Virgo Logbook

This morning, a small helicopter could be heard and seen flying repeatedly up and down the canal, passing several times close to the central building. This is clearly seen in the microphone of the central building, see fig 1. It is always the same small, yellow/blue helicopter which appears to be training or playing in the area. I have seen it flying also yesterday and wouldn't be surprised if it is the same one that caused an unlock 2 weeks ago. If someone with sharp eyes can read its registration number or can track it down in some other way, a polite request to go fly somewhere else would be appropriate. For future science runs, I would seriously investigate the possibility to get some sort of restricted airspace of say 500 meters around our buildings, either officially or as an informal request to the nearby airports.

Fig 2 shows the spectrogram of a number of close passes. Some of these are clearly flagged by the BRMS monitor in the 64-128 Hz band, but others are just below threshold. I suggest to add a new frequency-band of say 32-64 Hz, which should be more sensitive to the low-frequency noise of the helicopters. For comparison, fig 3 shows the spectrogram of a small, military aircraft (about the size of a private jet) that flew straight above the central building towards the WE. This one (and also the big C-130 transport planes) typically make noise around 100 Hz.