Wetland classification for Swedish CORINE Land Cover adopting a semi-automatic interactive approach

In a collaboration between the Swedish Space Corporation and the National Land Survey of Sweden, work has been carried out to develop a satellite-data-based method for mapping wetlands for the Swedish CORINE Land Cover database. The aim was two-fold: (1) develop a method for mapping the wetlands in five classes, namely "inland marshes", "wet mires", "other mires", "exploited peatlands", and "salt marshes", with a minimum mapping unit of 1 ha; and (2) investigate if the classes "wet mires" and "other mires" could be obtained more reliably from satellite data than directly from I : 50 000 scale topographic maps. Data sources used in the project included geo-referenced Landsat thematic mapper (TM) images, digital topographic map data, digital vegetation data, and colour infrared aerial photographs. The development work included analysis of spectral signature characteristics, classification tests, method definition, method verification, pilot production, and accuracy assessment. The method developed to obtain the five wetland classes is a combination method. The classes inland marshes, salt marshes, and exploited peatlands are mapped using geographical information system (GIS) operations, combining information from the topographic maps, and visual interpretation of Landsat TM data. For the classes wet mires and other mires, a stepwise semi-automatic approach was adopted, where level slicing in ratios or in single Landsat TM bands is used to produce the classes. The evaluation showed high accuracy for all five classes, with overall accuracies ranging from 90% to 100%. It was also concluded that the semi-automatic interactive approach used to produce wet mires and other mires gave the same high accuracy as the topographic map, or a better result than the map for areas in northern Sweden where the representation of wet mires on the map is not as good. The method described is used for production of the wetland classes for the Swedish CORINE Land Cover.