Vl Lucieer

Object-oriented classification of sidescan sonar data for mapping benthic marine habitats

This research presents an object‐oriented technique for habitat classification at different segmentation levels based on the use of imagery from an Edgetech 272 side scan sonar. We investigate the success of object parameters such as shape and size as well as texture in discriminating reef from sand habitat. The results are evaluated using traditional digitization, based on visual assessment of the sidescan imagery, and video transects. Whereas the application of traditional pixel‐based classification results in a pixelized (salt and pepper) representation of habitat distribution, the object‐based classification technique results in habitat objects (raster or vector). The object‐oriented classification results are cross‐validated using confusion matrices in image classification software and error matrices from underwater video transects showing an overall accuracy of 80% based on two classes within the image at three segmentation levels and an overall accuracy of 60% based on three classes at two segmentation levels. This is compared with the digitized layer accuracy of 81% for two classes and 72% for three classes, and this demonstrates the successful application of object‐oriented methods for habitat mapping. This technique retains spatially discrete habitat pattern information in a classified vector shape file with methods that are automated, repeatable, objective, and capable of processing many sidescan records in a more efficient manner.

Variation and Uncertainty in Bathymetric Slope Calculations Using Geographic Information Systems

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.

Choosing between strategies for designing surveys: autonomous underwater vehicles

Autonomous underwater vehicles (AUV), which collect images of marine habitats, are now an established sampling tool. The use of AUVs is becoming more widespread as they offer a non-destructive method to survey substantial spatial areas. The design of AUV surveys has historically been based on expert knowledge andAUVspecific considerations, such as reducing geolocation error. The expert knowledge encompasses intuition, previous surveying experiences and holistic knowledge of the study region. 2. We investigate the statistical aspects to AUV survey design for estimation of percentage cover of key benthic biota. We investigate the presence of spatial autocorrelation in AUV data using model-based geostatistics and examine the effect of autocorrelation on survey design by examining different design strategies – methods for placing AUV transects. The design strategies are assessed by inspecting the expected bias and the expected standard deviation ofmodel predictions, where the model depends on the choice of design. 3. The AUV data exhibited a wide range of autocorrelation, from non-existent to substantial. The design strategies varied in their statistical performance and nearly all strategies had shortcomings. Design strategies that were consistently poor performers had (i) transects placed in parallel in a single spatial dimension and (ii) made no attempt to spread out the transects in space. The superior design types had more transect-to-transect separation (but not toomuch) and effectively spanned important covariates. 4. The results give guidelines to researchers designing AUV surveys for biological mapping and for monitoring. In particular, we demonstrate that any spatial design should seek spatial balance, such as would be introduced by a systematic or stratified component within a randomized design. Knowledge of the system under study should be incorporated and, if possible, should be done so in a formalmanner that is objective and repeatable.

Mapping Habitats and Developing Baselines in Offshore Marine Reserves with Little Prior Knowledge: A Critical Evaluation of a New Approach

The recently declared Australian Commonwealth Marine Reserve (CMR) Network covers a total of 3.1 million km2 of continental shelf, slope, and abyssal habitat. Managing and conserving the biodiversity values within this network requires knowledge of the physical and biological assets that lie within its boundaries. Unfortunately very little is known about the habitats and biological assemblages of the continental shelf within the network, where diversity is richest and anthropogenic pressures are greatest. Effective management of the CMR estate into the future requires this knowledge gap to be filled efficiently and quantitatively. The challenge is particularly great for the shelf as multibeam echosounder (MBES) mapping, a key tool for identifying and quantifying habitat distribution, is time consuming in shallow depths, so full coverage mapping of the CMR shelf assets is unrealistic in the medium-term. Here we report on the results of a study undertaken in the Flinders Commonwealth Marine Reserve (southeast Australia) designed to test the benefits of two approaches to characterising shelf habitats: (i) MBES mapping of a continuous (~30 km2) area selected on the basis of its potential to include a range of seabed habitats that are potentially representative of the wider area, versus; (ii) a novel approach that uses targeted mapping of a greater number of smaller, but spatially balanced, locations using a Generalized Random Tessellation Stratified sample design. We present the first quantitative estimates of habitat type and sessile biological communities on the shelf of the Flinders reserve, the former based on three MBES analysis techniques. We contrast the quality of information that both survey approaches offer in combination with the three MBES analysis methods. The GRTS approach enables design based estimates of habitat types and sessile communities and also identifies potential biodiversity hotspots in the northwest corner of the reserve’s IUCN zone IV, and in locations close to shelf incising canyon heads. Design based estimates of habitats, however, vary substantially depending on the MBES analysis technique, highlighting the challenging nature of the reserve’s low profile reefs, and improvements that are needed when acquiring MBES data for small GRTS locations. We conclude that the two survey approaches are complementary and both have their place in a successful and flexible monitoring strategy; the emphasis on one method over the other should be considered on a case by case basis, taking into account the survey objectives and limitations imposed by the type of vessel, time available, size and location of the region where knowledge is required.

The application of automated segmentation methods and fragmentation statistics to characterise rocky reef habitat

The techniques presented in this study remove the qualitative assessment of rocky reef patch identification by applying robust methods for automated reef delineation from sidescan sonar records using a segmentation algorithm. Object texture, shape and size are investigated to discriminate reef from sand habitat. These results are applied to spatially explicit fragmentation statistics to examine the role of scale and habitat arrangement in determining habitat distribution patterns on the east coast of Tasmania.

Comparing Selections of Environmental Variables for Ecological Studies: A Focus on Terrain Attributes

Selecting appropriate environmental variables is a key step in ecology. Terrain attributes (e.g. slope, rugosity) are routinely used as abiotic surrogates of species distribution and to produce habitat maps that can be used in decision-making for conservation or management. Selecting appropriate terrain attributes for ecological studies may be a challenging process that can lead users to select a subjective, potentially sub-optimal combination of attributes for their applications. The objective of this paper is to assess the impacts of subjectively selecting terrain attributes for ecological applications by comparing the performance of different combinations of terrain attributes in the production of habitat maps and species distribution models. Seven different selections of terrain attributes, alone or in combination with other environmental variables, were used to map benthic habitats of German Bank (off Nova Scotia, Canada). 29 maps of potential habitats based on unsupervised classifications of biophysical characteristics of German Bank were produced, and 29 species distribution models of sea scallops were generated using MaxEnt. The performances of the 58 maps were quantified and compared to evaluate the effectiveness of the various combinations of environmental variables. One of the combinations of terrain attributes–recommended in a related study and that includes a measure of relative position, slope, two measures of orientation, topographic mean and a measure of rugosity–yielded better results than the other selections for both methodologies, confirming that they together best describe terrain properties. Important differences in performance (up to 47% in accuracy measurement) and spatial outputs (up to 58% in spatial distribution of habitats) highlighted the importance of carefully selecting variables for ecological applications. This paper demonstrates that making a subjective choice of variables may reduce map accuracy and produce maps that do not adequately represent habitats and species distributions, thus having important implications when these maps are used for decision-making.

Characterization of Shallow Inshore Coastal Reefs on the Tasman Peninsula, Southeastern Tasmania, Australia

Multibeam data of coastal bedrock reefs and associated sediments on the southeastern coast of Tasmania, Australia, were recently collected as part of the Commonwealth Environmental Research Facilities Marine Biodiversity Hub. The main aim of the surveys was to test a range of physical environmental parameters of nearshore reefs in southeast Tasmania as surrogates to predict patterns of benthic biodiversity. Two data sets were collected: (1) high-resolution bathymetry and seabed acoustic reflectance (backscatter) from a multibeam system and (2) high-resolution spatially rectified stereo still photographs of the seafloor collected by an autonomous underwater vehicle. In this analysis, the degrees of change of the slope of the seabed over a distance of 6 m and the seabed morphology are examined as surrogates for classifying seabed substrate. The distribution of the biological communities over different seabed morphologies is examined as a first step in the process of linking biological data to seabed substrate.

Analyzing Uncertainty in Multibeam Bathymetric Data and the Impact on Derived Seafloor Attributes

ABSTRACT Multibeam bathymetric data provide critical information for the modeling of seabed geology and benthic biodiversity. The accuracy of these models depends on the accuracy of the bathymetric data, which contain uncertainties that are stochastic at individual soundings but exhibit a distinct spatial distribution with increasing magnitude from nadir to the outer beams. A restricted spatial randomness method that simulates both the stochastic and spatial characteristics of the data uncertainty performed better than a complete spatial randomness method in analyzing the impact of bathymetric data uncertainty on derived seafloor attributes.

Artefacts in Marine Digital Terrain Models: A Multiscale Analysis of Their Impact on the Derivation of Terrain Attributes

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.

Integrating Seafloor Habitat Mapping and Fish Assemblage Patterns Improves Spatial Management Planning in a Marine Park

ABSTRACT Malcolm, H.A., Jordan, A., Schultz, A.L., Smith, S.D.A., Ingleton, T., Foulsham, E., Linklater, M., Davies, P., Ferrari, R., Hill, N., and Lucieer, V., 2016. Integrating seafloor habitat mapping and fish assemblage patterns improves spatial management planning in a marine park. In: Vila-Concejo, A.; Bruce, E.; Kennedy, D.M., and McCarroll, R.J. (eds.), Proceedings of the 14th International Coastal Symposium (Sydney, Australia). Journal of Coastal Research, Special Issue, No. 75, pp. 1292 - 1296. Coconut Creek (Florida), ISSN 0749-0208. Marine Protected Areas (MPAs) are important spatial mechanisms for managing human activities, if effectively planned. The Solitary Islands Marine Park (SIMP), covering 720 km2 of coastal waters in New South Wales, Australia, includes reef and unconsolidated habitats up to 17 km from shore and 75 m depth. When established in 1991, there was limited knowledge of biotic patterns, seafloor habitats and habitat-biotic relationships in the multiple-use SIMP, which constrained effective conservation planning. Subsequent mapping of sub-tidal habitats from aerial photography and single-beam acoustics improved habitat representation following rezoning in 2002 using Comprehensive, Adequate, Representative (CAR) principles and assisted site selection for diver surveys of fishes, a key surrogate taxon. In 2006, a swath acoustic mapping program commenced, which mapped ~35% of the MPA. This has produced high-resolution data on seafloor habitats, including depths >50 m. Bathymetry and backscatter layers have facilitated targeted deployment of Baited Remote Underwater Video (BRUV) to test hypotheses about associations between fishes and physical habitat characteristics. Strong and persistent patterns in fish assemblage composition in relation to particular habitat characteristics provided the basis for a Habitat Classification Scheme (HCS) to be refined with the following categories: substratum (consolidated, unconsolidated), cross-shelf position (inshore, mid, offshore) and depth (shallow, intermediate, deep). Further refinement of unconsolidated substratum into gravel and sand habitats, which were mapped using backscatter layers, improves this classification. The HCS, which integrates habitat and biotic patterns, greatly increases the potential for effective spatial management planning in the SIMP when used with spatial planning tools (e.g. Marxan).