Abstract
We present an assessment of the calibration of the Suomi NPP VIIRS thermal emissive bands (TEB) M13 (4.05 micron), M15 (10.76 micron), and M16 (12.013 micron) based on comparison between CrIS and VIIRS SDR Earth radiance data, obtained at the same time and with the same view geometry. A correction to the VIIRS calibration coefficients, based on the CrIS calibration, is derived from the comparison. The incentive to attempt an alternative approach to the VIIRS TEB calibration, independent from the VIIRS on-board Black Body (BB) data – routinely used to adjust VIIRS TEB calibration at every scan, and to derive calibration coefficients during warm-up cool-down (WUCD) events – is that while in general agreement, the BB WUCD results and pre-launch estimates of the calibration coefficients show some systematic differences, especially for the zeroth order coefficients (offsets). These differences could arise from radiative model inadequacies, or from real differences in the offsets on-orbit compared to pre-launch.
The VIIRS TEB calibration coefficients derived from comparison with CrIS are band-average (over all detectors and HAM-sides), derived under the assumption of a linear relation between CrIS and VIIRS radiance, and derived at three different scan angles (nadir and ±49 deg) to explore the possibility of uncorrected VIIRS background path differences (function of the scan-angle) affecting the calibration. Data from over 10 orbits was used, including orbits during a recent (12/2012) WUCD – when the VIIRS calibration was affected by the BB temperature change – as well as nominal operational data.
The results are consistent between WUCD and nominal operations, as well as between the three scan angles used. The derived offset for M13 is close (slightly lower) to the pre-launch value, while for M15 and M16 the offset is higher than the pre-launch and consistent with WUCD results.
SNPP VIIRS Emissive Bands Calibration Assessed via a CrIS-VIIRS Data Comparison
We present an assessment of the calibration of the Suomi NPP VIIRS thermal emissive bands (TEB) M13 (4.05 micron), M15 (10.76 micron), and M16 (12.013 micron) based on comparison between CrIS and VIIRS SDR Earth radiance data, obtained at the same time and with the same view geometry. A correction to the VIIRS calibration coefficients, based on the CrIS calibration, is derived from the comparison. The incentive to attempt an alternative approach to the VIIRS TEB calibration, independent from the VIIRS on-board Black Body (BB) data – routinely used to adjust VIIRS TEB calibration at every scan, and to derive calibration coefficients during warm-up cool-down (WUCD) events – is that while in general agreement, the BB WUCD results and pre-launch estimates of the calibration coefficients show some systematic differences, especially for the zeroth order coefficients (offsets). These differences could arise from radiative model inadequacies, or from real differences in the offsets on-orbit compared to pre-launch.
The VIIRS TEB calibration coefficients derived from comparison with CrIS are band-average (over all detectors and HAM-sides), derived under the assumption of a linear relation between CrIS and VIIRS radiance, and derived at three different scan angles (nadir and ±49 deg) to explore the possibility of uncorrected VIIRS background path differences (function of the scan-angle) affecting the calibration. Data from over 10 orbits was used, including orbits during a recent (12/2012) WUCD – when the VIIRS calibration was affected by the BB temperature change – as well as nominal operational data.
The results are consistent between WUCD and nominal operations, as well as between the three scan angles used. The derived offset for M13 is close (slightly lower) to the pre-launch value, while for M15 and M16 the offset is higher than the pre-launch and consistent with WUCD results.