Mapping and modeling eelgrass Zostera marina distribution in the western Baltic Sea

In the northern hemisphere, eelgrass Zostera marina L. is the most important and widespread seagrass species. Despite its ecological importance, baseline data on eelgrass distribution and abundance are mostly absent, particularly in subtidal areas with relatively turbid waters. Here, we report a combined approach of vegetation mapping in the Baltic Sea coupled to a species distribution model (SDM). Eelgrass cover was mapped continuously in the summers of 2010 and 2011 with an underwater towed camera along ~400 km of seafloor. Eelgrass populated 80% of the study region and occurred at water depths between 0.6 and 7.6 m at sheltered to moderately exposed coasts. Mean patch length was 128.6 m but was higher at sheltered locations, with a maximum of >2000 m. The video observations (n = 7824) were used as empiric input to the SDMs. Using generalized additive models, 3 predictor variables (depth, wave exposure, and slope), which were selected based on Akaike’s information criterion, were sufficient to predict eelgrass presence/absence. Along with a very good overall discriminative ability (area under the receiver-operating characteristic curve ROC/AUC = 0.82), depth (as a proxy for light), wave exposure, and slope contributed 66, 29, and 5%, respectively, to the final model. The estimated total areal extent of eelgrass in the study region amounts to 140.5 km2 and comprises about 11.5% of all known Baltic seagrass beds. The present work is, to the best of our knowledge, the largest study undertaken to date on vegetation mapping and the first to assess distribution of eelgrass quantitatively in the western Baltic Sea

AN INTEGRATED SIMULATION APPROACH FOR AUV IMAGE-BASED SLAM NAVIGATION

This thesis develops a simulation framework for undersea feature-based navigation. Using an autonomous underwater vehicle (AUV) to locate an item of interest on the seafloor is a capability that would greatly benefit the Navy. AUVs provide a gateway toward removing the workforce requirement; however, they are still costly both in acquisition and maintenance. A solution to this problem is using two AUVs, one with increased capability and charged with finding and marking seafloor items with a beacon. An expendable AUV outfitted with cost-effective sensors would relocate, identify and neutralize the threat. Using undersea imaging to correlate seafloor images to an a priori image mosaic together with a ultra short baseline (USBL) beacon allows the AUV to complete challenging mission objectives without traditional navigation systems. Incremental Smoothing and Mapping 2 (iSAM2) is a Simultaneous Localization and Mapping (SLAM) technique that can be used by the AUV for position localization and is an appropriate technique, with image and USBL sensing, for real-time navigation operations. A simulation framework provides the ability to evaluate an AUV's performance while minimizing the risk of real-world operations. The framework is composed of a software architecture that allows for testing using the same software applied in real-world operations. This thesis demonstrates this framework and provides analysis for its usability for image-based SLAM.Lieutenant, United States NavyApproved for public release. Distribution is unlimited

Selected Papers from the 2018 IEEE International Workshop on Metrology for the Sea

This Special Issue is devoted to recent developments in instrumentation and measurement techniques applied to the marine field. ¶The sea is the medium that has allowed people to travel from one continent to another using vessels, even today despite the use of aircraft. It has also been acting as a great reservoir and source of food for all living beings. However, for many generations, it served as a landfill for depositing conventional and nuclear wastes, especially in its deep seabeds, and we are assisting in a race to exploit minerals and resources, different from foods, encompassed in it. Its health is a great challenge for the survival of all humanity since it is one of the most important environmental components targeted by global warming. ¶ As everyone may know, measuring is a step that generates substantial knowledge about a phenomenon or an asset, which is the basis for proposing correct solutions and making proper decisions. However, measurements in the sea environment pose unique difficulties and opportunities, which is made clear from the research results presented in this Special Issue

The Bubble Box: Towards an Automated Visual Sensor for 3D Analysis and Characterization of Marine Gas Release Sites

Several acoustic and optical techniques have been used for characterizing natural and anthropogenic gas leaks (carbon dioxide, methane) from the ocean floor. Here, single-camera based methods for bubble stream observation have become an important tool, as they help estimating flux and bubble sizes under certain assumptions. However, they record only a projection of a bubble into the camera and therefore cannot capture the full 3D shape, which is particularly important for larger, non-spherical bubbles. The unknown distance of the bubble to the camera (making it appear larger or smaller than expected) as well as refraction at the camera interface introduce extra uncertainties. In this article, we introduce our wide baseline stereo-camera deep-sea sensor bubble box that overcomes these limitations, as it observes bubbles from two orthogonal directions using calibrated cameras. Besides the setup and the hardware of the system, we discuss appropriate calibration and the different automated processing steps deblurring, detection, tracking, and 3D fitting that are crucial to arrive at a 3D ellipsoidal shape and rise speed of each bubble. The obtained values for single bubbles can be aggregated into statistical bubble size distributions or fluxes for extrapolation based on diffusion and dissolution models and large scale acoustic surveys. We demonstrate and evaluate the wide baseline stereo measurement model using a controlled test setup with ground truth information

Advanced perception, navigation and planning for autonomous in-water ship hull inspection

Inspection of ship hulls and marine structures using autonomous underwater vehicles has emerged as a unique and challenging application of robotics. The problem poses rich questions in physical design and operation, perception and navigation, and planning, driven by difficulties arising from the acoustic environment, poor water quality and the highly complex structures to be inspected. In this paper, we develop and apply algorithms for the central navigation and planning problems on ship hulls. These divide into two classes, suitable for the open, forward parts of a typical monohull, and for the complex areas around the shafting, propellers and rudders. On the open hull, we have integrated acoustic and visual mapping processes to achieve closed-loop control relative to features such as weld-lines and biofouling. In the complex area, we implemented new large-scale planning routines so as to achieve full imaging coverage of all the structures, at a high resolution. We demonstrate our approaches in recent operations on naval ships.United States. Office of Naval Research (Grant N00014-06-10043)United States. Office of Naval Research (Grant N00014-07-1-0791

Guidance for benthic habitat mapping: an aerial photographic approach

This document, Guidance for Benthic Habitat Mapping: An Aerial Photographic Approach, describes proven technology that can be applied in an operational manner by state-level scientists and resource managers. This information is based on the experience gained by NOAA Coastal Services Center staff and state-level cooperators in the production of a series of benthic habitat data sets in Delaware, Florida, Maine, Massachusetts, New York, Rhode Island, the Virgin Islands, and Washington, as well as during Center-sponsored workshops on coral remote sensing and seagrass and aquatic habitat assessment. (PDF contains 39 pages) The original benthic habitat document, NOAA Coastal Change Analysis Program (C-CAP): Guidance for Regional Implementation (Dobson et al.), was published by the Department of Commerce in 1995. That document summarized procedures that were to be used by scientists throughout the United States to develop consistent and reliable coastal land cover and benthic habitat information. Advances in technology and new methodologies for generating these data created the need for this updated report, which builds upon the foundation of its predecessor

Remote measurements of waves and currents over complex bathymetry

Waves are the primary input of energy in the nearshore region, and together with the currents forced through the transfer of momentum that occurs during the wave breaking process they are the principal mechanism for sediment transport in the nearshore. The basic physics of waves and currents are thought to be well understood, and simple models for waves and current interacting with simple (alongshore-uniform bathymetry) generally agree with in situ measurements. However, alongshore variability is ubiquitous, and the predictability of waves and currents over complex bathymetry is an important research topic. Significant effort has been placed into understanding and predicting (modeling) the kinematics and dynamics of waves and currents, but the accuracy of these models are largely untested, due to the lack of appropriate wave and current measurements. This dissertation first details the development and application of an optical remote sensing technique to measure the shape of wave frequency-direction spectra over large scale complex bathymetry. The optical wave spectral estimation technique is based on the wave slope dependence of reflected skylight, and while not a metric of the absolute wave energy, the measurement technique is shown to agree with the frequency and directional distributions of in situ measurements. Simultaneously, the optical technique offers increased directional resolution. Maps of the wave direction field over a submarine canyon, using the optical technique, show dramatic changes in the wave divergence and convergence which coincides with details of the large scale bathymetry gradients. The last section of this dissertation analyzes 14 months of surf zone longshore currents measured from a two-dimensional array using a previously described optical remote sensing technique. Based on metrics developed in the study, the longshore currents are shown to be alongshore nonuniform for the majority (70%) of the observations, suggesting that a simple one-dimensional force balance circulation model is not generally applicable. Related tests of a point model only show moderate skill when predicting the peak longshore current (rms error 0.38 m/s). Though cases of two-dimensional circulation (i.e. rip currents) are shown to coincide with alongshore-variable bathymetry, a metric of the degree of alongshore bathymetry variability, γB, has poor skill of predicting the strength of spatial longshore current variability

A light in the dark: using cabled seafloor observatories to study abundance and behaviour of seafloor megafauna in response to environmental change

Surface primary productivity forms the base of most marine food webs and contributes significantly to global carbon cycling, providing a key link from surface to seafloor. High seasonal primary productivity along temperate latitude coastlines provides crucial nutrients for seafloor communities, driving spatiotemporal patterns in abundance, behaviour, biodiversity, and distribution of benthic megafauna. Many factors, including ocean warming, deoxygenation, and increasing frequency and duration of marine heatwaves (MHW), may alter the dynamics governing primary production, threatening benthic organisms that depend on the seasonal input of phytodetritus for food. The focus of this thesis is to make use of two seafloor observatories, NEPTUNE near Vancouver Island, British Columbia, and a new platform in Conception Bay, NL, to examine variability in abundance, behaviour, and composition of seafloor communities in response to environmental change across temporal scales. First, the response of the deep-sea pink urchin Strongylocentrotus fragilis to a recent MHW on the continental margin off the coast of Vancouver Island was investigated using a combination of benthic trawls (2004-2018) and seafloor observatory data (2013-2020). Sea urchin density declined during the MHW, likely in response to reduced kelp subsidies from coastal waters. Next, the new Holyrood Underwater Observatory in Conception Bay was used to study benthic community response to the spring phytoplankton bloom. High-frequency variability in seafloor environmental dynamics was documented during the winter-spring transition, and the unexpected emergence of >200 sea cucumbers (Psolus sp.) coinciding with the arrival of phytodetritus at the seafloor was observed. These data will provide a baseline against which to monitor changes in phenology as climate change progresses. This work comes at a critical point in ocean observing as we approach global climate tipping points. Now more than ever, it is essential to document the current state of marine communities to understand and predict community responses to changing ocean conditions, and to sustainably manage ocean resources