← Back to Gallery

Session: Sensing Technologies and their Latest Developments [Poster]

Type: Poster

Date: 10/7/2024

Time: 05:00 PM

Room: Stanley Park Ballroom

Comparison of DAS Recordings With a Calibrated Underground Strain Meter Array

The power of distributed acoustic sensing (DAS) lies in its ability to sample deformation signals along an optical fiber at hundreds of locations with one interrogator only. While the interrogator is calibrated to record ‘fiber strain’, the properties of the cable and its coupling to the rock control the ‘strain transfer rate’ and such how much of ‘rock strain’ is represented in the recorded signal. We use DAS recordings in an underground installation (BFO observatory) colocated to an array of strainmeters in order to measure the ‘strain transfer rate’ in situ. A tight-buffered cable and a standard loose-tube telecommunication cable are used, where a section of both cables covered by sand and sandbags is compared to a section, where cables are just unreeled on the floor. The ‘strain transfer rate’ is largely independent of frequency in the band from 0.05 Hz to 1 Hz and varies between 0.15 and 0.55 depending on cable and installtion type. The sandbags show no obvious effect and the tight-buffered cable generally provides a larger ‘strain transfer rate’. The noise background for ‘rock strain’ in the investigated band is found at about an rms-amplitude of 0.1 nstrain in 1/6 decade for the tightbuffered cable. This allows a detection of the marine microseisms at times of high microseism amplitude. We recently cemented a "naked" optic fibre into the concrete floor of the observatory and the collected data will be presenred, which should give new insight into the cable coupling an sensitivity limits of the DAS recordings.

Presenting Author: Andreas

Additional Authors