Minimize SCIAMACHY Product Handbook

Introduction

 
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CHAPTER 1

1. Introduction

The handbook version 1.0 is based in parts on the SCIAMACHY book (Gottwald et al. 2006) and has been updated to cover the Level 1 version 8, and the Level 2 version 6 SCIAMACHY operational processors.

This chapter explains the background of SCIAMACHY.

 

The recognition, that significant changes in the composition of the Earth’s atmosphere are occurring on both short and long timescales and thereby modifying our environment and climate, has resulted in scientific debate as well as public concern, and emphasises the need for global measurements of atmospheric constituents at representative spatial and temporal sampling. Established examples, where change has been identified, are:

 
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the precipitous loss of Antarctic and Arctic stratospheric ozone (O3) resulting from the tropospheric emission of chlorofluorocarbon compounds (CFCs, halones, and HFCs) (WMO 2003),

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the global increase of tropospheric O3 (WMO 1995) and its impact on air quality,

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the trans-boundary transport and transformation of pollution resulting for example in acidic deposition and impacting air quality far from pollution sources (WMO-IGACO 2004),

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global dimming attributed to changes in aerosol and clouds (Wild et al. 2005),

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the observed increase of tropospheric greenhouse gases such as CO2, CH4, N2O and O3 and its impact on climate change (IPCC 2001), and

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the coupling between stratospheric ozone loss and increased greenhouse gas concentrations (Shindell et al. 1998).


In order to assess the significance of such changes a detailed understanding of the physical and chemical processes controlling the global atmosphere is required. The accurate assessment of the impact of current and future anthropogenic activity or natural phenomena on the behaviour of the system, comprising the atmosphere and the Earth’s surface, requires quantitative knowledge about the temporal and spatial behaviour of several atmospheric trace constituents (gases, aerosol, clouds) from the local to global scales in the troposphere, stratosphere and mesosphere. These data sets are also needed to test the predictive ability of the theories currently used to model the atmosphere.

The SCanning Imaging Absorption spectroMeter for Atmospheric CHartographY (SCIAMACHY, ‘SCIAMACHY’ is a Greek expression, which means chasing or hunting shadows and is equivalent to do the impossible task) as part of the atmospheric chemistry payload on-board the Environmental Satellite (ENVISAT) of the European Space Agency (ESA) was conceived to make a significant contribution to the required data sets and the understanding of climate change.

Prior to the advent of space flight, measurements of atmospheric composition were limited in geographical coverage. The development of satellite platforms in low-Earth and geostationary orbit over the last three decades has provided the opportunity to observe the Earth and its atmosphere in novel viewing geometries. The potential to make near simultaneous observations at the global scale for the first time has facilitated the emergence of Earth System Science. In particular the atmospheric sciences have gained from satellite observations. This is because remote regions of the atmosphere over the land and oceans, where ground-based stations or ship-borne measurements are usually rare, can now be probed regularly from space and variations of geophysical parameters on small and large scales, both spatially and temporally, can be studied.

Passive atmospheric sounding from space can be achieved in two ways – either by analysing absorption or emission spectra, both requiring accurate measurement of radiation leaving the top of the atmosphere. Absorption and emission processes in the atmosphere produce spectra, which are characteristic for the emitting or absorbing atom or molecule.

Emission spectra consist of the signals from atmospheric constituents which radiate mainly in the infrared and microwave spectral range according to their characteristic thermal excitation. They can be regarded as the thermal ‘fingerprint’ of the atmosphere. From the emission line properties trace gas concentrations are derived.
Measuring solar absorption spectra at the top of the atmosphere is the approach utilised in SCIAMACHY. Atoms, molecules and particles absorb, emit and scatter the incoming solar electromagnetic radiation. The incoming solar radiation is described to a good approximation by the emission from a black body having a temperature of about 5800 K, modulated by atomic absorption lines, the solar Fraunhofer lines. The upwelling radiation at the top of the atmosphere from the Ultraviolet (UV) to Short-Wave Infrared (SWIR) comprises – after travelling through the atmosphere – the solar output, modified by scattering, absorption and emission processes along its light path through the atmosphere and reflected as well as scattered at the Earth’s surface.
 


 
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