Recent Improvements in Deriving Sea-Surface Temperatures from the NOAA-6 Satellite System

Sea-surface temperatures are computed operationally at the National Earth Satellite Service (NESS) of NOAA from a combination of AVHRR window channel data and HIRS-2 sounder data obtained from the NOAA-6 spacecraft. Datafrom one of the HIRS-2 water vapor channels, channel 11 centered at 7.33 ,um, is used to correct the AVHRR window channel measurement for atmospheric absorption by water vapor. Recent studies have demonstrated a considerable bias in accuracy between the winter and summer hemispheres in the mid-latitude and polar regions. It has been found that this bias is associated with a variation in the temperature lapse rate of the atmosphere between the hemispheres. An additional correction to the sea-surface temperature data based on lapse rate information obtained from the HIRS-2 instrument has resulted in a very considerable reduction of this bias.