Conclusion

This paper documents the implementation and exploitation of a vegetation index whose purpose is to identify and monitor the presence of live green vegetation over a wide diversity of terrestrial surfaces, observed under a variety of atmospheric and angular conditions by the SeaWiFS instrument. The proposed approach is based on a two step procedure. The first step aims at rectifying the red and near-infrared bands from the perturbing effects due to the atmosphere and the changes in the relative geometry of illumination and observation. The second step consists in optimizing the index formula to approximate a one-to-one relationship between the index value and the Fraction of Absorbed Photosynthetically Active Radiation, used as a proxy for detecting the presence of healthy vegetation. The procedure capitalizes on the availability of advanced, coupled, surface-atmosphere radiation transfer models that are exploited to construct the training data set against which the SeaWiFS index optimization is achieved.

A quantitative evaluation of the performance of SeaWiFS-VI has been established through an analysis of actual SeaWiFS observations. This application has shown the capability of the optimized index to be much less sensi tive than NDVI to perturbing effects. It also illustrates the ability of this index to distinguish between various biome types on the basis of a single day image. The new products available from this algorithm include the rectified red and near-infrared channels in addition to the final FAPAR estimates. These geophysical products are well suited to address a number of issues related to the documentation and monitoring of land surfaces.

0 0

Post a comment