SCIAMACHY limb/nadir mode measurements

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About this exercise type...

In a limb mode scan, the SCIAMACHY spectrometer is scanning _ in the flight direction. In a nadir mode scan, on the other hand, the spectrometer is scanning _. SCIAMACHY performs a group of nadir scans in immediate sequence. This group of scans is termed a _, it has a total duration of about _ and about _ of these groups of scans are performed during the _ part of the orbit.

Each group of nadir mode scans measures the spectra from a region directly _ the instrument. This radiation has been _ and reflected at the Earth's surface and in the volume of _ through which it has passed. The characteristic _ of radiation by trace gases, which allows us to measure their _ can occur on the _ path of the solar radiation as well as on its return path. In contrast, limb mode scans measure the spectra from a volume of atmosphere about _ km ahead of the current orbital position. The flight of the satellite brings the spectrometer directly _ this volume of atmosphere after about _. SCIAMACHY then performs a _ scan on this region. Whereas the GOME spectrometer covers the entire surface of the Earth in _ days, because of the alternation of nadir and limb mode scans SCIAMACHY takes _ days to cover the Earth's surface.

The importance of the alternation of nadir and limb mode scanning in SCIAMACHY is that the same volume of atmosphere is observed from two directions. The limb mode scan can be used to measure concentrations of trace gases in the _. Nadir mode scans, on the other hand, measure concentrations in both the _. The concentrations measured in limb mode can therefore be _ the concentrations measured by the nadir mode scans to isolate the concentrations for the _vertical column only.