## 1 Introduction  
Distributed Acoustic Sensing, sometimes known as DAS, is a relatively new technique for gathering seismic data that is quickly becoming more popular as a potential substitute for geophones in borehole seismic sensors. DAS acquires seismic data using fiber optic cables as sensors to measure acoustic waves. Compared to other seismic data acquisition methods, such as traditional geophones or seismometers, DAS has several advantages including providing continuous seismic data over long distances, high spatial resolution, flexibility for deployment in a wide range of environments, and a cost-effective alternative to traditional seismic data acquisition methods. Multiple recent field experiments in onshore [1] and offshore [2] wells suggest that DAS is a feasible seismic method. The DAS offers a one-of-a-kind and highly accurate means of measuring seismic activity. It possesses a high resolution in both space and time, and it is able to record a significant quantity of seismic data across a distance of several kilometers. If an optical fiber is placed inside of the well, then DAS will be able to provide continuous and dense recording from the well. This does not in any way interfere with any of the other activities that are going on in the well. A signal with a high signal-to-noise ratio (SNR) will be produced by an installation with an adequate amount of fiber coupling. In addition to this, fiber is more resistant to changes in temperature and pressure [3], which enables it to function as a sensor for a longer period of time. DAS is used in a variety of applications, including but not limited to the following: recording earthquakes [4], identifying fault zones [5], and reconstructing subsurface structures [6; 7]. Because dedicated downhole deployments of DAS target shorter seismic wavelengths, they have much superior SNR and make full use of the sampling resolution and density [8]. Deep sensor deployment also helps to bypass the obstacles that are provided by the dissipative and complex character of the near-surface or the overburden, both of which are problematic for the signal processing that is captured at or near the surface [9; 10]. A DAS system is a specialized method for collecting seismic information, which utilizes an optical fiber cable inserted in the well [11]. The system consists of two main components: a surface-mounted interferometer, also known as a light-box or interrogator unit, and the fiber optical cable [12], as depicted in Figure 1. This system is similar to an array of geophones placed throughout the full fiber length [13]. The interrogator unit delivers brief laser pulses into the fiber, and by analyzing the Rayleigh-scattering, the strain along the cable can be determined. As the pulse travels along the fiber, a portion of the energy is reflected to the surface by the minute flaws in the fiber. The amplitude and phase of the backscattered signal at a specific site in the fiber are random, but the change in phase-lag between two locations at two different times is proportional to the strain in that segment of the fiber [14; 15]. Thus, by analyzing the phase-lag, DAS can detect and quantify the strain along the cable, and this is used to collect seismic information. This method provides a unique and superior method of seismic measurement, as it has a high resolution both spatially and temporally, and it can record a dense amount of seismic data over several kilometers [16; 17]. DAS systems can be deployed in different ways in a well, depending on the application and specific requirements of the well [18; 19; 20]. One common method of DAS deployment in wells is through a \"permanently installed\" system, where fiber-optic cables are permanently installed in the wellbore during the well construction phase [20]. This method involves embedding the fiber-optic cable within the cement sheath of the wellbore or attaching it to the outside of the production tubing or casing.