Limb, nadir and occultation measurements are made during every orbit. Trace gases, aerosols, clouds and the surface of the Earth modify the light observed by SCIAMACHY via absorption, emission and scattering processes. Inversion of the radiance and irradiance measurements allows retrieval of the amounts and distributions of a significant number of constituents from their spectral signatures.
The Initial Phases of SCIAMACHY
A first attempt to perform DOAS from space, MAP (Measurement of Atmospheric Pollution) was made by J.P. Burrows, D. Perner and P.J. Crutzen at the Max Planck Institut für Chemie in early 1985, in response to an ESA call for research instruments to fly on EURECA, a free-flying platform to be released from the Space Shuttle for making measurements over several months. During the period from 1985 to 1988 the concepts for remote sounding of atmospheric chemical constituents and parameters was refined and developed further. Additional scientists joined a growing scientific team. The concept of SCIAMACHY resulted from these endeavours.
The SCIAMACHY proposal (Burrows et al. 1988a) was submitted in July 1988 by the SCIAMACHY Science Team – and supported by the German Space Agency DARA GmbH (now DLR) – in response to ESA’s call for experiments to fly on-board the Polar Platform, an element of the Columbus Programme. This mission, the Polar Orbiting Earth Observation Mission (POEM-1), finally evolved into the mission now better known as ENVISAT.
In February 1989 a peer review selected SCIAMACHY to be part of the payload of ENVISAT and a phase A feasibility study was initiated in summer 1989. During Phase A the Dutch Space Agency (NIVR) supported Dutch industry to join the SCIAMACHY consortium. Later in Phase B, the Belgian Federal Science Policy Office decided to also participate in the SCIAMACHY programme by cooperating with the Dutch partner.
In April 1989, SCIAMACHY was also identified to become part of the payload of the German research program ATMOS of the German Ministry of Science and Technology (BMFT). The aim of ATMOS was to investigate the use of instrumentation on a dedicated small satellite platform for Earth System Science. After the decision was made to support ESA’s Polar Platform with a full complement of Earth observation instruments, the ATMOS program focused on the development of SCIAMACHY in Germany and providing some additional support to aspects of the ESA developed instruments MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) and MERIS (Medium Resolution Imaging Spectrometer).
After phase A, lasting from 1989 to 1990, SCIAMACHY was selected for flight by ESA as a national contribution to the ENVISAT project. The ESA conference at ministerial level approved the ENVISAT mission in November 1992 and around this time also the German and Dutch governments initiated the development of the SCIAMACHY instrument hardware. These early decisions triggered the development of one of the major national space projects in Germany and The Netherlands in the past decade.
It is interesting to note that under the impression of the observation of the precipitous loss of ozone in austral spring mid of the 1980’s, ESA was recommended at the ESA User Consultation meeting in Paris, during November 1988, to start measurements of relevance to atmospheric composition earlier than the launch of ENVISAT. In this context ESA announced a call for experiments to measure atmospheric constituents from ERS-2, which was under construction at that time. As a result, J.P. Burrows and P. Crutzen proposed the SCIA-mini experiment (Burrows et al. 1988b), being derived from the SCIAMACHY instrument concept. This proposal was selected but subsequently recommended for simplification. After this exercise, including for example descoping of the limb measurement mode, the re-named instrument GOME was accepted for flight on ERS-2. Based on the original SCIAMACHY concept and benefiting from its scientific and industrial development work, it was ‘fast tracked’ ahead of its much more challenging successor. GOME fitted into redundant platform resources, known to be available aboard ERS-2 and was successfully designed, constructed and made ready for launch in 1995 within only four years. The instrument was flying on the ERS-2 satellite until deorbiting in 2011. Its success has demonstrated the feasibility and capabilities of this new instrument concept. Much of the experience gained with GOME can be used directly for SCIAMACHY.