4 is complete failure (oceancolor.gsfc.nasa.gov/DOCS/modis_sst). In contrast,
AVHRR Pathfinder quality flags vary from 0 to 7, with 0 being the lowest and 7 the
highest (www.nodc.noaa.gov/sog/pathfinder4km/userguide.html). For most applications, using SST observations with quality levels of 4–7 for AVHRR Pathfinder, or
0–2 for MODIS, is typical. For applications requiring the most accurate observations
(at the expense of the number of observations), only the highest quality levels should
be used (Kilpatrick et al. 2001) and remaining values masked out of the analysis.
Significant progress on improving cloud-screening, atmospheric aerosol detection
and flagging algorithms to provide increased sensitivity and performance is
expected in the next decade as climate-quality SST data are derived from a variety of
sensors (Casey et al. 2010; Donlon 2010).
12.2 Thermal Data Products and Analysis
12.2.1 AVHRR Pathfinder Series
Of the many oceanic parameters capable of being observed from space, only SST
from the NOAA AVHRR series enjoys an unbroken, nearly 30 year long history of
observation from the same class of instrument. The AVHRR observations date
back to 1981, and are expected to continue for perhaps another 10 years (Casey
et al. 2010). The Pathfinder Program was conceived in 1990 as a NOAA and
NASA Cooperative Agreement to support the needs of the US Global Change
Research Program (King and Greenstone 1999) and to provide unprecedented
access to large volumes of consistently processed satellite datasets. The official
goals of the AVHRR Pathfinder project, as presented in 1992, were to produce: (a)
long-term global datasets for research, modeling, and trend analysis; (b) datasets
consistently processed with the best available community consensus algorithms;
(c) multiple geophysical products from a common input stream using integrated
processing concepts; and (d) a consistent, low maintenance, readily accessible
archive for AVHRR data with browse and online access capabilities (Casey et al.
2010). Thus, the Pathfinder objective was to ‘‘find the path’’ forward in preparation
for the ambitious Earth Observing System series of instruments and missions that
followed (Casey et al. 2010).
Over its 20 year history, the Pathfinder SST Program has produced five distinct
versions of SST products, and is currently developing its sixth. The Pathfinder SST
algorithm is based on the Non-Linear SST (NLSST) algorithm (Walton et al. 1998;
Kilpatrick et al. 2001), with numerous modifications over time to improve algorithm performance (Casey and Cornillon 1999; Kilpatrick et al. 2001; Casey et al.
2010). In 2002, the term ‘‘Climate Data Record’’ had emerged and the Pathfinder
SST Program entered a new phase to deliver Pathfinder SST Version 5, a more
accurate, consistent, and finer resolution SST data set than was available previously. Improvements in spatial resolution (4 km), the land mask, and the quality
318
S. J. Weeks et al.
AVHRR Pathfinder quality flags vary from 0 to 7, with 0 being the lowest and 7 the
highest (www.nodc.noaa.gov/sog/pathfinder4km/userguide.html). For most applications, using SST observations with quality levels of 4–7 for AVHRR Pathfinder, or
0–2 for MODIS, is typical. For applications requiring the most accurate observations
(at the expense of the number of observations), only the highest quality levels should
be used (Kilpatrick et al. 2001) and remaining values masked out of the analysis.
Significant progress on improving cloud-screening, atmospheric aerosol detection
and flagging algorithms to provide increased sensitivity and performance is
expected in the next decade as climate-quality SST data are derived from a variety of
sensors (Casey et al. 2010; Donlon 2010).
12.2 Thermal Data Products and Analysis
12.2.1 AVHRR Pathfinder Series
Of the many oceanic parameters capable of being observed from space, only SST
from the NOAA AVHRR series enjoys an unbroken, nearly 30 year long history of
observation from the same class of instrument. The AVHRR observations date
back to 1981, and are expected to continue for perhaps another 10 years (Casey
et al. 2010). The Pathfinder Program was conceived in 1990 as a NOAA and
NASA Cooperative Agreement to support the needs of the US Global Change
Research Program (King and Greenstone 1999) and to provide unprecedented
access to large volumes of consistently processed satellite datasets. The official
goals of the AVHRR Pathfinder project, as presented in 1992, were to produce: (a)
long-term global datasets for research, modeling, and trend analysis; (b) datasets
consistently processed with the best available community consensus algorithms;
(c) multiple geophysical products from a common input stream using integrated
processing concepts; and (d) a consistent, low maintenance, readily accessible
archive for AVHRR data with browse and online access capabilities (Casey et al.
2010). Thus, the Pathfinder objective was to ‘‘find the path’’ forward in preparation
for the ambitious Earth Observing System series of instruments and missions that
followed (Casey et al. 2010).
Over its 20 year history, the Pathfinder SST Program has produced five distinct
versions of SST products, and is currently developing its sixth. The Pathfinder SST
algorithm is based on the Non-Linear SST (NLSST) algorithm (Walton et al. 1998;
Kilpatrick et al. 2001), with numerous modifications over time to improve algorithm performance (Casey and Cornillon 1999; Kilpatrick et al. 2001; Casey et al.
2010). In 2002, the term ‘‘Climate Data Record’’ had emerged and the Pathfinder
SST Program entered a new phase to deliver Pathfinder SST Version 5, a more
accurate, consistent, and finer resolution SST data set than was available previously. Improvements in spatial resolution (4 km), the land mask, and the quality
318
S. J. Weeks et al.