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Meteorological sounding data provided by atmospheric imaging sounders have applications in weather forecasting, atmospheric chemistry, and climate monitoring. Realistic scenes for these instruments vary in both spatial and spectral content and such variations can impact the radiometric performance of these instruments. As sounders are developed to provide climate records with demanding long-term radiometric accuracy requirements, it becomes increasingly important to understand the effect of scene variations on the performance of these instruments. We have examined the noise performance and radiometric accuracy of two geostationary sounder architectures in cloudy scenes: a Fourier transform spectrometer (FTS) and a dispersive spectrometer. Factors such as stray light, ghosting, scattering, and line-ofsight jitter in the presence of scene inhomogeneities are considered. For each sounder architecture, quantitative estimates of the radiometric errors associated with sounding in cloudy scenes are made. We find that in a dispersive system the dominant error in a cloudy scene originates from ghosting within the instrument, while in an FTS the dominant error originates from scene modulation created by line-of-sight jitter in a partially cloudy scene coupling into signal modulation over the scale of the changing optical path length of the interferometer. In this paper we describe the assumptions made and the modeling performed. We also describe how each factor influences the radiometric performance for that architecture. |
