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Sensitivity test for the optimization

of the atmospheric line shape

 

In the reference FM the atmospheric line shape was modelled up to ±25 cm-1 from the line centre.

Sensitivity tests were conducted to evaluate the impact on computing time and FM accuracy of modelling the atmospheric line shape for non-target species (i.e., all the simulated species except H2O, CO2 and O3) up to ±10 cm-1 from the line centre.

 

Figure 11 shows the difference between the spectrum simulated with and without this approximation in the model of atmospheric line shape. The simulation was performed on the full spectral range covered by IASI. In the figure is also reported the nominal instrumental noise as reference for the approximation. The larger differences are observed around 1250 cm-1, but they never exceed the nominal instrumental noise.

 

We conclude that the error introduced by this approximation does not affect the CO2 information.

 

klima_figure 11.jpg

 

Figure 11

Difference between the spectrum simulated with and without atmospheric line shape approximation.

The red line is the nominal instrumental noise;

the green line in the nominal instrumental noise reduced by a factor