-neon laser has a wavelength of 633 nm and an accuracy of 2.5x10e-11. In 2012 the FG5-220 of the Institut für Erdmessung (IfE) was upgraded to the FG5X-220. The upgrade included a new dropping chamber with a longer free fall and new electronics including a new rubidium oscillator. The metrological traceability to measurement units of the Système International d’unités (SI unit) is ensured by two complementary and successive approaches: the comparison of frequencies with standards of higher order and the comparison of the measured g to a reference measured by absolute gravimeters defined as primary standards within the SI. A number of experiments to test the rubidium oscillator were performed. The oscillator showed a linear drift of 0.2x10e-3 Hz per month (= 0.3 nm/s² per month) in the first 18 months of use. A jump in the frequency of 0.01 Hz (=20 nm/s²) was revealed recently and the drift rate changed to 0.4x10e-3 Hz/month

Results of the International Comparison of Absolute Gravimeters in Walferdange (Luxembourg) of November 2003

The results of an international comparison of absolute gravimeters held in Walferdange Luxembourg in November 2003 are presented. The absolute meters agreed with one another with a standard deviation of less than 2 µGal (1 Gal = 1 cm/s2) (if we exclude one prototype instrument from the analysis). For the first time, the ability of the operators was put to the test. The comparison indicates that the errors due to the operator are less than 1 µGal, i.e. within the observational errors

Results of the European Comparison of Absolute Gravimeters in Walferdange (Luxembourg) of November 2007

The second international comparison of absolute gravimeters was held in Walferdange, Grand Duchy of Luxembourg, in November 2007, in which twenty absolute gravimeters took part. A short description of the data processing and adjustments will be presented here and will be followed by the presentation of the results. Two different methods were applied to estimate the relative offsets between the gravimeters. We show that the results are equivalent as the uncertainties of both adjustments overlap. The absolute gravity meters agree with one another with a standard deviation of 2 μgal (1 gal = 1 cm/s2)