A method for measuring an amount ( c x ) of a gaseous species ( G x ) present in a gas, the gaseous species being able to absorb light in an absorption spectral band (Δ x ), the method comprising the following steps: a) placing the gas between a light source and a measurement photodetector , the light source being able to emit an incident light wave , the incident light wave propagating through the gas toward the measurement photodetector , the measurement photodetector being able to detect a light wave transmitted by the gas, in the absorption spectral band; b) illuminating the gas ( G ) with the light source ; c) measuring, with the measurement photodetector , an intensity ( I ( k )), called the measurement intensity, of the light wave transmitted by the gas, in the absorption spectral band; d) measuring, with a reference photodetector , an intensity ( I ref ( k )), called the reference intensity, of a light wave (12 ref ), called the reference light wave, the reference light wave being emitted by the light source in a reference spectral band (Δ ref ); steps b) to d) being implemented at a plurality of measurement times (1... K ), the method also comprising the following steps: e) correcting the reference intensity ( I ref ( k )) detected at the various measurement times; f) estimating an amount ( c x ( k )) of the gaseous species ( G x ), at the various measurement times, from the reference intensity I ref ′ k corrected in step e) and from the measurement intensity (I(k)) resulting from step c); the method being characterized in that step e) comprises the following substeps: ei) taking into account a parametric model, defined using the parameters ( θ̂ , θ̂ k ), modelling a temporal variation in the reference intensity ( I ref ( k )) detected at the various measurement times, the temporal variation expressing a decrease in the reference intensity; eii) estimating the parameters ( θ̂ , θ̂ k ) of the model using the reference intensities measured at the various measurement times; eiii) estimating a reference intensity called the corrected reference intensity ( I' ref ( k )) at each measurement time depending on the estimated parameters ( θ̂ , θ̂ k ) of the model. a) placing the gas between a light source and a measurement photodetector , the light source being able to emit an incident light wave , the incident light wave propagating through the gas toward the measurement photodetector , the measurement photodetector being able to detect a light wave transmitted by the gas, in the absorption spectral band; b) illuminating the gas ( G ) with the light source ; c) measuring, with the measurement photodetector , an intensity ( I ( k )), called the measurement intensity, of the light wave transmitted by the gas, in the absorption spectral band; d) measuring, with a reference photodetector , an intensity ( I ref ( k )), called the reference intensity, of a light wave (12 ref ), called the reference light wave, the reference light wave being emitted by the light source in a reference spectral band (Δ ref ); e) correcting the reference intensity ( I ref ( k )) detected at the various measurement times; f) estimating an amount ( c x ( k )) of the gaseous species ( G x ), at the various measurement times, from the reference intensity I ref ′ k corrected in step e) and from the measurement intensity (I(k)) resulting from step c); ei) taking into account a parametric model, defined using the parameters ( θ̂ , θ̂ k ), modelling a temporal variation in the reference intensity ( I ref ( k )) detected at the various measurement times, the temporal variation expressing a decrease in the reference intensity; eii) estimating the parameters ( θ̂ , θ̂ k ) of the model using the reference intensities measured at the various measurement times; eiii) estimating a reference intensity called the corrected reference intensity ( I' ref ( k )) at each measurement time depending on the estimated parameters ( θ̂ , θ̂ k ) of the model. <EOS>