[S-TT42] Applying optic fiber sensing to earth science

[STT42-03] Ambient temperature effect on long-period DAS measurement

*Hiroyuki Matsumoto¹, Eiichiro Araki¹, Takashi Yokobiki¹ (1.Japan Agency for Marine-Earth Science and Technology)

The previous study suggests that the apparent strain on the Distributed Acoustic Sensing (DAS) is measured near the Tosabae near the submarine cable off Muroto, Japan. It is interpreted that this can be attributed to the ambient temperature change (Ide et al., 2021). For this reason, we planned to deploy temperature sensors during the DAS measurement and compare DAS with co-located temperature sensors directly. Simultaneous measurement of ambient temperature and DAS using a submarine cable were conducted for a period of 50 days (i.e., from 2021/08/16 through 2021/10/04) to qualify the contribution of ambient temperature change on DAS in this region. Temperature sensors were carried and deployed near the submarine cable by a Remotely Operational Vehicle (ROV); however it was impossible to detect the cable itself visually. Correlation between the DAS and the ambient temperature measurements suggests that the location of the temperature sensor was at 24.75 km in fiber length from the laser, corresponding to the cable route determined by the air-gun hydroacousitc signals. The DAS correlates well with the ambient temperature in the long period range, while the noise is predominant in the short period range. Our observation suggests that the coefficient between strain and temperature is 4 to 7 micro-strain per degree Celsius. We also observed the in-situ current; however it seems that the effect is less than the ambient temperature.