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Laser pistonphone for absolute microphone calibration in low frequency range has been realized at UME. According to the operation principle of pistonphone, the motion of a piston, which is driven electro-mechanically in a closed acoustical coupler, produces a sound pressure. Accurate measurements of the piston displacement by laser interferometry enable accurate determination of the sound pressure and, as a result, the pressure sensitivity of the microphone exposed to the sound pressure inside the coupler. Homodyne Michelson interferometer with He-Ne laser was used for displacement measurements. Since the pistonphone is operating at low frequencies, the fringe-counting method was used for the signal processing. Calibrations of LS1P microphones with the uncertainty less that 0. 15 dB have been performed using laser pistonphone. Other possible metrological applications of laser pistonphone are also described in the paper.

Main text The key comparison CCAUV.A-K6 has been carried out under the auspices of the Consultative Committee on Acoustics, Ultrasound and Vibration (CCAUV) of the International Committee of Weights and Measures (CIPM). This comparison is concerned with primary pressure calibration of laboratory standard microphones type LS2P. The participating NMI's are HBK-DPLA (Denmark), CENAM (Mexico), GUM (Poland), INMETRO (Brazil), KRISS (Korea), LNE (France), METAS (Switzerland), NMIA (Australia), NMIJ (Japan), NMISA (South Africa), NRC (Canada), UME (Turkey) and VNIIFTRI (Russia). The role of Pilot laboratory was undertaken by LNE (France). The measurements took place between March 2019 and December 2020. Two LS2P microphones were circulated. This report includes the measurement results from the participants, information about their calibration methods, and the analysis leading to the assignment of the Key Comparison Reference Values (KCRV) and Degrees of Equivalence (DoE). To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/. The final report has been peer-reviewed and approved for publication by the CCAUV, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

We described the first results of an on-going study of absolute gravity changes after the 17 August 1999 Izmit earthquake in Marmara region. Repeated absolute gravity measurements were carried out six stations with an A10 absolute gravimeter from 2009 to 2011 in the region. A gravimetric calibration baseline (of the range of about 415 milliGal (mGal), 1 mGal = 10 −5 ms −2 ) was established in the region for the purposes of the calibration of the relative gravimeters. The absolute gravity measurements, repeated twice a year (October, June), can resolve gravity changes with a precision better than 5 microGal (μGal)/yr interval.The absolute gravity stations indicate a statistically significant gravity decrease at one of the absolute gravity stations in the calibration baseline, but the other stations do not. Generally, the absolute gravity difference agrees well with the general trend of the relative gravity changes. In addition, the precise vertical gravity gradients with relative gravity measurements have been determined at the absolute gravity stations for the reduction of measured gravity to the benchmark. The gradients scatter around the nominal constant (3.086 μGal/cm) between 2.82-3.73 μGal/cm as a result of the local density anomalies. The difference from the nominal gradient causes the error around 7-14 μGal by applying the normal vertical gradient instead of the directly measured one.

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