4 km AVHRR Pathfinder Project

***ANNOUNCEMENT September 14: NCEI releases AVHRR Pathfinder Version 5.3 for August 1981 through December 2014***

The NOAA National Centers for Environmental Information (NCEI) develops and maintains the high resolution, long-term, climate data record (CDR) of global satellite sea surface temperature (SST) called Pathfinder SST. These SST values are generated at approximately 4 km resolution using Advanced Very High Resolution Radiometer (AVHRR) instruments aboard NOAA polar-orbiting satellites going back to 1981. The AVHRR Pathfinder Version 5.3 (PFV53) is the newest release of the PF SST products. This is a step forward in preparation for the future Version 6 (PFV6) data set. (No release date has yet been established for PFV6.) SST values are generated at approximately 4 km resolution using Advanced Very High Resolution Radiometer (AVHRR) instruments aboard NOAA polar-orbiting satellites going back to 1981. The Pathfinder SST algorithm is applied consistently over the full time period (August 1981 - December 2014) and is based on the Non-Linear SST algorithm using the modernized NASA SeaWiFS Data Analysis System (SeaDAS). Coefficients for this SST product were generated using regression analyses with co-located in situ and satellite measurements based on Kilpatrick, Podesta and Evan (2001) and Baker-Yeboah, Saha, Zhang, Casey, Evans, and Kilpatrick (2016, AGU Poster and manuscript in progress). Notably, the data were processed in the Amazon Web Service cloud and are made available through all of the modern web visualization and subset services provided by the THREDDS Data Server, the Live Access Server, and the OPeNDAP Hyrax Server.  Building on the long historical aspect of Pathfinder SST (Casey et. al., 2011), quarterly updates will be maintained to continue this long (>33 years), consistently processed, global high-resolution SST climate data record.

Consistent with 52, PF53 is provided in netCDF-4 (classic model, with internal compression and chunking) and are nearly 100% compliant with the GHRSST Data Specification Version 2.0 (GDS2.0) for L3C  products (and to be provided: L2P and L3U products). These data deviate from that standard only in that the sses_bias, sses_standard_deviation, and sst_dtime variables are empty. Data for 1981-2014 are available. All of the PFV53 data are available through NCEI’s ftp, http, OPeNDAP, and THREDDS access systems:

• HTTP: http://data.nodc.noaa.gov/pathfinder/Version5.3/L3C
• FTP: ftp://ftp.nodc.noaa.gov/pub/data.nodc/pathfinder/Version5.3/L3C
• OPeNDAP: http://data.nodc.noaa.gov/opendap/pathfinder/Version5.3/L3C
• THREDDS: http://data.nodc.noaa.gov/thredds/catalog/pathfinder/Version5.3/L3C/catalog.html

This SST PF53 Climate Data Record uses the NOAA -7, -9, -11, -14, -16, -17, -18, -19 AVHRR sensors and maintains both wet and dry coefficients to improve accuracy of retrievals. Updates to PF53 include

• Included all SST values of all quality levels (Figures 1 for PF53 versus Figure 2 for PF52)​. The user can turn of the lowest quality level of pixels, when comparing the olde version 5.2 (Figure 2) to the new version 5.3 (Figure 3).​
• Better identified and flagged anomalous hotspots at landwater boundaries;
• Updated land mask (based on Global Lakes and Wetlands Database) and sea ice data over the Antarctic ice shelves masked as ice;
• Improved handling of sun glint areas (no longer masked out);
• Consistent cloud tree tests for NOAA07 and NOAA-19 with respect to other sensors;
• Improved flagging of a very small percentage of pixels with SST values > 39.8 degrees C (see l2p_flags).
• NetCDF file format improvements to ensure consistency with the Group for High Resolution SST (GHRSST) requirements;
• Processing done using Amazon Web Service cloud computation under NOAA cloud pilot project.

Overall, PF53 compares well with other GHRSST products (see Figures 4 and 5) and validation results corresponding to Pathfinder Level 3 skin SST minus sub-surface buoy SST show a global mean difference of -0.2 K with a standard deviation of 0.5 K (Baker-Yeboah, Saha, Zhang, Casey, Evans, and Kilpatrick, 2016: AGU Poster and manuscript in progress).

Figure 1-3 Pathfinder SST examples from (A) version 5.3 with all pixel values available for the user, (B) version 5.2, which did not have all pixels available for the user, and (C) version 5.3 with zero quality level pixels removed..
Figure 1. Pathfinder SST version 5.3 with all pixel values available for the user.	Figure 2. Pathfinder SST version 5.2 did not have all pixels available for the user.	Figure 3. Pathfinder SST version 5.3 with zero quality level pixels removed.

The following table lists known issues with the PFV53 data set:

In the coming weeks, we will update these web pages to provide additional details on PFV53.

Figure 4. PFSST (5.2 & 5.3) data compare well to the CMC0.2 Global Foundation SST, but differs as expected for a skin SST measurement. Day and night binning to be resolved.

Figure 5. Differences between PFSST 5.3 and the daily OISST fall within the range of ± 2°C.

Acknowledgment & Citation:

If you use Pathfinder 4km data, please acknowledge the use of these data with the following statement: "These data were provided by GHRSST and the US NOAA National Centers for Environmental Information (NCEI). This project was supported in part by a grant from the NOAA Climate Data Record (CDR) Program for satellites". Please cite the following publication:

Baker-Yeboah, S., K. Saha, D. Zhang, K. S. Casey, R. Evans, and K. A. Kilpatrick (2016). “Pathfinder Version 5.3 AVHRR Sea Surface Temperature Climate Data Record’’, Fall AGU 2016 Poster (manuscript in progress).

Casey, K.S., T.B. Brandon, P. Cornillon, and R. Evans (2010). "The Past, Present and Future of the AVHRR Pathfinder SST Program", in Oceanography from Space: Revisited, eds. V. Barale, J.F.R. Gower, and L. Alberotanza, Springer. DOI: 10.1007/978-90-481-8681-5_16. (Click here for a PDF copy).

Kilpatrick, K. A., G. P. Podesta, and R.H. Evans. 2001. "Overview of the NOAA/NASA Pathfinder algorithm for Sea Surface Temperature and associated Matchup Database." J. Geophys Res., 106: 9179-9198. 13497- 13510.