A comparison of the Antarctic Dome C and Sonoran Desert sites for the cal/val of visible and near infrared radiometers

Stable earth sites are essential for comparing the measurements from different satellite instruments in the visible and near-infrared in order to maintain the consistency of radiometric calibration, and for quantifying the sensor degradation over time. This study focuses on the radiometric and spectral characterization and comparison between two potential calibration sites, Dome C and Sonoran Desert. The long-term TOA reflectance time series analysis using MODIS observation shows that the radiometric stability of Dome C and Sonoran Desert is better than 2% over the period of 8 years. The study also shows that Dome C is much affected by seasonal variation due to bi-directional reflection, compared to the Sonoran Desert, although the BRDF normalization reduced the uncertainty of Dome C observations to less than 2% for both the visible and NIR band. For AVHRR band 2, at Sonoran Desert, a large variability (>6%) is observed compared to that of MODIS (<2%) due to water vapor absorption. The spectral characteristics of these sites studied using EO-1 Hyperion sensor further show the water vapor absorption differences at the two sites. Nevertheless, the operationally calibrated AVHRR TOA reflectance at both Dome C and Sonoran Desert are significantly lower than that of MODIS, primarily due to calibration traceability issues. The study suggests that, both Dome C and Sonoran Desert sites can be used for postlaunch calibration/validation of the visible/near-infrared bands with uncertainty less than 2% excluding channels affected by water vapor.