Remedy 1: Improved traceability of uncertainties in FTIR measurements
Within the NDACC FTIR working group, the technical implementation of the uncertainty propagation (both random and systematic) is fully achieved within the EU QA4ECV and GAIA-CLIM projects. However, each PI must determine a good estimate of site-specific uncertainties on the parameters used as input to the retrieval setup. During the QA4ECV and GAIA-CLIM projects, it was observed that there is not full agreement within the FTIR working group on how the estimation of random and systematic uncertainties for these input parameters should be done. Also, there is no full agreement across the two main retrieval software packages SFIT4 and PROFFIT. Random and systematic uncertainty sources are often assumed differently for different sites/different retrieval software. Although the current data products generated during the QA4ECV and GAIA-CLIM projects are highly harmonzied across participating sites, the network will benefit from a further harmonisation of the uncertainty source assumption. A clear distinction between systematic and random uncertainties implemented network-wide, is important for determining accuracy and precision, e.g. when comparing to satellite data, and uncertainty of an average of data.
Recipes to evaluate random and systematic parts of the uncertainty sources will be promoted, but that does not mean yet that they will be implemented at each FTIR site by the end of GAIA-CLIM.
All these gaps deal with the characterisation of the data quality of FTIR. Thus, they should all be considered at the same time as or prior to the resolution of the current gap.
There is no clear agreement yet within the FTIR community on the distinction and characterisation of the random and systematic components of the uncertainty in FTIR measurements. As a consequence, no common approach is available on how to evaluate these components appropriately leading to a degree of heterogeneity in the global FTIR network.