A multi-resolution satellite imagery approach for large area mapping of ericaceous shrubs in Northern Quebec, Canada |
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| Authors: | Olivier R van Lier Richard A Fournier Robert L Bradley Nelson Thiffault |
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| Institution: | 1. Centre d’Applications et de Recherche en Télédétection, Département de géomatique appliquée, Université de Sherbrooke, Sherbrooke, QC, Canada J1K 2R1;2. Centre d’Étude de la Forêt, Département de biologie, Université de Sherbrooke, Sherbrooke, QC, Canada J1K 2R1;3. Direction de la recherche forestière, Ministère des Ressources Naturelles et de la Faune du Québec, Québec, QC, Canada G1P 3W8 |
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| Abstract: | Invasive ericaceous shrubs (e.g. Kalmia angustifolia, Rhododendron groenlandicum, Vaccinium spp.) may reduce the regeneration and early growth of black spruce (Picea mariana) seedlings, the most economically important boreal tree species in Quebec. Our study focused, therefore, on developing a method for mapping ericaceous shrubs from satellite images. The method integrates very high resolution satellite imagery (IKONOS) to guide classifiers applied to medium resolution satellite imagery (Landsat-TM). An object-oriented image classification approach was applied using Definiens eCognition software. An independent ground survey revealed 80% accuracy at the very high spatial resolution. We found that the partial use (70%) of classified polygons derived from the IKONOS images were an effective way to guide classification algorithms applied to the Landsat-TM imagery. The results of this latter classification (78.4% overall accuracy) were assessed by the remaining portion (30%) of unused very high resolution classified polygons. We further validated our method (65.5% overall accuracy) by assessing the correspondence of an ericaceous cover classification scheme done with a Landsat-TM image and results of our ground survey using an independent set of 275 sample plots. Discrimination of ericaceous shrub cover from other land cover types was achieved with precision at both spatial resolutions with producer accuracies of 87.7% and 79.4% from IKONOS and Landsat, respectively. The method is weaker for areas with sparse cover of ericaceous shrubs or dense tree cover. Our method is adapted, therefore, for mapping the spatial distribution of ericaceous shrubs and is compatible with existing forest stand maps. |
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| Keywords: | Multi-resolution Object-oriented classification Ericaceous shrubs Forestry |
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