Skip to main content

Über dieses Buch

This university-level reference work covers a range of remote sensing techniques that are useful for mapping and visualizing benthic environments on continental shelves. Chapters focus on overviews of the history and future of seafloor mapping techniques, cartographical visualisation and communication of seafloor mapping, and practical applications of new technologies. Seabed mapping is referenced by high-resolution seismic methods, sidescan sonar, multibeam bathymetry, satellite imagery, LiDAR, acoustic backscatter techniques, and soundscape ecology monitoring, use of autonomous underwater vehicles, among other methods. The wide breadth of subjects in this volume provides diversified coverage of seafloor imaging. This collection of modern seafloor mapping techniques summarizes the state of the art methods for mapping continental shelves.



Historical Development of Seafloor Mapping and Survey


1. History of Modern Seafloor Mapping

Over the last century, remotely sensed mapping of continental shelf seafloor topography has had a rich history of applied research with varying techniques, all of which strive to accurately visualize the submarine benthos. Many early techniques (e.g., three-dimensional hachure maps) relied solely on the researcher’s knowledge and cartographic skills in absence of technological advances yet to be made. Acoustic mapping practices were then derived from war-time sonar sweeps that painted a surprisingly vivid picture of the seafloor through the use of sound. Through time, more sophisticated acoustic remote sensing techniques were developed and used as either sidescan sonar, single beam echo sounders, or multibeam reflection sounders. More powerful ground-penetrating seismic techniques have also been used to not only map the surface layer of the seafloor, but to also visualize what lies below the benthic interface. However, aircraft and satellite-assisted techniques enabled researchers to recently make considerable advancements in the visualization of benthic environments. Once mainly used as military reconnaissance procedures for strategic planning, the advent of high-resolution aerial photography and orthoimagery has proven to be among the most effective techniques for visualizing shallow, low turbid waters along continental shelves. Equally as effective for clear waters within the nearshore of the continental margin are airborne laser bathymetry (ALB) methods, which use pulses of light to acquire bathymetric and topographic configurations based on airborne laser reflectance. Lastly, hyperspectral and multispectral sensors onboard orbiting satellites (e.g., IKONOS, Landsat, MODIS, SPOT) provide a continuous stream of benthic environment visualization without the logistical inconveniences of deploying a vessel or aircraft every time images are to be acquired. A historical review of advances in seafloor mapping methods shows that remote sensing techniques led to new ways of visualizing dynamic benthic environments that ranged from broadly generalized geomorphological features to specific biological coverages.
Christopher Makowski, Charles W. Finkl

Environmental/Biological Survey of Coastal and Shelf Environments


2. Emerging Mapping Techniques for Autonomous Underwater Vehicles (AUVs)

Seafloor environments at ever increasing depths on the continental shelf are being resolved at ever higher resolutions as a result of changing sensor technologies and, in part, with the emergence of Autonomous Underwater Vehicles (AUVs) as stable survey platforms. The new age of underwater robots to act as platforms which we can use to deploy sensors to gather information in the ocean is only limited by our imagination. This chapter provides an overview of this technology for applications on the continental shelf. It explores the basic fundamentals of AUV operation and the types of associated instrumentation, the current state of commercial and academic activity and the broad disciplines across which AUVs are currently been employed. AUVs are highly effective tools for sampling in continental shelf marine environments because: (1) they are untethered and can conduct non-destructive sampling in remote habitats (e.g. under ice shelves and over complex terrain) and in depths > 1000 m; (2) they can repeat spatial surveys with a high degree of precision over time; and (3) they can be equipped with a wide range of tools and sensors to sample both physical, chemical and biological data. Unfortunately by the time this chapter is in print, it realistically will already be out of date, as a result of the speed of the technological advancement in this discipline of underwater engineering.
Vanessa L. Lucieer, Alexander L. Forrest

3. Remote Sensing Technologies for the Assessment of Marine and Coastal Ecosystems

This chapter reviews the Remote Sensing (RS) technologies that are particularly appropriate for marine and coastal ecosystem research and management. RS techniques are used to perform analysis of water quality in coastal water bodies; to identify, characterize and analyze river plumes; to extract estuarine/coastal sandy bodies; to identify beach features/patterns; and to evaluate the changes and integrity (health) of the coastal lagoon habitats. For effective management of these ecosystems, it is essential to have satellite data available and complementary accurate information about the current state of the coastal regions, in addition to well-informed forecasts about its future state. In recent years, the use of space, air and ground-based RS strategies has allowed for the rapid data collection, Image processing (Pixel-Based and Object-Based Image Analysis (OBIA) classification) and dissemination of such information to reduce vulnerability to natural hazards, anthropic pressures, and to monitoring essential ecological processes, life support systems and biological diversity.
Francisco Gutierres, Ana Cláudia Teodoro, Eusébio Reis, Carlos Neto, José Carlos Costa

4. A Review of Remote Sensing Techniques for the Visualization of Mangroves, Reefs, Fishing Grounds, and Molluscan Settling Areas in Tropical Waters

Globally there has been tremendous progress in space technology especially in the field of satellite remote sensing applications during the past five decades. Satellite based sensors provide a repetitive and synoptic coverage of inaccessible/larger areas which generated a time series database useful in identification and mapping of environment and resources. These databases form a scientific tool for various stakeholders to device suitable strategies for management of coastal and marine resources. This chapter analyses the various applications of satellite remote sensing and numerical modelling on identification and mapping of mangroves, coral reefs, fishing and molluscan grounds in the coastal marine ecosystems with relevant case studies and illustrations. The mapping methods for mangroves explains the classification protocols, advantages in using different remote sensing techniques and the comparison of different mapping techniques. In case of reef mapping, the vulnerability mapping of reefs due to extreme events is also discussed. Fish movement in a dynamic environment and the mapping of these movements with the help of proxy indicators are also detailed. Molluscan mapping is done based on the biomass differences during different seasons and their physical attributes.
Thankam Theresa Paul, A. Dennis, Grinson George

5. Remote Sensing of Submerged Aquatic Vegetation

Submerged Aquatic Vegetation (SAV), such as eelgrass, provides important ecological functions including food and habitat for ducks, geese, crabs, fish, clams, and other species. SAV also filters out excess nutrients from storm water that runs off into coastal waters, thus improving water quality. Eelgrass meadows can decrease the damaging effects of waves and reduce shoreline erosion. To protect these vital ecosystems, scientists need to monitor coastal vegetation changes as the sea level continues to rise and the coastal population keeps expanding. New satellites, sensors and data analysis techniques are providing remotely sensed data that are effective for monitoring coastal features and processes. Multispectral and hyperspectral imagers, LiDAR and radar systems are available for mapping coastal marshes, submerged aquatic vegetation (SAV), coral reefs, beach profiles, water turbidity, chlorophyll concentration and eutrophication. Since coastal ecosystems, such as SAV beds, have high spatial complexity and temporal variability, they must be observed with high spatial, spectral and temporal resolutions. New satellites, carrying sensors with fine spatial (0.4–4 m) or spectral (200 narrow bands) resolution are now more accurately detecting changes in salt marsh and SAV extent, health, productivity and habitat quality. Using time-series of images enables scientists to study the health of SAV and other coastal ecosystems and to determine long- term trends and short- term changes.
Victor V. Klemas

6. Combining Cetacean Soundscape Ecology and Niche Modeling to Contribute in the Mapping of the Brazilian Continental Shelf

This chapter will introduce readers to the marine soundscape ecology through a cetacean study perspective. Unravelling the behavioral ecology of whales and dolphins in the southwestern Atlantic Ocean provides information about the marine habitat in which they live, in this case, the continental shelf. The study also describes methods for underwater mapping such as bioacoustics, photo-video recordings, GIS and behavioral observations.
Marcos R. Rossi-Santos, Guilherme de Oliveira

Physical Surveys of Coasts and Seafloor Exploration on Continental Shelves


7. Global Overview of Continental Shelf Geomorphology Based on the SRTM30_PLUS 30-Arc Second Database

We report the results of a multivariate analysis of geomorphic features occurring on the global continental shelf that were mapped based on the Shuttle Radar Topography Mapping (SRTM30_PLUS) 30-arc sec database. The analysis was based on 11 input variables as follows: (1) the mean continental shelf depth; (2) mean shelf break depth; (3) mean shelf width; (4) percent area of low relief shelf; (5) percent area of medium relief shelf; (6) percent area of high relief shelf; (7) percent area of glacial troughs; (8) percent area of shelf valleys; (9) percent area of basins perched on the shelf; (10) the percent of submarine canyons that are shelf-incising; and (11) the percent area of coral reef. For the analysis the global shelf was divided into 551 reporting blocks, each approximately 500 km in along-shelf length. Eight shelf morphotypes were defined by multivariate analysis of the 11 input variables, and they can be grouped into four broad categories: narrow-shallow shelves; wide-flat shelves; intermediate shelves; and deep-glaciated shelves. There is a negative correlation between shelf width and active plate margins, although there are examples of most shelf morphotypes occurring on both active and passive margins. Glaciation plays a major role in determining shelf geomorphology and characterizes around 21 % of the global shelf. In particular, we find a very strong correlation between mean shelf depth and the percentage area of glacial troughs, indicative of the role played by glaciation and glacial erosion in shaping the global shelf. Coral reef growth is an important factor for one morphotype, which covers 427,000 km2 or about 1.3 % of all continental shelves. The hypsometric curve for mean shelf depth exhibits a peak at a depth of 40 m that coincides with a persistent position of sea level during the last 500,000 years based on one published sea level curve. The geomorphic characterization and classification of the continental shelf at a global scale could be advanced using predictive modeling tools (for tidal sand banks, for example) but is otherwise dependent upon improved resolution bathymetric data becoming available.
Peter T. Harris, Miles Macmillan-Lawler

8. Seismic Profiling of the Seabottoms for Shallow Geological and Geotechnical Investigations

This chapter presents the seismic profiling of the seabottoms for shallow geological and geotechnical investigations. Both methodology and equipment needed to perform the deep and shallow seismic surveys shall be discussed as well as the presentation of the results on the example of the Polish Baltic Sea. Of utmost importance, in identifying the geological structure of the Quaternary substrate deposits occurring on the seabed, is the seismoacoustic research. In this study the interpretation of the results is based on the analysis of different reflective levels, the nature of the borderlines of reflective horizons, their relative clarity and angles. Then, the correlation is made between seismoacoustic materials and geology of the adjacent land area. This correlation is based on the use of geological maps and drilling cores from the coastal zone, taking into account the lithology, stratigraphy and depth of occurrence of certain reflective levels and the surface of angular discordance. This allows an initial presentation of the bedrock structure and establishing the correlation between sub-Quaternary surface and lithological composition of deposits. The conducted seismoacoustic investigations within the Quaternary sediments provides a basis for separation of certain seismostratigraphic units, which refer strictly to the separate litostratigraphic levels of the analyzed geological period. An important aspect of the interpretation of seismic records is to analyze the degree of the acoustic energy absorption through the different layers of Quaternary sediments along with characterization of the records’ texture. An important element in the analysis of seismoacoustic registrations is also the tracking of the leading acoustic horizons and the analysis of angular discordance of individual reflectors. The role of seismoacoustic investigations in the geotechnical recognition of the seabottom is also very important because, conducted on a large-area and with a set accuracy, these tests can determine the limits of occurrence of particular soils that have specific physical and mechanical properties. An important aspect of seismoacoustic investigations in the geotechnical recognition of the seabed is also to specify the thickness of geological layers that can become the selected substrate for the foundation of certain buildings and marine constructions.
Leszek J. Kaszubowski

9. Using Multibeam and Sidescan Sonar to Monitor Aggregate Dredging

Marine aggregate dredging in the UK occurs within individually licensed areas, and before dredging is allowed to begin a Government permission (Licence) to dredge is required. This is accompanied by detailed monitoring conditions based on the environmental effects and sensitive receptors present at each site. Monitoring methods typically used in the UK include multibeam bathymetric and side scan sonar surveys and this Chapter will provide a Case Study of monitoring at one particular licence area – Area 401/2. Multibeam data showed bathymetric changes resulting from aggregate extraction limited to the direct footprint of dredging; and mobile sandwaves could be seen. Sidescan sonar data showed no changes in the overall interpretation when comparing datasets from 2013 to 2009. Minor changes in the distribution of Sabellaria spinulosa were noted, but no additional areas of conservation significance were identified and no changes to the mitigation were proposed. Fifty-two archaeological anomalies were identified during the analysis of the 2013 survey data, eight of which required mitigation. The monitoring of dredging activity at Area 401/2 has shown limited impacts arising from aggregate extraction and mitigation measures have been appropriate.
Dafydd Lloyd Jones, Robert Langman, Ian Reach, John Gribble, Nigel Griffiths

10. Landscape-Level Imaging of Benthic Environments in Optically-Deep Waters

Optical imaging of coral reefs and other benthic communities present below one attenuation depth, the limit of effective airborne and satellite remote sensing, requires the use of in situ platforms such as autonomous underwater vehicles (AUVs), remotely-operated vehicles (ROVs), towed platforms and drop cameras. High-resolution optical data from AUV and ROV sensors has provided unprecedented information on the community structure and condition of the deeper zooxanthellate and azooxanthellate coral reefs of Puerto Rico and the US Virgin Islands. The high-resolution optical images and video also provide useful data for inventories of the fish species present as well as macro invertebrates associated with these habitats. The digital photo transects obtained by the Seabed AUV provided quantitative data on living coral, sponge, gorgonian, and macroalgal cover as well as coral species richness and diversity. AUV and ROV benthic assessments could provide the required information for selecting unique areas of high coral cover, biodiversity and structural complexity for habitat protection and ecosystem-based management.
Roy A. Armstrong

11. Terrestrial Laser Scanner Techniques for Enhancement in Understanding of Coastal Environments

Three dimensional terrestrial laser scanners have the potential to provide new insights into multidisciplinary coastal studies due to the extremely high spatial data resolution, speed of surveys and availability of additional parameters, namely return signal intensity and RGB color information. Not only can high resolution morphological maps be produced, but quantities such as sediment type, surface roughness, surface moisture and vegetation cover can be inferred from the point density and additional parameters. This chapter firstly provides a review of the state of the art of use of terrestrial laser scanners in coastal environments, paying particular attention to the use of data abundance to derive additional information beyond morphology. Terrestrial laser scanners have been used more extensively in other fields of study and hence relevant studies from these sectors are also described. Secondly a case study will be presented of terrestrial laser scanner usage: a terrestrial laser scanner has been used to study barrier and cusp evolution on a composite sand-gravel beach. This will demonstrate the scanners ability to measure fine scale morphological features, surface roughness and will demonstrate techniques to define sand and gravel regions via RGB color properties. Finally some discussion into the future potential and caveats to the use of terrestrial laser scanners are presented. These caveats are primarily the short range of many instruments and the data surplus for some more uniform coastlines. These mean that the appropriateness of a terrestrial laser scanner survey will depend upon both the site and the scales of the physical processes being investigated.
I. Fairley, T. Thomas, M. Phillips, D. Reeve


Weitere Informationen