Prior to this reprocessing, the reference temperature for focal plane temperatures used in the SeaWiFS on-orbit calibration has been set at 20°C, the reference temperture used in the prelaunch calibrations of the instrument. The range of focal plane temperatures observed on orbit during lunar calibrations is shown in Figure 2 and the range of temperatures observed during ocean data collection is shown in Figure 3.
Figure 2: Focal Plane Temperatures During Lunar Calibrations
Figure 3: Focal Plane Temperatures During Ocean Data Collection
The 20°C reference temperature is above the observed range of focal plane temperatures for the lunar calibrations for most of each year and is completely above the observed range of focal plane temperatures for ocean data collection. As a result, the change in the band 8 focal plane temperature correction in mid 2005 introduced a discontinuity into the instrument calibration at that point. As is shown in these two figures, and as is plotted in Figure 3, a 16°C reference temperature lies well within the observed temperature ranges for both the lunar and ocean observations. With this reprocessing, the reference temperature has been reset to 16°C and the counts-to-radiance conversion coefficients have been renormalized accordingly.
