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The primary scientific objective of the SCanning Imaging Absorption SpectroMeter for Atmospheric CHartographY (SCIAMACHY) is the global measurement of various trace gases in the troposphere and stratosphere, which are retrieved from the instrument by observation of transmitted, backscattered, and reflected radiation from the atmosphere in the wavelength range between 240 nm and 2400 nm.
The large wavelength range is also ideally suited for the determination of aerosols and clouds. The nadir and limb viewing strategy of SCIAMACHY yields total column values as well as profiles for trace gases and aerosols in the stratosphere.
Additionally, this enables estimates of global trace gas and aerosol content and distribution in the lower stratosphere and troposphere.
The same volume of the atmosphere are seen under the two gemoetries
The measurements obtained from SCIAMACHY enable the investigation of a wide range of phenomena which influence atmospheric chemistry, such as:
- measurement in the troposphere: biomass burning, pollution, arctic haze, forest fires, dust storms, industrial plumes
- measurement in the stratosphere: ozone chemistry, volcanic events, solar proton events
In order to achieve the scientific objectives, measurements are performed by observing the atmosphere under different viewing angles. In nadir mode, the global distribution (total column values) of the atmospheric trace gases and aerosols are observed. Additionally, cloud measurements are obtained. To obtain the altitude distribution of trace gases, SCIAMACHY performs observations in limb over an altitude range of 100 km, with a vertical resolution of 3 km.
Starting at Earth's horizon, the atmosphere is scanned tangentially over a 1000 km-wide swath. After each azimuth scan, the elevation is increased until the maximum altitude of 100 km is reached.
Differential optical absorption spectroscopy is applied in Sun and moon occultation measurements, where Sun or moon are either tracked, or a vertical scan over the complete Sun/moon surface is performed. The obtained spectra can then be compared with suitable calibration spectra to yield the differential absorption of the atmosphere.
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