The modifications to the instrument calibration between Reprocessing 4.1 and Reprocessing 5 are as follows:

  • the exponential fits were performed using the 85 lunar calibrations obtained through the end of the SeaWiFS mission; the fits for Reprocessing 4.1 were based on 76 calibrations.
  • the long period time constant in the exponential fits was changed from 1600 days to 2500 days; the short period time constant remains at 200 days.
  • only band 4 is now fit by a single long-period exponential; for Reprocessign 4.1, band 3 was also fit by a single exponential.
The effects of these changes on the instrument gain is shown in the following plot:

Changes in SeaWiFS Gains, Reprocessing 4.1 to Reprocessing 5

The gains for the new calibration increase after day 1500 because the calibration for Reprocessing 4.1 no longer tracked the response of the instrument and because of the change in the long-period time constant. The early gain increase centered around day 400 because the relative contributions of the short-period exponential and the long-period exponential to the simultaneous fit changes as a result of the change in the long-period time constant. The relative contributions of the short-period and long-period exponentials to the fit are shown here.

The changes in the calibration are the most significant for bands 7 and 8, which are the atmospheric correction bands. Consequently, the gain ratios for bands 7 and 8 are evident in the comparisons of normalized water-leaving radiances in the the test results for Reprocessing 5 ( Effect of updated lunar cal & switch to Thuillier).