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Open-File Report 2014–1018

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### Sea-Floor Geology in Northwestern Block Island Sound, Rhode Island 

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## Methods

| Title PageList of FiguresConversion FactorsAbstractIntroductionSetting**Methods**BathymetrySidescan SonarSedimentsBottom PhotographyGIS Data CatalogSummaryAcknowledgmentsReferencesContactsIndexClick on figures for larger images**Figure 3.**Photograph of the National Oceanic and Atmospheric  Administration ship *Thomas Jefferson*,  which collected bathymetric data in the study area. **Figure 4.**Photograph of National Oceanic and Atmospheric  Administration survey launch *3102*,  one of two launches used in the study area to collect bathymetric and  sidescan-sonar data.**Figure 5.**Photograph of the RESON SeaBat 7125 multibeam  echosounder transducer used to collect bathymetric data in the study area. **Figure 6.**Photograph of the Klein 5000 sidescan-sonar system  hull-mounted on a survey launch.**Figure 7.**Photograph of the U.S. Geological Survey research  vessel *Rafael* used to collect  bottom photography and sediment samples in the study area. **Figure 8.**Photograph of the small Seabed Observation and  Sampling System, a modified Van Veen grab sampler with attached video  and still cameras. **Figure 9.**Chart showing the relations among phi sizes,  millimeter diameters, size classifications, and American  Society for Testing and Materials and Tyler sieve sizes.**Figure 10.**Sediment-classification scheme from Shepard, as  modified by Schlee and Poppe and others.
MBES and sidescan-sonar data were collected aboard the  NOAA ship *Thomas Jefferson* (fig. 3) and  aboard two of its survey launches, *3101* and *3102* (fig. 4). RESON SeaBat 7125  MBES (fig. 5), with a frequency of 400 kilohertz (kHz), were used to collect  MBES data on the *Thomas Jefferson* and  both survey launches. Sidescan-sonar data were collected using Klein 5000  systems (fig. 6), with a frequency of 455 kHz, on the survey launches. Sounding  data are referenced to mean lower low water level and were corrected for tides  using National Water Level Observation Network stations in Newport, R.I., New  London, Connecticut, and Montauk, New York. Horizontal positioning was determined  using differential global positioning system (DGPS) equipment with corrections  from U.S. Coast Guard DGPS stations in Moriches, N.Y., and Acushnet,  Massachusetts. Neither MBES nor sidescan-sonar data cover the entire study  area; some locations have large gaps between lines and others have no data  collection. 

 MBES data were acquired using Hypack 2009 software and  converted to CARIS data format by NOAA.  A swath bathymetry adjusted for statistical  error (BASE) surface was created in CARIS by USGS, which was interpolated to  fill in small gaps (less than 10 meters (m) wide) in the data. Esri grids and  GeoTIFFS were exported from CARIS. Sidescan-sonar data were acquired using  Klein SonarPro software, and processed using CARIS SIPS to apply slant-range and  beam-pattern corrections, and create a mosaic with 1-m resolution.  More detailed information on the data  acquisition and processing for this survey is provided in National Oceanic and  Atmospheric Administration (2011a, b) and in the metadata files located in the Geographic  Information System Data Catalog section of this report.

 Sediment samples and bottom photography were collected  aboard the research vessel (RV) *Rafael* (fig. 7) during USGS cruise 2012-002-FA in June 2012. Sediment samples were  obtained using a small Seabed Observation and Sampling System (SEABOSS)—a Van  Veen grab with still and video cameras attached (fig. 8). Sediment samples were  taken from the top 2 centimeters (cm) of the sea floor and were analyzed for  grain size at the USGS Woods Hole Coastal and Marine Science Center’s Sediment  Lab following the procedures outlined in Poppe and others (2005). Coarse  fractions (diameters equal to or greater than 0.0625 millimeters (mm)) of the  samples were analyzed with sieves, whereas the fine fractions (diameters less  than 0.0625 mm) were analyzed with a Coulter Counter. Gravel-sized shells were  removed from the samples because they are not considered to be representative  of the sedimentary environment since they often form in situ and, hydraulically,  they do not behave in the same manner as similarly sized sediment. Sediment  descriptions are based on the modified nomenclature of Wentworth (1922; fig. 9)  and modified size classifications of Shepard (1954; fig. 10). 

 At each station, the SEABOSS drifted over the sea floor  for several minutes while bottom video was recorded and 3 to 7 still  photographs were simultaneously taken along the transect at the discretion of  the operator. Photographs were taken with a Canon G12 digital camera from an  optimal height of about 60 cm above the sea floor, resulting in images showing  30-cm to 1-m widths of the sea floor. Images of the still photographs can be  viewed in the Bottom Photography section of this report, and full-resolution  images and photograph location data are available in the Geographic Information  System Data Catalog section of this report. 

Interpretations presented in this report are based on  bathymetric, sidescan-sonar, sediment, and photographic data. Bedforms are  characterized on the basis of morphology and height. 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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U.S. Department of the Interior |            U.S. Geological Survey                                                URL: http://pubs.usgs.gov/of/2014/1018/html/methods.html            Page Contact Information: GS Pubs Web Contact                        Page Last Modified: Friday, February 21, 2014, 12:27:41 PM |
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