| Summary: | The AVHRR Pathfinder Version 5.3 (PFV53) L3C Sea Surface Temperature data set is a collection of global, twice-daily (Day and Night) 4km sea surface temperature (SST) data produced by the NOAA National Centers for Environmental Information (NCEI). L3C is generated with measurements combined from a single instrument into a space-time grid. In this process multiple passes/scenes of data are combined. PFV53 was computed with data from the AVHRR instruments on board NOAA's polar orbiting satellite series using an entirely modernized system based on SeaDAS (version 6.4). This system incorporates several key changes from its predecessors (mainly version 5.2: PFV52). The SSTs in PFV53 are now available for all quality levels, including quality '0' which was left out of PFV52 due to a memory issue in the version 5.2 code. The Sun glint regions are better represented in the data. Cloud tree tests for NOAA-7 and NOAA-19 are now consistent with the rest of the sensors in contrast to PFV52 where they were inconsistent. PFV53 also includes L2P (Level 2 Pre-processed) and L3U (Level 3 Uncollated) product levels for the very first time. All previous versions of Pathfinder only included L3C products. Note that these L2P and L3U are archived in a separate set of accessions. PFV53 L2P and L3U include the sst_dtime variable; However, it is still not included in L3C (it was not included in PFV52 either). The global and variables attributes in netCDF files are revised, have better CF and ACDD compliance, and are consistent with the NCEI netCDF templates. Anomalous hot-spots at land-water boundaries are better identified and flagged in PFV53. The PFV53 land mask has been updated (based on Global Lakes and Wetlands Database: Lakes and Wetlands Grid Level 3, 2015). Sea ice data over the Antarctic ice shelves are marked as ice and flagged as 100% ice cover. The PFV53 output are netCDF version 4 in "classic" mode, whereas in PFV52 the netCDF-4 files were not explicitly identified as "classic". An extra bit (bit 6) is used under l2p_flags variable to flag out the daytime unrealistic SST values (>39.8°C) that remain in pf_quality_level 4 to 7. Users are recommended to avoid these values. Importantly, PFV53 data provided in netCDF-4 (classic model, with internal compression and chunking) are nearly 100% compliant with the GHRSST Data Specification Version 2.0 (GDS2.0 revision 5) requirements. However, it must be noted that in L3C data the variables sses_bias, sses_standard_deviation, and sst_dtime are still empty. PFV53 data were collected through the operational periods of the NOAA-7 through NOAA-19 Polar Operational Environmental Satellites (POES), and are available from 1981 through 2014. Data for all these years are available as multiple NCEI accessions.
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