## 1 The ECOAL Project  
The scientific research project \"_ECOAL--Ecological Management of Coal Waste Piles in Combustion_\" (2012-2015) was a transnational project consisting of a consortium of five partners from three European countries (Portugal, Spain, and France), with representatives from academia and research units, combining geological and geosciences expertise with optoelectronic competences and complementary know-how in fiber optic sensing, ranging from fundamentals to system development and field tests. The Portuguese institutions were the _Institute for Systems and Computer Engineering of Porto--INESC Porto_ and the _Faculty of Sciences, University of Porto_, in Spain the partners were the _University of Alcala_ (Madrid) and _Universidad Publica de Navarra_ (Pamplona), while from France it involved the _XLIM UMR CNRS Universite de Limoges_. This project was supported by the SUDOE--Interreg IV B program, and was designed and planned to contribute to the management of the environmental problems associated to the self-burning coal waste piles, involving continuous assessment of their status and identification of evolution scenarios, looking at the implementation of corrective/preventive actions to minimize the impact of these natural combustion processes.  
Several works ([1,2] and references therein) reported the application of the fiber optic-based systems for monitoring of ambient conditions in underground coal mines, which have strong implications in safety, productivity, and operation costs. However, the application of fiber optic-based sensing technologies for monitoring of coal-related fires, which cause serious impacts on environment and human health, was never developed.  
The ECOAL project was developed aiming the remote, multi-point, and continuous monitoring of gas emissions and combustion temperature in a self-burning coal waste pile using advanced optical fiber sensing technology. The combustion of coal wastes resulting from mining is of particular environmental concern, so the importance of proper management involving real-time assessment of their status and identification of probable evolution scenarios is recognized. The motivation for the continuous monitoring of combustion temperature and emission levels of certain gases is that it opens up the possibility of planning corrective actions to minimize their negative impact on the surroundings. Optical fiber technology is well suited to this purpose, which is why it was decided to project a fiber optic sensing system to gather data on distributed temperature and gas emissions in these harsh environments.  
After the laboratory development of fiber optic-based systems for distributed temperature and gas emission measurements, a prototype was installed in S. Pedro da Cova waste pile, which resulted from coal mining in Douro Coalfield (North of Portugal).  
The integration and analysis of the results obtained in the project [3, 4, 5, 6, 7, 8, 9] allowed for the study of the dynamics and evolution pathways of the combustion process within the coal waste pile, as well as the identification of potential hazards to the environment and human health. In addition, the acquired knowledge and experience enable system optimization, opening up its widespread application in other self-burning coal waste piles as well as in other similar environments, such as coal storage piles.