AVHRR compatible vegetation index derived from MERIS data.

Kurzfassung

The Advanced Very High Resolution Radiometer (AVHRR) compatible vegetation index derived from data of the MEdium Resolution Imaging Spectrometer (MERIS) is regarded as a continuity index for the well known Normalized Difference Vegetation Index (NDVI) derived from AVHRR with 300 meter resolution. For deriving the AVHRR compatible vegetation ndex MERIS full resolution (FR) top of atmosphere radiances (ESA L1b data) are used as input. The design of the ‘‘AVHRR compatible NDVI’’ is based on radiative transfer models for simulating the reflectance of the broad spectral channels of the NOAA – AVHRR and the narrow spectral bands of MERIS. Linear combinations of the MERIS reflectances in the red and near-infrared describe the AVHRR reflectance in channel 1 and 2. The weighting factors for adjusting the reflectances of both sensors are determined from the results of the modelling approach taking into account atmospheric effects by using the Simplified Method for Atmospheric Correction (SMAC), by regarding canopy and soil reflectance and transmission using the Scattering of Arbitrarily Inclined Leaf (SAIL) model and by calculating leaf reflectance and transmittance using the Stochastic model for Leaf Optical Properties Extended for fluorescence (SLOPE). The first validation results show good agreement between the AVHRR NDVI and the ‘‘AVHRR compatible NDVI’’. The mean difference between the two vegetation indices is of the order of 0.025 units. In 2005 the ‘‘AVHRR compatible NDVI’’ will be available for Europe as maximum value composite (daily, 10-days and monthly) on a regular basis from the German Aerospace Centre (DLR).