Separating bathymetric data representing multiscale rhythmic bed forms: A geostatistical and spectral method compared

Abstract

[1] The superimposition of rhythmic bed forms of different spatial scales is a common and natural phenomenon on sandy seabeds. The dynamics of such seabeds may interfere with different offshore activities and are therefore of interest to both scientists and offshore developers. State-of-the-art echo sounding accuracy allows for the analysis of bed form dynamics on unprecedented spatial and temporal scales. However, the superimposition of bed forms complicates the automated determination of morphodynamic parameters of individual bed form components. In this research we present the extension and comparison of two well-known, automated signal-processing methods for the 1-D and 2-D separation of bathymetric data derived from multibeam echo soundings into different components that each represents a bed form of a particular length scale. One method uses geostatistical filtering, and the other uses a Fourier decomposition of the bathymetric data. The application of both methods in two case studies of the North Sea shows that both methods are successful and that results correspond well. For example, megaripples up to 0.83 m height could be separated from 1.49-2.28 m high sand waves, and regionally averaged lengths and heights of sand waves, as calculated in either method, differ only 0.42-8.2% between methods. The obtained sand wave migration rates differ 7-11% between methods. The resulting morphometric and morphodynamic bed form quantification contributes to studies of empirical behavior and morphodynamic model validation and is valuable in risk assessments of offshore human activities.Citation: van Dijk, T. A. G. P., R. C. Lindenbergh, and P. J. P. Egberts (2008), Separating bathymetric data representing multiscale rhythmic bed forms: A geostatistical and spectral method compared,

Remote sensing and spatial analysis of aeolian sand dunes: A review and outlook

“…Methodologies outlined in two recent studies stand out. van Dijk et al (2008) compared geostatistical (factorial kriging) and spectral filtering (Fourier analysis) as methods to discriminate different sub-aqueous bedform hierarchies detected in bathymetric data from the North Sea. The outcomes are similar to the residual relief separation technique used by Hugenholtz and Barchyn (2010); however, the methodology is based on objective, automated approaches, whereas the approach developed by Hugenholtz and Barchyn (2010) involves some user input.…”

Quantified sea-bed dynamics of the Netherlands continental shelf and the Wadden Sea: a morphological and sedimentological approach

“…As part of these analyses, the bathymetric signal was separated into bedform types of different spatial scales by truncating a Fourier approximation at certain frequencies [cf. Van Dijk et al, 2008]. From the smoothed bedform signal, locations of crest, trough and inflection points were then determined in a semi-automated way, from which the geometry and dynamics of individual bedforms were calculated.…”

“…Duffy and Hughes-Clarke, 2005;Knaapen, 2005;Buijsman and Ridderinkhof, 2008;Van Dijk et al, 2008;Dorst et al, 2011]. Recently, a regional-scale study of morphodynamics was carried out for the German coastal zone [Winter, 2011].…”

Quantified and applied sea-bed dynamics of the Netherlands Continental Shelf and the Wadden Sea

“…Duffy and Hughes-Clarke, 2005;Knaapen, 2005;Van Dijk and Kleinhans, 2005;Winter and Ernstsen, 2007;Buijsman and Ridderinkhof, 2008;Van Dijk et al, 2008;Dorst et al, 2009;Dorst et al, 2011]. Although recently performed for the German coastal zone [Winter, 2011], a large-scaled study of the morphodynamics of the Netherlands Continental Shelf (NCS) does not exist.…”