Ongoing projects
Sensitivity test for the optimization
of the CO2 Line Mixing Model
In the reference forward model line-mixing effects are taken into account, by adding to the simulated radiances the contribution of CO2 line mixing modelled over the full spectral range covered by IASI. A significant reduction of the computing time is obtained in the ARM by evaluating the contribution of line-mixing on a sub-set of spectral intervals.
In order to identify the minimum sub-set compatible with the accuracy requirements of the ARM, we calculated the difference between synthetic spectra simulated over the full IASI spectral range, with and without the contribution of CO2 line-mixing. The residuals are plotted in Figure 9, along with the nominal instrumental noise.
The modelling of CO2 line-mixing can be limited to the spectral intervals, where these differences are larger than the nominal instrument noise, i.e. to the bands [650-800] cm-1 and [2000-2500] cm-1.
Figure 9
Difference between the spectrum simulated with and without the CO2 line mixing model.
The red line is the nominal instrumental noise;
the green line in the nominal instrumental noise reduced by a factor 10