POSSIBLE CAUSES OF CALIBRATION DEGRADATION OF THE ADVANCED VERY HIGH-RESOLUTION RADIOMETER VISIBLE AND NEAR-INFRARED CHANNELS

Gradual deterioration of calibration of the Advanced Very High Resolut ion Radiometer (AVHRR) can be explained by the erasion of the scanning mirror as a result of interaction with interplanetary dust. Other ele ments of the instrument (optical filters, detector, electronics) were also examined for their behavior in space conditions and were found mo st likely to be stable and not responsible for the decrease in sensiti vity. Calculations show that the erosion of the scanning mirror is of the order of 4.5% per year, although this erosion is very variable bec ause of the variability of the density of interplanetary dust. This er osion can easily explain the 3-5% per year deterioration of the AVHRR sensors on NOAA-7 and NOAA-9.