Das Projekt "MCEOC European Metrology Centre for Earth Observation and Climate: In-flight on-board transfer standards" wird vom Umweltbundesamt gefördert und von Physikalisch-Technische Bundesanstalt durchgeführt. The research addresses 'on-board standards' specifically tailored for in-flight calibration of air- and space-borne spectroradiometers. In this case study limb sounders have been chosen as an application area. The purpose is the development, characterization and application of a series of large aperture on-board radiance standards for the in-flight calibration of imaging IR spectroradiometers used to measure atmospheric radiance for climate variables such as temperature fields, cloud parameters, aerosols, water vapour, ozone and other trace species by e.g. limb sounding. The output of the research will enable significant improvements to be made to the calibration strategies of future IR hyperspectral imagers, and indeed other IR sensors and ensure that SI traceable uncertainties now demanded by the climate community can be achieved. The uncertainty requirement is highly demanding with the following standard uncertainties being the target: - uncertainty of absolute radiance measurement: u = 0.01 - uncertainty of relative radiance measurement (spatially and spectrally): u = 0.001 (0.0025 threshold). Air- and space-borne atmospheric observation systems are generally optimized to operate close to their physical sensitivity limits. This provides a limit to the required minimum time per measurement and consequently to their spatial resolution, as the observation target point moves with high speed through the field of view. Spatial resolution can therefore only be improved through use of multiple detectors, and the development of high performance mid-infrared detector arrays is a major advance for the next generation of instruments. The use of arrays, however, requires more accurate calibrations: As a rough approximation, in limb sounding the retrieved temperatures and trace species are proportional to the temperature difference between adjacent tangent heights. This has two consequences: 1) increased vertical resolution requires smaller uncertainties of the individual pixel measurements and 2) measurement uncertainties, which are anti-correlated between adjacent tangent altitudes, are strongly amplified. For a conventional instrument, measuring all tangent altitudes with the same single element detector, calibration uncertainties are correlated between different heights. For an array this depends very much on the quality of the overall calibration. Similarly, it is important to reduce spectrally uncorrelated uncertainties. For example at moderate spectral resolution a number of interfering trace species have to be retrieved simultaneously. Uncertainties uncorrelated between the various spectral windows degrade the accuracy of the retrieved trace species more strongly than errors correlated over a wide spectral range. usw.