## 5 Conclusions  
As fiber optic technology, DAS has been shown to be efficient in geophysics exploration such as VSP, reservoir monitoring, microseismic detection, and the application of ML approaches, as discussed in the previous chapter. Over the years, the oil and gas sector has made advancements in implementing DAS technology, mostly due to its cost-effectiveness in deploying optical fiber cables along linear assets like pipelines and wells [89]. However, considering prevailing economic conditions, there arises a necessity to optimize data processing within subsurface images and harness existing datasets for enhanced reservoir monitoring in the application of DAS. Based on the reviewed literature, it can be concluded that SMF has been shown to be a better fiber optic cable than MMF, as it is more widely used and capable in long-distance and higher-resolution sensing [28; 57]. The cable deployment method and acquisition parameters become essential in evaluating these two types of fiber optic cable in geophysics exploration. VSP provides high confidence in seismic data along the borehole, and reservoir monitoring is a good tool for exploring reservoirs, whereas microseismic measurement provides physical data at low frequencies but is limited in terms of operation for accessible exploration. These DAS data sources are highly complex and, in most cases, are contaminated by optical noise, although they have been employed to obtain accurate and excellent measurements of subsurface images. The integration of many data sources is beneficial in enhancing imaging capabilities, with DAS data specifically proving valuable for subsurface imaging purposes. SMF has been shown to be effective in subsurface imaging but faces some limitations, such as interference signals in Rayleigh backscattered light [90], as well as existence of the noise floor [62]. These limitations are addressed by employing proper active DAS measurement sources, enhanced spatial resolution, and SNRs; the use of a deliberate cable deployment method; and selection of relevant acquisition parameters. Although MMF also faces its own inherent limitations, its strengths make it preferable when it comes to DTS and shorter-distance cable-length deployments due to lower prices. Combined SMF and MMF in the same cable deployment provides various places for measurement, with SMF used for DAS and MMF used for DTS measurement. The primary conclusions of our review are presented below. 1. Successfully employed SMF cables in the domain of surface and subsurface geophysics exploration was inspected in this review. The various SMFs were used to record acoustic properties of a signal along the cable and have become the most used type of fiber optic cable for DAS. However, in this review, when SMF and MMF were combined, MMF was found to be preferable for DTS measurement in most research studies in terms of temperature variations and high bandwidth. 2. The cable deployment technique is a crucial initial factor, leading to considerable efforts with respect to its DAS data processing and application in the field of geophysics exploration. This can be improved by the enhancement of preprocessing steps not limited to the control of DAS acquisition parameter optimization, improving SNR values, in addition to a comparison with other seismic measurement tools such as conventional geophones. 3. DAS VSP is the most popular technique used to image the subsurface along the borehole. Furthermore, DAS for microseismic measurement was able to detect small microseismic events with high resolution. Although this method works well, it has some major drawbacks that may lead to reduced imaging resolution due to various noise for both SMF and MMF. To achieve a satisfactory resolution of the DAS data, preprocessing steps are imperative to improve data denoising. Subsequently, the ML algorithm approach offers automated DAS data denoising with high accuracy.