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Remote Sensing and Wetland Ecology: a South African Case Study
Laboratory of Aquatic Ecology and Evolutionary Biology, Katholieke Universiteit Leuven, Charles Deberiotstraat 32, 3000 Leuven, Belgium
Laboratory of Hydrology and Water Management, Ghent University, Coupure links 653, 9000 Ghent, Belgium
Department of Hydrology and Hydraulic Engineering, Vrije Universiteit Brussel, Pleinlaan 2, 1050 Brussels, Belgium
Department of Earth and Environmental Sciences, Katholieke Universiteit Leuven, Celestijnenlaan 200e - bus 2410, 3001 Heverlee, Belgium
Department of Earth Sciences, University of the Western Cape, P Bag X17, Bellville 7535, Cape Town, South Africa
* Author to whom correspondence should be addressed.
Received: 29 April 2008; Accepted: 15 May 2008 / Published: 26 May 2008
Abstract: Remote sensing offers a cost efficient means for identifying and monitoring wetlands over a large area and at different moments in time. In this study, we aim at providing ecologically relevant information on characteristics of temporary and permanent isolated open water wetlands, obtained by standard techniques and relatively cheap imagery. The number, surface area, nearest distance, and dynamics of isolated temporary and permanent wetlands were determined for the Western Cape, South Africa. Open water bodies (wetlands) were mapped from seven Landsat images (acquired during 1987 – 2002) using supervised maximum likelihood classification. The number of wetlands fluctuated over time. Most wetlands were detected in the winter of 2000 and 2002, probably related to road constructions. Imagery acquired in summer contained fewer wetlands than in winter. Most wetlands identified from Landsat images were smaller than one hectare. The average distance to the nearest wetland was larger in summer. In comparison to temporary wetlands, fewer, but larger permanent wetlands were detected. In addition, classification of non-vegetated wetlands on an Envisat ASAR radar image (acquired in June 2005) was evaluated. The number of detected small wetlands was lower for radar imagery than optical imagery (acquired in June 2002), probably because of deterioration of the spatial information content due the extensive pre-processing requirements of the radar image. Both optical and radar classifications allow to assess wetland characteristics that potentially influence plant and animal metacommunity structure. Envisat imagery, however, was less suitable than Landsat imagery for the extraction of detailed ecological information, as only large wetlands can be detected. This study has indicated that ecologically relevant data can be generated for the larger wetlands through relatively cheap imagery and standard techniques, despite the relatively low resolution of Landsat and Envisat imagery. For the characterisation of very small wetlands, high spatial resolution optical or radar images are needed. This study exemplifies the benefits of integrating remote sensing and ecology and hence stimulates interdisciplinary research of isolated wetlands.
Keywords: Wetland monitoring; wetland distribution and density; wetland ecology; Landsat; Envisat
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De Roeck, E.R.; Verhoest, N.E.; Miya, M.H.; Lievens, H.; Batelaan, O.; Thomas, A.; Brendonck, L. Remote Sensing and Wetland Ecology: a South African Case Study. Sensors 2008, 8, 3542-3556.
De Roeck ER, Verhoest NE, Miya MH, Lievens H, Batelaan O, Thomas A, Brendonck L. Remote Sensing and Wetland Ecology: a South African Case Study. Sensors. 2008; 8(5):3542-3556.
De Roeck, Els R.; Verhoest, Niko E.; Miya, Mtemi H.; Lievens, Hans; Batelaan, Okke; Thomas, Abraham; Brendonck, Luc. 2008. "Remote Sensing and Wetland Ecology: a South African Case Study." Sensors 8, no. 5: 3542-3556.