The primary scientific objective of SCIAMACHY is the global measurement of various trace gases in the troposphere and stratosphere, which are retrieved from the instrument by observation of transmitted, back scattered 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. This enables, in addition, estimates of global trace gas and aerosol content and distribution in the lower stratosphere and troposphere.
The measurements obtained from SCIAMACHY enable the investigation of a wide range of phenomena which influence atmospheric chemistry:
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 will be observed. Additionally, cloud measurements are obtained. In this mode, the instrument is scanning across-track, with a swath width of ±500 km with respect to the subsatellite track.
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 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.
In the SCIAMACHY optical assembly, the light from the atmosphere is feed by the scanner unit consisting of an azimuth and an elevation scanner into the telescope which directs it onto the entrance slit of the spectrometer. The spectrometer contains a pre-disperser which separates the light into three spectral bands followed by a series of dichroïc mirrors which further divide the light into a total of eight channels.
A grating is located in each channel to diffract the light into
a high resolution spectrum which is then focused onto eight
detectors. The pre-disperser also serves as a Brewster window to
separate polarised light, a part of
Each spectrometer channel is equipped with a Detector Module
consisting of the detectors and their Detector Module Electronics
(DME). Each DME controls its
To achieve the required instrument performance the detectors of the Optical Assembly have to be cooled to around 200 K for the visible and NIR channels 1 to 6 and to around 135 K for the IR channels 7 and 8. This cooling is provided by the SCIAMACHY Radiant Cooler which is coupled through a Thermal Bus Unit (TBU) to the detectors of the Optical Assembly.
The TBU is build up from two cryogenic heatpipes which cool the
The Power, Mechanism and Thermal Control Unit (PMTC) provides
secondary power to all equipment and controls the scanners (via the
A Decontamination Heater Control Module (DHCM) performs the Radiant Cooler decontamination on/off control and the thermal knife control.
SCIAMACHY is developed by a trilateral German/Dutch/Belgian activity under DLR, NIVR and OSTC contract involving Dornier Satellitensysteme GmbH and Fokker Space as the leading companies.