On the importance of ground validation and methodology for wetland mapping in Canada

Abstract. In this study, existing national wetland maps were compared with ground truth sites used to map wetlands in four areas of interest (AOIs) located in Eastern Canada . By comparing methods used for each map, we identified the following important elements to consider when mapping wetland using remotely sensed data: 1) the five Canadian Wetland Classification System (CWCS) classes (bog, fen, swamp, marsh, shallow water) are broad and can create spectral confusion (it is preferable to use wetland subclasses and then merge them into the broad classes); 2) it is important to add SAR imagery to the classification, given that the radar imagery can detect many wetland characteristics related to the site wetness and vegetation structure. 3) ancillary data, such as DEM, topographic metrics, are a valuable addition to the classification; 4) it is recommended to use multi-seasonal images to consider the temporal variation in the vegetation phenology and in both surface and groundwater levels (both are critical elements for delineating wetlands and periodically flooded areas); 5) images used should have a spatial resolution small enough to have a minimum mapping unit low enough to be able to detect small landscape features; and 6) it is recommended to have a dense network of ground-truth sites representative of the AOI. This study showed that mapping wetlands at the scale of Canada is very challenging, due in part to the diversity of wetland types, which complicates the definition of standardised wetland classes, as well as to the logistical challenges in obtaining data.