4 - Empirical Vegetation Indices

Vegetation indices (VIís) have a long history of use over a wide range of applications, such as vegetation monitoring; climate and hydrologic modelling; agricultural activities; drought studies and public health issues. As shown in chapter 3, vegetation has unique spectral signatures, which evolve with the plant life cycle. VIís are dimensionless radiometric measures, which combine information from different channels, particularly in the red and NIR portions of the spectrum, to enhance the 'vegetation signal'. Such indices allow reliable spatial and temporal inter-comparisons of terrestrial photosynthetic activity and canopy structural variations. They are generally computed for all pixels in time and space, regardless of biome type, land cover condition and soil type, and thus represent true surface measurements. Due to their simplicity, ease of application, vegetation indices have a wide range of usage within the user community.