Privacy Policy and Important Notices
Updated: 09 September 2009
The SeaWiFS lunar calibration time series, with the updated radiometric and temperature calibrations, is shown in the above figure. The fits to the time series, shown as the solid line for each band, were computed using the 129 lunar calibrations obtained through February 2009. As of September 2009 five additional calibrations have been collected, all of which are consistent with the trend lines of the fits. This plot does not include the Gain 3 drift correction, since that correction only concerns the application of the radiometric calibration to the ocean data. As the SeaWiFS mission has gone on, the optimum fitting function for the time series has evolved due to extensive analyses of the behavior of Band 8. The current fit uses a decaying exponential function of time with a time constant of 400 days in conjunction with a linear function of time to fit the data.
Two different decay mechanisms are responsible for the changes in response of
each of the bands. The first mechanism caused a rapid decrease in response
that decayed away after approximately the first year of the mission. The
second mechanism has been in effect over the entire mission. The long-period
decay for the shorter wavelength bands (bands 1-4) most likely arises from
yellowing of the instrument optics on orbit. The long-period decay for the
longer wavelength bands (bands 5-8) most likely arises from charged-particle
induced damage to the silicon photodiodes.
The SeaWiFS lunar calibration data have to be normalized to a common viewing
geometry to produce the time series shown above. The U.S. Geological Survey ROLO (RObotic Lunar Observatory) photometric model of the Moon has been used to perform the geometric corrections for the Sun-Moon and instrument-Moon distances and for the phase and libration angles of the observations. In addition, the individual lunar images must be corrected for the oversampling of the lunar data during the lunar calibration maneuvers. The oversampling correction is computed by ratioing the measured size if the Moon in each lunar image with the actual size of the Moon at the time of the observations.
Privacy Policy and Important Notices
Updated: 09 September 2009