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.