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, four-dimensional (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 acoustic-based 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.
Highlights
1.1 BackgroundStudies of geomorphology have improved our understanding of many of the Earth’s systems and surface processes (Smith et al, 2011; Bishop et al, 2012)
While qualitative descriptions of terrain morphology from digital terrain models (DTMs) are common in the literature, the current review focuses on modern geomorphometry, i.e. the extraction of quantitative information from depth models to describe terrain characteristics
multibeam echo sounders (MBESs) are currently the main source of bathymetric data for applications of marine geomorphometry, these data are limited in terms of coverage: “Multibeam soundings are the gold standards, but such mapping has been concentrated in coastal zones, along shipping lanes, and in regions harbouring hydrocarbon or mineral deposits” (Normile, 2014, p. 964)
Summary
Studies of geomorphology have improved our understanding of many of the Earth’s systems and surface processes (Smith et al, 2011; Bishop et al, 2012). The entire ocean floor has been mapped to a resolution of a few kilometres using satellites, which has created an estimated surface of global bathymetry (Smith and Sandwell, 1994) These coarse-resolution data are often inadequate for many scientific, economic, public safety, and management purposes. Li et al, 2014; Podobnikar and Székely, 2015) These methods are relevant for underwater applications and have been increasingly used in the last decade (Lecours et al, 2015a), but differences in the nature of the input data (e.g. no need to hydrologically correct the surface model, little to no ability to validate measurements on the terrain) can sometimes produce different results than expected from land-based studies, creating the additional need for a dedicated scientific effort in marine geomorphometry.
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