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In recent years, there is an increasing interest to establish a global integrated network of calibration sites
for the purpose of tracking sensor performance, conducting cross-sensor comparison and assessing data
quality and consistency. Based on such a need, the Committee on Earth Observation Satellites (CEOS)
proposed eight instrumented sites for which surface measurements can be acquired through field
campaigns and five pseudo-invariant desert sites typically consisting of sand dunes. In this study, we
select one site from each category to study the calibration stability of reflective solar channels of NOAA-
19 Advanced Very High Resolution Radiometer (AVHRR) (launched on February 6, 2009). Since
AVHRR does not have an onboard calibrator for the reflective solar channels and vicarious calibration
often needs long-term observations to derive reliable trends, this study will provide an early assessment of
sensor on-orbit calibration performance and establish a preliminary trend to examine its calibration
consistency with other sensors. The Antarctic Dome C site is selected primarily to monitor the on-orbit
calibration performance whereas Libya 4 test site is used to evaluate the cross-calibration consistency of
AVHRR with other sensors. A site-specific Bi-directional Reflectance Distribution Function (BRDF)
model developed based on observations made by Moderate Resolution Imaging Spectroradiometer
(MODIS) is used to normalize AVHRR observed Top-of-Atmosphere (TOA) reflectances. Impact due to
calibration applied to NOAA-19 AVHRR L1B is assessed separately using a constant detector response.
Results show that for NOAA-19 AVHRR solar channels 1 and 2, variations in reflectance during the first
year after launch are still around 6% and more than 10%, respectively, either due to sensor change or
improper adjustment of calibration coefficients. While two sites provide consistent trends for the visible
channel, the Dome C site is more suitable for the near-infrared channel as impacts of the absorption by
atmospheric water vapor are minimal.
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