*2.3. SST Observations*

We use infrared GHRSST SST images captured by several orbiting satellites, particularly, we explored AVHRR-METOP-A (OSISAF) [30], VIIRS and MODIS. In order to find cloud free images, we automatically browsed the entire L2 data catalog for a given region and extracted granules that satisfied a priori selection criteria. The selection procedure consists in dividing the granules in small patches of a fixed size (100 × 100 pixels) and evaluating the ratio of free cloud pixel for each patch individually. To ensure a good spatial coverage, the granule is selected if cloud-free pixel ratio is equal or higher than 80% in at least 30 patches. Finally, the selected granules are remapped onto a regular grid with a spatial resolution of 0.02◦. We have explored the L2 data archive from 1 January 2014 to 31 December 2016 for AVHRR-METOP, VIIRS and MODIS.
