A comparison of channel selection for the assimilation of CrIS radiances for NWP

Abstract

Abstract With hyperspectral instruments measuring radiation emitted by the earth and its atmosphere in the thermal infrared range in multiple channels, several studies were made to select a subset of channels in order to reduce the number of channels to be used in a data assimilation system. An optimal selection of channels based on information content depends on several factors related to observation and background error statistics and the assimilation system itself. An optimal channel selection for CrIS was obtained and then compared to selections made for different NWP systems. For instance, the channel selection of Carminati (2022) has 224 channels also present in to our optimal selection which includes 455 channels. However, in terms of analysis error variance, the difference between the two selections is small. Integrated over the whole profile, the relative difference is equal to 15.3 % and 4.5 % for temperature and humidity respectively. Also, different observation error covariance matrices were considered to evaluate the impact of this matrix on channel selection. Even though the channels selected optimally were different in terms of which channels were selected for the various R matrices.