The new Mediterranean optimally interpolated pathfinder AVHRR SST Dataset (1982-2012)

The long time series (1982-2012) of Pathfinder v.5.2 (PFV52) Advanced Very High Resolution Radiometer (AVHRR) sea surface temperature (SST) data has been used to build daily (nighttime), high-resolution, reprocessed gap-free SST maps (REP L4) covering the Mediterranean Sea. This effort has been pursued with the objective to create a spatially complete, accurate, homogeneous and stable, i.e. free of spurious trends, long term SST dataset. Indeed, these are the essential attributes for its usage in climate applications. The interpolation of Level 3 (L3, i.e. daily collated images) PFV52 data to L4 has been carried out at the original 4 km Pathfinder resolution by adapting to the PFV52 dataset the Mediterranean near-real-time SST processing chain set up within the MyOcean projects and now operational in the framework of the European Copernicus Marine Environment Monitoring Service (CMEMS). The homogeneity and consistency of the MyOcean/CMEMS REP L4 SST dataset is guaranteed by Pathfinder, since PFV52 dataset is built from the same class of sensors and reprocessed with the same algorithm. On the other hand, in order to quantify the accuracy and demonstrate the stability of both PFV52 and REP L4 SST data, a thorough validation has been performed by comparison with an independent in situ dataset, built from all the available in situ observations covering the entire reprocessing period. The validation indicates that this new optimally interpolated time series represents a valuable SST dataset for climate studies. In addition, the REP L4 dataset extends and improves previous similar datasets covering the Mediterranean Sea, presently resulting as the longest time series at 4 km resolution. Future releases of the Pathfinder SST dataset will then be used to update this time series in the framework of the CMEMS.