Preliminary studies on coral mapping in Tung Ping Chau of the eastern Hong Kong using high-resolution SPOT satellite imagery

Abstract

Applying remote sensing techniques to hard coral mapping in Hong Kong using SPOT satellite imagery is divided into two stages. At stage 1, any potential coral signals in the satellite imagery are detected by two methods. At stage 2, field spectral measurements are applied to the mapping, which will be conducted in the future work. Method 1 involves scanning the imagery and seeking the plant-like spectral signature that is associated with the symbiotic unicellular algae living inside the hard corals. Method 2 involves processing the imagery with per-pixel analysis using both supervised and unsupervised classifications. Without the field spectral measurements, the spectral signatures of the main habitats are derived from the imagery according to field map and informal field observation. They are first applied to supervised classification. Then, the unclassified class in the coastal submerged zone is analysed by unsupervised classification. The attempt to detect the potential coral distribution from the satellite imagery is not successful. It is found that the spectral resolution (both the band number and bandwidth) in the visible range determines the mapping success, in terms of the distinctiveness of the spectral signatures of the main habitats underwater and the effectiveness of water column correction, mainly depth.

Keywords:

• coral mapping
• remote sensing
• SPOT