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The Road to SCIAMACHY

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The SCIAMACHY project has from its outset the aim to utilise all the information contained in the radiation upwelling from the atmosphere to space in order to derive the amounts and distributions of atmospheric constituents, parameters and selected surface phenomena. This task requires – beside high quality measurements – an accurate understanding and knowledge of the absorption spectroscopy and the scattering of electromagnetic radiation in the atmosphere and at the Earth’s surface.


1.1 The Road to SCIAMACHY

Recognising the need for global observations of the Earth system, the scientific community has proposed for research and monitoring purposes global observing systems. Over the past three decades pioneering efforts have been made by the scientific community to establish networks of ground based instruments and satellite projects. The overall objectives are:


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to improve our understanding of the physical and chemical processes determining the behaviour of the atmosphere,

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to demonstrate and assess the capability and applicability of remote sensing from space for Earth System and Atmospheric Science, and

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to move towards a global observing system adequate to meet the needs of Earth System Science and to provide the global data needed for policymakers.


The first measurements of atmospheric ozone from space were made by the Soviet space program in the middle of the 1960’s. In the early 1970’s NASA initiated its efforts to make global measurements of atmospheric ozone with the Backscattered Ultra Violet (BUV) instrument aboard the NASA Nimbus 4 satellite. This instrument was significantly enhanced and extended to both the Solar Backscatter Ultraviolet (SBUV) and Total Ozone Mapping Spectrometer (TOMS), which flew on NASA’s Nimbus 7 satellite. Subsequently NOAA was responsible for a series of SBUV-2 instruments on its operational meteorological platforms while NASA operated several TOMS instruments on a variety of satellites (see figure 1-1). Useful solar occultation measurements began in 1978 with the launch of SAM-II (Stratospheric Aerosol Measurement) which was followed by the Stratospheric Aerosol and Gas Experiment (SAGE-I, SAGE-II) and the Russian occultation spectrophotometer SFM-2. The research mission SME (Solar Mesospheric Explorer) was launched in 1983 and made limb scanning measurements of solar backscattered radiation to determine ozone and nitrogen dioxide. Another milestone in the exploration of the atmosphere from space is the Upper Atmosphere Research Satellite (UARS), which carried instruments to sound the upper atmosphere like the Microwave Limb Sounder (MLS) and the Halogen Occultation Experiment (HALOE). UARS was launched in 1991 and the measurements of HALOE were extended into 2005.

The European participation in remote sounding of atmospheric constituents and parameters was focused initially on the development of the geostationary METEOSAT programme. Initiated by ESA and finally transferred to EUMETSAT, it provided measurements of meteorological parameters. While the first polar orbiting European Research Satellite (ERS-1), primarily a platform for microwave and radar sensors, did not address the needs of the atmospheric chemistry community, the second European Remote Sensing satellite (ERS-2), carrying the Global Ozone Monitoring Experiment (GOME), took Europe a large step forward towards ozone and atmospheric composition measurements. GOME on ERS-2 was a smaller scale version of SCIAMACHY derived from the original SCIAMACHY concept, measuring in nadir viewing geometry the upwelling radiation at the top of the atmosphere between 240 and 793 nm. ERS-2 was launched on April 20th, 1995 into a sun-synchronous orbit with an equator crossing time in descending node of 10:30 a.m. The feasibility of the SCIAMACHY instrument and retrieval concepts could be successfully demonstrated for nadir observations with GOME. The absorptions of the trace gases O3, NO2, BrO, OClO, H2O, SO2, and HCHO could be observed as predicted and the retrieval of total and tropospheric column information from GOME measurements was achieved (Burrows et al. 1999 and references therein). In addition, similarly to SBUV, O3 profiles including some information on tropospheric ozone were retrieved from GOME observations (Munro et al. 1998). ERS-2 has been deorbited on July 4th, 2011.


Recently, several new missions were launched and contribute significantly to research in the fields of atmospheric chemistry and physics: NASA's Earth Observing System (EOS) satellites TERRA, AQUA and AURA, the Japanese Advanced Earth Observing System (ADEOS1/2), the Canadian/Swedish ODIN mission and ESA’s ENVISAT.

SCIAMACHY was part of the atmospheric chemistry payload on-board ENVISAT. Following the call for Earth Observation instrumentation in the Announcement of Opportunity for the Polar Platform issued by ESA, the SCIAMACHY proposal was – after peer review – selected as part of the payload for the satellite now known as ENVISAT, which was launched in March 2002 and was in operation until April 2012.

 

Click image to enlarge

 

fig. 1-1:

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Atmospheric science spaceborne instruments and missions from 1970 to 2006 with relevance for SCIAMACHY. The list of missions is not intended to be complete but to illustrate the progress in space borne instrumentation for atmospheric composition monitoring. (Graphics: DLR-IMF)


The heritage of the SCIAMACHY instrument lies in both, the ground based measurements using Differential Optical Absorption Spectroscopy (DOAS) and previous satellite atmospheric remote sensing missions like SBUV, TOMS, SME, and SAGE. SCIAMACHY combined and extended the measurement principles and observational modes of the nadir scattered sunlight recording instruments SBUV and TOMS, the solar occultation instrument SAGE and the limb scattered sunlight measuring instrument SME within one instrument. SCIAMACHY observed in the wavelength range from 214-2386 nm:

 


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the scattered and reflected spectral radiance in nadir and limb geometry,

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the spectral radiance transmitted through the atmosphere in solar and lunar occultation geometry,

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the extraterrestrial solar irradiance and the lunar radiance.

 

Table 1-1:

 

 

Instrument Name Measurement Altitude1 Target Species Observation Geometry2
TR ST ME N L SO LO STO
BUV Backscatter Ultraviolet Ozone Experiment   X   O3 X        
GOME-1 Global Ozone Monitoring Experiment X X   O3, NO2, H2O, BrO, OClO, SO2, HCHO, CHOCHO, IO, clouds and aerosols X        
GOME-2 Global Ozone Monitoring Experiment X X   O3, NO2, H2O BrO, OClO, SO2, HCHO, CHOCHO, IO, clouds and aerosols X        
GOMOS Global Ozone Monitoring by Occultation of Stars X3 X X O3, NO2, H2O, NO3, aerosols, T         X
HALOE Halogen Occultation Experiment       CO2, H2O, O3, NO2, HF, HCl, CH4, NO     X    
IASI Infrared Atmospheric Sounding Interferometer X3 X   O3, H2O, CO, CH4, N2O, T X        
ILAS I, II Improved Limb Atmospheric Spectrometer   X   O3, NO2, N2O, H2O, CFC11, CH4, aerosols     X    
IMG Interferometric Monitor for Greenhouse Gases X X   O3, N2O, H2O, CH4, CO, CO2 X        
MIPAS Michelson Inferometer for Passive Atmospheric Sounding   X X O3, NOx, N2O5 ClONO2, CH4, CFCs, HNO3, and more, T and P   X      
MLS Microwave Limb Sounder   X X ClO, O3, H2O, HNO3, T and P   X      
MLS-2 Microwave Limb Sounder   X X CO, HCL, ClO, O3, H2O, BrO, N2O, SO2, HCN, CH3CN   X      
MOPITT Measurement of Pollution in the Troposphere X     CO, CH4 X        
OMI Ozone Monitoring Instrument X X   O3, SO2, NO2, BrO, CHOCHO, HCHO, aerosols X        
OSIRIS Optical Spectrograph and Infrared Imaging System   X X NO, OClO, O3, NO2, aerosols   X      
POLDER Polarization and Directionality of the Earth’s Radiance X     polarisation, aerosols, clouds X        
SAM II Stratospheric Aerosol Measurement II   X   aerosols     X    
SAGE I Stratospheric Aerosol and Gas Experiment I   X   O3, NO2, aerosols     X    
SAGE II Stratospheric Aerosol and Gas Experiment II   X   O3, NO2, H2O, aerosols     X    
SAGE III Stratospheric Aerosol and Gas Experiment III   X   O3, OClO, H2O, BrO, NO2, NO3, aerosols     X X  
SBUV Solar Backscatter Ultraviolet Ozone Experiment X X   O3, SO2 X        
SBUV-2 Solar Backscatter Ultraviolet Ozone Experiment 2 X X   O3, SO2 X        
SCIAMACHY Scanning Imaging Absorption Spectrometer for Atmospheric Chartography X X X O3, O2, O2(1Δ), O4, NO, NO2, N2O, BrO, OClO, H2O, HDO/H2O, SO2, HCHO, CHOCHO, IO, CO, CO2, CH4, cloud, aerosols X X X X  
SFM-2 Spectrophotometer   X   O3, aerosols     X    
SME Solar Mesospheric Experiment   X X O3, O2(1Δ), NO2   X      
TES Tropospheric Emission Spectrometer X X   HNO3, O3, NO, H2O, CH4, CO, SO2 X X      
TOMS Total Ozone Monitoring Spectrometer X X   O3, SO2, aerosols X        

 

Table 1-1: The different passive satellite instruments designed to determine trace gas distributions in the atmosphere, coverage of their measurements, species measured and observation geometries. The list of sensors refers to figure 1-1.

 


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1) TR = troposphere, ST = stratosphere, ME = mesosphere

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2) N = nadir, L = limb, SO = solar occultation, LO = lunar occultation, STO = stellar occultation

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3) upper troposphere

 

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