Operational calibration of the Advanced Very High Resolution Radiometer (AVHRR) visible and near infrared channels
The Advanced Very High Resolution Radiometer (AVHRR) visible and near infrared channels must be calibrated after launch to maintain the accuracy of data derived from these channels for quantitative utilizations. The postlaunch calibration of these channels can only be carried out vicariously. The National Oceanic and Atmospheric Administration (NOAA) National Environmental Satellite, Data, an Information Service (NESDIS) has been using the Libyan Desert as reference for operational calibration of AVHRR visible and near infrared channels since 1995. A previous algorithm was successful correcting for the long term instrument degradation in recalibration but had difficulty updating instrument calibration in near real time operation. This paper describes the operational calibration algorithm implemented since 2003, which overcomes the existing shortcomings by reducing target contamination and accounting for the effects of target bidirectional reflectance distribution function. Application of the algorithm shortens the latency of postlaunch calibration from 3 to 4 years for NOAA 14 and NOAA 16 to less than 2 years for NOAA 17 and to a few months for later satellites. Compared with the previous algorithm, the current algorithm enhances the calibration precision from 1.7% to 0.9% for channel 1.