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 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 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.