Operational calibration of solar reflectance channels of the advanced very high resolution radiometer (AVHRR)

The AVHRR solar reflectance channels need on-orbit calibration that can only be done vicariously. For over a decade, NOAA/NESDIS has paid particular attention to the vicarious calibration based on the Libyan Desert. A previous algorithm was remarkably precise (<2%) in predicting the long term instrument degradation, but because it omitted the seasonal variation caused by the bidirectional reflectance distribution function of the target, the postlaunch calibration was much less precise (~5%). Careful selection of more uniform target and better detection of contaminated measurements (by clouds, dust storm, and wet surface after rain) further reduced noises in the data used to monitor instrument degradation. Together, these improvements reduced latency of post-launch calibration from 3-4 years to 18 months, with enhanced statistical confidence.