Examination of calibration performance of multiple POS sensors using measurements over the Dome C site in Antarctica

Abstract

The Dome C site, located at Dome Concordia in Antarctica, has one of the most homogeneous land surfaces on Earth in terms of reflectance and temperature. An in-situ research-based automatic weather station (AWS) provides a continuous record of surface climate conditions. The extreme cold, dry and clean atmosphere of the site is ideal to collect overpass data for sensor validation and inter-comparison study. This study uses measurements from multiple sensors on-board polar orbiting satellites including both Terra/Aqua MODIS and NOAA-15 to 18 AVHRR that overpass the Dome C site to examine each sensor's long-term calibration stability and biases between two similar sensors. Validation is performed based on observed near-nadir top-of-atmosphere (TOA) reflectances of one visible and near-IR spectral band and brightness temperatures of two atmospheric window bands. Trends of the reflectance show that they are strongly anisotropic and thus a BRDF (bi-directional reflectance distribution) model developed based on near surface reflectance measurements over Antarctic snow surface is applied to normalize the TOA reflectances. The BRDF normalization produces stable trends of reflectance with variations of within 1.5% for Terra/Aqua MODIS and 1% and 2% for NOAA- 16 and 17 AVHRR, respectively. For the atmospheric window bands, observed brightness temperatures are referenced to the same time near-surface temperatures collected at the AWS. Trending results show that the atmospheric window bands are maintained to be stable, while the temperature differences among NOAA-15 to 18 AVHRR are up to 2.0K, compared with small differences of within 0.10K found between Terra and Aqua MODIS.