The Obs4MIPs dataset produced from the ESA Climate Change Initiatve Sea Surface Temperature v2.1 analysis, has been obtained from post-processing of >4 trillion individual skin sea surface
temperature (SST-skin) retrievals from infra-red imagery of sensors on Earth observing
satellites.

The main post-processing steps are:
1) the addition to the SST-skin of adjustments to daily-mean SST at a nominal depth of
20 cm, resulting in an estimate of “SST-depth”
2) the uncertainty-weighted combination of SST-depth values from all the sensors to
make a daily-gap-free SST analysis at 0.05 degree latitude-longitude resolution
3) the averaging and uncertainty propagation from the daily SST analysis to monthly 1 degree
data

In the processing, ERA-Interim fields are used as ancillary information with minimized
influence on the SST outcome. Consistent fields of sea ice fraction and sea fraction are also
provided. The sea ice fraction is obtained from the Ocean and Sea-Ice Satellite Application
Facility [and the sea fraction accounts for ice from the same product and also the
presence or not of land in the cell, determined from a surface classification dataset.

For a high-level description of the processing steps see Merchant et al, 2019