203 research outputs found
Limitations of predicting substrate classes on a sedimentary complex but morphologically simple seabed
The ocean floor, its species and habitats are under pressure from various human activities. Marine spatial planning and nature conservation aim to address these threats but require sufficiently detailed and accurate maps of the distribution of seabed substrates and habitats. Benthic habitat mapping has markedly evolved as a discipline over the last decade, but important challenges remain. To test the adequacy of current data products and classification approaches, we carried out a comparative study based on a common dataset of multibeam echosounder bathymetry and backscatter data, supplemented with groundtruth observations. The task was to predict the spatial distribution of five substrate classes (coarse sediments, mixed sediments, mud, sand, and rock) in a highly heterogeneous area of the south-western continental shelf of the United Kingdom. Five different supervised classification methods were employed, and their accuracy estimated with a set of samples that were withheld. We found that all methods achieved overall accuracies of around 50%. Errors of commission and omission were acceptable for rocky substrates, but high for all sediment types. We predominantly attribute the low map accuracy regardless of mapping approach to inadequacies of the selected classification system, which is required to fit gradually changing substrate types into a rigid scheme, low discriminatory power of the available predictors, and high spatial complexity of the site relative to the positioning accuracy of the groundtruth equipment. Some of these issues might be alleviated by creating an ensemble map that aggregates the individual outputs into one map showing the modal substrate class and its associated confidence or by adopting a quantitative approach that models the spatial distribution of sediment fractions. We conclude that further incremental improvements to the collection, processing and analysis of remote sensing and sample data are required to improve map accuracy. To assess the progress in benthic habitat mapping we propose the creation of benchmark datasets
Benthic habitat mapping in coastal waters of south–east Australia
The Victorian Marine Mapping Project will improve knowledge on the location, spatial distribution, condition and extent of marine habitats and associated biodiversity in Victorian State waters. This information will guide informed decision making, enable priority setting, and assist in targeted natural resource management planning. This project entails benthic habitat mapping over 500 square kilometers of Victorian State waters using multibeam sonar, towed video and image classification techniques. Information collected includes seafloor topography, seafloor softness and hardness (reflectivity), and information on geology and benthic flora and fauna assemblages collectively comprising habitat. Computerized semi-automated classification techniques are also being developed to provide a cost effective approach to rapid mapping and assessment of coastal habitats.Habitat mapping is important for understanding and communicating the distribution of natural values within the marine environment. The coastal fringe of Victoria encompasses a rich and diverse ecosystem representative of coastal waters of South-east Australia. To date, extensive knowledge of these systems is limited due to the lack of available data. Knowledge of the distribution and extent of habitat is required to target management activities most effectively, and provide the basis to monitor and report on their status in the future.<br /
Understanding the marine environment : seabed habitat investigations of the Dogger Bank offshore draft SAC
This report details work carried out by the Centre for Environment, Fisheries and
Aquaculture Science (Cefas), British Geological Surveys (BGS) and Envision Ltd. for the
Joint Nature Conservation Committee (JNCC). It has been produced to provide the JNCC
with evidence on the distribution and extent of Annex I habitat (including variations of these
features) on the Dogger Bank in advance of its possible designation as a Special Area of
Conservation (SAC). The report contains information required under Regulation 7 of the
Conservation (Natural Habitats, &c.) Regulations 2007 and will enable the JNCC to advise
the Department for Environment, Food and Rural Affairs (Defra) as to whether the site is
deemed eligible as a SAC. The report provides detailed information about the Dogger Bank
and evaluates its features of interest according to the Habitats Directive selection criteria and
guiding principles. This assessment has been made following a thorough analysis of existing
information combined with newly acquired field survey data collected using ‘state of the art’
equipment.
In support of this process acoustic (sidescan sonar and multibeam echosounder) and groundtruthing
data (Hamon grabs, trawls and underwater video) were collected during a 19-day
cruise on RV Cefas Endeavour, which took place between 2-20 April 2008. Existing
information and newly acquired data were combined to investigate the sub-surface geology,
surface sediments and bedforms, epifaunal and infaunal communities of the Dogger Bank.
Results were integrated into a habitat map employing the EUNIS classification. Key results
are as follows:
• The upper Pleistocene Dogger Bank Formation dictates the shape of the Dogger Bank.
• The Dogger Bank is morphologically distinguishable from the surrounding seafloor
following the application of a technique, which differentiates the degree of slope.
• A sheet of Holocene sediments of variable thickness overlies the Dogger Bank
Formation. At the seabed surface, these Holocene sediments can be broadly delineated
into fine sands and coarse sediments.
• Epifaunal and infaunal communities were distinguished based on multivariate analysis
of data derived from video and stills analysis and Hamon grab samples. Sediment
properties and depth were the main factors controlling the distribution of infauna and
epifauna across the Bank.
• Epifaunal and infaunal community links were explored. Most stations could be
categorised according to one of four combined infaunal/epifaunal community types (i.e.
sandy sediment bank community, shallow sandy sediment bank community, coarse
sediment bank community or deep community north of the bank).
• Biological zones were identified using modelling techniques based on light climate and
wave base data. Three biological zones, namely infralittoral, circalittoral and deep
circalittoral are present in the study site.
• EUNIS level 4 habitats were mapped by integrating acoustic, biological, physical and
optical data. Eight different habitats are present on the Dogger Bank.
This report also provides some of the necessary information and data to help the JNCC
ultimately reach a judgement as to whether the Dogger Bank is suitable as an SAC. In
support of this process the encountered habitats and the ecology of the Dogger Bank are
compared with other SACs known to contain sandbank habitats in UK waters. The
functional and ecological importance of the Dogger Bank as well as potential anthropogenic impacts is discussed. A scientific justification underlying the proposed Dogger Bank dSAC
boundary is also given (Appendix 1). This is followed by a discussion of the suitability and
cost-effectiveness of techniques utilised for seabed investigations of the Dogger Bank.
Finally, recommendations for strategies and techniques employed for investigation of Annex
I sandbanks are provided
Insights into the short-term tidal variability of multibeam backscatter from field experiments on different seafloor types
Three experiments were conducted in the Belgian part of the North Sea to investigate short-term variation in seafloor backscatter strength (BS) obtained with multibeam echosounders (MBES). Measurements were acquired on predominantly gravelly (offshore) and sandy and muddy (nearshore) areas. Kongsberg EM3002 and EM2040 dual MBES were used to carry out repeated 300-kHz backscatter measurements over tidal cycles (~13 h). Measurements were analysed in complement to an array of ground-truth variables on sediment and current nature and dynamics. Seafloor and water-column sampling was used, as well as benthic landers equipped with different oceanographic sensors. Both angular response (AR) and mosaicked BS were derived. Results point at the high stability of the seafloor BS in the gravelly area (2 dB and 4 dB at 45° respectively. The high-frequency backscatter sensitivity and short-term variability are interpreted and discussed in the light of the available ground-truth data for the three experiments. The envelopes of variability differed considerably between areas and were driven either by external sources (not related to the seafloor sediment), or by intrinsic seafloor properties (typically for dynamic nearshore areas) or by a combination of both. More specifically, within the gravelly areas with a clear water mass, seafloor BS measurements where unambiguous and related directly to the water-sediment interface. Within the sandy nearshore area, the BS was shown to be strongly affected by roughness polarization processes, particularly due to along- and cross-shore current dynamics, which were responsible for the geometric reorganization of the morpho-sedimentary features. In the muddy nearshore area, the BS fluctuation was jointly driven by high-concentrated mud suspension dynamics, together with surficial substrate changes, as well as by water turbidity, increasing the transmission losses. Altogether, this shows that end-users and surveyors need to consider the complexity of the environment since its dynamics may have severe repercussions on the interpretation of BS maps and change-detection applications. Furthermore, the experimental observations revealed the sensitivity of high-frequency BS values to an array of specific configurations of the natural water-sediment interface which are of interest for monitoring applications elsewhere. This encourages the routine acquisition of different and concurrent environmental data together with MBES survey data. In view of promising advances in MBES absolute calibration allowing more straightforward data comparison, further investigations of the drivers of BS variability and sensitivity are required
Characterising the ocean frontier : a review of marine geomorphometry
Geomorphometry, the science that quantitatively describes terrains, 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 (GIS) has prompted interest in
employing geomorphometric techniques to investigate the marine environment. Over the last decade, a suite of
geomorphometric techniques have been applied (e.g. terrain attributes, feature extraction, automated classification) to investigate the characterisation of 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 geomorphology applications and it is important that, in developing the
science and application of marine geomorphometry, we build on the lessons learned from terrestrial studies. We note, however, that not all terrestrial solutions can be adopted by marine geomorphometric studies since the dynamic, four-
dimensional nature of the marine environment causes its own issues, boosting the need for a dedicated scientific effort in
marine geomorphometry.
This contribution offers the first comprehensive review of marine geomorphometry to date. It addresses 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 from terrestrial geomorphometry. We conclude
with recommendations and reflections on the future of marine geomorphometry.peer-reviewe
THE ROLE OF THE ROV WITHIN INTEGRATED GEOTECHNICAL AND HYDROGRAPHIC SITE INVESTIGATION
The acquisition of marine survey data is traditionally undertaken from surface vessels including
boats and temporary rigs. Translation of these techniques to the nearshore zone is a complex task
and requires equipment adaptation and. often the sacrifice of data coverage. The remotely operated
vehicle (ROV) offers the potential for overcoming some of the standard nearshore survey Concems,
providing remote intervention and data acquisition in areas of restricted access.
In situ testing is the most efficient and reliable method of acquiring data with minimal sediment
disturbance effects. Research has been undertaken into the viability of nearshore cone penetration
testing (CPT) which has shown the T-Bar flow round penetrometer to be a possible solution. Data
could be acquired in sediments with undrained shear strengths of up to 300 kPa from a bottom
crawling ROV weighing 260 kgf and measuring 1 m in length by 0.6 m in width. The collection of
sediment cores may be necessary in areas requiring ground truthing for geophysical or in situ
investigations. A pneumatic piston corer has been designed and manufactured and is capable of
collecting sediment cores up to 400 mm in length, 38 mm in diameter, in sediment with undrained
shear strength of 17 kPa. To ascertain additional sediment characteristics in situ, a resistivity subbottom
profiling system has also been designed and tested and allows for discrimination between
sediment types ranging in size from gravel to silt.
The integration of equipment and testing procedures can be fiirther developed through the use of
integrated data management approaches such as geographical information systems (GIS). An offthe-
shelf GIS, Arclnfo 8, was used to create a GIS containing typical nearshore data using the Dart
estuary as a case study location.Britannia Royal Naval Colleg
A review of marine geomorphometry, the quantitative study of the seafloor
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 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.peer-reviewe
Evaluation of seabed mapping methods for fine-scale classification of extremely shallow benthic habitats – application to the Venice Lagoon, Italy
Recent technological developments of multibeam echosounder systems (MBES) allow mapping of benthic habitats with unprecedented detail. MBES can now be employed in extremely shallow waters, challenging data acquisition (as these instruments were often designed for deeper waters) and data interpretation (honed on datasets with resolution sometimes orders of magnitude lower). With extremely high-resolution bathymetry and colocated backscatter data, it is now possible to map the spatial distribution of fine scale benthic habitats, even identifying the acoustic signatures of single sponges. In this context, it isnecessary to understand which of the commonly used segmentation methods is best suited to account for such level of detail. At the same time, new sampling protocols for precisely georeferenced ground truth data need to be developed to validate the benthic environmental classification. This study focuses on a dataset collected in a shallow (2–10 m deep) tidal channel of the Lagoon of Venice, Italy. Using 0.05-m and 0.2-m raster grids, we compared a range of classifications, both pixel- based and object-based approaches, including manual, Maximum Likelihood Classifier, Jenks Optimization clustering, textural analysis and ObjectBased Image Analysis. Through a comprehensive and accurately geo-referenced ground truth dataset, we were able to identify five different classes of the substrate composition, including sponges, mixed submerged aquatic vegetation, mixed detritic bottom (fine and coarse) and unconsolidated bare sediment. We computed estimates of accuracy (namely Overall, User and Producer Accuracies) by cross tabulating predicted and reference instances. Overall, pixel based segmentations produced the highest accuracies and that the accuracy assessment is strongly dependent on the choice of classes for the segmentation. Tidal channels in the Venice Lagoon are extremely important in terms of habitats and sediment distribution, particularly within the context of the new tidal barrier being built. However, they had remained largely unexplored until now, because of the surveying challenges. The application of this remote sensing approach, combined with targeted sampling, opens a new perspective in the monitoring of benthic habitats in view of a knowledge-based management of natural resources in shallow coastal areas
Object-based mapping of temperate marine habitats from multi-resolution remote sensing data
PhD ThesisHabitat maps are needed to inform marine spatial planning but current methods of field
survey and data interpretation are time-consuming and subjective. Object-based image
analysis (OBIA) and remote sensing could deliver objective, cost-effective solutions informed
by ecological knowledge. OBIA enables development of automated workflows to segment
imagery, creating ecologically meaningful objects which are then classified based on spectral
or geometric properties, relationships to other objects and contextual data. Successfully
applied to terrestrial and tropical marine habitats for over a decade, turbidity and lack of
suitable remotely sensed data had limited OBIA’s use in temperate seas to date. This thesis
evaluates the potential of OBIA and remote sensing to inform designation, management and
monitoring of temperate Marine Protected Areas (MPAs) through four studies conducted in
English North Sea MPAs.
An initial study developed OBIA workflows to produce circalittoral habitat maps from
acoustic data using sequential threshold-based and nearest neighbour classifications. These
methods produced accurate substratum maps over large areas but could not reliably predict
distribution of species communities from purely physical data under largely homogeneous
environmental conditions.
OBIA methods were then tested in an intertidal MPA with fine-scale habitat heterogeneity
using high resolution imagery collected by unmanned aerial vehicle. Topographic models
were created from the imagery using photogrammetry. Validation of these models through
comparison with ground truth measurements showed high vertical accuracy and the ability
to detect decimetre-scale features.
The topographic and spectral layers were interpreted simultaneously using OBIA, producing
habitat maps at two thematic scales. Classifier comparison showed that Random Forests
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outperformed the nearest neighbour approach, while a knowledge-based rule set produced
accurate results but requires further research to improve reproducibility.
The final study applied OBIA methods to aerial and LiDAR time-series, demonstrating that
despite considerable variability in the data, pre- and post-classification change detection
methods had sufficient accuracy to monitor deviation from a background level of natural
environmental fluctuation.
This thesis demonstrates the potential of OBIA and remote sensing for large-scale rapid
assessment, detailed surveillance and change detection, providing insight to inform choice of
classifier, sampling protocol and thematic scale which should aid wider adoption of these
methods in temperate MPAs.Natural Environment Research Council and Natural
Englan
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