The GeoStationary Scanning Imaging absorption Spectrometer (GeoSCIA) as part of the Geo Stationary Tropospheric Pollution Explorer (GeoTROPE) Mission: Objectives and Requirements

One of the major challenges facing atmospheric sciences is to assess, understand and quantify the impact of natural and anthropogenic pollution on the quality of life on Earth on a local, regional and continental scale. To understand the effects of regional pollution on a continental scale there is the requirement to link diurnal with seasonal and annual timescales, as well as local with regional and continental spatial scales, which can be addressed by performing sub-hourly measurements at appropriate horizontal and vertical resolution. Tropospheric observations from low-Earth orbit (LEO) platforms with instruments like TOMS and GOME have already demonstrated the potential of detecting constituents relevant for air quality but they are limited, for example by the daily revisit time and local cloud cover statistics. Measurements from geostationary orbit (GEO) offer an practical approach to the observation of diurnal variation from space with the pertinent horizontal resolution. As a consequence the geostationary tropospheric pollution explorer (GeoTROPE) mission has been proposed. It consists of two instruments: The geostationary Fourier imaging spectrometer (GeoFIS) covering the thermal infrared and the geostationary scanning imaging absorption spectrometer (GeoSCIA) covering the ultraviolet–visible and short-wave-infrared (UV–VIS–SWIR) regions. This paper summarises the potential and feasibility of tropospheric remote sensing from geostationary orbit by measuring the backscattered solar radiance with an UV–VIS–SWIR imaging spectrometer (GeoSCIA). GeoSCIA is a medium resolution imaging grating spectrometer using 2-D CCDs for spectral and spatial imaging. Instrument requirements, concepts and capabilities will be presented. The estimated retrieval precisions for the tropospheric constituents will be discussed. The combined analysis of the solar backscatter measurements with measurements in the thermal IR by GeoFIS demonstrates that the unique combination of observations in these spectral ranges allow to measure the concentrations of the relevant constituents down to the boundary layer or the cloud top height with good accuracy