Bedforms are key components of Earth surfaces and yet their evaluation typically relies on manual measurements that are challenging to reproduce. Several methods exist to automate their identification and calculate their metrics, but they often exhibit limitations where applied at large scales. This paper presents an innovative workflow for identifying and measuring individual depositional bedforms. The workflow relies on the identification of local minima and maxima that are grouped by neighbourhood analysis and calibrated using curvature. The method was trialed using a synthetic digital elevation model and two bathymetry surveys from Australia’s northwest marine region, resulting in the identification of nearly 2000 bedforms. The comparison of the metrics calculated for each individual feature with manual measurements show differences of less than 10%, indicating the robustness of the workflow. The cross-comparison of the metrics resulted in the definition of several sub-types of bedforms, including sandwaves and palaeoshorelines, that were then correlated with oceanic conditions, further corroborating the validity of the workflow. Results from this study support the idea that the use of automated methods to characterise bedforms should be further developed and that the integration of automated measurements at large scales will support the development of new classification charts that currently rely solely on manual measurements.
Abstract. High-resolution bathymetry forms critical datasets for marine geoscientists.
It can be used to characterize the seafloor and its marine habitats, to
understand past sedimentary records, and even to support the development of
offshore engineering projects. Most methods to acquire bathymetry data are
costly and can only be practically deployed in relatively small areas. It is
therefore critical to develop cost-effective and advanced techniques to
produce regional-scale bathymetry datasets. This paper presents an integrated workflow that builds on satellites images
and 3D seismic surveys, integrated with historical depth soundings, to
generate regional high-resolution digital elevation models (DEMs). The
method was applied to the southern half of Australia's North West Shelf and
led to the creation of new high-resolution bathymetry grids, with a
resolution of 10 × 10 m in nearshore areas and 30 × 30 m elsewhere. The vertical and spatial accuracy of the datasets have been assessed using
open-source Laser Airborne Depth Sounder (LADS) and multibeam echosounder
(MBES) surveys as a reference. The comparison of the datasets indicates that
the seismic-derived bathymetry has a vertical accuracy better than 1 m + 2 % of the absolute water depth, while the satellite-derived bathymetry
has a depth accuracy better than 1 m + 5 % of the absolute water depth.
This 30 × 30 m dataset constitutes a significant improvement of the
pre-existing regional 250 × 250 m grid and will support the onset of
research projects on coastal morphologies, marine habitats, archaeology, and
sedimentology. All source datasets are publicly available, and the methods are fully
integrated into Python scripts, making them readily applicable elsewhere in
Australia and around the world. The regional digital elevation model and the
underlying datasets can be accessed at https://doi.org/10.26186/144600 (Lebrec et al., 2021).
Calcareous sediments are prominent throughout the low-latitudinal offshore environment and have been known to be problematic for offshore foundation systems. These fascinating soils consist largely of the skeletal remains of single-celled marine organisms (plankton and zooplankton) and can be as geologically complex as their onshore siliceous counter parts. To enable an adequate understanding of their characteristics, in particular, their intra-granular micro-structure, it is important that geotechnical engineers do not forget about the multifaceted biological origins of these calcareous sediments and the different geological processes that created them. In this paper, the 3D models of soils grains generated from micro-computed tomography scans, scanning electeron microscope images, and optical microscope images of two calcareous sediments from two different depositional environments are presented and their geotechnical implications discussed. One is a coastal bioclastic sediment from Perth, Western Australia that is geologically similar to carbonate sediments typically used in micro-mechanics and particle crushing studies in the literature. The other is a hemipelagic sediment from a region of the North West Shelf of Australia that has historically been geotechnically problematic for engineers. The results show there is a marked difference between coastal bioclastic and hemipelagic sediments in terms of geological context and the associated particle micro-structures. This brings into question whether a coastal bioclastic calcareous sediment is a good micro-mechanical substitute for a hemipelagic one.
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