This L4 SST product is produced at high resolution (UHR) on a 0.1 x 0.1 degree grid (approximately 10 x 10 km) for the Global Ocean, every 24 hours. Optimal interpolation (OI) techniques are used to combine coincident swath measures of SST from different types of sensor and to fill gaps where no observations are available. Whereas swath data essentially represent the skin or sub-skin SST, the L4 SST product is defined to represent the SST foundation (SSTfnd). SSTfnd is defined within GHRSST-PP as the temperature at the base of the diurnal thermocline. It is so named because it represents the foundation temperature on which the diurnal thermocline develops during the day. SSTfnd changes only gradually along with the upper layer of the ocean, and by definition it is independent of skin SST fluctuations due to wind- and radiation-dependent diurnal stratification or skin layer response. It is therefore updated at intervals of 24 hrs. SSTfnd corresponds to the temperature of the upper mixed layer which is the part of the ocean represented by the top-most layer of grid cells in most numerical ocean models. It is never observed directly by satellites, but it comes closest to being detected by a microwave radiometer which penetrates the skin, at dawn when the previous day's diurnal stratification can be assumed to have decayed and SSTsubskin, SSTdepth and SSTfnd are equal.
|Инструменты||AATSR, AMSR-E, TMI, AVHRR, GOES|