Fig. 1. Measurement system of CH₄ absorption spectrum at high temperature and pressure

Fig. 2. Absorption spectrum of 2.05% CH₄ at 200 ^oC and different pressure. (a) 0.5 × 10⁶ Pa; (b) 1.0 × 10⁶ Pa;(c) 1.5 × 10⁶ Pa; (d) 2.0 × 10⁶ Pa; (e) 2.5 × 10⁶ Pa; (f) 3.0 × 10⁶ Pa

Fig. 3. Absorption spectrum of 2.05% CH₄ at 400 ^oC under different pressure. (a) 0.5 × 10⁶ Pa; (b) 1.0 × 10⁶ Pa;(c) 1.5 × 10⁶ Pa; (d) 2.0 × 10⁶ Pa; (e) 2.5 × 10⁶ Pa; (f) 3.0 × 10⁶ Pa

Fig. 4. Absorption spectrum of 5%–30% CH₄ at 26 ^oC room temperature and 2 × 10⁶ Pa pressure.(a) 5%–30%; (b) 5%; (c) 15%; (d) 25%

Fig. 5. Inversion results according to the measured absorption spectrum of 2.05% CH₄ at 200 ^oC and 0.5×10⁶–3.0 × 10⁶ Pa pressure. (a) Temperature; (b) Concentration; (c) Pressure

Fig. 6. Inversion results according to the measured absorption spectrum of 2.05% CH₄ at 400 ^oC and 0.5 × 10⁶–3.0 × 10⁶ Pa pressure. (a) Temperature; (b) Concentration; (c) Pressure

Fig. 7. Inversion results according to the measured absorption spectrum of 5%–30% CH₄ at 26 ^oC temperature and 2 × 10⁶ Pa pressure. (a) Temperature; (b) Pressure; (c) Concentration