The accuracy with which well-calibrated satellite infrared radiometers can measure sea surface temperature is limited by the validity of the correction applied for the modification of the electromagnetic radiation before it reaches the radiometer. An accurate numerical line-by-line model of the radiative transfer through the atmosphere is used to simulate measurements of the advanced very high resolution radiometer (AVHRR/2) on the NOAA series of near-polar-orbiting satellites for conditions of the region of the Greenland, Iceland, and Norwegian Sea. A set of regionally optimzed zenith-angle dependent coefficients for the ''split-window'' algorithm is derived and its error characteristics are discussed. While the benefit of using such coefficients is demonstrated, the errors resulting from failing to account properly for seasonal changes in this particular region are shown to be relatively small. ¿ American Geophysical Union 1990