The spatial distribution of indigenous forest and its composition in the Wellington region, New Zealand, from ETM+ satellite imagery

In order to improve biodiversity management in the Wellington region of New Zealand, it is necessary to make an inventory of the indigenous forest—where is it, and what type is it? The single greatest impediment to making a spatially (i.e., 1:50,000 scale) and thematically detailed inventory from satellite imagery has been the topography of the three mountainous ranges in the Wellington region. The effective irradiance of incoming light varies with slope orientation, as does the proportion of light that is reflected towards the satellite (the bidirectional reflectance). In this paper, we show how satellite imagery may be processed to standardised spectral reflectance, which is a property of the vegetation alone, independent of sun position, slope, and view direction. Because of this, the use of automatic methods to map vegetation and provide spatially and thematically detailed maps is greatly simplified. Using this method, we produce a land-cover map of the Wellington region, with eight classes, to a classification accuracy of approximately 95%. We also show how the proportions of conifer, broad-leaved, and beech trees may be determined for indigenous forest to provide a framework for forest-type inventory.