Abstract
Abstract. Several maps of wetland areas in central New Brunswick, Canada, were produced by applying the Random Forests classifier to different combinations of optical Landsat-5 TM images, dual-polarized (HH, HV) Radarsat-2 C-band and Alos-1 PalSAR L-band Synthetic Aperture Radar (SAR) images and digital elevation data. The resulting maps were compared to 199 GPS wetland sites that were visited between 2012 and 2018 as well as to a combination of two wetland maps currently used by the Province of New Brunswick. The number of correctly identified GPS wetland sites was the highest when both the Alos-PalSAR and Radarsat-2 images are used (97.9%). This percentage of correctly identified sites were well above the accuracy of the official New Brunswick wetland maps (44.7 %). With the best-classified image, the misidentifications were due to wetlands not being classified in the right wetland class, and just one case was a wetland site being classified in a non-wetland class. For the NB wetland map, about a quarter of the wetland validation sites were classified in a non-wetland class, and about the same number of sites were classified in the wrong wetland class.
Highlights
Wetlands are important ecosystems that perform a variety of services that are beneficial to society and the environment
Among all the visited sites, 346 sites (147 training sites and 199 validation sites) were considered as a wetland site, according to Tiner (1999)’s criteria: the water table was close to or at the surface, or we found indicator plants, soil hydromorphy, or other evidence of an area that is very often saturated with water
3.1 Effect of wetland water level on the images The effect of the different water levels in the wetlands is visible in the true-colour composite of the Landsat-5 Thematic Mapper (TM) images (Figure 2), as well as in the false-colour composites of the Radarsat-2 (Figure 3) and of the Alos-PalSAR images (Figure 4)
Summary
Wetlands are important ecosystems that perform a variety of services that are beneficial to society and the environment They are crucial for groundwater recharge, flood control, water quality improvement, and mitigation of erosion (Li, Chen, 2005). Developing a mapping method to extract information about wetland areas from satellite imagery is essential for mapping large scale regions such as the Province of New Brunswick (Canada). Satellite images provide a practical approach to mapping wetlands in New Brunswick, given the remoteness of some parts of the province. Optical images like those acquired by Landsat, SPOT or Sentinel-2 satellites were already tested for mapping wetlands (e.g., Amani et al 2017). Optical imagery has the additional inconvenience of having an availability, which is limited to clear sky conditions
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