AVHRR compatible NDVI derived from MERIS data (MERIS_AVHRR_NDVI)


The "AVHRR compatible Normalized Difference Vegetation Index derived from MERIS data (MERIS_AVHRR_NDVI)" was developed in a co-operative effort of DLR (German Remote Sensing Data Centre, DFD) and Brockmann Consult GmbH (BC). For the generation of regional specific value added MERIS level-3 products, MERIS full-resolution (FR) data are processed on a regular (daily) basis using ESA standard level-1b and level-2 data as input. The regular reception of MERIS-FR data is realized at DFD ground station in Neustrelitz.

Scientific Background

The Medium Resolution Imaging MERIS on Board ESA's ENVISAT provides spectral high resolution image data in the visible-near infrared spectral region (412-900 nm) at a spatial resolution of 300 m. For more details on ENVISAT and MERIS see http://envisat.esa.int. The Advanced Very High Resolution Radiometer (AVHRR) compatible vegetation index (MERIS_AVHRR_NDVI) derived from data of the MEdium Resolution Imaging Spectrometer (MERIS) is regarded as a continuity index with 300 meter resolution for the well known Normalized Difference Vegetation Index (NDVI) derived from AVHRR (given in 1km spatioal resolution). The NDVI is an important factor describing the biological status of canopies. This product is thus used by scientists for deriving plant and canopy parameters. Consultants use time series of the NDVI for advising farmers with best practice.

Product example

Quicklokk of the "AVHRR compatible NDVI based on MERIS data (MERIS_AVHRR_NDVI)" as monthly composite for July, 2005.
Ocean and lake areas are presented in blue, clouds are masked out as bad values (white).

Algorithm Summary

For deriving the AVHRR compatible vegetation index MERIS full resolution (FR) top of atmosphere radiances (ESA L1b data) are used as input. The design of the continuity index is based on radiative transfer models for simulating the reflectance of the broad spectral channels of the NOAA - AVHRR and the small 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 Leaves (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 new continuity index. The mean difference between the two vegetation indices is of the order of 0.025 units.

Product Description

The "AVHRR compatible Normalized Difference Vegetation Index derived from MERIS data (MERIS_AVHRR_NDVI)" is a fixed grid map (in Lambert Azimuthal Equal Area projection ) with a spatial resolution of 300m at the center of the satellite map at 53.33 N / 13.07 E. The "nearest neighbour" technique is applied to resample the pixels into the map. The total size of the maps is 14336 samples by 14336 lines covering an area of app. 4300km x 4300km. The corners of the maps are given in the table below.
The continuity index will be available for Europe as maximum value composite (daily, 10-days and monthly) on a regular basis. Daily maps will be composed based on the Maximum Value (MV) criterion at every pixels' position which normally consist of three consecutive MERIS passages (east, central, west). From these daily products, 10-days and monthly synthesis maps are derived taking the daily MV.
The NDVI range starts with "-0.09968454" and is referred to grey value "1". The radiometric resolution is "0.0031546", grey value 254 is therefore referred to value "0.7" (maximum NDVI).

Together with Brockmann Consult GmbH (BC) the algorithm was implemented in an operational MERIS value-adding processor which is integrated into the operational processing environment at DFD. The data are delivered in hdf5 format.

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VISAT - a main component of the BEAM-software, developed by Brockmann Consult GmbH (BC), can be used for visualization, analyzing and processing of MERIS data.