Sea surface images that are obtained by a thermal infrared camera, are synchronized with visible images of whitecaps to investigate the skin sea surface effect on the radiometrically measured sea surface temperature. It is observed that the temperature differences between the skin sea surface and sub-surface bulk water are found to depend on relative humidity and wind velocity, i.e. a lower humidity expands the temperature difference and a decrease of wind velocity reduces it. An empirical relationships between the temperature difference and those environmental parameters are determined.