Habitat suitability for marine fishes using presence-only modelling and multibeam sonar

Improved access to multibeam sonar and underwater video technology is enabling scientists to use spatially-explicit, predictive modelling to improve our understanding of marine ecosystems. With the growing number of modelling approaches available, knowledge of the relative performance of different models in the marine environment is required. Habitat suitability of 5 demersal fish taxa in Discovery Bay, south-east Australia, were modelled using 10 presence-only algorithms: BIOCLIM, DOMAIN, ENFA (distance geometric mean [GM], distance harmonic mean [HM], median [M], area-adjusted median [Ma], median + extremum [Me], area-adjusted median + extremum [Mae] and minimum distance [Min]), and MAXENT. Model performance was assessed using kappa and area under curve (AUC) of the receiver operator characteristic. The influence of spatial range (area of occupancy) and environmental niches (marginality and tolerance) on modelling performance were also tested. MAXENT generally performed best, followed by ENFA-GM and -HM, DOMAIN, BIOCLIM, ENFA-M, -Min, -Ma, -Mae and -Me algorithms. Fish with clearly definable niches (i.e. high marginality) were most accurately modelled. Generally, Euclidean distance to nearest reef, HSI-b (backscatter), rugosity and maximum curvature were the most important variables in determining suitable habitat for the 5 demersal fish taxa investigated. This comparative study encourages ongoing use of presence-only approaches, particularly MAXENT, in modelling suitable habitat for demersal marine fishes.

Understanding fish-habitat associations using video observations and sonar imaging

This thesis was motivated by the increasing role of species distribution models in managing marine fishes and their habitats. These models provided new information about fish-habitat associations. However, models are potentially influenced by fish behaviour towards underwater video systems.

Submarine sonar FX

Submarine Sonar FX is a sound effect of a submarine/nautical type of sonar.

Evaluation of four supervised learning methods for benthic habitat mapping using backscatter from multi-beam sonar

An understanding of the distribution and extent of marine habitats is essential for the implementation of ecosystem-based management strategies. Historically this had been difficult in marine environments until the advancement of acoustic sensors. This study demonstrates the applicability of supervised learning techniques for benthic habitat characterization using angular backscatter response data. With the advancement of multibeam echo-sounder (MBES) technology, full coverage datasets of physical structure over vast regions of the seafloor are now achievable. Supervised learning methods typically applied to terrestrial remote sensing provide a cost-effective approach for habitat characterization in marine systems. However the comparison of the relative performance of different classifiers using acoustic data is limited. Characterization of acoustic backscatter data from MBES using four different supervised learning methods to generate benthic habitat maps is presented. Maximum Likelihood Classifier (MLC), Quick, Unbiased, Efficient Statistical Tree (QUEST), Random Forest (RF) and Support Vector Machine (SVM) were evaluated to classify angular backscatter response into habitat classes using training data acquired from underwater video observations. Results for biota classifications indicated that SVM and RF produced the highest accuracies, followed by QUEST and MLC, respectively. The most important backscatter data were from the moderate incidence angles between 30° and 50°. This study presents initial results for understanding how acoustic backscatter from MBES can be optimized for the characterization of marine benthic biological habitats. © 2012 by the authors.

Comparison of a self-processed EM3000 multibeam echosounder dataset with a QTC view habitat mapping and a sidescan sonar imagery, Tamaki Strait, New Zealand

A methodology for automatically processing the data files from an EM3000 multibeam echosounder (Kongsberg Maritime, 300 kHz) is presented. Written in MatLab, it includes data extraction, bathymetry processing, computation of seafloor local slope, and a simple correction of the backscatter along-track banding effect. The success of the latter is dependent on operational restrictions, which are also detailed. This processing is applied to a dataset acquired in 2007 in the Tamaki Strait, New Zealand. The resulting maps are compared with a habitat classification obtained with the acoustic ground-discrimination software QTC View linked to a 200-kHz single-beam echosounder and to the imagery from a 100-kHz sidescan sonar survey, both performed in 2002. The multibeam backscatter map was found to be very similar to the sidescan imagery, quite correlated to the QTC View map on one site but mainly uncorrelated on another site. Hypotheses to explain these results are formulated and discussed. The maps and the comparison to prior surveys are used to draw conclusions on the quality of the code for further research on multibeam benthic habitat mapping.

Granitic coastal geomorphology: Applying integrated terrestrial and bathymetric LiDAR with multibeam sonar to examine coastal landscape evolution

Coasts composed of resistant lithologies such as granite are generally highly resistant to erosion. They tend to evolve over multiple sea level cycles with highstands acting to remove subaerially weathered material. This often results in a landscape dominated by plunging cliffs with shore platforms rarely occurring. The long-term evolution of these landforms means that throughout the Quaternary these coasts have been variably exposed to different sea level elevations which means erosion may have been concentrated at different elevations from today. Investigations of the submarine landscape of granitic coasts have however been hindered by an inability to accurately image the nearshore morphology. Only with the advent of multibeam sonar and aerial laser surveying can topographic data now be seamlessly collected from above and below sea level. This study tests the utility of these techniques and finds that very accurate measurements can be made of the nearshore thereby allowing researchers to study the submarine profile with the same accuracy as the subaerial profile. From a combination of terrestrial and marine LiDAR data with multibeam sonar data, it is found that the morphology of granite domes is virtually unaffected by erosion at sea level. It appears that evolution of these landscapes on the coast is a very slow process with modern sea level acting only to remove subaerially weathered debris. The size and orientation of the joints determines the erosional potential of the granite. Where joints are densely spaced (<2 m apart) or the bedrock is highly weathered can semi-horizontal surfaces form.

Accounting for uncertainty in volumes of seabed change measured with repeat multibeam sonar surveys

Seafloors of unconsolidated sediment are highly dynamic features; eroding or accumulating under the action of tides, waves and currents. Assessing which areas of the seafloor experienced change and measuring the corresponding volumes involved provide insights into these important active sedimentation processes. Computing the difference between Digital Elevation Models (DEMs) obtained from repeat Multibeam Echosounders (MBES) surveys has become a common technique to identify these areas, but the uncertainty in these datasets considerably affects the estimation of the volumes displaced. The two main techniques used to take into account uncertainty in volume estimations are the limitation of calculations to areas experiencing a change in depth beyond a chosen threshold, and the computation of volumetric confidence intervals. However, these techniques are still in their infancy and, as a result, are often crude, seldom used or poorly understood. In this article, we explored a number of possible methodological advances to address this issue, including: (1) using the uncertainty information provided by the MBES data processing algorithm CUBE, (2) adapting fluvial geomorphology techniques for volume calculations using spatially variable thresholds and (3) volumetric histograms. The nearshore seabed off Warrnambool harbour - located in the highly energetic southwest Victorian coast, Australia - was used as a test site. Four consecutive MBES surveys were carried out over a four-months period. The difference between consecutive DEMs revealed an area near the beach experiencing large sediment transfers - mostly erosion - and an area of reef experiencing increasing deposition from the advance of a nearby sediment sheet. The volumes of sediment displaced in these two areas were calculated using the techniques described above, both traditionally and using the suggested improvements. We compared the results and discussed the applicability of the new methodological improvements. We found that the spatially variable uncertainty derived from the CUBE algorithm provided the best results (i.e. smaller confidence intervals), but that similar results can be obtained using as a fixed uncertainty value derived from a reference area under a number of operational conditions.

Permutations with a distinct difference property

The topic of this paper arose out of a consideration of Costas sequences, which are used in sonar and radar applications. These sequences have the defining property that all differences of elements the same distance apart, are different. Several infinite families of Costas sequences are known; but there are many existence questions for length greater-or-equal to 32. In this article, we restrict ourselves to sequences with the weaker property that all adjacent differences are different. We give a recursive construction for these, as well as building several infinite families.

Victorian marine habitat mapping project

Deakin University along with the CRC for Coastal Zone, Estuary and Waterway Management, the Glenelg Hopkins CMA and the Marine & Coastal Community Network have formed a partnership to map the benthic habitats at 14 sites across approximately 5% of Victorian State waters. The project is funded through the Federal Government by the Natural Heritage Trust and brings together expertise from universities, government agencies and private enterprise. We will be using hydro-acoustic sonar technologies, towed video camera and remotely operated vehicles to collect information on the types of substrate and bathymetry to derive habitat maps. The coastal fringe of Victoria encompasses rich and diverse ecosystems which support a range of human uses including commercial and recreational fisheries, whale watching, navigation, aquaculture and gas development. The Deakin lead initiative will map from the 10-metre contour (safe ship passage) to the three nautical mile mark for selected regions and will provide a geospatial framework for managing and gaining better understanding of the near-shore marine environment Research products will be used for management, educational and research purposes over the coming years.

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.

Low cost underwater robot sensor suite

One of the most expensive parts of underwater robotics is the sensors. This paper looks at modifying off the shelf components to create a sensor suite on a small budget. A big saving is made with sonar using a cheap commercial product to create a four sonar array. A depth sensor and acceleration navigation system are also developed.

RF communication between surface and underwater robotic swarms

In order for underwater robots to communicate with land and air based robots on an equal basis, high speed communications is required. If the robots are not to be tethered then wireless communications is the only possibility. Sonar communications is too slow. Unfortunately radio waves are rapidly attenuated under water due to phenomena such as skin depth. These experiments attempt to extend the range of underwater radio communications.

Risk assessment of child-victim sex offenders for extended supervision in New Zealand

Recently enacted legislation in New Zealand, the Parole (Extended Supervision) Amendment Act 2004, allows for the imposition of up to 10 years of supervision in the community for child-victim sex offenders following their release from prison. The Act requires reports to be written specifically assessing the risk of sexual re-offending against children. This study examined the application of actuarial measures used by the New Zealand Department of Corrections in these assessments, including a computer-scored instrument based on static factors (the Automated Sexual Recidivism Scale; ASRS) and a clinically-based judgement of dynamic risk factors (the SONAR). It was expected that a conservative approach would be taken in making recommendations for or against extended periods of supervision, such that a high score on either measure would predict a recommendation for extended supervision. It was found, however, that a more individualized approach was often taken, whereby a baseline assessment of risk as predicted by the ASRS was adjusted by clinicians based on SONAR ratings. Implications for the practice of risk assessment in sexual re-offending are discussed.

Seafloor mapping data, Victoria

The collection includes three major data types

- Seafloor structure information: Collation of seafloor structure information (bathymetry and softness hardness) collected using multibeam sonar systems as part of the Victorian Marine Habitat Mapping Project and bathymetric light detection and ranging data (LiDAR) collected as part of the future coats program. The geographic is Victorian State waters (~1400km2 multibeam sonar & ~4000 km2 for LiDAR as of 2012

- Video information: ~800 linear kilometres of precisely georeferenced towed video data from depths of 10-100m in Victorian coastal waters. 300 baited stereo video drops in Hopkins and Discovery Bay site locations. All video has been classified to the lowest taxonomic resolution possible with the video systems employed and converted to spatial data layers in the GIS environment.

- Habitat maps: Predicted habitat models integrating seafloor structure and video information developed using classification algorithms and remote sensing technologies.