Intertidal surface type mapping in the Danish Wadden Sea

A map of the intertidal surface sediment types in the central and northern part of the Danish Wadden Sea has been constructed on the basis of a thematic classification of a Landsat ETM+ scene combined with information from two texture measure images derived from orthophotos and an extensive ground truth collection. The mapped intertidal area covers 397 km2 in three tidal regions: Grådyb, Knudedyb and Juvre Dyb. The classification of the surface types reveals that tidal flats cover 71% and water permanently covers 29% of the mapped area. Four tidal flat types could be distinguished: mudflat 2%, mixed flat (wet/moist) 12%, low (wet) sand flats 46%, and high (dry) sand flat 11%. The fine-grained tidal flat types (mud and mixed flats) are primarily located in the northern tidal area of Grådyb (8.4%). Their areal coverage decreases towards the south (Knudedyb, 4.6%; Juvre Dyb, 1.1%) which reflects a similar decreasing southern trend in the import of fine-grained material.