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Figure 3. The National Oceanic and Atmospheric Administration Ship Thomas Jefferson.

Figure 4. The National Oceanic and Atmospheric Administration launch 3101.

Figure 5. RESON SeaBat 8101 used to collect bathymetric data on National Oceanic and Atmospheric Administration launch 3102 during survey H11446.

Figure 6. RESON SeaBat 8125 used to collect bathymetric data on National Oceanic and Atmospheric Administration launch 3101 during survey H11446.

Figure 7. Klein 5000 hull-mounted to National Oceanic and Atmospheric Administration launch 3102 to collect sidescan-sonar data during survey H11446.

Figure 8. The U.S. Geological Survey R/V Rafael used to collect bottom photography and sediment samples on cruise 2010-010.

Figure 9. The small SEABed Observation and Sampling System (SEABOSS), a modified Van Veen grab sampler equipped with still and video photographic systems, mounted on the aft starboard side of the R/V Rafael.

Figure 10. Chart showing the relationship between phi sizes, millimeter diameters, size classifications (Wentworth, 1922), and American Society for Testing and Materials and Tyler sieve sizes.

Figure 11. Sediment-classification scheme from Shepard (1954), as modified by Schlee (1973).

Bathymetric and Sidescan-Sonar Data

Survey launches deployed from the NOAA Ship Thomas Jefferson collected multibeam bathymetry and sidescan-sonar data during hydrographic survey H11446 from September 22 to October 21, 2008 (figs. 3 and 4). Launch 3101 collected bathymetric data and Launch 3102 collected sidescan-sonar and bathymetric data. Positioning on the two 8.5-m aluminum launches was determined by differential global positioning system (DGPS) navigation systems with corrections from U.S. Coast Guard beacons at Moriches, NY, and Acushnet, MA. Vertical datum is mean lower low water level. Detailed information on the bathymetric and sidescan-sonar data acquisition and equipment used is located in the H11446 Descriptive Report (National Oceanic and Atmospheric Administration, 2008).

Bathymetric data were acquired with RESON SeaBat 8101 and 8125 multibeam echosounders (operating at frequencies of 240 kilohertz (kHz) and 455 kHz, respectively) that were hull-mounted on the two launches (figs. 5 and 6). The data were acquired in extended Triton data format (XTF) and recorded digitally through an ISIS data acquisition system. The data were processed by using CARIS Hydrographic Image Processing System (HIPS) software to perform a quality assessment and to incorporate sound velocity and tidal corrections. Sound velocity corrections were derived from frequent SEACAT conductivity-temperature-depth (CTD) profiles. Typically, a CTD cast was conducted every 3 to 4 hours during multibeam acquisition. Tidal zone corrections were calculated from data acquired at the New London and New Haven Harbor, CT, tidal gages. The vertical resolution of the multibeam data is approximately 0.5 percent of the water depth. The data were gridded to 2-m resolution and saved as a CARIS HIPS database. An Environmental Systems Research Institute (ESRI) grid was created by using Interactive Visualization Systems (IVS) Fledermaus and ArcGIS software. A vertically exaggerated (x5), hill-shaded image (illuminated from 0° N. at an angle of 45°) was created by using IVS Fledermaus software.

The sidescan-sonar data were acquired with a Klein 5000 sidescan-sonar system, hull-mounted to launch 3102 (fig. 7). The system was set to sweep 100 m to either side of the launch tracks. The system has a vertical beam angle of 40° and transmits at 455 kHz. The data were acquired in XTF, recorded digitally through a Triton ISIS data acquisition system, and processed using CARIS Sidescan Image Processing System (SIPS) software to perform a quality assessment, and to produce a composite sidescan-sonar image with 1-m horizontal resolution. As part of this process, the sidescan-sonar data were demultiplexed and filtered to remove speckle noise and to correct for slant-range distortions. Image "shine through" (to account for areas of overlap) and auto-contrast adjustment were applied. The final mosaic was projected from Universal Transverse Mercator (UTM) Zone 18 to a World Geodetic System 1984 (WGS84) geographic coordinate system to produce the final enhanced images in both local and geographic coordinates. Backscatter tones were inverted from the original image, such that lighter tones indicate higher acoustic reflectivity and darker tones indicate lower acoustic reflectivity.

Sediment Samples and Bottom Photography

During USGS cruise 2010-010 on the research vessel (R/V) Rafael (fig. 8) in April 2010, sediment samples and bottom photographs were collected from 26 stations in the study area. The small SEABed Observation and Sampling System (SEABOSS; fig. 9), a modified Van Veen grab sampler with still and video cameras attached, collected samples and photographic data. Still and video photography was used to help characterize the sea-floor environments, observe floral and faunal communities, and view environments where samples could not be collected because of the presence of either boulders or rough seas. A gallery of sea-floor images collected during the cruise is in the Bottom Photography section of this report, and location information for each photograph is in the Data Catalog section.

Sediment samples were collected from the uppermost 2 cm of the sea floor at 14 stations in the study area in order to classify the sediment size, whereas field observations were used to classify the sediment at the other 12 stations because of the presence of coarse sediment or rough sea conditions that prevented sample collection. Grain-size analysis of the sediment samples was performed by using sieves and a Coulter counter. Samples were wet-sieved to separate the coarse (diameters greater than or equal to 0.0625 mm) and fine (diameters less than 0.0625 mm) fractions. The fine fraction was analyzed with a Coulter counter; the coarse fraction was analyzed by dry-sieving. Sediment descriptions are based on Wentworth's (1922) nomenclature (fig. 10) and Shepard's (1954) size classifications (fig. 11). For detailed information on grain-size analysis procedures see Poppe and others (2005). Grain-size analysis data are presented in the Sediments and Data Catalog sections of this report.

Interpretations presented in this report are based on bathymetric, sidescan-sonar, sediment, and photographic data. Morphology and height are used to characterize bedforms. Sand waves are higher than 1 m; megaripples are 0.2 to 1 m high; ripples are less than 0.2 m high (Ashley, 1990). Bathymetric data are not to be used for navigation.

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