Modelling Bathymetric Uncertainty

Modelling depth measurement uncertainty during data collection and processing has become common practice since the release of S-44 4th Edition (IHO, 1998). Hydrographic Offices have also attempted to model uncertainty of legacy bathymetry in order to determine their fitness for various uses. Additional uncertainty can be introduced into representative bathymetry models by various gridding techniques that interpolate depths between measurements. This article reviews sources of measurement uncertainty, looks at methods for estimating uncertainty in legacy data sets and uncer-tainty that is introduced into bathymetry (digital elevation/depth) models (DEMs/DDMs) by gridding. Applications that could benefit from bathymetric/DEM/DDM uncertainty information include bridge risk management and tsunami inundation modelling.Keywords: bathymetry, uncertainty, digital elevation modelsLa modelización de la incertidumbre de las medidas de profundidad durante la recogida y el procesa-do de datos se ha convertido en una práctica común desde la publicación de la 4ª Edición de la S-44 (OHI, 1998). Los Servicios Hidrográficos han intentado también modelar la incertidumbre de la batimetría tradicional para determinar su idoneidad para varios usos. Puede introducirse una incerti-dumbre adicional en modelos de batimetría representativos mediante varias técnicas de reticulado que interpolan profundidades entre las medidas. Este artículo revisa las fuentes de incertidumbre en las medidas, estudia métodos para estimar la incertidumbre en las colecciones de datos tradicionales y la incertidumbre que se introduce en modelos de batimetría (elevación digital/profundidad) (DEMs/DDMs) mediante el reticulado. Las aplicaciones que podrían beneficiar de información relativa a una incertidumbre batimétrica/DEM/DDM incluyen la gestión de los riesgos de puente y la modelización de las inundaciones causadas por los tsunamis.Palabras clave: batimetría, incertidumbre, modelos de elevación digitales.La modélisation de l‘incertitude des mesures des profondeurs pendant la collecte et le traitement des données est devenue pratique commune depuis la publication de la 4ème Edition de la S-44 (OHI, 1998). Les Services hydrographiques se sont également efforcés de modéliser l’incertitude de la bathymétrie traditionnelle afin de déterminer leur aptitude à différentes utilisations. Une incertitude supplémentaire peut être introduite dans des modèles de bathymétrie représentatifs au moyen de différentes techniques de quadrillage qui interpolent les profondeurs entre les mesurages. Cet article passe en revue les sources d‘incertitude dans les mesurages, examine les méthodes d‘estimation de l‘incertitude dans les ensembles de données traditionnels et l‘incertitude introduite dans les modèles d‘élévation ou de profondeurs numériques (DEM/DDM) bathymétriques à l‘aide du quadrillage. Les applications qui pourraient bénéficier d‘informations sur l‘incertitude bathymétrique/DEM/DDM incluent la gestion des risques sur la passerelle et la modélisation des inondations en cas de tsunami.Mots clés : bathymétrie, incertitude, modèles d’élévation numérique

Quantitative Comparison of Benthic Habitat Maps Derived From Multibeam Echosounder Backscatter Data

In the last decade, following the growing concern for the conservation of marine ecosystems, a wide range of approaches has been developed to achieve the identification, classification and mapping of seabed types and of benthic habitats. These approaches, commonly grouped under the denominations of Benthic Habitat Mapping or Acoustic Seabed Classification, exploit the latest scientific and engineering advancements for the exploration of the bottom of the ocean, particularly in underwater acoustics. Among all acoustic seabed-mapping systems available for this purpose, a growing interest has recently developed for Multibeam Echosounders (MBES). This interest is mainly the result of the multiplicity of these systems’ outputs (that is, bathymetry, backscatter mosaic, angular response and water-column data), which allows for multiple approaches to seabed or habitat classification and mapping. While this diversity of mapping approaches and this multiplicity of MBES data products contribute to an increasing quality of the charting of the marine environment, they also unfortunately delay the future standardization of mapping methods, which is required for their effective integration in marine environment management strategies. As a preliminary step towards such standardization, there is a need for generalized efforts of comparison of systems, data products, and mapping approaches, in order to assess the most effective ones given mapping objectives and environment conditions. The main goal of this thesis is to contribute to this effort through the development and implementation of tools and methods for the comparison of categorical seabed or habitat maps, with a specific focus on maps obtained from up-to-date methodologies of classification of MBES backscatter data. This goal is attained through the achievement of specific objectives treated sequentially. First, the need for comparison is justified through a review of the diversity characterizing the fields of Benthic Habitat Mapping and Acoustic Seabed Classification, and of their use of MBES data products. Then, a case study is presented that compare the data products from a Kongsberg EM3000 MBES to the output map of an Acoustic Ground Discrimination Software based on data from a Single-beam Echosounder and to a Sidescan Sonar mosaic, in order to illustrate how map comparison measures could contribute to the comparison of these systems. Next, a number of measures for map-to-map comparison, inspired from the literature in land remote sensing, are presented, along with methodologies for their implementation in comparison of maps described with different legends. The benefit of these measures and methodologies is demonstrated through their application to maps obtained from the acoustic datasets presented previously. Finally, a more typical implementation of these measures is presented as a case study in which the development of two up-to-date classification methodologies of MBES backscatter data is complemented by the quantitative comparison of their output maps. In the process of developing and illustrating the use of methods for the assessment of map-to-map similarity, this thesis also presents methodologies for the processing and classification of backscatter data from MBES. In particular, the potential of the combined use of the spatial and angular information of these data for seabed classification is explored through the development of an original segmentation methodology that sequentially divides and aggregates segments defined from a MBES backscatter mosaic on the basis of their angular response content

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

EM 2000 Microbathymetric and HYDROSWEEP DS-2 Bathymetric Surveying – a Comparison of Seafloor Topography at Porcupine Bank, west of Ireland

One of the latest discoveries in the world oceans are carbonate structures in the North-East Atlantic. In the frameworks of several European projects, the research vessel POLARSTERN and underwater robot VICTOR 6000 were engaged to explore these areas. The data described in this thesis were collected during the expedition ARK XIX/3 between 16 - 19th June 2003. Bathymetric and microbathymetric data in parts of the Pelagia Province, located on the northern Porcupine Bank, west of Ireland, were measured with two multibeam sonar systems deployed at different distances from the bottom. The four compared models come from a KONGSBERG SIMRAD EM 2000 multibeam sonar system and an ATLAS ELEKTRONIK HYDROSWEEP DS-2 multibeam sonar system. After necessary corrections of the data, digital terrain models were created, subtracted and correlated using appropriate software. This thesis begins with a description of the historical background of bathymetry, followed by a description of the principles of navigation and underwater navigation, inertial navigation systems, and the calibration of these systems. Systematic errors will be pointed out. It examines the measurement principles of the echo sounders used on the ARK XIX/3a expedition and accompanying necessary procedures, such as CTD measurements. A discussion of how the data are processed from raw data to edited results, and the effects of the errors, follows. One chapter is dedicated to a comparison and interpretation of the data. Sidescan, mosaic and PARASOUND data from the Hedge and Scarp Mounds are introduced as complementary information

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

Coastline Accuracy Assessment Developed By Using Multi Data Source

Coastline Modeling Accuracy Assessment Developed By Using from Multi-Source Data. The coastal regions need to be developed because many big cities in Indonesia are located in these areas. However, it is crucial to determine the distance from the beach that is safe as the requirement for development along the coastal zone. The term of the beach is very closely affiliated with the coastline. The method of determining the coastline continues to be developed to fulfill the many needs related to the coastline. The coastline has a dynamic position. The land contour along the coast and the tide's state become several things that affect the coastline. Therefore, a dynamic model is required to define coastline positioning because both conditions are easy to change. The coastline determination from multi-source data modeling using DEM results is rarely done. In this study, coastline determination uses land height contours combined with sea depth contours and uses Mean Sea Level (MSL) value for vertical reference using the DEM model. The model's accuracy is tested by comparing the coastline delineation model and the Geospatial Information Agency coastline to test the DEM model generated before determining the coastline using this model as the reference. Based on this study, the compared shoreline models and delineation have gaps. This gap might be influenced by the data source, the model's resolution, and the data collection method

Seafloor mapping using multibeam sonar

Seafloor habitat and its marine community have greatly affected by anthropogenic pressures from various human activities. Efforts to conserve and manage the marine habitat are challenging due to the difficulty to get the details of the seafloor data. Attention has been focused towards the multibeam echo sounder system (MBES), a tool in mapping the seafloor habitats, due to its ability to produce a detailed seafloor map. The aim of this study is to utilize MBES output, namely the bathymetry, backscatter, and its derivatives in order to produce a seafloor habitat map using automated classification technique in Malaysian water. The objectives are: (i) to investigate the correlation between MBES backscatter image and signal-based method for seafloor sediment classification; (ii) to evaluate the importance of bathymetry and its derivatives in producing coral reef classification map; (iii) to perform automated technique in producing the coral reef classification map, and finally (iv) to assess the accuracy of the coral reef classification maps constructed from the techniques above. The study was conducted in two different locations: Sembilan Island, Perak and Tawau, Sabah. The results of the data reduction analysis using the Principal Component Analysis (PCA), Linear Pearson Correlation, and variable importance analysis showed four most significant derivative layers for the production of coral reef classification map were identified: (i) bathymetry, (ii) benthic position index (BPI), (iii) slope, and (iv) grey level co-occurrence matrices (GLCM) mean. The classification map constructed with the selected MBES derivatives using four different techniques (Support Vector Machine, Neural Network, QUEST decision trees, and CRUISE decision trees) had shown an encouraging results with two classifiers achieved the accuracy of more than 70% (Support Vector Machine with 73.61% and Neural Network with 70.14%). In sum, this classification seafloor habitat map has enhanced coral reef spatial distribution information, and this finding has an important contribution to the seafloor habitat mapping in Malaysia

ACOUSTIC METHODS FOR MAPPING AND CHARACTERIZING SUBMERGED AQUATIC VEGETATION USING A MULTIBEAM ECHOSOUNDER

Submerged aquatic vegetation (SAV) is an important component of many temperate global coastal ecosystems. SAV monitoring programs using optical remote sensing are limited by water clarity and attenuation with depth. Here underwater acoustics is used to analyze the water volume above the bottom to detect, map and characterize SAV. In particular, this dissertation developed and applied new methods for analyzing the full time series of acoustic intensity data (e.g., water column data) collected by a multibeam echosounder. This dissertation is composed of three separate but related studies. In the first study, novel methods for detecting and measuring the canopy height of eelgrass beds are developed and used to map eelgrass in a range of different environments throughout the Great Bay Estuary, New Hampshire, and Cape Cod Bay, Massachusetts. The results of this study validated these methods by showing agreement between boundaries of eelgrass beds in acoustic and aerial datasets more in shallow water than at the deeper edges, where the acoustics were able to detect eelgrass more easily and at lower densities. In the second study, the methods developed for measuring canopy height in the first study are used to delineate between kelp-dominated and non-kelp-dominated habitat at several shallow rocky subtidal sites on the Maine and New Hampshire coast. The kelp detection abilities of these methods are first tested and confirmed at a pilot site with detailed diver quadrat macroalgae data, and then these methods are used to successfully extrapolate kelp- and non-kelp-dominated percent coverages derived from video photomosaic data. The third study examines the variability of the acoustic signature and acoustically-derived canopy height under different tidal currents. Submerged aquatic canopies are known to bend to accommodate the drag they generate in response to hydrodynamic forcing, and, in turn, the canopy height measured by acoustics will not be a perfect representation of canopy height as defined by common seagrass monitoring protocols, which is usually measured as the length of the blade of seagrass. Additionally, the bending of the canopy affects how the blades of seagrass are distributed within the footprint of the sonar, changing the acoustic signature of the seagrass canopy. For this study, a multibeam echosounder, a current profiler and an HD video camera were deployed on a stationary frame in a single eelgrass bed over 2 tidal cycles. Acoustic canopy heights varied by as much as 30 cm over the experiment, and although acoustic canopy height was correlated to current magnitude, the relationship did not follow the predictive flexible vegetation reconfiguration model of Luhar and Nepf (2011). Results indicate that there are significant differences in the shape of the return from a deflected (i.e., bent-over) canopy and an upright canopy, and that these differences in shape have implications for the accuracy of bottom detection using the maximum amplitude of a beam time series. These three studies clearly show the potential for using multibeam water column backscatter data for mapping coastal submerged aquatic vegetation while also testing the natural variability in acoustic canopy height measurements in the field

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