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The side-scan sonar mosaic map. Three different acoustic patterns were recognized along the study area: pattern with isolated reflections (b 1 ), pattern of weak backscatter (b 2 ), and pattern of strong backscatter (b 3 ).
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Bubble streams were detected from natural seep sites to the west of Jubal Island. They produced obvious signatures on acoustic images rising from the sea bottom to the water surface. The gas bubbles produced high backscatter, while the oily gas bubbles produced acoustic backscatter shadows. The oil coating the bubbles generated specific signatures,...
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Context 1
... guide for the acoustic backscatter of the ocean bottom. Three diverse acoustic backscatter patterns were perceived from the seafloor: pattern with disconnected or isolated reflections (b 1 ), pattern of powerless or weak backscatter (b 2 ), and pattern of strong solid backscatter (b 3 ). All of them were represented on the backscatter mosaic map (Fig. ...
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... first pattern ''isolated backscatter pattern"(b 1 ) corresponds to a wide extension along the border of the study area adjacent to the islands and it is characterized by a concentration of coral reef communities. As indicated by the ground truth study by utilizing ROV record images; this pattern is representing the hard coral reef (Fig. 4). It appears as a moderately raised zone from the surrounding ocean bottom that was illustrated from the wide expansion shadow in the sonar image (Hillman et al., ...
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... addition, the weakness backscatter pattern (b 2 ) shows up as uniform dim tones of fine sand to silt sediments as per the ROV Images and collected sediment samples (Fig. 4). This pattern (b 2 ) covers the central parts of the survey site. These very fine sediments were deposited due to the N-S trending sedimentation process prevailing in the area (Hamouda and El-Wahhab, 2009). In contrast, the solid strong backscatter design (b 3 ), which appears as lighter tones, covers diverse parts on the seabed of the ...
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... in the area (Hamouda and El-Wahhab, 2009). In contrast, the solid strong backscatter design (b 3 ), which appears as lighter tones, covers diverse parts on the seabed of the survey area as demonstrated in the mosaic map. The sediment samples and clear ROV images show that this pattern is related to fine to medium sand overlaying dead hard coral (Fig. 4). It is mainly located at a discrete location along the western and eastern part of the survey site. The seafloor of the survey site is mainly composed of friable sand with clusters of carbonate rocks. The influence of the seepage of hydrocarbons was detected and observed as small clusters along the hard and soft coral reefs, which were ...
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... northern and central parts related to the presence of the medium and coarse sand. This shows that the current velocity magnitude and its direction has shaped the seabed and controlled the distribution of the sediments along the study area (Hamouda and Abdel-Salam, 2010). Which clearly discern from the backscattered image of the side-scan sonar (Fig. ...
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Citations
... The side-scan sonar techniques comprise two sidewayslooking transducers that transmit out two across-track wide sound beams, so the backscatter intensity of the seafloor is recorded at fixed time intervals [4]. The SSS produces sideways profiles of the seafloor, which could provide the sediment distribution, surface bedforms, large features, and sediment transport directions maps [5][6][7]. ...
The Alamein New City is one of the newly established capital cities in Egypt. The study of the offshore extension is important to define the morpho-sedimentary seafloor features and evaluate the structure of the seafloor, sand resources, and the quantities of sediments that are responsible for beach renourishment. To achieve the purpose of the study, the marine acoustic geophysical techniques (MBES, SSS, and SBP) with video-camera attached in the ROV as a ground truth tool, were used. That has proven to be extremely powerful techniques in coastal applications.
The integration of the marine geophysical data obtained from the bathymetric, shallow seismic surveys, and the validity of these data that was confirmed by SSS backscatter sonograph, in addition, the images obtained by using the ROV, divided the study area into three main zones. The southern zone (Z1) was rugged, which coincided with sandy mounds in the area, and has gradual backscatter strength from high to moderate with the direction of the prevailing current describing the rugosity of sand ripple. This zone has characterized by the thickest layer of sediment in the study area. Whereas the middle zone (Z2) showed the highest values of rugosity due to the slope where the ridge exists and has complex backscatter strength with finer thick of sediment. The northern zone (Z3) was characterized mostly by intermediate rugosity and gradual backscatter strength from high to moderate aligned with the direction of the current, describing the rugosity of sand ripple. The northern zone has the second thickest layer of sediment.
The gentle sloping of the seafloor with the existence of the mounds and the submerged ridge are allowing the waves to break and scatter their energy provide natural protection for the beaches of Alamein New City.
The marine acoustic techniques are powerful tools to investigate and identify the seabed objects by applying different processing and interpretation steps. Two types of marine acoustic imaging techniques used in this study; Side Scan Sonar (SSS) that mapping seabed features and identifies the objects on it, and Sub-Bottom Profiling (SBP) that providing information about sediment thicknesses and stratigraphic structure. The integration between these two marine acoustic techniques, as well as, ground truth data obtained from an underwater camera, was used to distinguish seabed objects; coastal boulder accumulations that are documented along the western Mediterranean coast of Egypt. The study and analysis of the collected data demonstrated that: the combination between side scan sonar, chirp sub-bottom profiling systems, and ROV images can successfully distinguish different types of objects. Generally, objects observed from SSS are indicated in the SBP as weak backscatter curves. The case study results, from analysis of SBP with ROV image to the object detected by SSS utilized three objects making a shadow in SSS seabed: boulder, hard substrate, and seagrass. The integration of these techniques resulting specifies the location of the geo-hazards area.
Marine geophysical methods are quite valuable in geoarchaeological investigations and remote seabed classifications due to their capability to cover vast areas in a short time and reveal fine details of the seafloor and subsurface features in unexcavated sites. The present study aimed to reconstruct the depositional history of the uppermost sediment sequence of the ancient Royal port of Alexandria during different historical periods, and point out the impact of the post-glacial eustatic sea-level rises and natural hazards that took place through the last 2000 years. To resolve this riddle, seismic and geomorphologic surveys were conducted by using a sub-bottom profiler and side scan sonar respectively in integration with previous sediment core data, to extrapolate the vertical extent of the strata and monitor the recent seafloor situation. The results of this study confirmed the subsidence of the ancient port mainly as a result of sea-level rises and the 365 AD tsunami. Seismic interpretations suggested a depositional scenario through successive stages from the Royal port’s construction until its abandonment, also the detailed analyses of backscatter images showed significant variations on the seafloor geomorphology that took place through the recent years which in turns give prominence to the impact of the short-term winds and storms as well.
