Limits...
Remote Sensing and Wetland Ecology: a South African Case Study

View Article: PubMed Central

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.

No MeSH data available.


Fraction of detected wetlands belonging to different size classes (in ha) in summer and in winter, with indication of the standard deviation.
© Copyright Policy
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3675558&req=5

f2-sensors-08-03542: Fraction of detected wetlands belonging to different size classes (in ha) in summer and in winter, with indication of the standard deviation.

Mentions: In general many small and only few large wetlands were detected in both summer and winter images (Figure 2). On average 68% of summer wetlands and 79% of winter wetlands were smaller than one hectare. More small wetlands were detected in winter than in summer (Figure 2). The ground survey in winter 2005 revealed that about 73% of the wetlands (which were mostly temporary) in the study area could not be detected, since they were smaller than the resolution of the Landsat imagery (0.081 ha). Another 15% of wetlands observed in the field covered an area of about one pixel. Due to a high chance of misclassification they were excluded from this study. Consequently, only about 12% of wetlands present in the study area could be detected by Landsat classifications.


Remote Sensing and Wetland Ecology: a South African Case Study
Fraction of detected wetlands belonging to different size classes (in ha) in summer and in winter, with indication of the standard deviation.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3675558&req=5

f2-sensors-08-03542: Fraction of detected wetlands belonging to different size classes (in ha) in summer and in winter, with indication of the standard deviation.
Mentions: In general many small and only few large wetlands were detected in both summer and winter images (Figure 2). On average 68% of summer wetlands and 79% of winter wetlands were smaller than one hectare. More small wetlands were detected in winter than in summer (Figure 2). The ground survey in winter 2005 revealed that about 73% of the wetlands (which were mostly temporary) in the study area could not be detected, since they were smaller than the resolution of the Landsat imagery (0.081 ha). Another 15% of wetlands observed in the field covered an area of about one pixel. Due to a high chance of misclassification they were excluded from this study. Consequently, only about 12% of wetlands present in the study area could be detected by Landsat classifications.

View Article: PubMed Central

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.

No MeSH data available.