Abstract
VIIRS (Visible Infrared Imager Radiometer Suite), one of five instruments onboard the recently launched Suomi NPP (National Polar-orbiting Partnership) satellite, acquired its first measurements in November 2011. To achieve the required quality of the radiometrically and geometrically corrected sensor data records, VIIRS performance and accuracy of its data products are continuously evaluated. Since the finding of an accelerated degradation of VIIRS sensitivity in selected spectral bands, frequent monitoring of VIIRS radiometric performance became even more essential. In the presented work, we used two methods to evaluate radiometric calibration of the VIIRS sensor data records: (1) imaging of radiometrically stable Earth’s surfaces and (2) SNO (Simultaneous Nadir Overpass) observations by VIIRS and other satellite instruments. TOA (Top-of-Atmosphere) reflectance measurements acquired by VIIRS at the Antarctic Dome C site provided time series of radiometric response estimates during the degradation anomaly investigation in the initial months of the NPP mission. After mitigating snow bidirectional reflectance effects by calculating band ratios, our analysis of the time series has confirmed stability of the VIIRS spectral bands not affected by the degradation and enabled us to estimate degradation rates for the affected bands. The Earth View measurements at the invariant Dome C site not only supplemented measurements from the VIIRS onboard calibrator, but also were in good agreement with the solar diffuser data. SNO measurements in the polar regions have provided many opportunities for comparisons between VIIRS and the MODIS instruments from the Aqua and Terra satellites. TOA reflectance values measured by VIIRS during the SNO events were found to be highly correlated with the MODIS data for the corresponding spectral bands. Observed discrepancies of a few percent can be attributed to differences between spectral responses of VIIRS and MODIS, as shown by estimates from hyperspectral measurements and radiative transfer modeling. Remote sensing measurements at the Dome C polar plateau and during the SNO opportunities in polar regions have enabled both validation of VIIRS radiometric calibration and long-term monitoring of sensor performance. Experience gained with the NPP satellite will be used during calibration and validation of the VIIRS instruments deployed on the future JPSS (Joint Polar Satellite System) satellites.
VIIRS Radiometric Calibration for Reflective Solar Bands: Antarctic Dome C Site and Simultaneous Nadir Overpass Observations
VIIRS (Visible Infrared Imager Radiometer Suite), one of five instruments onboard the recently launched Suomi NPP (National Polar-orbiting Partnership) satellite, acquired its first measurements in November 2011. To achieve the required quality of the radiometrically and geometrically corrected sensor data records, VIIRS performance and accuracy of its data products are continuously evaluated. Since the finding of an accelerated degradation of VIIRS sensitivity in selected spectral bands, frequent monitoring of VIIRS radiometric performance became even more essential. In the presented work, we used two methods to evaluate radiometric calibration of the VIIRS sensor data records: (1) imaging of radiometrically stable Earth’s surfaces and (2) SNO (Simultaneous Nadir Overpass) observations by VIIRS and other satellite instruments. TOA (Top-of-Atmosphere) reflectance measurements acquired by VIIRS at the Antarctic Dome C site provided time series of radiometric response estimates during the degradation anomaly investigation in the initial months of the NPP mission. After mitigating snow bidirectional reflectance effects by calculating band ratios, our analysis of the time series has confirmed stability of the VIIRS spectral bands not affected by the degradation and enabled us to estimate degradation rates for the affected bands. The Earth View measurements at the invariant Dome C site not only supplemented measurements from the VIIRS onboard calibrator, but also were in good agreement with the solar diffuser data. SNO measurements in the polar regions have provided many opportunities for comparisons between VIIRS and the MODIS instruments from the Aqua and Terra satellites. TOA reflectance values measured by VIIRS during the SNO events were found to be highly correlated with the MODIS data for the corresponding spectral bands. Observed discrepancies of a few percent can be attributed to differences between spectral responses of VIIRS and MODIS, as shown by estimates from hyperspectral measurements and radiative transfer modeling. Remote sensing measurements at the Dome C polar plateau and during the SNO opportunities in polar regions have enabled both validation of VIIRS radiometric calibration and long-term monitoring of sensor performance. Experience gained with the NPP satellite will be used during calibration and validation of the VIIRS instruments deployed on the future JPSS (Joint Polar Satellite System) satellites.