## 4 Discussion on Practical Open Issues and Future Development
According to [PERSON], distributed temperature sensing \"has fundamentally transformed the ability of the scientific community to understand the hydrological processes and has allowed the testing of conceptual models that synthesize the understanding across scales.\" In the same manner, we believe that DOFSs have the same potential in geo-hydroological monitoring; however, it is necessary that a strong effort be made by scientists and researchers to make these new measurement paradigms fully accepted by the community acting on geo-hydroological monitoring. Only an effort towards making the technology more \"transparent\" will promote the spread of DOFS throughout the community. With the term transparent we mean that the device/technology must fade into the background and become a mere tool. Typical actors of geo-hydroological monitoring need to focus on more important aspects rather than the technology in use, and must rely on reliable and straightforward monitoring tools. Occasionally, they might want to adjust some settings, but most of the time the system has to work almost automatically or according to consolidated routines. About this, FBGs--as they are capable of replicating the working principle and features of standard consolidated sensors--have a significant advantage over DOFSs. In light of this, we believe that DOFSs for geo-hydrological monitoring may greatly benefit from a strong effort towards four main directions:  
* To extend the range of physical fields that can be effectively measured and propose more efficient ways to measure actual physical fields (i.e., _sensing mechanism_);
* To further ameliorate the performance and reliability of the interrogator systems (i.e., _hardware_);
* To introduce data analysis and interpretation models of raw measurements, still substantially not mature (i.e., _software_);
* To implement replicable tools supporting the installation (i.e., _practice_). Due to the fundamental phenomena at the basis of DOFSs that limit the sensitivity mainly to temperature and strain, the first need must be tackled with the proposal of novel transducing mechanisms; for instance, by innovative fibre cable designs. For example, we have reported that DTS surveys can locally estimate soil moisture, but the measurements are affected by too many other factors such that its use in practice is not viable. A similar concern can be raised for distributed pressure sensing, at least in the range and sensitivity of pressure required by geo-hydrological monitoring. Regarding the need for performance improvement and data analysis/interpretation, the many recent research papers about new achievements in distributed sensing scheme and about experiments in physical models represent encouraging replies. The last topic is instead mostly ignored by the technical and industrial community, and each installation practice is a result of operators' background and inventiveness. Remarkably, all of these actions will promote the spread of the technology; as a positive side effect, economies of scale (at least for some DOFSs) will be enabled. This will determine a reduction of the cost of the interrogators, still far too large compared to traditional and FBG systems, supporting a positive feedback loop. To conclude with the point of view of the public or private policy/decision makers, the lack of specific and widely accepted protocols and guidelines represents an additional major obstacle to win over sceptic stakeholders and to penetrate into geo-hydrological monitoring practice, which is traditionally quite conservative.