Improved Calibration Coefficients for NOAA-12 and NOAA-15 AVHRR Visible and Near-IR Channels

A time history of the calibration coefficients for channels 1 and 2 of the Advanced Very High Resolution Radiometer (AVHRR) on the NOAA-12 and NOAA-15 spacecraft is presented. The history is based on reflectances observed for the interior zones of the Antarctic and Greenland ice sheets previously obtained with the NOAA-9 AVHRR, which serves as the calibration standard. Reflectances observed in December and January for the Antarctic ice sheet are used to characterize sensor performance. Reflectances observed in May and June for the interior of the Greenland ice sheet are used to detect any substantial midyear shifts in the coefficients. Prelaunch calibration coefficients for the NOAA-12 AVHRR are shown to be in error and the coefficients drift with time. The coefficients are compared with those reported in earlier studies, and the time rate of change of the calibration is found to be smaller than previously reported. The observations for the NOAA-15 AVHRR are consistent with the prelaunch calibration coefficients for channel 1 but indicate a slight shift in the coefficients for channel 2. The calibration coefficients for the NOAA-15 AVHRR appear to be stable. A slight drift in the response of channel 2 in the low-reflectance range is barely detectable