## 4 Application of Fiber Optic Cables in Geophysics Exploration
### Vsp of Smf
The configuration of the DAS system used a homodyne DAS interrogator, which was systematically connected to fiber stretchers. This configuration was used for its capacity to integrate all supplementary seismic source signals that directly connected into the optical data stream while the obtained data were in velocity. This integration was accomplished with a sequence of piezoelectric fiber stretchers positioned in line with the SMF cable. The DAS system was able to continuously monitor the stretching fiber. The DAS maximum data sampling frequency for SMF was able to reduce the noise power spectral density of the DAS data stream to achieve real-time processing. The data processing workflow was conducted by converting raw DAS data to strain rate with weighted stacking for certain shot points and correlated with vibroseis sweep wavelets and common-mode noise denoising in SEG-Y format. The signal strength for SMF cable from DAS VSP shot records was computing SNR in the first break, and the noise level from RMS energy indicated a lower SNR along the channel. The findings demonstrated that utilizing an SMF cable in a DAS system facilitates an efficient data acquisition process and enables real-time generation of seismic and navigation data sampled at specific intervals. These DAS data adhere to geophysics seismic data formats, reducing the time delay between data acquisition and the transfer of field data outputs. Reservoir Monitoring of SMF  
Fiber optic applications have achieved remarkable outcomes when deployed in high-spatial-resolution seismic sensors using cost-effective telecommunications fiber optics installed along the drilled well to monitor hydrocarbon reservoirs [57; 58; 59]. Permanently installing a seismic array cable within a borehole can streamline equipment deployment, decrease operational complexities, and offer notable advantages such as enhanced repeatability and the potential for real-time data acquisition [60]. SMF has been widely used to monitor reservoirs in various subsurface targets. Research was conducted to evaluate DAS image quality of subsea carbon storage reservoirs and assess monitoring design concepts [61]. Subsea DAS was deployed within a single ultra-low-loss signal transmission SMF cable through subsea infrastructure that connects the DAS interrogator unit to a borehole SMF deployed within a dual-transmission SMF with a remote circulator. This concept was employed to counteract diminished optical signals by using an enhanced backscatter of SMF. The synthetic shot records were augmented with raw DAS records in terms of optical noise to replicate the varying SNR in SMF scenarios, namely a base case involving a dry tree with common SMF and a subsea scenario entailing a single transmission fiber and common SMF. The subsea environment with a single transmitting fiber and standard SMF had a negative value of net DAS noise gain and lower DAS pulse repetition rate loss. The alteration in the DAS noise floor within the context of the two scenarios involving SMF was assessed by analyzing the overall gains or losses resulting from various physical factors influencing system performance. The result highlighted the repercussions of low SNR in terms of subsea DAS image resolution. The authors concluded that employing a single transmitting fiber with standard SMF was not preferable for the subsea environment, especially for characterizing reservoir formations. The single signal transmitted in fiber optics with standard SMF was filled with noise, in contrast with the other situation for subsea transmission fiber. These findings can inform the selection of reservoir monitoring and data acquisition designs using SMF during offshore reservoir research. A possible further improvement of subsea DAS is enhancement by selecting an appropriate vendor of DAS SMF interrogator units to handle noise. This would involve the choice of a relevant interrogator vendor before conducting the subsea DAS survey.