The relation between Normalized Difference Vegetation Index and vegetation moisture content at three grassland locations in Victoria, Australia

Abstract

The supposition that, for most practical purposes, a single, generic, widely applicable relation exists between Normalized Difference Vegetation Index (NDVI) and grassland vegetation moisture content is tested. An experiment is described in which the vegetation moisture content at three Victorian grassland sites of varying composition is measured over the course of a complete curing episode. For each site, corresponding satellite radiation measurements are used to extract surface reflectances corrected for atmospheric and view-angle effects, and NDVI values based on these. On relating NDVI so obtained to the field measurements of vegetation moisture expressed in terms of a parameter commonly employed in assessing grassland fire risk, namely Fuel Moisture Content (FMC), separate relations for each site are clearly identified. When the relation appropriate to each site is used to derive FMC for that site, accurate estimates are obtained. Accuracy decreases markedly if the relation appropriate to one site is used to derive estimates of FMC at the other sites. When FMC values are transformed to another commonly employed parameter of grassland vegetation moisture content, namely Grassland Curing Index (GCI), the loss of accuracy becomes much greater. More accurate estimates of GCI are obtained using a direct relation between NDVI and GCI.