Satellite Atmospheric Sounder IRFS-2 1. Outgoing Radiation Spectra Measurement Analysis
The outgoing radiation spectra which were measured by IRFS-2 spectrometer onboard “Meteor-M” № 2 have been analyzed. Some statistical parameters of more then 106 spectra measured in spring of 2015 have been calculated. The radiation brightness temperature has been variated from ~300 K (surface temperature) up to ~210 K (tropopause temperature). A variability of the longwave measured region radiation has been demonstrated to be high enough. A signal/noise relation is appreciably goes down in the shortwave region (shorter then 1300 cm–1). Intercomparisons of IR sounders IRFS-2, IASI and CrIS spectra showed that the discrepancies of the mean spectra and the spectra variability are no more then measurement errors in the spectral region 660–1300 cm–1. The comparison of specially chosen pairs of the simultaneously measured spectra showed that the differences between IRFS-2 and European instruments in the region of the 15 microns CO2 band and the transparence windows 8–12 μm are less than the differences between two instruments IASI (-A и -B). The differences between measured and simulated spectra are less than 1 mWt/(m2 sr cm–1) in the mean part of CO2 band, but after 720 cm–1 appear values up to 2–4 mWt/(m2 sr cm–1). The reason is an absent of the precise information about a surface temperature. The further investigation of the radiation model of atmosphere need in order to understand the reasons of the differences and to decrease the differences.  Keywords: thermal radiation, IR radiation, satellite sounding of the atmosphere, Fourier spectroscopy, Fourier spectrometry