Long-Range Hydrogen Gas Measurement via Raman and Rayleigh-Brillouin Backscattering.

Hydrogen (H2) is a promising energy carrier, but its wide flammability range requires rapid and reliable leak detection. In this study, we developed a non-contact stand-off ultraviolet (UV) light detection and ranging (lidar) system that simultaneously acquires Raman and Rayleigh-Brillouin backscattering signals for long-range H2 measurement. A 360 nm UV excitation source was used, and the system was evaluated at distances of 1, 3, 5, 10, 20, and 30 m using standard gases containing 10-1000 ppm H2. Quantitative analysis based on partial least squares (PLS) regression showed high linearity across the full distance range, with coefficients of determination (R2) of 0.97-0.98 and standard errors of calibration (SECs) of 40-70 ppm. The Rayleigh-Brillouin channel provided a useful complementary signal, particularly at longer distances, improving the robustness of concentration prediction when combined with the Raman response. These results demonstrate the feasibility of real-time, long-range H2 monitoring in large spaces and support the use of combined Raman and Rayleigh-Brillouin backscattering for safety monitoring in hydrogen-related facilities.