Abstract
A light detection and ranging canopy height model (CHM) was used as training data for a segment-based classification of woody patches. The classifier is accurate (∼92%) and suitable for use at the national scale. Height thresholds and percentage cover of vegetation from the CHM were used to produce larger quantities of reliable training data compared to other, mostly point or plot-based, ground-truthing approaches. It was found that the regional-scale differentiation between woody and nonwoody vegetation might be achieved by a combination of L-band dual-polarized Phased Array type L-band synthetic aperture radar data (HV) with multispectral optical data that include a short-wave infrared band. The application of a support vector machine algorithm to these data proved successful. The versatility of these algorithms regarding the discrimination function and their ability to solve classification problems with multiple output classes were critical factors for success. The identified and classified woody patches constitute a valuable addition and enhancement of the national land cover database.
Highlights
The New Zealand Land Cover Database[1] (LCDB) is a digital thematic map of land cover and land use
Segmentation was based on the red, near-infrared (NIR), and short-wave infrared (SWIR) band of both Satellite Pour l’Observation de la Terre (SPOT) mosaics and the minimal segment size was set to 1 ha, according to the minimum mapping unit, which resulted in 277,838 segments in the Wellington region
Our results show that it is possible to create a successful classifier based on SPOT-5 or Phased Array type L-band SAR (PALSAR) dual-polarized data alone, but best results are achieved when the two data sources were combined
Summary
The New Zealand Land Cover Database[1] (LCDB) is a digital thematic map of land cover and land use. It is mainly produced by manual digitization using satellite imagery and aerial photographs. As the major aim of this study is to improve the information content of an existing dataset, such a method must be “conservative” in the sense that it only adds new polygons that are woody with a high probability. The improvement of manually digitized land cover maps is a problem that is not specific to the LCDB and the method could, be applied to regional and national land cover maps in other regions of the world
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