Development of a Combined Optical Fiber Distributed Temperature Sensing System using Raman and Rayleigh Scattering

This thesis presents the development and evaluation of an advanced distributed temperature sensing system. The primary aim was to implement a combined measurement approach utilizing Raman and Rayleigh scattering in a single fiber in order to achieve improved characteristics such as reliability, response characteristics and spatiotemporal behavior. Advancements in distributed temperature sensing are fundamental for future applications in industrial applications. The master thesis starts with an overview of the theoretical foundation of distributed fiber optic sensing systems and the involved measurement techniques. Furthermore, for the fusion of the measurement techniques, a brief discussion of wavelength division multiplexing and Kalman filtering was performed.

The measurement techniques have been evaluated for their response characteristics, utilizing exo\-thermic substance mixing of 2-propanol and water as a source of controlled temperature variation. The analysis of their performance served as a basis for comparison to subsequently demonstrate the improved characteristics resulting from the fusion. The results showed clear improvements in response time and variation of the measurement value in comparison to the conventional distributed temperature sensing approach. The possibility to measure simultaneously occurring vibrations and temperature variations in the system was evaluated and it was shown that the temperature variation has no influence on the vibrational measurements. Therefore, independent parallel measurements are possible.

To perform the measurements, a dedicated software framework was developed based on previous single routines. This framework covers the acquisition, calibration, data processing and visualization of measurements and is extendable for future applications in industry and research questions.

Overall, a robust methodology for distributed temperature measurement has been developed and tested. By the fusion of two complementary sensing principles, the limitations inherent to each individual approach are effectively mitigated, resulting in a more reliable and accurate measurement strategy. This measurement technology broadens the scope of potential industrial applications, particularly in domains requiring high accuracy, low noise distributed temperature monitoring.

Keywords: Fiber Optics , DAS, DTS, DTGS, LF-DAS, DFOS, WDM, Kalman-Filter