DESIGNING OPTIMAL SPECTRAL INDEXES FOR REMOTE-SENSING APPLICATIONS

Satellite remote sensing data constitute a significant potential sourc e of information on our environment, provided they can be adequately i nterpreted, Vegetation indexes, a subset of the class of spectral inde xes, represent one of the most commonly used approaches to analyze dat a In the optical domain, An optimal spectral index is very sensitive t o the desired information (e.g., the amount of vegetation), and as ins ensitive as possible to perturbing factors (such as soil color changes or atmospheric effects), Since both the desired signal and the pertur bing factors vary spectrally, and since the instruments themselves onl y provide data for particular spectral bands, optimal indexes should b e designed for specific applications and particular instruments, This paper describes a rational approach to the design of an optimal index to estimate vegetation properties on the basis of the red and near-inf rared reflectances of the AVHRR instrument, taking into account the pe rturbing effects of soil brightness changes, atmospheric absorption an d scattering, The rationale behind the Global Environment Monitoring I ndex (GEMI) is explained, and this index is proposed as an alternative to the Normalized Difference Vegetation Index (NDVI) for global appli cations. The techniques described here are generally applicable to any multispectral sensor and application.