A review of marine geomorphometry, the quantitative study of the seafloor

Abstract

Abstract. Geomorphometry, the science of quantitative terrain characterization, has traditionally focused on the investigation of terrestrial landscapes. However, the dramatic increase in the availability of digital bathymetric data and the increasing ease by which geomorphometry can be investigated using geographic information systems (GISs) and spatial analysis software has prompted interest in employing geomorphometric techniques to investigate the marine environment. Over the last decade or so, a multitude of geomorphometric techniques (e.g. terrain attributes, feature extraction, automated classification) have been applied to characterize seabed terrain from the coastal zone to the deep sea. Geomorphometric techniques are, however, not as varied, nor as extensively applied, in marine as they are in terrestrial environments. This is at least partly due to difficulties associated with capturing, classifying, and validating terrain characteristics underwater. There is, nevertheless, much common ground between terrestrial and marine geomorphometry applications and it is important that, in developing marine geomorphometry, we learn from experiences in terrestrial studies. However, not all terrestrial solutions can be adopted by marine geomorphometric studies since the dynamic, fourdimensional (4-D) nature of the marine environment causes its own issues throughout the geomorphometry workflow. For instance, issues with underwater positioning, variations in sound velocity in the water column affecting acousticbased mapping, and our inability to directly observe and measure depth and morphological features on the seafloor are all issues specific to the application of geomorphometry in the marine environment. Such issues fuel the need for a dedicated scientific effort in marine geomorphometry.This review aims to highlight the relatively recent growth of marine geomorphometry as a distinct discipline, and offers the first comprehensive overview of marine geomorphometry to date. We address all the five main steps of geomorphometry, from data collection to the application of terrain attributes and features. We focus on how these steps are relevant to marine geomorphometry and also highlight differences and similarities from terrestrial geomorphometry. We conclude with recommendations and reflections on the future of marine geomorphometry. To ensure that geomorphometry is used and developed to its full potential, there is a need to increase awareness of (1) marine geomorphometry amongst scientists already engaged in terrestrial geomorphometry, and of (2) geomorphometry as a science amongst marine scientists with a wide range of backgrounds and experiences.

On the Use of Maps and Models in Conservation and Resource Management (Warning: Results May Vary)

“…One of the main solutions that has been discussed widely in the ecological literature is to select variables with an ecological meaning for the studied area, species or habitat (Howell, 2010;Borja et al, 2014;Lecours et al, , 2016a. However, this makes comparability of maps in a broader context difficult; as previously discussed, there is no universal approach and variable selection is site-and case-specific (Pitcher et al, 2012).…”

“…distributions that can reach as much as thousands of square kilometers (Lecours et al, 2016a). One of the main solutions that has been discussed widely in the ecological literature is to select variables with an ecological meaning for the studied area, species or habitat (Howell, 2010;Borja et al, 2014;Lecours et al, , 2016a.…”

“…For example, when using unsupervised classifications of environmental data to identify distinct habitats, the classification accuracy can be evaluated using confusion matrices (e.g., Brown et al, 2012;Lecours et al, 2016a). Confusion matrices identify commission and omission errors, or the level of agreement and disagreement between the classification results and ground-truth data.…”

Seafloor change detection using multibeam echosounder backscatter: case study on the Belgian part of the North Sea

“…Predictor layers are a set of variables (in this analysis terrain and texture attributes) derived from the MBES backscatter and bathymetry which are combined to the observed substrate type points (response variable) to predict the full-coverage seafloor map (Lecours et al 2016). The relevance of the predictors was investigated by following the feature selection procedure provided by Kursa and Rudnicki (2010) using the Boruta RF wrapper function.…”

A Bathymetry- and Reflectivity-Based Approach for Seafloor Segmentation

“…Common methods to segment the seafloor into geoform elements use differential geometry and geo-morphometric proxies that are derived locally from the DEM by calculating a variable combination of first and second derivatives [24]. These methods offer several approaches for how the geo-morphometric variables are used (mainly, cell-based or object-based), with respect to the selected units of classification (landforms, landform elements, and physiographic units), and the adopted classifier (based on expert knowledge or driven by a machine learning algorithm) [25,26].…”