Derivation of Tropospheric Information

The retrieval range is limited at lower altitudes because the atmosphere becomes optically thick with respect to Rayleigh scattering and/or O3 absorption. Above about 40 km the O3 absorption signatures become too weak to be observed. However, normalised limb radiance profiles in the O3 Hartley and Huggins bands can also be used without further wavelength pairing for the derivation of ozone profiles in the upper stratosphere and lower mesosphere (Rohen et al. 2006). The O3 retrievals may be extended up to at least 65 km since the absorption cross sections in the Hartley and Huggins bands are significantly larger than in the Chappuis band.
The wide variety of retrieval algorithms currently applied to SCIAMACHY limb and occultation data are summarised in table 5-3, together with their corresponding references.

*Parameter*	*Spectral Window (nm)*	*Layer*	*Quantity*	*Retrieval Algorithm Reference*
O3	525, 600, 675525-590	stratosphere	profile	von Savigny et al. 2005 a Doicu et al. 2002, Doicu 2005
	240-310 (selected wavelengths)	mesosphere	profile	Rohen et al. 2006
	520-595	stratosphere	profile sun occultation	Meyer et al. 2005
	510-560	stratosphere	profile moon occultation	Amekudzi et al. 2005a
NO2	425-450(70)	stratosphere	profile limb	Rozanov et al. 2005 b Sioris et al. 2004 Doicu et al. 2002, Doicu 2005
	420-460	stratosphere	profile sun occultation	Meyer et al. 2005
	430-460	stratosphere	profile moon occultation	Amekudzi et al. 2005a
NO3	610-680	stratosphere	profile moon occultation	Amekudzi et al. 2005b
BrO	335-360	stratosphere	profile	Rozanov et al. 2005 b Dorf et al. 2005
OClO	365-389	stratosphere	profile
NLC	265-300	mesosphere	indicator, particle radius	von Savigny et al. 2004a
PSC	750, 1090	stratosphere	indicator	von Savigny et al. 2005b
Tmesopause	1515-1550	mesosphere	nighttime temperature at mesopause	von Savigny et al. 2004b

Table 5-3: Atmospheric geophysical parameters and retrieval algorithms – limb and occultation.

5.5 Derivation of Tropospheric Information

Of major scientific – and public – interest are distributions of trace gases in the troposphere. Two cases need to be distinguished:

	Constituents with the majority of the atmospheric amount residing in the lower troposphere (e.g. CO, CH4, CO2, HCHO, SO2, H2O): The total column derived from UV-VIS and SWIR solar backscatter measurements with the techniques derived in chapter 5.2 directly represents the tropospheric column amount including the boundary layer under cloud free conditions.
	Trace gases with comparable column amounts in the troposphere and stratosphere (e.g. BrO, NO2) or with the stratospheric amount dominating the total column (e.g. O3): Additional techniques have to be applied to separate tropospheric and stratospheric concentrations.