GM6.8

EDI
Advances in seabed mapping and classification

Detailed maps of the seabed, portraying the spatial distribution of geomorphic features, substrates, and habitats, are used for a wide range of environmental, scientific, and economic maritime applications. These maps are the scientific basis for informed ocean and coastal management at local to regional scales, and thereby provide cornerstones to national and international nature-conservation policies. Fundamental to seabed mapping are acoustic remote-sensing technologies, which include singlebeam and multibeam echosounders, along with sidescan, interferometric, and synthetic-aperture sonars. These are deployed on various platforms including crewed and uncrewed surface and underwater vessels. In relatively shallow and transparent waters, optical methods such as aircraft and satellite-based remote sensing and LiDAR are employed with increasing success. Innovative processing and classification software, image analysis, machine and deep-learning applications are advancing developments in seabed-recognition techniques, the application of which is increasing the resolution and confidence in the maps produced. We welcome submissions that provide insights into new developments, methods, and results in the field of seabed mapping and classification. This session also aims to showcase a range of applications for these datasets.

Co-organized by ESSI1/OS4
Convener: Markus Diesing | Co-conveners: Maria Judge, Benjamin MisiukECSECS, Rachel Nanson
vPICO presentations
| Thu, 29 Apr, 09:00–10:30 (CEST)

Session assets

Session materials

vPICO presentations: Thu, 29 Apr

Chairpersons: Markus Diesing, Maria Judge, Benjamin Misiuk
09:00–09:05
09:05–09:10
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EGU21-7751
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solicited
Dayton Dove, Rachel Nanson, Lilja Bjarnadóttir, Janine Guinan, Joana Gafeira, Alix Post, Margaret F.J. Dolan, Heather Stewart, and Riccardo Arosio

In 2016, through a collaboration between marine mapping programmes in Norway, Ireland, and the UK, we published a new classification scheme to aid the characterisation of seabed geomorphology (Dove et al., 2016). The classification scheme was developed to address shared objectives and challenges in seabed mapping, particularly to enable more consistent classification where required. The novel aspect of this framework was the effort to independently describe seabed features according to their observed physical 1-Morphology, and the more subjective interpretation of their origin and evolution (2-Geomorphology). Initial application of the approach within our own groups and externally proved promising, and through the welcome involvement of colleagues from Geoscience Australia, we continued to progress and improve the approach.

We are now within the second phase of the project, which involves the development of glossaries for both parts of the classification scheme. The glossary for part-1 Morphology was recently completed and published (Dove et al., 2020). This glossary includes a revised list of feature names, with definitions and representative diagrams for each feature. Feature definitions are in-part drawn from the International Hydrographic Organization (IHO) guide for undersea feature names, which were modified and augmented with additional terms to ensure the final feature catalogue and glossary encompasses the diversity of morphologies observed at the seabed.

Part-2 Geomorphology glossary is now in development. We anticipate it to be more complicated than the Morphology glossary due to the (often) variable meaning of different terms between different fields and individual scientists. But as for Part 1, our primary objective is to produce a useful and robust framework (applicable from the coastal zone to the abyss), that minimises duplication and/or ambiguity as much as possible. The Geomorphology glossary will include example bathymetry images to add further value.

Dove, D., Bradwell, T., Carter, G., Cotterill, C., Gafeira Goncalves, J., Green, S., Krabbendam, M., Mellett, C., Stevenson, A., Stewart, H. and Westhead, K., Scott, G., Guinan, J., Judge, M., Monteys, X., Elvenes, S., Maeten, N., Dolan, M., Thorsnes, T., Bjarnadottir, L., Ottesen, D., 2016. Seabed geomorphology: a two-part classification system. British Geological Survey, Open Report OR/16/001.

Dove, D., Nanson, R., Bjarnadóttir, L.R., Guinan, J., Gafeira, J., Post, A., Dolan, M.F.J., Stewart, H., Arosio, R. and Scott, G., 2020. A two-part seabed geomorphology classification scheme:(v. 2). Part 1: morphology features glossary.

How to cite: Dove, D., Nanson, R., Bjarnadóttir, L., Guinan, J., Gafeira, J., Post, A., Dolan, M. F. J., Stewart, H., and Arosio, R.: Development of a Seabed Geomorphology classification approach; aspiring towards a robust tool to support comprehensive and consistent seabed mapping , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7751, https://doi.org/10.5194/egusphere-egu21-7751, 2021.

09:10–09:12
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EGU21-1414
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ECS
Vincent Lecours

It is increasingly recognized that environmental variables must be considered at multiple spatial scales to produce maps of the seabed that better capture and represent geomorphic features and marine habitats. In this paper, the ability of new multiscale geomorphometric variables to classify different types of seabed habitats is tested. A digital terrain model of an area of coastal Florida with different types of intertidal habitats was used in the geospatial data analysis platform Whitebox Tools to generate multiscale measures of roughness, maximum deviation from mean elevation, maximum anisotropy in elevation deviation, maximum difference from mean elevation, and maximum spherical standard deviation. Results show that oyster reefs, muddy areas, and areas with aquatic vegetation have different multiscale terrain signatures, highlighting the potential of multiscale terrain attributes to inform seabed classification.

How to cite: Lecours, V.: Developing multiscale terrain signatures for seabed classification, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1414, https://doi.org/10.5194/egusphere-egu21-1414, 2021.

09:12–09:14
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EGU21-11157
Ron Abileah

The Golfe d’Arguin (NW Mauritania) is a 15,000 km2 shelf, 150 km in N-S, and 150 km offshore.  The Golfe is subdivided into inner and outer shelves.  The shallow (<10m) inner shelf, also known as Banc d’Arguin, is part of a UNESCO World Heritage Site and renowned for a richly diverse marine ecosystem.   A steep escarpment separates the deeper (20-200 m) outer shelf.    The bottom morphology of both zones is a complex system of shoals, canyons, and channels. 

              The water is too turbid for traditional optical remote sensing bathymetry.  The alternative is bathymetry derived from ocean wave celerity as waves shoal over the shelf.

              The celerity method has been practiced for several decades, but only with small sensor footprints (typically 10-100 km2).    The Sentinel 2 satellites (now two, with plans to expand to four) have a 290 km push-broom image swath, capturing 2100 km2 per second.  The entire Earth is imaged every 4-5 days.  The imagery is free, very accessible, and easy to process.   The Sentinel 2 image archive is five years and growing daily.  Mapping large regions such as the Golfe d’Arguin is made possible.

              This presentation describes the Sentinel 2 bathymetry workflow.   The Golfe d’Arguin is an excellent case study.  Long swell waves from mid-Atlantic storms are frequent.  Long waves are best for sensing the bottom depth.  (Conversely, the method does not work in locations such as the Persian Gulf shielded from oceanic wave systems.)

              For the test case, the horizontal resolution is 200m, covers depths 0 to 35 m, and accuracy is 5% of depth.   Comparisons are made with the General Bathymetric Chart of the Oceans (GEBCO), EMODnet DTM, and various literature sources.    GEBCO compares very poorly.  EMODnet is better but with much lower spatial resolution and does not capture the morphological detail seen in Sentinel 2 derived bathymetry.

              There is very limited ground truth bathymetry, e.g., Multibeam, in this area for rigorous validation.   Other validation methods are presented.  One is Sentinel 2 bathymetry of the Perth Australia area,  with wave conditions similar to Mauritania, and a LiDAR survey for ground truth.   Another is repeatability with images from different dates.

              Below links preview Golfe d’Arguin bathymetry with Sentinel 2 and EMODnet for comparison.  GoogleEarth can be used to view.

                                       http://jOmegak.com/vEGU/28QBH.Sentinel2.kmz
                                       http://jOmegak.com/vEGU/28QBH.EMOD.kmz

How to cite: Abileah, R.: The utility of Sentinel 2 for bathymetry in turbid waters:  a case study in the Gulf d’Arguin, Mauritania, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11157, https://doi.org/10.5194/egusphere-egu21-11157, 2021.

09:14–09:16
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EGU21-11160
Alessio Sanfilippo, Sergey Skolotnev, and Alexander Peyve and the A.N. Strakhov Expedition S50 Science Party

The Charlie Gibbs offsetting by ~340 km the Mid Atlantic Ridge (MAR) axis between 52°-53° N is one of the main transform systems of the North Atlantic. Located between long mid-ocean ridge segments influenced to the south by the Azores and to the north by the Iceland mantle plume, this transform system has been active since the early phases of North Atlantic rifting. Object of several surveys in the ‘70 and ‘80, Charlie Gibbs received great attention for its unique structure characterized by two long-lived right-lateral transform faults linked by a short ~40 km-long intra-transform spreading centre (ITR) with parallel fracture zone valleys extending continuously towards the continental margins. In October 2020 expedition S50 of the R/V A.N. Strakhov surveyed an area of 54552 km2 covering the entire Charlie Gibbs transform system and the adjacent MAR spreading segments. We collected new bathymetric, magnetic and high-resolution single channel seismic data, along with basaltic, gabbroic and mantle rocks from 21 dredges. In this contribution we present preliminary data from cruise S50 and discusses the large-scale architecture of this unique, long-lived transform system.

How to cite: Sanfilippo, A., Skolotnev, S., and Peyve, A. and the A.N. Strakhov Expedition S50 Science Party: Geology of the Charlie Gibbs transform system (52-53ºN, Mid Atlantic Ridge): preliminary results from Akademik Nikolaj Strakhov Expedition S50, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11160, https://doi.org/10.5194/egusphere-egu21-11160, 2021.

09:16–09:18
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EGU21-16227
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Highlight
Roberta Ivaldi, Maurizio Demarte, Massimiliano Nannini, Giuseppe Aquino, Cosimo Brancati, Massimo Ercolani, Agnese Fares, Matteo Guideri, Luca Labella, Mauro Marro, Federica Maurantonio, Roberto Nardini, and Alberto Niccolini

New hydro-oceanographic data were collected in the Arctic Ocean during HIGN NORTH20 marine geophysical campaign performed in July 2020, in a COVID-19 pandemic period. HIGH NORTH20 was developed as part of the IT-Navy HIGH NORTH program, a Pluriannual Joint Research Program in the Arctic devoted to contribute to oceans knowledge in order to ensure ocean science improving conditions for sustainable development of the Ocean in the aim of United Nations Decade of Ocean Science for Sustainable development and the GEBCO - SEABED 2030 project. In order to contribute in exploration and high-resolution seabed mapping new data was collected using a multibeam echosounder (EM 302 - 30 kHz). The particular sea ice environmental condition with open-sea allowed to survey and mapping the Molloy Hole, the deepest sector of the Arctic Ocean, a key area in the global geodynamics and oceanographic context. A 3D model of the Molloy Hole (804 km2) and the detection of the deepest seafloor (5567m - 79° 08.9’ N 002° 47.0’ E) was obtained with a 10x10m grid in compliance to the IHO standards.

How to cite: Ivaldi, R., Demarte, M., Nannini, M., Aquino, G., Brancati, C., Ercolani, M., Fares, A., Guideri, M., Labella, L., Marro, M., Maurantonio, F., Nardini, R., and Niccolini, A.: High resolution mapping of the Arctic Ocean deepest area: Molloy Hole, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16227, https://doi.org/10.5194/egusphere-egu21-16227, 2021.

09:18–09:20
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EGU21-7521
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ECS
Mapping gravel beds combining multibeam data, underwater video, and grab samples with continuous spatial modeling by random forest
(withdrawn)
Giacomo Montereale Gavazzi, Vera Van Lancker, and Steven Degraer
09:20–09:22
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EGU21-8254
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ECS
Signe Schilling Hansen, Verner Brandbyge Ernstsen, Mikkel Skovgaard Andersen, Zyad Al-Hamdani, Ramona Baran, Manfred Niederwieser, Frank Steinbacher, and Aart Kroon

Stones on the seabed in coastal marine environments form an important hard substrate for macroalgae, and hence for coastal marine reefs. Such reef areas constitute important ecosystem services, e.g. storage of organic carbon in macroalgae or “blue carbon” as well as important habitats to fish for living, hiding and feeding. Information and knowledge about stone locations and geometry in coastal marine environments are often obtained as part of seabed habitat mapping. Usually, seabed habitat mapping is based on geophysical surveys using multibeam echo sounding along with side-scan sonar imaging in combination with biological ground-truthing. However, coastal areas are challenging to map with full spatial coverage due to the shallow water conditions. Furthermore, the research vessels often have too large drafts to sail in very shallow water close to the coastline. An alternative is to use airborne LiDAR technology. Topo-bathymetric LiDAR (green wavelength of 532 nm) has made it possible to derive high-resolution data of the bathymetry in coastal zones (e.g. Andersen et al., 2017). This technology can cover the transition zone between land and water, and the time consumption for data acquisition is small compared to vessel borne methods. However, the processing of the data still requires manual decision steps, which makes it rather time consuming, and to some extent subjective.

The aim of this study was to investigate the possibility of developing an automated method to classify stones from topo-bathymetric LiDAR data in coastal marine environments with shallow water (<6 m). The Rødsand lagoon in Denmark, where topo-bathymetric LiDAR data were acquired in 2015, was used as test. The classification was done using the random forest machine learning algorithm. The study resulted in the development of a nearly automated method to classify stones from topo-bathymetric LiDAR data. The classification accuracy was between 80 and 90% for the test site. The obtained knowledge about stone locations can provide important information about the ecosystem services and improved management of the coastal marine environment.

 

Acknowledgement:

This work is part of the project "ECOMAP - Baltic Sea environmental assessments by opto-acoustic remote sensing, mapping, and monitoring", supported by BONUS (Art 185), funded jointly by the EU and the Innovation Fund Denmark.

 

References

Andersen MS, Gergely A, Al-Hamdani Z, Steinbacher F, Larsen LR, Ernstsen VB (2017). Processing and performance of topobathymetric lidar data for geomorphometric and morphological classification in a high-energy tidal environment. Hydrology and Earth System Sciences, 21: 43-63, DOI: 10.5194/hess-21-43-2017.

How to cite: Hansen, S. S., Ernstsen, V. B., Andersen, M. S., Al-Hamdani, Z., Baran, R., Niederwieser, M., Steinbacher, F., and Kroon, A.: Classification of stones in coastal marine environments using random forest machine learning on topo-bathymetric LiDAR data, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8254, https://doi.org/10.5194/egusphere-egu21-8254, 2021.

09:22–09:24
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EGU21-10605
Peter Feldens, Agata Feldens, Anne Herbst, Alexander Darr, and Svenja Papenmeier

The identification of marine cobbles and boulders (stones) based on acoustic remote sensing is important for the detection, delineation and for an ecological assessment of important seafloor habitats. Due to the large areas involved and the required high-resolution data, a manual interpretation is not feasible. In recent years, automated methods for stone detection were developed. However, these developments were only applied in comparatively small proof of concept areas, and a common barrier to practical implementation by authorities is the required upscaling. This case study aims to apply automated methods for boulder detection based on convolutional neural networks to larger areas, by identifying and validating boulder densities over several hundred km2 in the western Baltic Sea in acoustic backscatter data and derived datasets. The use of distributed training sites of less than 0.5 km2  in size is proposed to improve the model capacity to adapt to variations of boulder appearance in remote sensing data related to local geological variation and survey conditions. Distributed validation sites of similar size are suggested to provide quality control during reprocessing with adapted models. Current limitations for the automated identification of individual boulders in backscatter data are demonstrated, which can be caused by survey geometry, data quality or obstacles and seafloor with similar acoustic characteristics.

How to cite: Feldens, P., Feldens, A., Herbst, A., Darr, A., and Papenmeier, S.: Large-Scale Mapping of Boulder Distribution in Acoustic Backscatter Data of the Baltic Sea by Neural Networks , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10605, https://doi.org/10.5194/egusphere-egu21-10605, 2021.

09:24–09:26
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EGU21-15899
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ECS
Mikkel Skovgaard Andersen, Lars Øbro Hansen, Zyad Al-Hamdani, Signe Schilling Hansen, Manfred Niederwieser, Ramona Baran, Frank Steinbacher, and Verner Brandbyge Ernstsen

Bubbling reefs are submarine structures formed by aggregating carbonate resulting from leaking gases. The reef formations can form pillars rising several meters above the sea floor. They support a high diversity of benthic communities, and in the EU Habitat Directive they are specifically mentioned as a natural habitat type that require conservation.

Knowledge about the presence, locations and shape of bubbling reefs are usually obtained by geophysical surveying using multibeam echosounder (MBES), sidescan sonar and/or seismic acquisition systems, combined with ground truth verification. However, this traditional survey method is time consuming, especially for full coverage surveys in shallow water. Full coverage surveys are a requirement to capture the bubbling reefs due to their relatively small spatial extent. Besides, traditional geophysical vessel borne surveys have their limitations in shallow water due to low spatial coverage and vessel draft.

In recent years, airborne topobathymetric (green wavelength) lidar has emerged as a new possible surveying method in shallow water (e.g. Andersen et al., 2017). Compared to vessel borne MBES, full coverage lidar surveys can be conducted within hours instead of days/weeks, while also including full coverage in the shallow water and a seamless transition between land and water. Thus, topobathymetric lidar may be a good choice for carrying out full coverage surveys in large shallow water areas. However, the accuracy and the resolution of the collected dataset are important in these surveys, not least when mapping small scale features such as bubbling reefs.

In this study, we investigated the potential of mapping bubbling reefs in shallow water (<10 m) using topobathymetric lidar. The main objective was to assess the performance of airborne topobathymetric lidar to detect and resolve small scale objects, i.e. bubbling reefs, by comparison to MBES data. Both MBES and lidar data were acquired in spring 2019 in a designated Natura 2000 area close to Hirsholmene in the northern Kattegat region in Denmark. The comparison of the two datasets included a quantification of the accuracy, and an assessment of the performance for mapping bubbling reefs.

 

Reference:

Andersen M.S., Gergely A., Al-Hamdani Z., Steinbacher F., Larsen L.R., Ernstsen V.B. (2017). Processing and performance of topobathymetric lidar data for geomorphometric and morphological classification in a high-energy tidal environment. Hydrology and Earth System Sciences, 21: 43-63, DOI: 10.5194/hess-21-43-2017.

How to cite: Andersen, M. S., Hansen, L. Ø., Al-Hamdani, Z., Hansen, S. S., Niederwieser, M., Baran, R., Steinbacher, F., and Ernstsen, V. B.: Mapping shallow water bubbling reefs – a method comparison between topobathymetric lidar and multibeam echosounder, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15899, https://doi.org/10.5194/egusphere-egu21-15899, 2021.

09:26–09:28
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EGU21-102
Riccardo Arosio, Peter Mitchell, Jon Hawes, Stefan Bolam, Lisa Benson, and John Sperry

This study, conducted under the auspices of the Commonwealth Marine Economies Programme (CMEP), involved the characterisation of geomorphology and benthic assemblage groups around the previously unmapped western St. Lucian coastline. A high-resolution (2 x 2 m) seabed map was then produced, specifically focussing on the economically important regions.

Two hundred twelve video tow transects were acquired by CEFAS and associated to Multibeam echosounder (MBES) data collected by the United Kingdom Hydrographic Office (UKHO). Through object-based image analysis, MBES data and derivatives were categorized into eight basic morphological classes (e.g. slope, flat), with manual intervention required to further discriminate more complex forms (e.g. anthropogenic scours). Percentage coverage of epibenthic biota and substrate type data were extracted from still seabed images using the CATAMI[1] morphological classification system and a randomised point count approach. Benthic community assemblages were then defined based on K-means clustering. A random forest model was used to predict benthic community groups. Predictive layers included MBES-derived physical properties, geomorphological classes and wave exposure (using GREMO[2]). The resulting model had a predictive accuracy of 80%.

St. Lucia is characterised by gently sloping exposed plateaus (~30 m deep), extending for several km offshore in the north and south of the island. These appear to be mostly covered by an algal-dominated gravelly substratum. Bioturbated mud and sand with pockmarks occur typically in sheltered bays, near river mouths or within paleochannels that incise the seabed. Seagrass patches were more difficult to predict (50% producer’s accuracy) but are generally limited to very shallow coastal waters habitats. Finally, coral and sponge-dominated reef communities appear to generally be associated with raised “staircase” platforms and bommie features close to the coast, however, these were also observed further from shore and in deeper waters.

The seabed habitat maps produced will support the St. Lucian government to manage their shallow seabed resources. In particular, the maps will assist the systematic characterisation of the coral reef habitats and, therefore, improve delineations of marine reserves, especially around the town of Soufrière and the Pitons UNESCO world heritage site.

 

[1]           Althaus, F., N. and many others. 2015. A standardised vocabulary for identifying benthic biota and substrata from underwater imagery: The CATAMI classification scheme. PLoS ONE 10:1–18.

[2]           Pepper, A. and Puotinen, M. L., 2009. GREMO: A GIS-based generic model for estimating relative wave exposure. The 18th World IMACS Congress and MODSIM09 Int. Congress on Modelling and Simulation (pp. 1964-1970). Cairns, Australia.

How to cite: Arosio, R., Mitchell, P., Hawes, J., Bolam, S., Benson, L., and Sperry, J.: Small Island Developing States (SIDS) and the sea: creating high resolution habitat maps to support effective marine management in St. Lucia, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-102, https://doi.org/10.5194/egusphere-egu21-102, 2020.

09:28–09:30
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EGU21-11688
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ECS
Daphnie Galvez, Svenja Papenmeier, Alexander Bartholomä, and Karen Helen Wiltshire

Recent studies on seafloor mapping have presented different modelling methods to map and classify marine sediment distribution. However, are these methods classify different sediment classes the same way? And how do we choose the right model for a certain set of sediment classes? In this study, we aim to address these issues by using ensemble modelling to map the distribution of different sediment class on a dynamic, shallow continental shelf. Our data were derived from side-scan mosaics and multibeam data repeatedly collected from 2016 to 2018 in the Sylt Outer Reef (German Bight). We used a probabilistic approach for each class separately and then compared the predicted probability for each class, to see which class is more likely to be assigned to the location. Each sediment class was predicted using a combination of different classification modelling techniques, and then the result of these models was ensembled to produced one final prediction. This approach avoids selecting one single method, limits model selection bias and can provide information on the trends and variation across models.  Furthermore, we also looked on the temporal changes in sediment distributions by comparing the sediment class predictions from 2016 to 2018.

Our analysis suggest that combining different modelling techniques  (i.e. random forest, boosting regression trees etc.) provide higher predictive accuracy than using one single modelling method. The resulting sediment distribution maps are more objective and are produced faster than manual delineated maps often considered by stakeholders. We also identify some limitations in having small sample size and we proposed that by combining certain models and choosing the proper amount of pseudo-absence or background data can address this issue.

How to cite: Galvez, D., Papenmeier, S., Bartholomä, A., and Wiltshire, K. H.: Seafloor sediment classification of the Sylt Outer Reef, German Bight from 2016 -2018 using ensemble modelling , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11688, https://doi.org/10.5194/egusphere-egu21-11688, 2021.

09:30–09:32
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EGU21-10854
Francesco Mascioli and Tina Kunde

Seafloor mapping is the subject of several worldwide research programs dealing with the growing awareness that changes of the marine environmental conditions have to be accurately monitored. The monitoring requirements strongly stimulate the scientific interest in innovative mapping methods and tools, which should be exploitable within the extensive mapping programs carried out by governmental agencies and institutes.

The Coastal Research Station within the NLWKN is carrying out a long-term program to map subtidal areas of the Lower Saxony coastal and marine waters, adopting a methodological approach aimed to increase objectivity and repeatability of results.

The study area is one of the world’s largest tidal system encompassing a multitude of transitional zones between land, marine, and estuarine environments. The geological and geomorphological setting is closely related to the Late Quaternary evolution of the North Sea and the actual morphodynamic processes. The seabed is made of Holocene sand to silt deposits and peat layers. They overlay Pleistocene fluvioglacial deposits, made of sands, rocks, and boulders, which locally outcrop in small areas of the North Sea and in the deepest sectors of the Wadden Sea tidal inlets.

Even though existing maps provide a good broad-scaled representation of the sediments distribution, they were produced by the interpolation of grab-samples therefore lacking of spatial resolution and bedforms characterization. The ongoing mapping program provides full-coverage detailed sedimentological and geomorphological data, by means of swath-bathymetrical systems, subbottom profiler, and validation samples. The methodological approach integrates bathymetric, backscatter, and stratigraphic information to characterize bedforms and substrates. Bathymetry and seabed images are interpreted using geomorphometric as well as object-based image analysis, to increase the objectivity and generate reproducible results.

Maps outline common sedimentological and geomorphological features across all the observed Wadden Sea tidal inlets, which are made of fine sandy sediments and narrow outcrops of peat layers on the main tidal channels slopes. Both erosive and depositional geomorphological processes are present, represented by several orders of scarps, mainly connected to alternations of hard-substrates and unconsolidated sands, and medium to very large sand waves. Moreover, data reveal high-resolution information about hard-substrate outcrops in the North Sea area.

The mapping program provides new detailed geological-geomorphological features of a very dynamic coastal area, using repeatable and objective methods. The combination of different datasets and tools allows the quantitative analysis of the complex subtidal morphology, the correlation of bedforms and substrates. Resulting products will be further developed for habitat mapping purposes and morphological and hydro-dynamical modelling.

How to cite: Mascioli, F. and Kunde, T.: Sediments and bedform mapping of the Lower Saxony Wadden Sea and North Sea (Germany), EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10854, https://doi.org/10.5194/egusphere-egu21-10854, 2021.

09:32–09:34
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EGU21-6695
Laura Brothers, Seth Ackerman, David Foster, Brian Andrews, John Warner, Emily Himmelstoss, William Danforth, and Emily Huntley

Coastal erosion, intense storm events and sea-level rise pose threats to coastal communities and infrastructure. Managers and scientists often lack the high-resolution data needed to improve estimates of sediment abundance and movement, shoreline change, substrate heterogeneity and other seabed characteristics that influence coastal vulnerability. To address these and other needs the U.S. Geological Survey is conducting a multi-tiered research initiative consisting of shoreline change characterization, sediment transport numerical modeling and seafloor mapping in Cape Cod Bay, Massachusetts, USA. Here we present the seafloor mapping findings and their applications to an integrated coastal change analysis. Our comprehensive seafloor mapping technique includes the collection of multibeam and phase-discriminating data, seismic-reflection profile data, sediment samples, seabed imagery, as well as the synthesis of regional legacy datasets. A first-order comparison of the interdisciplinary results indicates that the presence of seafloor bedforms and the thickness of Late Holocene sediments correspond to patterns of modeled seabed elevation change and observed relative coastline stability. Analyses of these data are ongoing and may further resolve the relationships among shoreline change, nearshore processes and antecedent geology.

How to cite: Brothers, L., Ackerman, S., Foster, D., Andrews, B., Warner, J., Himmelstoss, E., Danforth, W., and Huntley, E.: Integrating Seafloor Mapping Data with Sediment Transport and Coastal Change Studies:  Preliminary Results from the Southern Gulf of Maine, USA, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6695, https://doi.org/10.5194/egusphere-egu21-6695, 2021.

09:34–09:36
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EGU21-6257
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ECS
Asaf Giladi, Mor Kanari, Timor katz, and Gideon Tibor

In 2017, the Israel Oceanographic and Limnological Research (IOLR) started an annual seafloor monitoring program. The aim of the program is to evaluate the rate of erosion/deposition and the influence of man-made infrastructures on the seabed along the Israeli continental shelf south of Akko. The survey program onboard R/V Bat-Galim includes a multibeam (Kongsberg EM2040), sub-bottom (Knudsen 3260 Chirp) mapping and box-core sediment sampling along 13 transects across the shelf, from WD 10-100 m. The multibeam was operated at 400-kHz yielding a horizontal resolution of 0.25-1.0 m (depending on water depth), and vertical uncertainty of several centimeters. Using the QPS FMGT software, both angular response curves (ARA) and 0.5 m horizontal resolution of Backscatter data (BS) were derived. The multibeam acoustic return intensities (BS) were locally calibrated at selected reference areas using in-situ sediment sampling. 
The main source of sediments along the Israeli continental shelf is the Nile Delta which undergoes erosion since 1960 when the Aswan dam was constructed. Along the Israeli inner-shelf, these sediments are transported northward and westward by wind-derived currents and storms. The analysis of the bathymetric surfaces from the consecutive years 2017-2020 shows that the shelf is stable in terms of sediment processes except along the marine infrastructures and natural seafloor features (e.g. rocky bottom outcrops) where patterns of sediment accumulation and erosion are observed. The variability along the marine infrastructures is mostly seen in the shallow water (less than 30 m) where yearly changes of up to +/-0.4 m of sediment accumulation/erosion in the vertical axis were measured.
The locally calibrated multibeam BS enabled grain size mode evaluation ranging from very fine gravel (-1 phi) to clay (9 phi). Additional in-situ sampling validated the reliability of the grain size classification method for the Israeli, continental shelf. Accordingly, we show that the Israeli continental shelf south of Haifa Bay is characterized by a sandy seafloor strip at WD 0-35 m and a muddy strip that extends west up to WD 100 m (in agreement with previous studies). Gravelly areas are identified at the coast-parallel Kurkar outcrops (Calcareous sandstone rocky ridges or rock patches) in water depths of 10-15m and 35-40m and in some places even at WD of 90 m. This demonstrates that grain size classification by locally calibrated multibeam BS is likely to be a very useful and fast method for monitoring changes in seafloor characteristics over large areas over time.

 

How to cite: Giladi, A., Kanari, M., katz, T., and Tibor, G.: Monitoring sediment transport and grain size dynamics along the Israeli continental shelf with multibeam bathymetry and backscatter data , EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6257, https://doi.org/10.5194/egusphere-egu21-6257, 2021.

09:36–09:38
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EGU21-15523
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ECS
Danai Lampridou, Kemron Beache, Aileen Bohan, Mohamed Elsaied, Travis Hamilton, Andy Hoggarth, Jaya Roperez, Karolina Zwolak, Ana Carolina Lavagnino, Tinah Martin, Victoria Obura, Seeboruth Sattiabaruth, Neil Tinmouth, and Rochelle Wigley

SEA-KIT USV Maxlimer successfully carried out a 22 day (24hrs per day), uncrewed survey operation offshore the United Kingdom in July-August 2020. The uncrewed vessel was controlled and manoeuvred from an operation room based in Essex, UK, while the data acquisition was performed by alumni of the Nippon Foundation/GEBCO Training Program, through the Map the Gaps NPO, spread across 10 countries. One of the main objectives of the trans-ocean survey was to test the remote survey capabilities through satellite communications, and also promote the contribution to seafloor mapping. CARIS Onboard, incorporating the new Sonar Noise Classifier tool via the CARIS Mira AI platform, was deployed to autonomously process the survey data in real-time, and provide products that could be streamed daily from SEA-KIT to ensure operations were successful and to help train the classifier as required. The data was post-processed with CARIS HIPS and SIPS using conventional and Ai techniques, and gridded at 10 m. The collected data size was 52.2 GB, surveyed area depth range from 57m to 1362 with 470m mean depth and around 900 km2 was totally covered.  CARIS Mira AI with traditional QC approach reduced data processing time to 77% regarding the conventional path.

The high-resolution bathymetric dataset provided the first detailed picture of the Brenot Spur, adjacent to Dangeart Canyon. Three major submarine canyon systems can be identified, cross-cutting the continental shelf nearly perpendicularly. The main axis of the first canyon, located at the far northern part of the surveyed area, is oriented NE-SW and becomes wider downstream. Both of the flanks are highly carved by gullies and tributaries, especially along the northern flank, where a complex system is developed depicting well-developed amphitheatric heads, indicating retrogressive erosion. Moreover, this network shows a high degree of incision and narrow interfluves. The second major canyon trends ENE-WSW and is a multi-fed system consisting of three sub-canyons that coalesce at 1095 m water depth. Although tributaries bisect the flanks of this system, they are not mature and have not yet breached the continental shelf, but are mostly confined on the slope. The final canyon is narrower than the previous ones and its  thalweg is nearly N-S oriented. Additionally, the flanks of the later differ substantially when it comes to their morphology. The western flank is undulated by linear wall gullies and several landslides indicated by the crescent like rim of high slope values, while the eastern flank is smooth and featureless. Along the SW continental slope, evidence for several old landslide events can be identified. The major failure scars are located right at the edge of the shelf at 560 m water depth.

How to cite: Lampridou, D., Beache, K., Bohan, A., Elsaied, M., Hamilton, T., Hoggarth, A., Roperez, J., Zwolak, K., Lavagnino, A. C., Martin, T., Obura, V., Sattiabaruth, S., Tinmouth, N., and Wigley, R.: Uncrewed bathymetric survey in UK waters: Testing CARIS Mira AI and globally-distributed Nippon Foundation/ GEBCO training program Alumni to produce data products, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15523, https://doi.org/10.5194/egusphere-egu21-15523, 2021.

09:38–09:40
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EGU21-3939
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ECS
Caroline Gini, Katleen Robert, John Jamieson, and Jeremy Dillon

With less than 20% of the seafloor mapped at a sufficiently high resolution for geological and biological studies (<50m), there is a need for new technological approaches to map and characterize the seafloor environment at higher resolutions. Here, we present preliminary results of an investigation into the use of interferometric synthetic aperture sonar (InSAS) as a new approach to help fill this gap. InSAS can provide very high-resolution acoustic imagery (3cm/pixel) and bathymetry (25 cm/pixel) as well as large coverage area (up to 150m across track per side while flying at a 15m altitude, at 6 knots). Compared to traditional sidescan sonars, high-resolution imagery in both along and across track directions is achieved by the synthetic aperture of the sonar array, which uses a large number of receiver arrays and a cm-size spacing between individual elements. This technique has so far mostly been used for military and industrial purposes.

Onboard the Atlantic Kingfisher in October 2020, we used Kraken Robotic Systems’ InSAS system on a Katfish towed vehicle to survey 85 km2 of the Tail of the Grand Banks, the southernmost extremity of the continental shelf offshore Newfoundland, Canada. During a survey, the sonar is set at a center frequency of 337 kHz and survey planning included data coverage overlap for 140% coverage of the seafloor. Kraken Robotic’s processing algorithm and the towing optic cable allowed for real-time processing of the data and initial post processing using Caris Onboard.

We show one of the first applications of InSAS for geological studies. This system is excellent for identifying fine-scale geological features as well as variations of seabed texture and composition at a large scale on flat seafloor. We identified distinct seafloor sedimentary textures on the imagery, such as relatively homogeneously spaced alternations of high and low backscatter (BS) strength corresponding to well-defined ripple marks, as well as multiple 1-10m wide circular depressions of high BS strength surrounding individual rocks and a lower BS strength on the seafloor surrounding depressions. With high coverage, speed and resolution, InSAS represents an effective tool for environmental, biological and geohazard monitoring.

How to cite: Gini, C., Robert, K., Jamieson, J., and Dillon, J.: Interferometric Synthetic Aperture Sonar as a tool for seafloor geological mapping on the Grand Banks offshore Atlantic Canada: preliminary results., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3939, https://doi.org/10.5194/egusphere-egu21-3939, 2021.

09:40–09:42
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EGU21-10389
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ECS
Peter Porskamp, Alexandre Schimel, Mary Young, Alex Rattray, Yoann Ladroit, and Daniel Ierodiaconou

Kelp forests worldwide are under ever increasing pressure from anthropogenic impacts including kelp harvesting, pollution, and higher sea surface temperatures due to climate change. Marine spatial planning requires accurate mapping of these habitat types to inform effective policy. Key data needed for benthic habitat maps to inform policy are acquired by multibeam echosounders, which collect high resolution bathymetry and backscatter of the seafloor. An additional and previously little used product of high resolution MBES are mid-water backscatter data, termed water-column data, that have been used to identify and map kelp species that extended above the seafloor. We show that incorporating water-column data as a variable for modeling benthic marine habitat distributions can significantly improve the accuracy of benthic habitat maps, specifically where habitat categories include large species of macroalgae on shallow (2-34m) subtidal reefs. The study site has full coverage multibeam bathymetry, backscatter and water-column data, alongside comprehensive observation surveys of benthic habitats using towed video. All towed video observations were classified using a hierarchal marine biotope classification scheme. Water-column data were processed into a mosaic-like product representing the acoustic energy in a layer 0-1m above the seabed. This processing included filtering of the sidelobe artefact. The volumetric water-column mosaic along with bathymetric and backscatter derivatives combined with towed video observations were used as input variables in a supervised random forest classification algorithm to create habitat maps for the study site. Variable importance was assessed for all variables and water-column performed well as it was retained in all models. Including water-column data increased overall map accuracy up to 1.18% and improved producer class accuracies that contained macroalgae up to 2.95%. With increasing pressure on temperate macroalgal communities due to a synergy of pressures arising from warming oceans, our work provides a timely advance for mapping and monitoring changes.

How to cite: Porskamp, P., Schimel, A., Young, M., Rattray, A., Ladroit, Y., and Ierodiaconou, D.: Integrating multibeam echosounder water-column data into benthic habitat mapping, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-10389, https://doi.org/10.5194/egusphere-egu21-10389, 2021.

09:42–10:30