The influence of viewing geometry on annual variations of NDVI

Since 1983 monthly digital maps of the vegetation index (NDVI) are processed from AVHRR-data in full resolution covering the area between 40°-55°N, and 7°W-17°E. Since 1989 this area and an additional one covering the Iberian Peninsula and parts of NW-Africa are processed daily. Geocoded AVHRR data are stored together with additional information records containing calibration and even conventional weather reports to give the opportunity for future sophisticated corrections and the derivation of additional products. The examination of daily NDVI data shows a considerable dependence on the bidirectional reflectance of the Earth´s surface and requires a careful interpretation of the course of NDVI over several years