Intercalibration of Vegetation Indices – an Update

In 2003 we addressed the issue of intercalibration of vegetation indices from different satellite-based optical sensor systems with differing spectral response functions in the visible and near-infrared bands (Steven et al., 2003). We used a database of spectroradiometric measurements made over a range of canopy densities, soils and foliage colours to simulate vegetation indices (NDVI, SAVI and OSAVI) to produce a table of intercalibration factors for the specific spectral response functions for 15 satellite instruments. We found that the indices are not identical, but are linearly related, allowing conversion from one system to another to a precision of 1–2%. Our results allow vegetation index data from different systems to be combined reliably. The present study extends the intercalibration of vegetation indices to include systems launched since our previous paper. We propose a standard pair of bands for the definition of vegetation indices and suggest that users apply our conversion coefficients to adjust vegetation index measurements to this standard. The margin of error in applying a two step conversion via the standard is at most 1% compared with a direct conversion from one system to the other. Independent validations of our conversion coefficients from a number of studies in the literature are discussed.