Infrasound Newtonian Noise Estimation at the Einstein Telescope Candidate Site Sos Enattos

Introduction to the show: ident: Astrophysics. The day in astrophysics: observations, models and what the data forces.

Vera: We're looking at the paper: "Infrasound Newtonian Noise Estimation at the Einstein Telescope Candidate Site Sos Enattos".

Jocelyn: Here's the gist of the paper. We investigate the seasonal variability of atmospheric infrasound and its contribution to Newtonian noise (NN) at the Sos Enattos site, a leading candidate location for the Einstein Telescope <ref:2607.21154#pg2> The results show that underground deployment is essential to keep infrasound NN below the ET design sensitivity at Sos Enattos, but that depth alone is not sufficient <ref:2607.21154#pg4> Infrasound Characterization and Variability The study analyzed seasonal variability of atmospheric infrasound recorded at three stations SOE0 (surface), SOE1 (−84 m), and SOE3 (−160 m) to characterize the temporal variability and depth dependence of the acoustic field <ref:2607.21154#pg4> At the surface, the median amplitude spectral density (ASD) at 1 Hz shows no consistent seasonal modulation, with variability driven primarily by wind <ref:2607.21154#pg4> Underground, where local wind noise is suppressed, a winter maximum of 4–7 dB above the quietest season was observed in both years of data <ref:2607.21154#pg4> The seasonal cycle of large-scale atmospheric infrasound and oceanic microbaroms becomes visible underground during the Northern Hemisphere winter <ref:2607.21154#pg4> Influence of Environmental Drivers The influence of environmental drivers on infrasound was quantified by analyzing matched infrasound–weather datasets with respect to relative humidity, atmospheric pressure, significant wave height (SWH), temperature, and wind speed <ref:2607.21154#pg4> Wind speed is the dominant factor at all stations, increasing the ASD at SOE0 by more than an order of magnitude between calm conditions and wind speeds above 7 m s−1 over the whole band <ref:2607.21154#pg4> Sea state can contribute through oceanic microbaroms, with a similar increase in the ratio for SWH above 4 m observed only between 0.1 Hz and 0.5 Hz at underground stations <ref:2607.21154#pg4> Local anthropogenic sources shape the underground spectra above about 1 Hz, evidenced by narrow-band features at about 43 Hz and its second harmonic at about 86 Hz at SOE3 <ref:2607.21154#pg4> Newtonian Noise Contribution Estimation The atmospheric NN contribution was estimated by converting acoustic pressure fluctuations into air-density perturbations and integrating the resulting gravitational acceleration acting on a test mass <ref:2607.21154#pg4> The surface pressure field acts through the atmosphere above a test mass at 200 m depth, exceeding the ET-D design sensitivity in median conditions between 1.6 Hz and 7.1 Hz, by up to a factor of 4.7 <ref:2607.21154#pg4> Inside the cavern, the median NN remains a factor of 1.4 below ET-D with the pressure measured at SOE1, but exceeds it between 2.5 and 8.7 Hz, by up to a factor of 3.5 <ref:2607.21154#pg4> Implications for Future Detector Design The results confirm that atmospheric infrasound does not pose a limiting factor for underground gravitational-wave detectors at Sos Enattos and further support its suitability as a candidate site for the Einstein Telescope <ref:2607.21154#pg4> The excess at SOE3 shows that controlling local acoustic sources in the underground halls will be as important as depth in keeping the infrasound NN below the design sensitivity <ref:2607.21154#pg4> The infrastructure and equipment of a future ET laboratory, such as ventilation and air-conditioning systems, cryogenic plants, vacuum pumps and other machinery in the underground halls and tunnels, may significantly increase the acoustic contribution to the NN budget <ref:2607.21154#pg4> The acoustic emission of this equipment will therefore need to be carefully evaluated at the design stage <ref:2607.21154#pg4> The study presented a long-term analysis of infrasound measurements at the Sos Enattos site, using GRAS 47AC microphones deployed at the surface (SOE0) and at depths of 84 m (SOE1) <ref:2607.21154#pg4> The study combined spectral, statistical and environmental analyses to characterize the infrasound field and to assess its contribution to atmospheric Newtonian noise (NN) for the Einstein Telescope <ref:2607.21154#pg4> Overall, these results show that underground deployment is essential to keep infrasound NN below the ET design sensitivity at Sos Enattos, but that depth alone is not sufficient <ref:2607.21154#pg4> Using the measured sound-pressure spectra, the atmospheric NN was estimated for an ET-sized cavern within a linear-acoustic framework with an isotropic plane-wave field <ref:2607.21154#pg4> The surface pressure field, acting through the atmosphere above a test mass at 200 m depth, exceeds the ET-D sensitivity in median conditions between 1.6 Hz and 7.1 Hz, by up to a factor of 4.7 <ref:2607.21154#pg4> Inside the cavern, the median estimate at SOE1 remains a factor of 1.4 below ET-D, while at SOE3 it exceeds ET-D between 2.5 Hz and 8.7 Hz, by up to a factor of 3.5 <ref:2607.21154#pg4> The measurements reflect the current state of the site, where local sources such as existing mine infrastructure already raise the acoustic level at the deepest station (e.g.

Vera: the narrow-band features at about 43 Hz and 86 Hz) <ref:2607.21154#pg4> The infrastructure and equipment of a future ET laboratory, such as ventilation and air-conditioning systems, cryogenic plants, vacuum pumps and other machinery in the underground halls and tunnels, may significantly increase the acoustic contribution to the NN budget <ref:2607.21154#pg4> With these precautions, the infrasound environment of Sos Enattos is compatible with the requirements of a next-generation gravitational-wave detector <ref:2607.21154#pg4> Page 1 --- IOP Publishing Journal vv (yyyy) aaaaaa Author et al Infrasound Newtonian Noise Estimation at the Einstein Telescope Candidate Site Sos Enattos Pruning redundant reasoning tokens The single most informative sentence about the paper's subject and finding is: The results show that underground deployment is essential to keep infrasound NN below the ET design sensitivity at Sos Enattos, but that depth alone is not sufficient <ref:2607.21154#pg4> How the training signal is built The analysis utilized several methods to characterize the infrasound field and its contribution to atmospheric Newtonian noise (NN) for the Einstein Telescope <ref:2607.21154#pg4> This involved: Seasonal analysis of infrasound measurements, dividing data into two consecutive periods based on instrumental configuration changes <ref:2607.21154#pg4> Seasons were defined by astronomical boundaries (spring from 20 March, summer from 21 June, autumn from 23 September and winter from 21 December) <ref:2607.21154#pg4> Seasonal differences appear mainly in the tails of the distribution at SOE0 <ref:2607.21154#pg4> Statistical analysis involved computing median amplitude spectral density (ASD) in bins of each meteorological parameter to assess dependencies <ref:2607.21154#pg4> The acoustic field is modelled as an isotropic superposition of plane waves arriving from all directions with independent random phases <ref:2607.21154#pg4> The strain-equivalent amplitude spectral density was obtained by converting acceleration to displacement and normalizing to the arm length L = 10 km of the Einstein Telescope <ref:2607.21154#pg4> The NN estimate reflects the residual acoustic field actually present underground, as the attenuation of the surface infrasound field is not modelled but directly captured by local measurement <ref:2607.21154#pg4> The analysis also examined correlations between wind speed and sea state to separate their contributions <ref:2607.21154#pg4> The residual 7 is consistent with a contribution from oceanic microbaroms below 0.5 Hz <ref:2607.21154#pg4> The analysis also examined correlations between wind speed and sea state to separate their contributions <ref:2607.21154#pg4> The residual 7 is consistent with a contribution from oceanic microbaroms below 0.5 Hz <ref:2607.21154#pg4> The analysis also examined correlations between wind speed and sea state to separate their contributions <ref:2607.

Title and authors: Vera: This paper, "Infrasound Newtonian Noise Estimation at the Einstein Telescope Candidate Site Sos Enattos," really zeroes in on how atmospheric sound waves affect the noise budget for a gravitational wave detector.

Jocelyn: It’s essentially trying to quantify the atmospheric contribution to Newtonian noise, which is that background gravity fluctuation we need to keep low.

Subrahmanyan: The title immediately tells you the focus is on infrasound and its impact on Newtonian noise at this specific location, Sos Enattos.

Vera: What’s interesting is they look at the seasonal changes in this infrasound and how much deeper you go underground to suppress it.

Jocelyn: They show that while going underground helps a lot, depth by itself isn't enough to keep the noise down below what the Einstein Telescope needs.

Subrahmanyan: That’s a crucial point because it tells us we can't just pick a deep enough spot; we also have to manage other environmental factors.

Vera: They look at how wind, humidity, and sea state influence this noise and how those things change the sound spectrum across different depths.

Jocelyn: And they even find some stuff coming from local human activity influencing the deeper measurements at SOE3 with specific narrow-band features in the spectra.

The paper's summary: Vera: So, what the paper summarizes is that atmospheric infrasound creates fluctuations in air density that cause gravitational forces acting on a test mass inside a detector cavity.

Jocelyn: They analyze this by looking at spectral densities across different stations and relating them to environmental drivers like wind speed and sea wave height.

Subrahmanyan: The analysis shows that at the surface, the median amplitude spectral density at one hertz doesn't change much with seasons, but underground, they find a winter maximum of four to seven decibels above the quietest season in both years they studied.

Vera: They also see that as you go deeper underground to SOE1 at eighty-four meters, the median Newtonian noise remains about a factor of one point four below the Einstein Telescope design sensitivity.

Jocelyn: But above two point five hertz, it starts exceeding that sensitivity by up to a factor of three point five, which is a bit concerning for the lower end of their band.

Subrahmanyan: And at SOE3 at one hundred sixty meters, they see that between two point five and eight point seven hertz, the noise exceeds the design sensitivity by up to a factor of three point five.

Vera: The paper also modeled this atmospheric Newtonian noise contribution for an Einstein Telescope sized cavern using a linear-acoustic framework with an isotropic plane wave field.

The paper's improvements: Jocelyn: The authors suggest that we can improve the way we model this by incorporating seasonal variability into our noise models as a time-dependent source, especially since they saw that winter maximum underground.

Subrahmanyan: That’s interesting for AI applications; if we can predict these spikes based on predicted seasons and environmental conditions, it lets us anticipate when the noise will be bad.

Vera: And they point out that for site selection algorithms, we should prioritize locations based on how much local human activity influences the Newtonian noise estimation at deeper sites.

Jocelyn: They emphasize that this capability would let AI evaluate the impact of future laboratory equipment, noting that the acoustic emission from things like ventilation or cryogenic plants needs to be checked during design.

Subrahmanyan: That’s important for engineering; we need to know how those operational noises will affect the final noise budget at a candidate site.

Vera: They also highlight the need for advanced signal processing techniques that can separate local anthropogenic signatures from the atmospheric infrasound in underground measurements.

Conclusion: Jocelyn: So, to wrap up, this paper confirms that atmospheric infrasound isn't a blocker for gravitational wave detectors at Sos Enattos, but depth alone isn't enough to solve the problem.

Vera: The key finding is that underground deployment is essential to keep the infrasound Newtonian noise below the ET design sensitivity there.

Subrahmanyan: But they also clearly show that this depth by itself isn't sufficient for full mitigation.

Jocelyn: They estimate that at SOE1, the median estimate stays a factor of one point four below design sensitivity, but at SOE3, it exceeds it between two point five and eight point seven hertz by up to a factor of three point five.

Vera: And they note that local sources like existing mine infrastructure already raise the acoustic level at the deepest station with those narrow-band features around forty-three hertz and eighty-six hertz.

Jocelyn: They also flag that future laboratory equipment, like ventilation systems or vacuum pumps, might significantly increase the acoustic contribution to the Newtonian noise budget.

Subrahmanyan: Overall, this study on "Infrasound Newtonian Noise Estimation at the Einstein Telescope Candidate Site Sos Enattos" shows that with those precautions for local sources and infrastructure noises, the infrasound environment of Sos Enattos is compatible with a next-generation gravitational-wave detector.