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International audience; A high-enthalpy source (HES) has been developed in Rennes either to heat gases up to 2000K in local thermodynamic equilibrium (LTE) or to generate hypersonic expansions. The HES prototype has been associated with a high-resolution Bruker IFS 120 HR Fourier transform spectrometer to record emission spectra of hot gases, in LTE conditions. A series of emission spectra of methane has been obtained at 1005, 1365, 1485, 1625 and 1820K in the pentad spectral region located around 3000 cm1, at Doppler-limited resolution (0.02 cm1). Spectra have been corrected for the transmission function that strongly affects the infrared radiation emitted by the hot gas. Line-integrated absorption cross sections have been extracted from the corrected spectra using an improved procedure for the calculation of the total partition function Q of methane at high temperature. This calculation included anharmonicity and rovibrational interaction effects, and was based on a multi-resolution fully converged direct partition sum. It has been shown that, as the temperature increases above 1000 K, the commonly used harmonic and rigid rotor double approximation to estimate Q leads to underestimated values.