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posted by janrinok on Tuesday September 03 2019, @07:07AM   Printer-friendly
from the all-wave-\o/ dept.

Arthur T Knackerbracket has found the following story:

It started with a relatively simple goal: create a prototype for a new kind of device to monitor the motion of underground structures at CERN. But the project—the result of a collaboration between CERN and the Joint Institute for Nuclear Research (JINR) in Dubna, Russia—quickly evolved. The prototype turned into several full-blown devices that can potentially serve as early warning systems for earthquakes and can be used to monitor other seismic vibrations. What's more, the devices, called precision laser inclinometers, can be used at CERN and beyond. The researchers behind the project are now testing one device at the Advanced Virgo detector, which recently detected gravitational waves—tiny ripples in the fabric of space-time that were predicted by Einstein a century ago. If all goes to plan, this device could help gravitational-wave hunters minimize the noise that seismic events have on the waves' signal.

Unlike traditional seismometers, which detect ground motions through their effect on weights hanging from springs, the precision laser inclinometer (PLI) measures their effect on the surface of a liquid. The measurement is done by pointing laser light at a liquid and seeing how it is reflected. Compared to weight–spring seismometers, the PLI can detect angular motion in addition to translational motion (up-and-down and side-to-side), and it can pick up low-frequency motion with a very high precision.

"The PLI is extremely sensitive, it can even detect the waves on Lake Geneva on windy days," says principal investigator Beniamino Di Girolamo from CERN. "It can pick up seismic motion that has a frequency between 1 mHz and 12.4 Hz with a sensitivity of 2.4 × 10−5 μrad/Hz½," explains co-principal investigator Julian Budagov from JINR. "This is equivalent to measuring a vertical displacement of 24 picometers (24 trillionth of a meter) over a distance of 1 meter," adds co-principal investigator Mikhail Lyablin, also from JINR.

[...] The results from the first tests are encouraging. With just 15 minutes of data taken on 6 August, the PLI picked up the same signals as devices already installed at Virgo, and from that day onwards it started running continuously and detected several small-magnitude earthquakes. The Virgo and PLI teams are now setting up the flow of data from the PLI to the Virgo data system. This will make it easier to compare data from different seismic devices and to assess the PLI's potential impact on Virgo's operation and detection of gravitational waves. "Virgo and the two LIGO detectors in the US have recently began another search for gravitational waves, one that will reach deeper into the universe than previous searches," says former Virgo spokesperson Fulvio Ricci from La Sapienza University, Rome. "We're confident that the PLI can play a part in this important search," he added.


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  • (Score: 2, Informative) by shrewdsheep on Tuesday September 03 2019, @02:35PM (1 child)

    by shrewdsheep (5215) on Tuesday September 03 2019, @02:35PM (#889192)

    "μrad/Hz^½", that's one big piece of a cryptic unit. Radians are synonymous to 1 IIRC, so we measure in s^{-1/2}. But why use urad instead of rad, and why the square root?

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  • (Score: 5, Informative) by Rupert Pupnick on Tuesday September 03 2019, @08:20PM

    by Rupert Pupnick (7277) on Tuesday September 03 2019, @08:20PM (#889282) Journal

    FWIW, in the communications world, power spectral density always has units of power per unit bandwidth, or in MKS units W/Hz. When you are working with amplitudes instead of power levels, you take the square root and end up in dimensions of V/(Hz)^0.5 (where there is understood to be a constant of proportionality related to the impedance level that gets you from volts to watts).

    So I guess that the gravity waves when measured as angular displacement represents amplitude, not power, hence the square root. The value of angular displacement that corresponds to the right triangle described in TFS: arcsin (24 E-12) = 2.4 E-11 rad.