Distributed Raman Sensing

Abstract

The Raman scattering effect constitutes one of the basic physical mechanisms exploited in optical fiber distributed temperature sensing. In particular Raman distributed temperature sensors (RDTS) have been developed for more than three decades, becoming today a mature technology that is widely applied to several strategic industrial fields. Making use of the thermally-activated spontaneous Raman scattering (SpRS) process, continuous measurements of a temperature profile over a sensing range of tens of kilometers can be obtained with high accuracy and meter-scale spatial resolution. Knowing the distributed temperature profile over large infrastructures provides a powerful technique for applications ranging from oil and gas to fire detection, and from energy production to transportation applications and environmental monitoring. Although this technology can be considered to be quite mature, research on Raman distributed temperature sensing is still active, with the main goal being extending the sensing distance while keeping high spatial resolution and a low cost of the system, and providing reliable and robust RDTS units able to operate in harsh environments. In this book chapter, after a first description of the physical mechanisms behind Raman scattering, the working principle of RDTS system is provided along with a description of the most-common system configurations. Then, advanced techniques to improve the RDTS performance (e.g., pulse coding and image processing) are presented. In the final section, some examples of RDTS industrial applications are addressed, presenting several field trials which demonstrate the effectiveness of RDTS as practical monitoring solutions in a wide range of industrial fields.