September 12, 2014

IASI first spectra

On the figure 1, the IASI spectra were convolved with the IIS ISRF to image at IASI resolution what is viewed by the IIS integrated imager. This is done to localize the verification spectra on a world map and select pixels with no cloud or low infrared gradients to get spectra really characteristic of the atmospheric state.

The spectra in Figure 2, 3 and 4 are respectively spectra in IASI band 1, 2 and 3. These are Level 0 spectra derived from verification interferograms. The location of selected spectra is shown on figure 1 (blue for B1, green for B2 and prune for B3).

B1 spectra (figure 2) show the dependency on mean atmospheric temperature: radiances are higher at low latitudes and colder at higher latitudes. On the left hand part, from 640 to 700 cm-¹, is the strong absorption band of CO2 where radiances correspond to emission by stratospheric layers. Curve 4 indicates a warm atmosphere. The Figure 5 correspond to a view of the Antarctic ice shelf. The spectrum is very cold and even the ozone absorption is weak (ozone depletion?). The spectra 6 and 7 show a different slope in the atmospheric window which can be due to slant atmospheric path or different emissivities.

On the B2 spectra (Figure 3), absorption bands of N2O/CH4 and all the water vapour lines are clearly evidenced.

Similarly on the B3 spectra (Figure 4) and specially on curves 4 and 6 the CO and N2O bands are very clearly present.

The figure 5 is an illustration of a Ozone pseudo channel computed with IASI Brightness temperatures. The same kind of products can be computed for pseudo channels sensitive to CO or CH4 or singular channels as well