G2.19   Line of sight and vertical averaging kernel are only approximations of the real 3D averaging kernel of a FTIR retrieval

Gap detailed description

The line of sight (LOS) is an important `first order’ characterization of the horizontal averaging for FTIR measurements. Tools exist to calculate the line of sight for individual FTIR measurement. The UVVIS GEOMS templates have introduced variables and can be transferred to the FTIR GEOMS template to store the LOS information. This is planned for the next FTIR GEOMS template update. Comparisons cannot yet account fully for the representativeness of the data, even though the LOS is used in such a comparison. To further characterize the horizontal averaging, a more detailed study of the 3D kernels should be issued.

Activities within GAIA-CLIM related to this gap

This gap is not addressed within GAIA-CLIM.

Gap remedy(s)

Remedy #1

Specific remedy proposed

Enhance the existing retrieval software packages so that the forward model allows non-uniform atmospheric states.

Measurable outcome of success

Updated retrieval software packages along with horizontal averaging kernels.

Achievable outcomes

Technological / organizational viability: medium

Indicative cost estimate: medium (< 1 million).


Horizontal averaging and off site location of the probed airmasses is important for validation activities.


5 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

Non-optimal validation results for gases and sites with strong spatial gradients.


Ambiguity in interpretation of the observed measurements, particularly in the prescence of strong gradients in the measured parameters. 

Work package: