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SCIAMACHY on ENVISAT

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2.2 SCIAMACHY on ENVISAT

SCIAMACHY formed part of the payload of ENVISAT (table 2-1, fig. 2-1). It had, besides AATSR and DORIS, the status of an Announcement of Opportunity Instrument (AOI) contrary to the remaining seven ESA developed instruments (EDIs). As an AOI, SCIAMACHY had been developed and provided by Germany and The Netherlands, including a Belgian contribution. From an operations point of view, however, SCIAMACHY was considered an integral part of ENVISAT’s payload following the same guidelines and rules as the EDIs.


ENVISAT Parameters  
Dimensions 26 m x 10 m x 5 m  
Total Mass  8140 kg 
Payload Mass  2050 kg 
Launcher  Ariane-5 
Launch  March 1st, 2002 
 

Table 2-1: ENVISAT characteristics

 

click to enlarge

fig. 2-1:

image
Artist's impression of ENVISAT in orbit. SCIAMACHY was located at the upper right corner of the payload front panel. (photo: ESA)
 

Together with MIPAS and GOMOS, SCIAMACHY formed ENVISAT’s atmospheric mission. The three atmospheric instruments utilized different wavelength ranges and measurement principles. They complement each other such that synergistic views became possible. While SCIAMACHY, as an absorption spectrometer in the UV-SWIR range requed sunlight, MIPAS – operating in the thermal infrared – could measure over the complete orbit. This was also the case for GOMOS, where the UV-VIS component of stars in occultation was used to probe the atmosphere. SCIAMACHY had been viewing in flight direction (limb mode) and towards the sub-satellite point (nadir mode). MIPAS looked along-track into anti-flight and across-track into anti-sun direction. GOMOS could steer its line of sight towards stars which set between anti-flight and across-track anti-sun direction. Additionally, the optical imaging instruments MERIS and AATSR (Advanced Along Track Scanning Radiometer) delivered data for scientific applications in the fields of clouds, aerosols and water vapour. Their nadir views overlapped with SCIAMACHY’s nadir geometry thus permitting synergistic analyses.

Orbit and Attitude

ENVISAT operated in a polar, sun-synchronous orbit with a morning descending node crossing (DNX) time (table 2-3). The selected local DNX time of 10 a.m., together with SCIAMACHY’s location at the upper right corner on the payload module front panel, was equivalent to the fact that the sun could only be seen when pointing the instrument’s line of sight to the left. Orbit perturbations slightly modified the specified reference orbit with time. Once orbit parameters exceeded their limits, an orbit control manoeuvre adjusted the actual orbit. These manoeuvres could either be In-Plane (to correct for the effect of air drag on altitude) or Out-of-Plane (to adjust the inclination which drifts due to solar and lunar gravity perturbations). SCIAMACHY was one of the instruments which continued with measurements during In-Plane manoeuvres. While executing an Out-of-Plane manoeuvre, SCIAMACHY measurements were interrupted but the thermal status of the Optical Bench Module (OBM) and the detectors remained unchanged.


 

 

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