Fig. 1. The structureof CH₄ detection using TDLAS technology

Fig. 2. Second harmonic signal

Fig. 3. Variation trend of CH₄ concentration at different temperature

Fig. 4. CH₄ absorption line intensity curve with temperature change

Fig. 5. Half width at half-maximum of CH₄ absorption line varies with temperature

Fig. 6. CH₄ line intensity and half width at half-maximum vary with temperature relative rate

Fig. 7. BP neural network and PSO-BP model forecast output

Fig. 8. Histogram of relative error distribution
(a): BP neural network; (b): PSO-BP model

Fig. 9. Experimental data graph before and after 0.04% CH₄ compensation