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New Zealand Plant Protection 55 (2002): 95-98

Satellite mapping of gorse at regional scales

J.D. Shepherd and W.G. Lee

ABSTRACT

The spatial distribution of gorse in the Wellington Region was mapped using Landsat satellite imagery. This satellite is capable of mapping at regional scales (1:50 000), with a large spatial extent (180 km x 180 km), and has spectral bands in both the visible and infrared parts of the spectrum (6 bands in total). A spring Landsat image distinguished flowering gorse, enabling mapping of gorse as a separate scrub type. We chose a minimum patch size of 0.5 ha with a boundary precision of 15 m. An error assessment using 1200 stratified random samples across the Wellington region compared the satellite classified result with colour aerial orthophotography and found the mapping accuracy of gorse to be 95%. Gorse area by catchment was calculated using an existing GIS of catchment boundaries. The area and percent cover of gorse within a catchment is a potential way to target management at regional scales.

Keywords: Ulex europaeus, monitoring, scrub weeds, satellite.

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