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Spectral analysis of seabed elevation from the Danish Wadden Sea

By Alice Lefebvre, Verner Brandbyge Ernstsen and Christian Winter

Abstract

Bedforms both reflect and influence shallow water hydrodynamics and sediment dynamics. A correct characterization of their spatial distribution and dimensions is required for the understanding, assessment and prediction of numerous coastal processes. A method to parameterize geometrical characteristics using two-dimensional (2D) spectral analysis is presented and tested on seabed elevation data from the Knudedyb tidal inlet in the Danish Wadden Sea, where large compound bedforms are found. The bathymetric data were divided into 20x20 m areas on which a 2D spectral analysis was applied. The most energetic peak of the 2D spectrum was found and its energy, frequency and direction were calculated. A power-law was fitted to the average of slices taken through the 2D spectrum; its slope and y-intercept were calculated. Using these results the test area was morphologically classified into 4 distinct morphological regions. The most energetic peak and the slope and intercept of the power-law showed high values above the crest of the primary bedforms and scour holes, low values in areas without bedforms, and intermediate values in areas with secondary bedforms. The secondary bedform dimensions and orientations were calculated. An area of 700x700 m was used to determine the characteristics of the primary bedforms. However, they were less distinctively characterized compared to the secondary bedforms due to relatively large variations in their orientations and wavelengths. The method is thus appropriate for morphological classification of the seabed and for bedform characterization, being most efficient in areas characterized by bedforms with regular dimensions and directions

Topics: Center for Marine Environmental Sciences; Direction; Fast Fourier Transform; Height; Knudedyb; Knudedyb inlet; LATITUDE; LONGITUDE; MARUM; seabed classification; Spectral energy; Spectral exponent; Spectral strength; UTM Easting, Universal Transverse Mercator; UTM Northing, Universal Transverse Mercator; UTM Zone, Universal Transverse Mercator; Vesterhavet, Denmark; Wavelength
Publisher: PANGAEA
Year: 2011
DOI identifier: 10.1594/PANGAEA.770136
OAI identifier: oai:pangaea.de:doi:10.1594/PANGAEA.770136
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