[1] Seafloor bathymetric data acquired with modern swath echo sounders provide coverage for only a small fraction of the global seabed yet are of high value for studies of the dynamic processes of seafloor volcanism, tectonics, mass wasting, and sediment transport that create and shape the undersea landscape. A new method for compilation of global seafloor bathymetry that preserves the native resolution of swath sonars is presented. The Global Multi-Resolution Topography synthesis consists of a hierarchy of tiles with digital elevations and shaded relief imagery spanning nine magnification doublings from pole to pole (http://www.marine-geo.org/portals/gmrt). The compilation is updated and accessible as surveys are contributed, edited, and added to the tiles. Access to the bathymetry tiles is via Web services and with WMS-enabled client applications such as GeoMapApp®, Virtual Ocean, NASA World Wind®, and Google Earth®.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/2008GC002332

Global Multi-Resolution Topography synthesis

Correlation of sidescan backscatter with grain size distribution of surficial seabed sediments

Comparative evaluation of airborne LiDAR and ship-based multibeam SoNAR bathymetry and intensity for mapping coral reef ecosystems

https://ccom.unh.edu/sites/default/files/publications/Goff_2004_MG_Seabed_characterization_New_Jersey_middle_outer_shelf.pdf

Seabed characterization on the New Jersey middle and outer shelf: correlatability and spatial variability of seafloor sediment properties

Marine spatial planning and conservation need underpinning with sufficiently detailed and accurate seabed substrate and habitat maps. Although multibeam echosounders enable us to map the seabed with high resolution and spatial accuracy, there is still a lack of fit-for-purpose seabed maps. This is due to the high costs involved in carrying out systematic seabed mapping programmes and the fact that the development of validated, repeatable, quantitative and objective methods of swath acoustic data interpretation is still in its infancy. We compared a wide spectrum of approaches including manual interpretation, geostatistics, object-based image analysis and machine-learning to gain further insights into the accuracy and comparability of acoustic data interpretation approaches based on multibeam echosounder data (bathymetry, backscatter and derivatives) and seabed samples with the aim to derive seabed substrate maps. Sample data were split into a training and validation data set to allow us to carry out an accuracy assessment. Overall thematic classification accuracy ranged from 67% to 76% and Cohen׳s kappa varied between 0.34 and 0.52. However, these differences were not statistically significant at the 5% level. Misclassifications were mainly associated with uncommon classes, which were rarely sampled. Map outputs were between 68% and 87% identical. To improve classification accuracy in seabed mapping, we suggest that more studies on the effects of factors affecting the classification performance as well as comparative studies testing the performance of different approaches need to be carried out with a view to developing guidelines for selecting an appropriate method for a given dataset. In the meantime, classification accuracy might be improved by combining different techniques to hybrid approaches and multi-method ensembles.

/pdf/mapping-seabed-sediments-comparison-of-manual-geostatistical-2y6kuoueid.pdf

Mapping seabed sediments: Comparison of manual, geostatistical, object-based image analysis and machine learning approaches

The dependence of acoustic backscatter variations on sediment grain-size distribution is examined using a combined analysis of 95 kHz side-scan data and approx. 300 grab samples from the New Jersey margin. We show that, under well-controlled circumstances, an unprecedented degree of correlation can be obtained between backscatter intensity and mean grain size. However, backscatter is disproportionately affected by larger grain sizes. Addition of just a few extra weight percentage of the larger grain sizes (>4 mm), which in our study is typically represented by more abundant shell hash among the older sediments at greater water depths, can completely degrade this correlation.

Correlation of side-scan backscatter intensity with grain-size distribution of shelf sediments, New Jersey margin

High-resolution swath sonar investigation of sand ridge, dune and ribbon morphology in the offshore environment of the New Jersey margin

Tracking the last sea-level cycle: Seafloor morphology and shallow stratigraphy of the latest Quaternary New Jersey middle continental shelf

Swath sonar bathymetry reveals sinuous furrows, 400 m wide, kilometers long, and 4 m deep inscribed in semilithified clays on the southern Hudson apron. We interpret these as keel marks created by floating icebergs detached from the retreating Laurentide ice sheet since ca. 25 ka. Keel-mark orientations suggest two phases of iceberg rafting. These phases could correlate with Heinrich meltwater events H2 and H1 ca. 25 and 17 ka, bracketing the late Wisconsinan glacial maximum ca. 22 ka. During Holocene transgression, some keel marks were reworked and reformed into oblique ridges where older, sandier sediments crop out at the seafloor. Relict glacial features on the New Jersey outer shelf provide a tie between the timing of Laurentide glacial retreat and the evolution of shallow stratigraphy on this mid-latitude shelf during the last global sea-level cycle (ca. 120 ka to present).

Catherine Schuur Duncan

Papers

Correlation of side-scan backscatter intensity with grain-size distribution of shelf sediments, New Jersey margin

High-resolution swath sonar investigation of sand ridge, dune and ribbon morphology in the offshore environment of the New Jersey margin

Tracking the last sea-level cycle: Seafloor morphology and shallow stratigraphy of the latest Quaternary New Jersey middle continental shelf

Relict iceberg keel marks on the New Jersey outer shelf, southern Hudson apron