A combined method to calculate superimposed 2-D dune morphological parameters

Two-dimensional (2-D) subaqueous dunes often superimpose on giant dunes, sand bars or sand ridges. Mega-ripples may also be further superimposed on the 2-D dunes. A combined method was developed to analyse the geometry of the 2-D subaqueous dunes in this case, including 2-D Fourier analysis, wavelet transform, zero-crossing analysis, and various filtering. The regional dominant orientation and individual geometry parameters of 2-D submarine dunes can thus be obtained automatically with input of bathymetries. This method was successfully applied with both synthetic and observed bathymetries. Marine and River Dune Dynamics – MARID VI – 1-3 April 2019 Bremen, Germany 244 vert water depth matrix into a 2-D power spectrum. The main wavenumber can be extracted to calculate the regional dominant orientation and wavelength of submarine dunes (Van Dijk et al., 2008; Lefebvre et al., 2011; Cazenave et al., 2013). Anisotropic covariance analysis is also applied on the basis that the covariance in the direction of 2-D dune crests is the smallest, and the range value of the semi-variogram model in the direction perpendicular to the dune crests is the regional dominant wavelength of the submarine dunes (Dorst, 2004; Pluymaekers et al., 2007; Van Dijk et al., 2008). Zero-crossing analysis can be easily applied to calculate the individual geometry parameters of submarine dunes. However, it would be challenged by the superimposition of bedforms with different scales. Thus, separating bedforms of different scales is necessary. Based on the geostatistical analysis, bedforms at different scales can be obtained by Kriging interpolation in a variety of resolutions (Van Dijk et al., 2008). 2-D discrete Fourier analysis combined with Butterworth high-pass filtering can effectively eliminate the background topographic effects (Cazenave et al., 2013). However, the spectral leakage of this method tends to underestimate wave height (Van Dijk et al., 2017). Although wavelet transform is applied for one-dimensional profiles, it has an outstanding performance in separation of dunes at different scales (Gutierrez et al., 2013). Different methods have good performance at different stages of 2-D dune morphology analysis. We create a combined method based on Matlab, including 2-D discrete Fourier transform, Wavelet transform, and zero-crossing analysis. With an input of coordinates and bathymetry data, the regional and individual geometry parameters of superimposed 2-D submarine dunes can be calculated automatically. The method was applied to a synthetic bathymetry, and two measured bathymetries. One is on a sand ridge off Jiangsu Coast, China, and the other is on a sandbank in the Dover Strait, UK. 2 METHODS AND MATERIALS