Automatic Mapping and Characterisation of Linear Depositional Bedforms: Theory and Application Using Bathymetry from the North West Shelf of Australia

Abstract

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.

An Approach for the Automatic Characterization of Underwater Dunes in Fluviomarine Context

“…We can also estimate different descriptors for the stoss and lee sides of the dune, as their width and sloping angles [18]. These descriptors are illustrated in Figure 6.…”

“…Dunes can also be characterized by different index values, which are calculated based on the dune measurements previously described. The dune symmetry index (1) is defined as the ratio between the stoss and lee side widths [18,26,32].…”

“…Different descriptors exist to describe the morphology of the dunes, such as the already defined length of the crest line. The dune sinuosity index (3) can be estimated based on the ratio between the length of the crest line (L c ) and the geodetic distance (D C ) between the crest line extremities [18,29,32].…”

“…An example is the computation of the angles of the sloping sides of the dunes. They are calculated based on the profile of the dune between the line connecting the crest line and the troughs of the dune [15,18]. Since we consider the dune as an object identified on the seafloor by its salient features, it can be characterized by different morphological descriptors related to its full surface rather series of sampled profiles.…”

“…Measurements for dune stoss and lee sides. W S , W L , α S , and α L represent, respectively, the width of the stoss side, the width of the lee side, the angle of the stoss side, and the angle of the lee side (adapted from[18]). Geosciences 2022, 12, x FOR PEER REVIEW 7 of 20…”