Sea Surface Temperature (SST)
AATSR has thermal infrared channels measuring upwelling radiance from the sea surface and the atmosphere at 3.7, 11 and 12 µm. From the calibrated top of the atmosphere Brightness Temperatures (BT) available from these bands, SST is calculated using the 11 and 12 µm channels during the day and the 11, 12 and 3.7 µm channels at night.
Very high levels of accuracy and precision are required to support global climate monitoring and change detection. Therefore, the AATSR instrument and ground processing system are required to produce SST retrievals routinely from the corresponding BTs with an absolute accuracy of better than 0.3K, globally, both for a single sample and when averaged over areas of 0.5° longitude by 0.5° latitude, under certain cloud free conditions (i.e. >20% cloud free samples within each area). The AATSR programme also aims to maintain an instrument stability of 0.1K during the mission lifetime.
It is important to note that the (A)ATSR instruments return SST measurements for the ocean's 'skin' and that the temperature of the sea skin surface is typically a few tenths of a degree cooler than the temperature a few centimetres below. Due to the limited penetration of thermal infrared radiation through the water column, the infrared radiometric temperature will be that of only the top few tens of micrometres, whereas the oceanographically understood SST is a measure of the temperature in the top 10 cm.