3.5 The Earth Surface and Beneath
SCIAMACHY’s realm is the Earth’s atmosphere. However, the measured earthshine spectra are also affected by surface reflection and absorption, i.e. by the broadband ground albedo, and by narrowband spectral structures of different origins. These features went unnoticed in trace gas retrieval algorithms for a long time. The initial approach is certainly to take them into account for improving the tropospheric trace gas information. However, these features can also be used to derive various surface parameters over land or even phytoplankton properties of the oceans.
Land Vegetation Characteristics
Vegetation is a unique property of the Earth. Understanding how it changes contributes to many applications, ranging from global climate change to predicting crop yield. Usually, vegetation indices exploit spectrally broadband differences in reflectivity between the red and NIR wavelength range. Atmospheric sensors like SCIAMACHY provide a higher spectral resolution, i.e. such differences can be analysed on a much finer spectral scale. While optimising DOAS trace gas retrievals, Wagner et al. (2007) noticed that the resulting residuals displayed distinct structures, particularly over vegetated land. These structures could be reduced in amplitude when vegetation data such as spectral reflectances of conifers, deciduous trees or grass were included in the spectral fitting. Fig. 3-27 shows the fit results for deciduous vegetation for summer 2003-2004. A correspondence to deciduous vegetation is obvious, but interference with other vegetation types and coastal waters is still present. Since retrieving vegetation information from remotely sensed atmospheric data is a rather novel approach, current results are still preliminary and require further investigations. There is a clear need to collect more spectral reference data at spectral resolutions similar to SCIAMACHY.