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1.2. Navigation, Clock, and Attitude Corrections
1.2.1. Apply satellite clock corrections using Earth time offset data
based on University of Miami DOMSAT recorded HRPT files.
1.2.2. Apply attitude corrections made using coastline comparison
data.
1.2.3. At this point, navigated, calibrated albedos/brightness
temperatures are available for all five channels. Note that
channels 1 and 2 are used in the Pathfinder Matchup Database
decision trees (see Kilpatrick et al., 2001, Fig. 7) and channel 3
is used only in assignment of a quality indicator (see Step
2.4.1).
Step 2: SST Calculation
2.1. Convert channel 4 and 5 brightness temperatures to SST in ◦ C using
the Pathfinder algorithm (Equation 16.1), which requires a set of
monthly coefficients.
2.2. These coefficients are derived using the Pathfinder Buoy Matchup
Database, a set of in-situ SST observations and collocated AVHRR
data. The in-situ data consist mainly of drifting buoys, but during
1981–1984 bias-corrected ship-based observations are also used.
2.3. The calculation of SST in Step 2.1 also requires a first-guess SST
field. This first-guess field is the OISSTv2 product for 1985–2009 and
the DOISST for 1981–1984. Note that Versions 1–4 of Pathfinder used
OISSTv1.
2.4. Quality Flag Assignment
2.4.1. A Channel 3, 4, and 5 brightness temperature test is
performed. The brightness temperatures were calculated in
Step 1.1.3.
2.4.2. The viewing angle is then evaluated using a satellite zenith
angle check.
2.4.3. Next, a reference field comparison check is made against the
OISSTv2/DOISST used in Step 2.3.
2.4.4. A stray sunlight test is then performed which requires
information on whether the data in question are to left or right
of nadir.
2.4.5. An edge test is performed next, which checks the location of
the pixel within a scan line and the location of the scan line
within the processing piece (a “piece” is a subset of an entire
orbit file).
2.4.6. Then, a glint test is performed which requires a glint index
calculated according to the Cox and Munk (1954) formulation.
2.4.7. Finally, these steps are all combined into an overall quality
flag assignment for each pixel.
K.S. Casey et al.
1.2. Navigation, Clock, and Attitude Corrections
1.2.1. Apply satellite clock corrections using Earth time offset data
based on University of Miami DOMSAT recorded HRPT files.
1.2.2. Apply attitude corrections made using coastline comparison
data.
1.2.3. At this point, navigated, calibrated albedos/brightness
temperatures are available for all five channels. Note that
channels 1 and 2 are used in the Pathfinder Matchup Database
decision trees (see Kilpatrick et al., 2001, Fig. 7) and channel 3
is used only in assignment of a quality indicator (see Step
2.4.1).
Step 2: SST Calculation
2.1. Convert channel 4 and 5 brightness temperatures to SST in ◦ C using
the Pathfinder algorithm (Equation 16.1), which requires a set of
monthly coefficients.
2.2. These coefficients are derived using the Pathfinder Buoy Matchup
Database, a set of in-situ SST observations and collocated AVHRR
data. The in-situ data consist mainly of drifting buoys, but during
1981–1984 bias-corrected ship-based observations are also used.
2.3. The calculation of SST in Step 2.1 also requires a first-guess SST
field. This first-guess field is the OISSTv2 product for 1985–2009 and
the DOISST for 1981–1984. Note that Versions 1–4 of Pathfinder used
OISSTv1.
2.4. Quality Flag Assignment
2.4.1. A Channel 3, 4, and 5 brightness temperature test is
performed. The brightness temperatures were calculated in
Step 1.1.3.
2.4.2. The viewing angle is then evaluated using a satellite zenith
angle check.
2.4.3. Next, a reference field comparison check is made against the
OISSTv2/DOISST used in Step 2.3.
2.4.4. A stray sunlight test is then performed which requires
information on whether the data in question are to left or right
of nadir.
2.4.5. An edge test is performed next, which checks the location of
the pixel within a scan line and the location of the scan line
within the processing piece (a “piece” is a subset of an entire
orbit file).
2.4.6. Then, a glint test is performed which requires a glint index
calculated according to the Cox and Munk (1954) formulation.
2.4.7. Finally, these steps are all combined into an overall quality
flag assignment for each pixel.