G2.22   FTIR cell measurements carried out to characterize ILS have their own uncertainties

Gap detailed description

Cell measurements carried out to characterize FTIR instrument line shape (ILS) have their own uncertainties. An ILS retrieval comes along with an uncertainty and an averaging kernel. In particular the averaging kernel for an ILS retrieval is often not adequately considered. For instance, in order to have ILS sensitivity for fine spectral signatures we need very low pressure cells. If the pressure is too high, the cell spectra will not contain information about the ILS at large optical path difference, which is important to understand the fine spectral signatures.  This problem is reported by the averaging kernel of the ILS retrieval. Inaccurate knowledge of the ILS leads to larger uncertainties on the retrieved concentrations (XCH4, XCO2).

Activities within GAIA-CLIM related to this gap

This gap is not remedied within GAIA-CLIM.

Gap remedy(s)

Remedy #1

Specific remedy proposed

This can be remedied by requiring that for each ILS retrieval, the averaging kernels are also reported.

Measurable outcome of success

Detailed description of the ILS uncertainties and its influence on the retrieved targets.

Achievable outcomes

Technological / organizational viability: high.

Indicative cost estimate: medium (<1million).


The reported uncertainty budgets will be more accurate.


2 years

Gap risks to non-resolution

Identified future risk / impact

Probability of occurrence if gap not remedied

Downstream impacts on ability to deliver high quality services to science / industry / society

Underestimation of the uncertainty on the retrieval targets


Inappropriate confidence assigned to the measurement series leading to erroneous conclusions in downstream applications.


Work package: