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Two methods for determination of the effective wavenumber of Gaussian beams in absolute gravimeters

Křen P., Pálinkáš V.

Metrology and Measurement Systems

2018

Vol. 25, nr 4

701--713

This paper presents two methods for evaluation of the effective wavenumber of nearly-Gaussian beams in laser interferometers that can be used for determination of a so called diffraction correction in absolute gravimeters. The first method, that can be simply used in situ, is an empirical procedure based on the evaluation of the variability of g measurements against the amount of light limited by an iris diaphragm and transmitted to a photodetector. However, precision of this method depends on the beam quality similarly as in the case of the conventional method based on measurement of a beam width. The second method, that is more complex, is based on beam profiling in various distances and on calculation of the effective wavenumber using the second spatial derivative of a non-ideal beam field envelope. The measurement results achieved by both methods are presented on an example of two absolute gravimeters and the determined diffraction corrections are compared with the results obtained by measurements of beam width. Agreement of methods within about 1 μGal have been obtained with average diffraction corrections slightly exceeding +2 μGal for three FG5(X) gravimeter configurations.

Effect of laser and clock stability and meteorological conditions on gravity surveyed with the A10 free-fall gravimeter - first results

Sekowski M., Krynski J., Dykowski P., Mäkinen J.

Reports on Geodesy

2012

z. 1/92

47--59

The Institute of Geodesy and Cartography in Warsaw, Poland, operates the A10-020 free-fall portable gravimeter since November 2008. Numerous gravity measurements with the A10-020 gravimeter, conducted under both laboratory and field conditions, provide a unique material for the estimation of accuracy as well as reliability of the determined gravity. Time series of regular, monthly measurements conducted with the A10-020 at the Borowa Gora Geodetic-Geophysical Observatory for over two years at two laboratory test sites and one field station has been analysed in terms of their internal consistency and compliance with the previous measurements performed with a few other absolute gravimeters (mainly FG5). The results of a number of calibrations of both, the rubidium oscillator and the polarization-stabilized laser interferometer of the A10-020 were considered in the analysis. The effect of applying the frequency standard as well as laser interferometer calibration data on the quality of gravity determined was investigated. In addition, the impact of weather conditions as well as variability of metrological parameters on surveyed gravity was taken into consideration when evaluating accuracy and reliability of gravity survey with the A10 gravimeter. Also the possibility of the occurrence of gross errors in gravity determination with the A10 gravimeter was discussed.