AVHRR Pathfinder version 5.0 global 4km sea surface temperature (SST) climatologies for 1985-2001

The 4 km-resolution time series used to create these seasonal climatologies is computed from 1985-2001 using the Version 5.0 Pathfinder algorithm, an improved version of the previously most successful of the many methods used to derive SST from AVHRR observations (see Barton (1995) for a review of earlier techniques), the University of Miami Pathfinder version v4.2 SST algorithm (described fully in Kilpatrick et al., 2001).

The v4.2 algorithm offered marked improvement over operational retrieval algorithms such as MCSST and was applied to AVHRR data to maximize accuracy and to minimize artificial fluctuations arising from the sequence of AVHRR instruments flown on NOAA's polar-orbiting satellites during the past 2 decades. The 9 km v4.2 Pathfinder SSTs have already been shown to be the highest quality product currently available for the construction of global climatologies (Casey and Cornillon, 1999) and longer-term SST trend determination (Casey and Cornillon, 2001), and have been demonstrated to be accurate within about 0.3 degrees C under optimal conditions (Kearns et al., 2000). Relative to the older 9 km v4.2 Pathfinder data, the new, ~ 4 km resolution Pathfinder Version 5.0 global SSTs increase detail by a factor of four simply by virtue of the increased resolution. The increase in detail over widely used but relatively coarse SST datasets such as Optimally Interpolated SST Version 2 (OISSTv2; Reynolds et al., 2002) and the Hadley Centre's Global Sea Ice and SST (HadISST1; Rayner et al., 2003) is far greater.

In addition to the increased resolution, significant improvements have been made in the Version 5.0 which enhance the usefulness of the SST fields. Currently, these enhancements include the use of sea ice in the quality level determination scheme, inclusion of many inland water bodies, and the use of a greatly improved land mask. The greatest improvements are seen in coastal zones, marginal seas, and boundary current regions where SST gradients are often large and their impact on operational or research products is greatest. Separate SST products for daytime and nighttime AVHRR retrievals are made to better understand the differences in skin and bulk temperatures, since mean differences between AVHRR-measured skin temperatures and bulk temperatures of 0.1 to 0.2 degrees C (Schluessel et al., 1990) and locally varying differences of up to 1.8 degrees C (Minnett et al., 2000) have been observed.

The following is information to be used when reading GeoTIFFs generated from the seasonal climatology data files:
Geotiff_Information: Version: 1
Key_Revision: 1.0
Tagged_Information:
ModelTiepointTag (2,3):0 0 0-180 90 0
ModelPixelScaleTag (1,3):0.0439453 0.0439453 0
End_Of_Tags.
Keyed_Information:
GTModelTypeGeoKey (Short,1): ModelTypeGeographic
GTRasterTypeGeoKey (Short,1): RasterPixelIsArea
GTCitationGeoKey (Ascii,17): 'LONG/LAT E005'
GeographicTypeGeoKey (Short,1): GCS_WGS_84
GeogAngularUnitsGeoKey (Short,1): Angular_Degree
ProjLinearUnitsGeoKey (Short,1): Linear_Meter
End_Of_Keys.
End_Of_Geotiff.
GCS: 4326/WGS 84
Datum: 6326/World Geodetic System 1984
Ellipsoid: 7030/WGS 84 (6378137.00,6356752.31)
Prime Meridian: 8901/Greenwich (0.000000/ 0d 0' 0.00""E)
Projection Linear Units: 9001/metre (1.000000m)
Corner Coordinates:
Upper Left (180d 0' 0.00"W, 90d 0' 0.00"N)
Lower Left (180d 0' 0.00"W, 90d 0' 0.00"S)
Upper Right (180d 0' 0.00"E, 90d 0' 0.00"N)
Lower Right (180d 0' 0.00"E, 90d 0' 0.00"S)
Center (0d 0' 0.00"E, 0d 0' 0.00"N)