Object-Based Classification of Ikonos Imagery for Mapping Large-Scale Vegetation Communities in Urban Areas
Mathieu, R and Aryal, J and Chong, AK, Object-Based Classification of Ikonos Imagery for Mapping Large-Scale Vegetation Communities in Urban Areas, Sensors, 2007, (7) pp. 2860-2880. ISSN 1424-8220 (2007) [Refereed Article]
Effective assessment of biodiversity in cities requires detailed vegetation maps.
To date, most remote sensing of urban vegetation has focused on thematically coarse land
cover products. Detailed habitat maps are created by manual interpretation of aerial
photographs, but this is time consuming and costly at large scale. To address this issue, we
tested the effectiveness of object-based classifications that use automated image
segmentation to extract meaningful ground features from imagery. We applied these
techniques to very high resolution multispectral Ikonos images to produce vegetation
community maps in Dunedin City, New Zealand. An Ikonos image was orthorectified and a
multi-scale segmentation algorithm used to produce a hierarchical network of image objects.
The upper level included four coarse strata: industrial/commercial (commercial buildings),
residential (houses and backyard private gardens), vegetation (vegetation patches larger than
0.8/1ha), and water. We focused on the vegetation stratum that was segmented at more
detailed level to extract and classify fifteen classes of vegetation communities. The first
classification yielded a moderate overall classification accuracy (64%, ê = 0.52), which led
us to consider a simplified classification with ten vegetation classes. The overall
classification accuracy from the simplified classification was 77% with a ê value close to
the excellent range (ê = 0.74). These results compared favourably with similar studies in
other environments. We conclude that this approach does not provide maps as detailed as those produced by manually interpreting aerial photographs, but it can still extract
ecologically significant classes. It is an efficient way to generate accurate and detailed maps
in significantly shorter time. The final map accuracy could be improved by integrating
segmentation, automated and manual classification in the mapping process, especially when
considering important vegetation classes with limited spectral contrast.