Information and disturbances contained in the reflected solar radiation spectra measured with space-borne Fourier Transform Spectrometer for greenhouse gas mapping

摘要

For measuring weak radiations with high spectral resolution, the Fourier Transform Spectrometer (FTS) is a powerful tool by virtue of its multiplex advantage. When we use this advantage for measuring Earth-reflected solar radiations from a moving satellite in space, however, we encounter a difficulty that during the acquisition of the interferogram, the optical characteristics of instantaneous filed of view (IFOV) could change. The change of IFOV radiance is caused by, e.g., the fluctuation of line-of-sight of the spectrometer, the change of reflection angle, the glittering of the water surface, or other causes. In this paper, we examine the effects of such pseudo signals contained in the interferograms on resultant spectra and retrieval accuracies of CO_2. Simulations showed that such pseudo signals could generate serious errors in CO_2 retrieval with the FTS of the GOSAT (Greenhouse Gases Observing Satellite). A method is shown to correct these types of disturbances on the interferograms. Together with these topics, we also discuss about other issues such as the ability of the measuring system of GOSAT-FTS to resolve the vertical density profiles of gases or the method to avoid the uncertainty of the existing data for high resolution spectra of solar radiance spectra.