抄録
In this paper a method is proposed to compress the multi-channel sounder data for global greenhouse gases monitoring into a small number of hypothetical channels loosing a negligible information content that the original channel has. Recent Earth observation satellites provide radiance data of thousands of channels at one observation point, piling up gigabyte of data per day. Meanwhile it has recently been recognized that the atmospheric field analysis for the numerical weather prediction produces a better result, when it uses the radiance data of satellite sounder rather than such the retrieved physical parameters, as the temperature and humidity. The difficulty of using radiance data of large number channels is that it uses too much resources in the assimilation loop of three, or four-dimensional variational formulation.
In the present work we propose a method to compress a large number of original channels to a small number of hypothetical channels, whose weighting functions are the eigenvectors made from the matrix of original weighting functions for various atmospheric and observational conditions. The original weighting functions of an arbitrary spectrum concerned are, in turn, expanded with the eigenvectors obtained as above. Using this relation, the radiances of hypothetical channels are obtained by a linear combination of originally observed radiances. The error covariance matrix of the hypothetical channels is also obtained from measurement error of original channels. Since, in the present method of hypothetical radiance, much more channels of original spectrum can be incorporated in the analysis, almost all the information that the original spectrum has is maintained. An example of the application is shown for the simulated radiance data of a remote sounder of the atmospheric greenhouse gases, which observes the solar radiation reflected in the Sun glint region of the water surface, with a high spectral resolution. The result showed that the 240 channels of original radiance data can be condensed to 5 channels or less of hypothetical radiances, with loosing negligible information that the original data has.
