High-resolution mapping of mines and ripples at the Martha's Vineyard Coastal Observatory
Mayer, Larry A.
Richardson, Michael D.
Traykovski, Peter A.
Trembanis, Arthur C.
MetadataShow full item record
KeywordHigh-resolution seafloor mapping; Hummocky bedforms; Mine burial and detection; Multibeam sonar; Rippled scour depressions; Sorted bedforms
High-resolution multibeam sonar and state-of-the- art data processing and visualization techniques have been used to quantify the evolution of seafloor morphology and the degree of burial of instrumented mines and mine-shapes as part of the U.S. Office of Naval Research (ONR, Arlington, VA) mine burial experiment at the Martha's Vineyard Coastal Observatory (MVCO, Edgartown, MA). Four surveys were conducted over two years at the experiment site with a 455-kHz, Reson 8125 dynamically focused multibeam sonar. The region is characterized by shore-perpendicular alternating zones of coarse-grained sand with 5?25-cm-high, wave orbital-scale ripples, and zones of finer grained sands with smaller (2?5-cm-high) anorbital ripples and, on occasion, medium scale 10?20-cm-high, chaotic or hummocky bedforms. The boundaries between the zones appear to respond over periods of days to months to the predominant wave direction and energy. Smoothing and small shifts of the boundaries to the northeast take place during fair-weather wave conditions while erosion (scalloping of the boundary) and shifts to the north-northwest occur during storm conditions. The multibeam sonar was also able to resolve changes in the orientation and height of fields of ripples that were directly related to the differences in the prevailing wave direction and energy. The alignment of the small scale bedforms with the prevailing wave conditions appears to occur rapidly (on the order of hours or days) when the wave conditions exceed the threshold of sediment motion (most of the time for the fine sands) and particularly during moderate storm conditions. During storm events, erosional ?windows? to the coarse layer below appear in the fine-grained sands. These ?window? features are oriented parallel to the prevailing wave direction and reveal orbital-scale ripples that are oriented perpendicular to the prevailing wave direction. The resolution of the multibeam sonar combined with 3-D visualization techniques provided realistic looking images of both both instrumented and noninstrumented mines and mine-like objects (including bomb, Manta, and Rockan shapes) that were dimensionally correct and enabled unambiguous identification of the mine type. In two of the surveys (October and December 2004), the mines in the fine-grained sands scoured into local pits but were still perfectly visible and identifiable with the multibeam sonar. In the April 2004 survey, the mines were not visible and apparently were completely buried. In the coarse-grained sand zone, the mines were extremely difficult to detect after initial scour burial as the mines bury until they present the same hydrodynamic roughness as the orbital-scale bedforms and thus blend into the ambient ripple field. Given the relatively large, 3-D, spatial coverage of the multibeam sonar along with its ability to measure the depth of the seafloor and the depth and dimensions of the mine, it is possible to measure directly, the burial by depth and burial by surface area of the mines. The 3-D nature of the multibeam sonar data also allows the direct determination of the volume of material removed from a scour pit.
Author Posting. © IEEE, 2007. This article is posted here by permission of IEEE for personal use, not for redistribution. The definitive version was published in IEEE Journal of Oceanic Engineering 32 (2007): 133-149, doi:10.1109/JOE.2007.890953.
Showing items related by title, author, creator and subject.
Hsu, Tian-Jian; Ozdemir, Celalettin E.; Traykovski, Peter A. (American Geophysical Union, 2009-05-14)Wave-supported gravity-driven mudflow has been identified as a major offshore fine sediment transport mechanism of terrestrial sediment into the coastal ocean. This transport process essentially occurs within the wave ...
High-resolution imaging of the Bear Valley section of the San Andreas fault at seismogenic depths with fault-zone head waves and relocated seismicity McGuire, Jeffrey J.; Ben-Zion, Yehuda (Blackwell Publishing, 2005-09-02)Detailed imaging of fault-zone (FZ) material properties at seismogenic depths is a difficult seismological problem owing to the short length scales of the structural features. Seismic energy trapped within a low-velocity ...
Signell, Richard P.; Chiggiato, Jacopo; Horstmann, Jochen; Doyle, James D.; Pullen, Julie; Askari, Farid (American Geophysical Union, 2010-04-24)The Adriatic Sea is regularly subjected to strong Bora wind events from the northeast during winter. The events have a strong effect on the oceanography in the Adriatic, driving basin-scale gyres that determine the transport ...