The Infrared Atmospheric Sounding Interferometer(IASI) is applied to perform cloud detection,by using the different responses to clouds between longwave and shortwave channels at CO₂ bands.First,IASI longwave channels are paired with shortwave channels based on weighing function altitudes and sensitivity to clouds.A linear relationship of the brightness temperatures between each pair of channels is then established to predict the shortwave channel from the longwave channel under clear sky conditions.Finally,a cloud emission and scattering index(CESI) can be defined as the difference in the paired shortwave channel between the regression model predicted and the observed brightness temperatures.The spatial distribution of the CESIs with weighting functions peaking at around 383 hPa is consistent with that of the cloud phase of ice,especially at the equator and low latitudes.The spatial distribution of CESIs with weighting functions peaking at around 790 hPa agrees well with the distribution of the low cloud top pressure.