Estimation of the ratio of sensor degradation between NOAA AVHRR channels 1 and 2 from monthly NDVI composites

Vegetation monitoring, based on the normalized difference vegetation index (NDVI) calculated from the Advanced Very High Resolution Radiometer (AVHRR) channels 1 and 2 data, requires continuous updates of calibration coefficients to correct for the sensor degradation in these channels. A method was developed to estimate calibration coefficients with monthly composited NDVI data from desert targets without recourse to the component channels 1 and 2 data. The method was tested on NDVI data from the AVHRR onboard the NOAA-7, -9, and -11 satellites for the period from 1982 until 1993. The results of the method outlined in this paper correlated high r, between 0.94 and 0.95, with the results from other studies that estimated sensor degradation for the individual AVHRR bands.