Effects of impedance mismatch and coaxial cable length on absolute gravimeters

Křen, Petr; Pálinkáš, Vojtech; Mašika, Pavel; Vaľko, Miloš

doi:10.1088/1681-7575/aa5ba1

Cited by 7 publications

(6 citation statements)

References 14 publications

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“…Therefore, we use a delay of about 31 ms from the top of the free fall as the beginning of the evaluation interval for the FG5X gravimeter. One reason of this practice is that the electronic dispersion of the fringe signal is large at low frequencies [14], which affects the evaluation of the free fall acceleration.…”

Section: Measurement Setup and Evaluation Principlementioning

confidence: 99%

Experiment with simultaneous measurements at two optical wavelengths in the FG5X absolute gravimeter

Křen,

Pálinkáš,

Hald

2023

Meas. Sci. Technol.

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The FG5X gravimeters are the most accurate commercially available absolute gravimeters at present. They traditionally use one optical wavelength in their interferometer to measure the gravity acceleration of the freely falling test mass in a vacuum. In this paper, for the first time, it is demonstrated the possibility to track the test mass simultaneously with two optical wavelengths of 633 nm and 771 nm and to evaluate the gravity acceleration from both these measurements. We show the technical solution, mathematical methods and error sources that have to be taken into account for the realization of simultaneous interferometric measurements. The achieved results show agreement of the gravity accelerations at the level of 2–4 microgals and increased low-frequency noise in residuals at 771 nm due to optical optimisation of a gravimeter to the wavelength of 633 nm. We evaluated the sensitivity of gravity measurements to the used wavelength as a new contribution in the uncertainty budget that for the FG5X gravimeter reached 0.25 μGal and 2 μGal at wavelengths of 633 nm and 771 nm, respectively. Further, we discuss that the optimisation of a gravimeter to a certain wavelength is related to the applied antireflective coating on the optical elements of the gravimeter among them the glass retroreflector plays the key role since its movements being dominant.

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Section: Measurement Setup and Evaluation Principlementioning

confidence: 99%

Experiment with simultaneous measurements at two optical wavelengths in the FG5X absolute gravimeter

Křen,

Pálinkáš,

Hald

2023

Meas. Sci. Technol.

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“…aviation transport). Also, Křen et al (2017Křen et al ( , 2019 identified, characterised and partially removed biases originating in the signal processing chain of FG5 gravimeters, e.g. due to cable length and fringe signal amplitude.…”

Section: Gravimeter Bias and Si Traceabilitymentioning

confidence: 99%

Gravity field modelling for the Hannover 10 m atom interferometer

Schilling

Wodey

Timmen

et al. 2020

J Geod

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Absolute gravimeters are used in geodesy, geophysics and physics for a wide spectrum of applications. Stable gravimetric measurements over timescales from several days to decades are required to provide relevant insight into geophysical processes. Users of absolute gravimeters participate in comparisons with a metrological reference in order to monitor the temporal stability of the instruments and determine the bias to that reference. However, since no measurement standard of higher-order accuracy currently exists, users of absolute gravimeters participate in key comparisons led by the International Committee for Weights and Measures. These comparisons provide the reference values of highest accuracy compared to the calibration against a single gravimeter operated at a metrological institute. The construction of stationary, large-scale atom interferometers paves the way for a new measurement standard in absolute gravimetry used as a reference with a potential stability up to $$1\,\hbox {nm}{/}{\hbox {s}^{2}}$$ 1 nm / s 2 at 1 s integration time. At the Leibniz University Hannover, we are currently building such a very long baseline atom interferometer with a 10-m-long interaction zone. The knowledge of local gravity and its gradient along and around the baseline is required to establish the instrument’s uncertainty budget and enable transfers of gravimetric measurements to nearby devices for comparison and calibration purposes. We therefore established a control network for relative gravimeters and repeatedly measured its connections during the construction of the atom interferometer. We additionally developed a 3D model of the host building to investigate the self-attraction effect and studied the impact of mass changes due to groundwater hydrology on the gravity field around the reference instrument. The gravitational effect from the building 3D model is in excellent agreement with the latest gravimetric measurement campaign which opens the possibility to transfer gravity values with an uncertainty below the $${10}\,\hbox {nm}{/}{\hbox {s}^{2}}$$ 10 nm / s 2 level.

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“…γ A = 300 µGal m −1 ) and a zero gradient (obtaining v * 0 and g * 0 ). Next, one can determine the effective measurement height by (7) and finally solve the following linear equation by least squares…”

Section: Theorymentioning

confidence: 99%

“…However, a noise at low (temporal or spatial) frequencies must be taken into account carefully. As an example, the effects of the self-attraction (SAE) [6], cable dispersion and impedance mismatch [7] are shown in figure 3. These effects are usually subtracted from the measured g-values by additional corrections represented by the constant values for a given effect.…”

Section: Perturbations In the Gravity Residualsmentioning

confidence: 99%

“…In section 3, we clearly demonstrate why the correct (unbiased) determination of VGG needs to carefully take into account all the effects that cause low-frequency noises in the gravity residuals. Namely, we will specify the influence of effects such as self-attraction (SAE) [6], cable length or impedance mismatch [7]. In section 4, an interesting finding is presented, the detection of a parasitic wave of period 0.13 m in the gravity residuals of FG5X-251, causing errors in the VGG estimates.…”

Section: Introductionmentioning

confidence: 99%

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On the determination of vertical gravity gradients by corner-cube absolute gravimeters

et al. 2019

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This paper describes a new approach for the determination of vertical gravity gradients (VGGs) from the measurements of corner-cube absolute gravimeters based on laser interferometry. The new approach has been obtained by the modification of the equation for linear least squares solution used in the determination of the g-values. It enables one to establish a clear mathematical relation between the gravity residuals and the VGG estimates. As it is shown, in the determination of gradients with an accuracy approaching 10 µGal m −1 (1 µGal = 1 × 10 −8 m s −2 ), it is necessary to correct directly the measured quantities (time and distance pairs) for 'known', or sufficiently well modelled, perturbations as e.g. selfattraction or cable effects. Generally, if the gradients are determined from the data of absolute gravimeters, systematic low frequency perturbation in the residuals have to be analysed carefully. In this way, hidden perturbations in the residuals can be identified, which might be important also for the correct estimation of the g-values and associated uncertainties. This is shown on the example of a parasitic wave detected in the residuals of the FG5X-251 gravimeter, reaching a period of about 0.13 m and amplitudes up to 40 pm. Finally, we compare the gravity gradients determined by the new approach with a more accurate method using relative gravimeters. This comparison shows that the gradient estimates from the FG5X-251 absolute gravimeter are biased by about 10 µGal m −1 and reach reproducibility of 14 µGal m −1 . The effort to determine VGGs from absolute gravimeters enhanced the analyses of the measured data, identified still existing artefacts in the gravity residuals, the explanation of which should lead to improvements in the measurement model in order to obtain more accurate estimates of the g-values, VGGs and their uncertainties.

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Effects of impedance mismatch and coaxial cable length on absolute gravimeters

Cited by 7 publications

References 14 publications

Experiment with simultaneous measurements at two optical wavelengths in the FG5X absolute gravimeter

Experiment with simultaneous measurements at two optical wavelengths in the FG5X absolute gravimeter

Gravity field modelling for the Hannover 10 m atom interferometer

On the determination of vertical gravity gradients by corner-cube absolute gravimeters

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