Optical Sensing Technologies: A Literature Review, Multi-Dimensional Taxonomy, and Case Study on Seabed Sediment Temperature Monitoring

Abstract

With the rapid growth of digitalization, there is an increasing demand for accurate, high-resolution, and real-time sensing technologies capable of measuring a wide range of parameters in industrial, environmental, and energy systems. Among the available solutions, optical sensing technologies have become particularly attractive due to their high sensitivity, wide measurement range, capability for remote and distributed sensing, and immunity to electromagnetic interference. However, the broad diversity of sensing mechanisms, hardware architectures, and application areas has made it difficult to systematically compare technologies and select the most suitable solution for a given application. Currently, there is still no classification method that provides a comprehensive multi-dimensional framework for organizing optical sensing technologies.

This thesis addresses that gap by making two major contributions. First, a systematic literature review of current classification methods has been conducted and subsequently, a multi-dimensional taxonomy of optical sensing technologies has been developed. The suggested taxonomy consists of four major categories. The first one concerns the way that optical signal encodes information. The second category deals with physical interaction of light with matter. The third category categorizes the sensors depending on their physical realization and implementation platform. Finally, the fourth category considers these technologies from their applications point of view. Second, a case study has been conducted to assess the applicability of Raman-backscatter DTS in practice. The study is based on field measurement data collected at the Suvilahti seabed sediment heat system located at the west coast of Vaasa, Finland. This is the first geothermal plant in Finland that uses the seabed sediment heat as a major source of energy for urban heating purposes. Temperature profiles along two heat-collection lines have been analyzed through different seasons and years. The analysis discovers four distinct thermal zones along the sediment field, each exhibiting different seasonal temperature variation and heat extraction behaviour. The findings show that DTS technology can accurately identify small spatial and temporal temperature gradients within a marine environment and provide information that can be used in the practical management of geothermal systems based on sediments.

The outcomes of the thesis provide a structured descriptive language for optical sensing domain as well as a proven approach to measurement in urban geothermal sensing, with identified directions for future research including the application of fiber-optic current sensors to DC current measurement in data center power distribution infrastructure.