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An Ocean of Possibilities: Applications and Challenges of Marine Geomorphometry



An increase in the use of geomorphometry in the marine environment has occurred in the last decade. This has been fueled by a dramatic increase in digital bathymetric data, which have become widely available as digital terrain models (DTM) at a variety of spatial resolutions. Despite many similarities, the nature of the input DTM is slightly different than terrestrial DTM. This gives rise to different sources of uncertainties in bathymetric data from various sources that will have particular implications for geomorphometric analysis. With this contribution, we aim to raise awareness of applications and challenges of marine geomorphometry.
An Ocean of Possibilities: Applications and
Challenges of Marine Geomorphometry
Vincent Lecours
Department of Geography
Memorial University of Newfoundland
St. John’s, Canada
Margaret F. J. Dolan
Geological Survey of Norway
Trondheim, Norway
Vanessa L. Lucieer
Institute for Marine and Antarctic Studies
University of Tasmania
Hobart, Australia
Aaron Micallef
Department of Physics
University of Malta
Msida, Malta
Abstract An increase in the use of geomorphometry in the
marine environment has occurred in the last decade. This has
been fueled by a dramatic increase in digital bathymetric data,
which have become widely available as digital terrain models
(DTM) at a variety of spatial resolutions. Despite many
similarities, the nature of the input DTM is slightly different than
terrestrial DTM. This gives rise to different sources of
uncertainties in bathymetric data from various sources that will
have particular implications for geomorphometric analysis. With
this contribution, we aim to raise awareness of applications and
challenges of marine geomorphometry.
Exploration and characterization of the ocean floor
continuously presents new possibilities and challenges. Thanks
to recent and ongoing improvements in acoustic remote
sensing technology, seabed relief can now be measured
rapidly, extensively and at fine spatial scales [1]. Among these
technologies, multibeam echosounder systems (MBES)
provide some of the most detailed and accurate data currently
available [2]. Most of the MBES data are collected during
navigational charting efforts, with a particular focus on
shallower coastal waters where the seabed relief can pose a
hazard to navigation. Due to potential safety concerns,
standards regarding data quality and uncertainty are high for
these shallow datasets. Datasets from deeper waters, however,
still lag behind in terms of quality and quantity. Owing to the
technological challenges and high costs associated with
bathymetric mapping of large and deeper parts of the seabed, it
is estimated that only 5-10% of the oceans are mapped with a
resolution comparable to that on land [3].
The adoption of terrestrial geomorphometric techniques to
investigate marine environments increased in the past decade
[e.g 4]. The primary digital terrain model (DTM) data source
for marine geomorphometry has been bathymetry (depth) grids
generated from MBES data. These DTMs are analyzed to
characterize geomorphological features of the seabed, which
can at times be sources of biological information (e.g. coral
reefs). Bathymetric data have proven their potential to help the
scientific community and government agencies advance their
understanding of seabed ecosystems and geomorphological
processes [5].
The terrestrial geomorphometric literature provides a rich
source of potential analytical techniques for marine studies [6].
It is important, however, to acknowledge that different data
collection and processing techniques used to create underwater
DTM makes the nature of the input DTM different. In addition,
it is more difficult to capture terrain variability underwater
since changes in topography are more subdued in comparison
to terrestrial landscapes. Issues encountered in terrestrial
geomorphometry, such as underlying data uncertainty and the
choice of the analysis algorithm and scale (resolution and
neighborhood size), are also relevant underwater, but they
manifest themselves differently due to the differences in the
input data.
In this contribution, we review some of the most common
applications and challenges encountered in marine
geomorphometry and explore potential future directions.
Lecours et al.
In: Geomorphometry for Geosciences, Jasiewicz J., Zwoliński Zb., Mitasova H., Hengl T. (eds), 2015. Adam Mickiewicz University in Poznań
- Institute of Geoecology and Geoinformation, International Society for Geomorphometry, Poznań
A. Geohazards, Hydrodynamic and Geomorphological
In dynamic environments such as the ocean, monitoring
and detecting change is often crucial. The action of
hydrodynamics on the seabed can cause changes in bathymetry
that can become hazards for navigation in coastal waters.
Hydrographic conditions, on the other hand, are directly related
to the morphology of the seabed at all scales [7]. For instance,
banks are known to have far-reaching effects on currents and
circulation patterns, which in turn can modify bedforms [7].
Local geomorphometric attributes have been used to
develop seabed hydrodynamic models. For instance, aspect can
be used as proxy for local and regional currents and gives
information on the exposure of the seabed at a particular
location. Curvature is thought to influence local
hydrodynamics. The ruggedness of the seabed affects
sedimentation and hydrological patterns near the seabed by the
drag or bottom friction that influences the currents. These
terrain attributes can also assist geomorphic and physiographic
classifications of the seabed, as demonstrated by [8]. Regional
geomorphometry can be used to study the legacy of glaciations
in the geomorphology of continental shelves. The retreat of
under sea ice margins leaves different geomorphic evidences
than terrestrial-based ice margins, which can be found on the
seabed [9] and identified using geomorphometric
classifications. For instance, submarine glacial landforms,
captured by multibeam bathymetric data in areas of hypothetic
ice-streams, provide evidence on the style of deglaciation, the
extent of ice-margins, the calving rates, and the sea level at
specific periods in time [10].
Mapping subaqueous geomorphological features is also
crucial in identifying potential underwater geohazards.
Adaptation of terrestrial geomorphometric techniques, such as
morphometric attributes and their statistical analyses, feature-
based quantitative representation, and automated topographic
classification, has been shown to be effective in improving
current understanding of the morphology and physical
processes that characterize submarine mass movements in
passive glaciated margins [e.g. 11, 12].
B. Habitat Mapping
Seabed habitat mapping is probably the field that has
benefitted the most from techniques of geomorphometry to
date. Habitat mapping involves characterizing a habitat in
terms of its physical, chemical and biological attributes [13].
Many of these attributes are known to be linked to terrain
morphology, thus highlighting the potential of terrain
derivatives to describe marine habitats. The abundance and
distribution of marine species can be strongly influenced by
many biotic and abiotic factors, but topography and
geomorphology are among the most important drivers of their
distribution at many scales [14]. Slope, aspect, curvatures and
measures of seabed roughness have all been used in habitat
mapping studies [15]. MBES data have become essential in
studying marine habitats due to their remoteness and the
difficulties in sampling them. Consequently, geomorphometric
analysis performed on bathymetric data is also increasingly
used to find surrogates (i.e. proxies) of species distribution [14,
15]. Seabed complexity and heterogeneity can allow us to
numerically quantify the spatial arrangement and structure of
habitats. Since the complexity of the seabed has been linked to
the distribution of species at different scales, terrain attributes
can be used as surrogates of species distribution [15]. The
quantitative nature of terrain attributes also facilitates the
analysis of relationships between environmental and biological
factors and provides a mean to compare between geographic
regions and also the same region over multiple time steps.
C. Human Dimension
It is estimated that more than 40% of all the Earth’s ocean
floor has already been altered by anthropogenic activities [16].
The physical disturbances of the seabed increase its roughness
and produce changes in hydrodynamic patterns and sediment
distribution that can then affect bedforms and species
distribution [5]. Mapping and analyzing seabed
geomorphology using geomorphometry allows monitoring
changes in the shape of the seabed and identifying these
variations in roughness, thus facilitating the assessment of
anthropogenic impacts on some areas and potential new
hazards for navigation [5].
Geomorphometric techniques can also be used in search
and rescue operations. The difficulties in locating the recently
vanished Malaysia Airlines aircraft (flight MH370) highlighted
the lack of knowledge of seabed features in the search area
[17]. The forecasting of the path of floating debris was limited
by the lack of knowledge of seabed roughness and topography
from which it is possible to estimate surface current directions
and ocean mixing rates, both essential to these predictions [18].
A. Spatial Scale
As in terrestrial geomorphometry, spatial scale is an
important issue to consider in marine applications. Most of the
phenomena studied are likely to be observed at different scales,
and the scale of analysis should always match the scale of the
phenomena being observed [19]. For instance, many terrain
attributes used in habitat mapping were found to be useful
Lecours et al.
surrogate for species distribution at a local scale while others
were more important at broader scales [14].
The spatial resolution and extent of MBES data is
dependent upon the footprint and frequency of the system. As
the distance between the seabed and the sensor increases, the
footprint gets bigger and the spatial resolution decreases. This
makes submarine DTMs more likely to include datasets of
different resolutions, meaning that geomorphometric
techniques, which are sensitive to data resolution, need to be
very robust in marine applications. The integration of different
datasets at different scales over large areas is very challenging
B. Technological Challenges
The dynamic nature of the oceans makes collection of
bathymetric data dependent upon a lot of different factors that
are likely to induce errors or artifacts in the final DTM.
Artifacts are common in bathymetric data and can strongly
affect the derivation of terrain attributes. Common errors in
depth measurements include errors in the acoustic
measurement itself, movements of the supporting platform, and
inaccuracies in sound velocity corrections [1]. Motion-induced
errors are among the most important source of errors and will
vary depending on the platform used (e.g. ship or underwater
vehicle). Positional accuracy is also an important challenge,
especially for the use of underwater vehicles such as remotely
operated vehicles (ROV) or autonomous underwater vehicles
(AUV). Unlike in satellite and airborne remote sensing,
underwater equipment and technologies cannot use the Global
Positioning System (GPS) to accurately georeference depth
measurements and location. All data are therefore positioned
relatively to surface GPS using acoustic telemetry systems: the
deeper the survey, the worse the positional accuracy gets [20].
When positional accuracy is lower than the spatial resolution
of the DTM, artifacts can be introduced and a mismatch
between the locations from different datasets can occur, which
is a critical issue in change detection where dataset registration
is very important. These challenges are greater in the deep sea
than in coastal environments.
A. Towards a Complete Coverage
Applications of geomorphometry in the marine
environment are likely to increase as more bathymetric data
become available in different types of seabed environment.
MBES allow for systematic collection of data, but when the
water becomes too shallow for surveying systems, it creates a
gap in the continuous data. The combination of bathymetric
LiDAR data with acoustic surveys will ultimately call for
seamless analysis from terrestrial to marine environment. Such
continuous dataset is likely to improve the study of large
landforms that overlap between land and the ocean and the
identification of geohazards in shallower waters, but will also
increase the challenge of integrating different datasets together.
On the other hand, the collection of higher resolution
bathymetric data in the deep sea will become easier and more
frequent with the increasing use of underwater vehicles. This
will help gain additional knowledge on the structure and
geomorphology of deeper environments. There is still much to
learn about the complexity of the seabed at different depths and
environmental settings. As stated in [5]: “It is generally
assumed that seabed structure becomes less complex as one
moves from the continental shelf to greater depths, but is it, or
does this simply reflect our lack of knowledge?”
B. Advances in Technologies and Techniques
The ability to produce a continuous acoustic image of the
surface of the seabed using multibeam acoustics has
revolutionized our ability to understand marine
morphodynamics and the composition and distribution of
sediments, which has in turn significantly improved our
knowledge of seabed processes. Technology and equipment to
survey the seabed is improving in quality, accuracy and cost-
efficiency, which will allow an increase in data availability and
quality. Algorithms that consider the specific characteristics of
underwater surveying, such as the CUBE (Combined
Uncertainty and Bathymetric Estimator) [21], are being
developed to improve bathymetric data processing and are
likely to become more accessible through processing software.
Availability of GIS tools to effectively combine multiple
datasets and perform geomorphometric analyses is key in
making marine geomorphometry accessible to marine
scientists with a wide range of background and experience [22,
23]. Better practices to report data type, quality and scale
within metadata will need to be implemented in order to allow
the most informed analysis of these data [24]. New techniques
are also likely to make the jump from the terrestrial literature to
the marine literature. For instance, geographic object based
image analysis (Geobia) has been gaining some traction in the
seabed mapping community as the spatial resolution of
acoustic data improves [e.g. 25, 26].
As stated in [6], “One way to promote better practice in the
use of quantitative terrain analysis from bathymetric data is to
ensure that studies of geomorphometry become more
widespread in the marine literature, thereby making the issues
surrounding quantitative terrain analysis more accessible to
marine scientists from a variety of backgrounds.” Marine
Lecours et al.
scientists need to be encouraged to apply geomorphometric
techniques underwater to make use of the full potential of their
expensive datasets.
With a few exceptions, most issues being investigated in
terrestrial geomorphometry, such as uncertainty and error
propagation, the choice of algorithms or the multiscale nature
of DTMs are rarely considered in marine geomorphometry
applications. Since the terrestrial geomorphometry community
is currently trying to tackle some of these issues, it will be
important for marine scientists to remain aware of
developments in this field, and to build up a marine
geomorphometry community to draw on experiences from
terrestrial techniques.
VL is funded by the Natural Sciences and Engineering
Research Council of Canada. AM is funded by Marie Curie
Career Integration Grant PCIG13-GA-2013 618149 within the
European Community Framework Programme.
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Lecours et al.
... The latter provide crucial information regarding the composition of the seabed. As a result, backscatter data have been considered as the primary feature for classifying and characterizing the seabed of a surveyed area ( [5], [6], [7], [8], [9], [10]). ...
... A number of classification methods based on MBES data have been developed in the last decades to characterize the seabed, considering both single and multifrequency backscatter data, bathymetry, and other data sources ( [3], [5], [6], [7], [8], [14], [15], [16], [17], [19]). Acoustic backscatter intensity together with bathymetry and bathymetry derived products, like slope, bathymetric position index (BPI) [20], etc., are the most common features used in seabed classification. ...
Full-text available
Given the recent increase in the availability of multispectral multibeam echosounder data, this work aims to identify suitable processing and classification methodologies for seabed classification based on such data. We propose a complete processing and classification pipeline and investigate the adequacy of state-of-the-art classification algorithms to perform seabed classification based on multispectral backscatter data alone, and when additional data sources are considered. Starting from raw acquisition data, we generate region-wide multispectral backscatter composite images through noise removal, inpainting/gap-filling and mosaicking. Ground truth data from in situ seabed samples are used. We have tried different classification methods, including random forests, support vector machines, and multilayer perceptrons, with the latter providing the best results. Quantitative and qualitative evaluation on five surveys indicate high classification performance based only on multispectral backscatter data, while additional features, like bathymetry, bathymetric positional index (BPI), or positional encoding, offer limited gains. We offer a web service for seabed classification from multispectral multibeam echosounder data to further support and increase interest in the topic.
... Geomorphometric studies (i.e., quantitative analysis of the Earth's surface; MacMillan & Shary, 2009) of particular marine areas, realized through the use of cutting-edge high-precision indirect approaches, are increasingly widespread due to the ability of these new technologies to target the slightest morphological change of the seabed and to realize extensive mapping of the study areas, essential for both their historical and geomorphological characterization, and otherwise impossible to achieve (Anderson, Holliday, Kloser, Reid, & Simard, 2008;Caporizzo et al., in press;Lecours, Dolan, Micallef, & Lucieer, 2016;Lecours, Lucieer, Dolan, & Micallef, 2015;Mattei, Rizzo, Anfuso, Aucelli, & Gracia, 2020;Mattei, Troisi, et al., 2019;Micallef, Berndt, Masson, & Stow, 2007;Passaro et al., 2016). ...
... In this article we focus on the geomorphometric characterization of the Neapolitan high-coast sectors derived from the application of a multibeam survey, one of the most accurate and detailed technologies in terms of seabed morphology data (Lecours et al., 2015;Schimel, Healy, Johnson, & Immenga, 2010), demonstrating the great utility of morpho-acoustic and remote sensing investigation techniques in the characterization of the seabed and its morpho-evolution over time. ...
Full-text available
This research aims to reconstruct the submerged morphologies of the high-coast sectors of Naples discriminating between landforms and anthropogenic structures, by analysing the high-resolution data of a multibeam survey in a GIS environment. In the case of natural landforms, a signal analysis was performed to characterize the seabed and discern between sandy and rocky bottom, together with a slope analysis pointing to the detection and mapping of different orders of palaeo-shore platforms at different bathymetric ranges and interpreted as erosional traces of the Holocene sea cliff retreat affecting the study area, mainly caused by a subsiding trend that exacerbated the glacio-hydro-isostatic sea-level rise. Then, the detected palaeo-shore platforms were further analysed to quantify their roughness degree and, consequently, the differential erosion affecting the rocky platforms. On the other hand, regarding the submerged anthropogenic structures, the multibeam survey allowed several underwater archaeological remains of Roman Age to be mapped, demonstrating the high cultural relevance of the study area.
... Geomorphometry gives a substantial contribution to the objective and quantitative analysis of bathymetry. Several studies prove its potential to help the scientific community and governmental agencies advance their understanding of seabed geology, geomorphological processes and habitats (Iampietro et al. 2005, Wilson et al. 2007, Lecours et al. 2015. Even though it has been successfully applied to a variety of subaerial environments (Jasiewicz et al. 2015 and references in), it still has a number of characteristics that make problematic the application of traditional geomorphometric techniques to the submarine landscape (Lecours et al. 2015). ...
... Several studies prove its potential to help the scientific community and governmental agencies advance their understanding of seabed geology, geomorphological processes and habitats (Iampietro et al. 2005, Wilson et al. 2007, Lecours et al. 2015. Even though it has been successfully applied to a variety of subaerial environments (Jasiewicz et al. 2015 and references in), it still has a number of characteristics that make problematic the application of traditional geomorphometric techniques to the submarine landscape (Lecours et al. 2015). The low availability of data, usually with different resolution, and a more smooth morphology makes the computation of morphometric parameters hard (Micallef et al. 2007). ...
The monitoring policies of subtidal marine areas, as regulated by the FFH and MSFD, require stable measures and objective interpretation methods to ensure accurate and repeatable results. The nature of Wadden Sea inlets seabed have been investigated trough the analysis of bathymetrical and backscatter data, collected simultaneously by means of high-resolution multibeam echosounder, in conjunction with validation samples. The datasets allowed a robust approach to characterize substrate and bedforms, using objective and repeatable methods. The geomorphometric approach gives a substantial contribution to extract quantitative information on morphology and bedforms from bathymetry. DEMs of four tidal inlets have been used to calculate morphometric parameters, compare the inlets morphology and provide a classification of slope and profile curvature. Classified morphometric parameters have been applied to a detailed characterization of Otzumer Balje seabed. Very steep slopes and breaks of slope potentially related to substrate variations have been mapped and statistically investigated with respect to their depth distribution and spatial orientation. The computation of multiscale Benthic Position Index identified morphological features and bedforms at broad and fine scales. The geological and geomorphological meaning of morphometric parameters were extracted by means of quantitative comparison with backscatter intensity and samples. Backscatter was processed for radiometric corrections, geometrical corrections and mosaicking, to get intensities representative of the substrate characteristics. Within this integrated approach, it was possible to quantitatively analyse the complex morphology of subtidal areas of the Wadden Sea tidal inlets. At detailed resolution, the integration of bathymetric and backscatter data provided a bedforms and substrate characterization according to the main habitat classification schemes.
... Following several key studies on seabed morphometry (e.g., Lundblad et al. 2006;Wilson et al. 2007), and efforts to provide guidelines on marine geomorphometry (e.g., Lecours et al. 2015b;Lecours et al. 2016b;Lucieer, Lecours, and Dolan 2018), there has been progress towards establishing standards for the use of digital terrain models (DTMs) and terrain attributes for benthic habitat mapping. Fundamental concepts from terrestrial geomorphometry are now being explored in a marine context, such as spatial scale and scale-dependence of terrain attributes (e.g., Dolan and Lucieer 2014;Giusti, Innocenti, and Canese 2014;Lecours et al. 2015a;Miyamoto et al. 2017;Misiuk, Lecours, and Bell 2018), and the selection of variables and algorithms (e.g., Dolan and Lucieer 2014;Bouchet et al. 2015;Lecours et al. 2016a). ...
Full-text available
The scale dependence of benthic terrain attributes is well-accepted, and multi-scale methods are increasingly applied for benthic habitat mapping. There are, however, multiple ways to calculate terrain attributes at multiple scales, and the suitability of these approaches depends on the purpose of the analysis and data characteristics. There are currently few guidelines establishing the appropriateness of multi-scale raster calculation approaches for specific benthic habitat mapping applications. First, we identify three common purposes for calculating terrain attributes at multiple scales for benthic habitat mapping: i) characterizing scale-specific terrain features, ii) reducing data artefacts and errors, and iii) reducing the mischaracterization of ground-truth data due to inaccurate sample positioning. We then define criteria that calculation approaches should fulfill to address these purposes. At two study sites, five raster terrain attributes, including measures of orientation, relative position, terrain variability, slope, and rugosity were calculated at multiple scales using four approaches to compare the suitability of the approaches for these three purposes. Results suggested that specific calculation approaches were better suited to certain tasks. A transferable parameter, termed the ‘analysis distance’, was necessary to compare attributes calculated using different approaches, and we emphasize the utility of such a parameter for facilitating the generalized comparison of terrain attributes across methods, sites, and scales.
... This rapid acquisition of topographic data is now possible at spatial resolutions and extents previously inconceivable (Lane and Chandler, 2003;Heritage and Hetherington, 2007) and has resulted in huge advances in monitoring geomorphic changes through repeat topographic surveys (Wheaton et al., 2010). Research areas such hydrology, land-use, archaeology, natural hazards and computer science (Sofia et al., 2016), and more recently seafloor geomorphometry (Lecours et al., 2015(Lecours et al., , 2016, are benefitting from these advances. ...
Understanding dynamic earth surface processes requires various spatial and temporal information to help produce patterns of landform change. Recent developments in sensor technology such as Structure from Motion (SfM), camera-mounted airborne Unmanned Aerial Vehicles (UAVs) and Terrestrial Laser Scanning (TLS) have provided a means of acquiring high-resolution spatial data on land surface topography. Through repeat surveys, these techniques enable much better understanding of what is termed ‘geomorphometry’, where we can examine a geomorphic surface for change over space and time. In coastal environments, change can involve significant alteration and generation of landforms over relatively short periods and, therefore, we require a means of measuring surface morphology quickly and over large areas. Here, we examine a section of a beach-dune system in NW Ireland using SfM-UAV and TLS plus baseline dGPS data points to assess the value of these techniques and to understand their effectiveness (and limitations). Issues such as accuracy, resolution and differences of Digital Elevation Models (DEMs) are assessed for their efficiency, associated challenges and relative performance over variations in terrain types and analytical approaches. We also examine the implications for differences in areal and volume calculations of the coastal landforms using both approaches. We find that sensor performance is highly dependent on the terrain being measured, with undulations, slope, vegetation cover, acquisition resolution (point density) and interpolation issues all having pronounced impacts on effectiveness and data quality. In general, the TLS performed better over flatter, low-angled topography containing sparse/non-vegetated areas than in areas with complex landforms where survey shadows appear to compromise final DEMs. The SfM-UAV shows good performance over different terrains with the exception of relatively flat, featureless areas such as sandy beaches and densely-vegetated surfaces where differences between techniques are >1 m. Data acquisition however is much (×30) faster using a SfM-UAV with more extensive survey areas covered than using a TLS.
... The widespread integration of geomorphometric tools into Geographic Information Systems (GIS) made geomorphometric analyses accessible to a wide range of end-users, many of whom are not necessarily aware of the science underpinning the tools [5]. Over the last decade, efforts have been made (e.g., [6][7][8][9][10][11][12][13]) to bridge the gap between the discipline of geomorphometry, which has traditionally focused on terrestrial and planetary applications, and the marine sciences. ...
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The use of spatial analytical techniques for describing and classifying seafloor terrain has become increasingly widespread in recent years, facilitated by a combination of improved mapping technologies and computer power and the common use of Geographic Information Systems. Considering that the seafloor represents 71% of the surface of our planet, this is an important step towards understanding the Earth in its entirety. Bathymetric mapping systems, spanning a variety of sensors, have now developed to a point where the data they provide are able to capture seabed morphology at multiple scales, opening up the possibility of linking these data to oceanic, geological, and ecological processes. Applications of marine geomorphometry have now moved beyond the simple adoption of techniques developed for terrestrial studies. Whilst some former challenges have been largely resolved, we find new challenges constantly emerging from novel technology and applications. As increasing volumes of bathymetric data are acquired across the entire ocean floor at scales relevant to marine geosciences, resource assessment, and biodiversity evaluation, the scientific community needs to balance the influx of high-resolution data with robust quantitative processing and analysis techniques. This will allow marine geomorphometry to become more widely recognized as a sub-discipline of geomorphometry as well as to begin to tread its own path to meet the specific challenges that are associated with seabed mapping. This special issue brings together a collection of research articles that reflect the types of studies that are helping to chart the course for the future of marine geomorphometry.
... The objective of this study was to develop correlative approaches of SDMs for predicting the abundance of European hake and the occurrence probability of recruits and large adults in the southcentral Mediterranean Sea. Abiotic factors with a strong implication in species distribution, i.e. depth and seafloor features such as slope, aspects, rugosity, etc. (Moore et al. 2009;McArthur et al., 2010;Monk et al., 2010;Pittmann & Brown, 2011;Lecours et al., 2015) were used as explanatory variables. Temperature and salinity which might play an important role as well were not used due to data limitation. ...
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The effective management and conservation of fishery resources requires knowledge of their spatial distribution and notably of their critical life history stages. Predictive modelling of the European hake (Merluccius merluccius L., 1758) distribution was developed in the south-central Mediterranean Sea by means of historical fisheries-independent databases available in the region. The study area included the international waters of the south-central Mediterranean Sea and the territorial waters of Italy, Malta, Tunisia and Libya. Distribution maps of predicted population abundance index, and probabilistic occurrence of recruits and large adults were obtained by means of generalized additive models using depth and seafloor characteristics as predictors. Presence/absence data of the two life stages was obtained using threshold values applied to the mean weight of the survey catches. Modelling results largely matched previously reported knowledge on habitat preference of the species and its critical life phases. Hake recruits showed an occurrence peak at 200 m depth with preference for soft bottoms. Large adults preferred deeper and harder bottom substrates. Prediction maps allowed to improve our knowledge on the distributional patterns of one of the most important shared stocks in the south-central Mediterranean. This knowledge is essential for an appropriate development of regional-spatial-based management plans.
... Developments in geomorphometry have traditionally focused on the exploration of terrestrial and extra-terrestrial environments, but recent efforts have been made to highlight the need for a dedicated science of marine geomorphometry [52], [53]; the nature of the marine environment and the techniques used to sample depth have implications for the subsequent geomorphometric analyses that are different than in terrestrial applications. The increased availability of multibeam echosounder systems (MBESs) that enable the collection of reliable continuous underwater terrain data representing water depths (i.e., bathymetric data or bathymetry) [7], [21] has revolutionized several fields of research and applications like marine geomorphology [42] and marine habitat mapping [75]. ...
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Data acquisition artefacts are commonly found in multibeam bathymetric data, but their effects on mapping methodologies using geographic information system techniques have not been widely explored. Artefacts have been extensively studied in terrestrial settings, but their study in a marine context has currently been limited to engineering and surveying technology development in order to reduce their amplitude during data collection and postprocessing. Knowledge on how they propagate to further analyses like environmental characterization or terrain analysis is scant. The goal of this paper is to describe the contribution of different types of artefacts to marine terrain attributes at multiple scales. Using multibeam bathymetric data from German Bank, off Nova Scotia (Canada), digital bathymetric models (DBMs) were computed at five different spatial resolutions. Ten different amplitudes of heave, pitch, roll, and time artefacts were artificially introduced to generate altered DBMs. Then, six terrain attributes were derived from each of the reference and altered DBMs. Relationships between the amplitude of artefacts and the statistical and spatial distributions of: 1) altered bathymetry and terrain attributes surfaces and 2) errors caused by the artefacts were modeled. Spatial similarity between altered and reference surfaces was also assessed. Results indicate that most artefacts impact spatial similarity and that pitch and roll significantly impact the statistical distribution of DBMs and terrain attributes while time and heave artefacts have a more subtle impact. Results also confirm the relationship between spatial data quality and spatial scale, as finer-scale data were impacted by artefacts to a greater degree than broader-scale data.
In recent years, the wealth of technological development revolutionised our ability to collect data in geosciences. Due to the unprecedented level of detail of these datasets, geomorphologists are facing new challenges, giving more in-depth answers to a broad(er) range of fundamental questions across the full spectrum of the Earth's (and Planetary) processes. This contribution builds on the existing literature of geomorphometry (the science of quantitative land-surface analysis) and feature extraction (translate land surface parameters into extents of geomorphological elements). It provides evidence of critical themes as well as emerging fields of future research in the digital realm, supporting the likely effectiveness of geomorphometry and feature extractions as they are advancing the theoretical, empirical and applied dimension of geomorphology. The review further discusses the role of geomorphometric legacies, and scientific reproducibility, and how they can be implemented, in the hope that this will facilitate action towards improving the transparency, and efficiency of scientific research, and accelerate discoveries in geomorphology. In the current landscape, substantial changes in landforms, ecosystems, land use, hydrological routing, and direct anthropogenic modifications impact systems across the full spectrum of geomorphological processes. Although uncertainties in the precise nature and likelihood of changes exist, geomorphometry and feature extraction can aid exploring process regimes and landscape responses. Taken together, they can revolutionise geomorphology by opening the doors to improved investigations crossing space and time scales, blurring the boundaries between traditional approaches and computer modelling, and facilitating cross-disciplinary research. Ultimately, the exploitation of the available wealth of digital information can help to translate our understanding of geomorphic processes, which is often based on observations of past or current conditions, into the rapidly changing future.
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Tidal inlets are extremely dynamic environments that are often strongly modified by anthropogenic intervention. In this study, we describe the rapid evolution of a highly human-impacted tidal inlet, studied through repeated high-resolution multibeam surveys and geomorphometric analysis. We document the rapid change induced by new hard coastal structures built to protect the historical city of Venice (Italy). A new breakwater erected between 2011 and 2013 induced the formation of large scour holes with the consequent erosion of about 170 · 10³ ± 15.6% m³ of sediment until 2016. The construction of a new island in the middle of the inlet and the restriction of the inlet channel caused a general change of the inlet sedimentary regime from depositional to erosive with a net sediment loss of about 612 · 10³ ± 42.7% m³, a reduction of the dune field area by more than 50% in about five years, and a coarsening in the sediment distribution. Our results give new insight on the tidal inlet resilience to changes, distinguishing two different phases in its recent evolution: (i) a very rapid response (from 2011 to 2013) of the seafloor morphology with scour-hole erosion at the new breakwater tips at a rate of about 45⋅10³ m³/year and the disappearing of dune fields at a rate of 104⋅10³ m²/year; and (ii) a general slowdown of the erosive processes from 2013 to 2016. Nevertheless, the erosion continues at the breakwater, though at a reduced rate, possibly representing a threat to the hard structure. In view of global mean sea level rise and consequent proliferation of hard structures along the coast all over the world, the combined use of very high resolution multibeam surveys and repeatable geomorphometric analysis proposed in this study will be crucial for the monitoring and future management of coastal environments.
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This study presents an analysis of the application of underwater video data collected for training and validating benthic habitat distribution models. Specifically, we quantify the two major sources of error pertaining to collection of this type of reference data. A theoretical spatial error budget is developed for a positioning system used to co-register video frames to their corresponding locations at the seafloor. Second, we compare interpretation variability among trained operators assessing the same video frames between times over three hierarchical levels of a benthic classification scheme. Propagated error in the positioning system described was found to be highly correlated with depth of operation and varies from 1.5m near the surface to 5.7m in 100m of water. In order of decreasing classification hierarchy, mean overall observer agreement was found to be 98% (range 6%), 82% (range 12%) and 75% (range 17%) for the 2, 4, and 6 class levels of the scheme, respectively. Patterns in between-observe
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Marine spatial planning and conservation need underpinning with sufficiently detailed and accurate seabed substrate and habitat maps. Although multibeam echosounders enable us to map the seabed with high resolution and spatial accuracy, there is still a lack of fit-for-purpose seabed maps. This is due to the high costs involved in carrying out systematic seabed mapping programmes and the fact that the development of validated, repeatable, quantitative and objective methods of swath acoustic data interpretation is still in its infancy. We compared a wide spectrum of approaches including manual interpretation, geostatistics, object-based image analysis and machine-learning to gain further insights into the accuracy and comparability of acoustic data interpretation approaches based on multibeam echosounder data (bathymetry, backscatter and derivatives) and seabed samples with the aim to derive seabed substrate maps. Sample data were split into a training and validation data set to allow us to carry out an accuracy assessment. Overall thematic classification accuracy ranged from 67% to 76% and Cohen’s kappa varied between 0.34 and 0.52. However, these differences were not statistically significant at the 5% level. Misclassifications were mainly associated with uncommon classes, which were rarely sampled. Map outputs were between 68% and 87% identical. To improve classification accuracy in seabed mapping, we suggest that more studies on the effects of factors affecting the classification performance as well as comparative studies testing the performance of different approaches need to be carried out with a view to developing guidelines for selecting an appropriate method for a given dataset. In the meantime, classification accuracy might be improved by combining different techniques to hybrid approaches and multi-method ensembles.
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We present the first digital seafloor geomorphic features map (GSFM) of the global ocean. The GSFM includes 131,192 separate polygons in 29 geomorphic feature categories, used here to assess differences between passive and active continental margins as well as between 8 major ocean regions (the Arctic, Indian, North Atlantic, North Pacific, South Atlantic, South Pacific and the Southern Oceans and the Mediterranean and Black Seas). The GSFM provides quantitative assessments of differences between passive and active margins: continental shelf width of passive margins (88 km) is nearly three times that of active margins (31 km); the average width of active slopes (36 km) is less than the average width of passive margin slopes (46 km); active margin slopes contain an area of 3.4 million km2 where the gradient exceeds 5°, compared with 1.3 million km2 on passive margin slopes; the continental rise covers 27 million km2 adjacent to passive margins and less than 2.3 million km2 adjacent to active margins. Examples of specific applications of the GSFM are presented to show that: 1) larger rift valley segments are generally associated with slow-spreading rates and smaller rift valley segments are associated with fast spreading; 2) polar submarine canyons are twice the average size of non-polar canyons and abyssal polar regions exhibit lower seafloor roughness than non-polar regions, expressed as spatially extensive fan, rise and abyssal plain sediment deposits – all of which are attributed here to the effects of continental glaciations; and 3) recognition of seamounts as a separate category of feature from ridges results in a lower estimate of seamount number compared with estimates of previous workers.
This chapter presents a broad synthesis and overview based on the 57 case studies. The case studies covered areas of seafloor ranging from 0.15 km2 to over 1,000,000 km2 and a broad range of geomorphic feature types. Of the many purposes for mapping benthic habitats, four stand out as preeminent: to support government spatial marine planning, management, and decision making; to support and underpin the design of marine protected areas (MPAs); to conduct scientific research programs aimed at generating knowledge of benthic ecosystems and seafloor geology; and to conduct living and nonliving seabed resource assessments for economic and management purposes. Out of 57 case studies, habitat mapping was intended to be part of an ongoing monitoring program in 24 cases, whereas the mapping was considered to be a one-off exercise in 33 cases. However, out of the 33 one-off cases, the authors considered that their habitat map would form the baseline for monitoring future changes in 24 cases. This suggests that governments and regulators generally view habitat mapping as a useful means of measuring and monitoring change. There appears to be a disconnect between the stated purpose of habitat mapping in most case studies (i.e., government management), and the end users and clients perceived by case study authors to be the main stakeholders. The data collected during a habitat mapping survey is composed of many types, including electronic data together with physical samples (sediments and biota) that must first be analyzed before numerical or classification type data are obtained.
Bathymetry data from multibeam echosounders and other acoustic sources are now widely available in the form of digital terrain models, which are conveniently displayed as raster grids in desktop geographic information systems. Calculation of terrain variables such as slope is a simple push-button operation in most geographic information systems; however, as we demonstrate here, there can be a great variation in the slope values obtained due to computation algorithms and resolution or analysis scale. This article also demonstrates how Monte Carlo simulation can be used to visualise uncertainty in the underlying bathymetry dataset and also how this uncertainty impacts on slope calculations. 50 copies of full text available here:
In a world that is increasingly connected, that grows smaller every day, and where so many human actions are exposed to prying eyes, it seems almost incomprehensible that the world's largest twinjet aircraft, with 239 passengers and crew, could vanish for more than 2 months. Determining the crash site of Malaysia Airlines Flight 370 (MH370) has become a scientific detective story, emerging through a combination of scientific technologies used to address problems for which they were never designed. The search for MH370 illustrates a humanitarian dividend from past investments in science as searchers attempt to bring closure to the families and friends of the victims of the tragedy.
On the morning of 8 March 2014, Malaysia Airlines flight MH370, from Kuala Lumpur to Beijing, lost contact with air traffic control shortly after takeoff and vanished. While the world waited for any sign of the missing aircraft and the 239 people on board, authorities and scientists began to investigate what little information was known about the plane's actual movements.
Using data sets collected north of San Francisco Bay (CA) an ArcGIS classification toolset was developed using supervised image classification tools to characterize potential shallow marine benthic habitats. First-derivative images and a topographic algorithm, called Bathymetric Position Index were created from the bathymetry data set using ArcGIS Spatial Analyst tools. Backscatter intensity was also analyzed by creating training samples based on the collected sediment samples and then applying multivariate statistical tools to delinate textural classes. The data collected revealed a rugged and complex seafloor and imaged in detail basement and bedrock outcrops, sand and gravel bedforms, and flat sediment covered seabed.