Abstract: Real-time and accurate measurement of gas concentration at the borehole outlet is essential for the intelligent management of gas tunnels. Currently, tunable diode laser absorption spectroscopy (TDLAS), the widely used technique, suffers from reduced detection accuracy in the complex environments of gas tunnels. To overcome this limitation, a TDLAS-based measurement system is developed by integrating wavelength modulation spectroscopy with a centroid-weighted Lagrange interpolation compensation algorithm. The system models and corrects measurement errors caused by fluctuations in gas composition, ambient pressure, and temperature at the borehole outlet, thereby improving measurement accuracy and stability under dynamic conditions. System performance is experimentally validated using standard gas samples. The main findings are: (1) A gas concentration inversion model based on the Beer-Lambert law and HITRAN database parameters is established, identifying absorption line shape function and line strength as the primary factors influencing measurement accuracy. The Lorentzian function is found to be more suitable under near-atmospheric pressure and dynamically disturbed conditions. (2) To compensate for line shift and broadening due to temperature and pressure variations, a centroid-weighted Lagrange interpolation algorithm is proposed, achieving accurate gas concentration correction under unsteady-state conditions with high numerical stability and adaptability. (3) Experimental validation using 0.5% and 4.5% standard gases over a temperature range of 0 － 40 ℃ demonstrates that the proposed compensation method maintains measurement errors within 0.5%, significantly outperforming uncompensated measurements. (4) The developed system enables high-precision, dynamic monitoring of single-borehole gas concentrations, exhibits strong environmental adaptability.

Key words: extraction borehole, gas tunnel, gas concentration, tunable diode laser absorption spectroscopy technology, compensation algorithm