On the potential of the 2041-2047 nm spectral region for remote sensing of atmospheric CO2 isotopologues

Pressing open questions about the carbon cycle can be addressed with precise measurements of the three most abundant CO2 isotopologues 16O12C16O, 16O13C16O, and O16C12O18. Such measurements can, e.g., help to further constrain oceanic and biospheric net fluxes or to differentiate between the gross biospheric fluxes photosynthesis and respiration. The 2041-2047nm (about 4885-4900cm−1) spectral region contains separated absorption lines of the three most abundant CO2 isotopologues. Their spectral properties make this spectral region well suited for the use of a light path proxy method for the retrieval of δC13 and δO18 (the ratio of heavier to lighter isotopologues relative to a standard). An optimal estimation based light path proxy retrieval for δC13 and δO18 has been set up, applicable to GOSAT (Greenhouse gases Observing Satellite) and ground-based FTS (Fourier transform spectrometer) measurements. Initial results show that it is possible to retrieve δC13 and δO18 from ground-based FTS instruments with a precision of 0.6-1.6‰ and from GOSAT with a precision of about 30‰. Comparison of the achievable precision with the expected atmospheric signals shows that ground-based FTS remote sensing measurements have the potential to gain valuable information on δC13 and δO18 if averaging a sufficient number of measurements. It seems unlikely that this applies also to GOSAT because of the lower precision and a conceptual larger sensitivity to scattering related errors in satellite viewing geometry.

► The 2041-2047 nm region is suited for remote sensing atmospheric CO2 isotopologues. ► A δC13 and δO18 retrieval was set up for ground-based FTS and the GOSAT satellite. ► The retrieval precision of δC13 and δO18 is about 0.6-1.6‰ (FTS) and 30‰ (GOSAT). ► FTS measurements can give valuable information on atmospheric δC13 and δO18.