This data release presents eelgrass distributions and bathymetry data derived from acoustic surveys of Bellingham Bay, Washington. Survey operations were conducted between February 16 and February 21, 2019 (USGS Field Activity Number 2019-606-FA) by a team of scientists from the U.S. Geological Survey Pacific Coastal and Marine Science Center and Washington State Department of Ecology. Eelgrass and bathymetry data were collected from the R/V George Davidson equipped with a single-beam sonar system and global navigation satellite system (GNSS) receiver. The sonar system consisted of a Biosonics DT-X single-beam echosounder and 420 kHz transducer with a 6-degree beam angle. Depths from the echosounder were computed using sound velocity data measured using a YSI CastAway CTD during the survey. Positioning of the vessel was determined at 5 Hz using a Trimble R9s GNSS receiver and Trimble Zephyr Model 2 antenna operating in real time kinematic (RTK) mode. Differential corrections were transmitted by a cellular modem to the GNSS receiver on the survey vessel at 1-Hz from a GNSS continuously operating reference station operated by the Washington State Reference Network (WSRN; http://www.wsrn3.org/
) located in the city of Bellingham (station BELI). Output from the GNSS and sonar systems were combined in real time by the Biosonics DT-X deck unit and output to a computer running HYPACK hydrographic survey software. Navigation information was displayed on a video monitor, allowing the vessel operator to navigate along predefined survey lines spaced at 25- to 100-m intervals alongshore at speeds of approximately 2 m/s. Acoustic backscatter data were analyzed using a custom graphical user interface (GUI) that implements a signal processing algorithm applied to each sonar sounding to extract the location of the bottom and presence of vegetation (Stevens and others, 2008 ). Individual acoustic returns along a survey line were grouped into packets of ten, and eelgrass percent cover was calculated as the fractional percent of acoustic returns that were classified as vegetated within each group, resulting in a estimate of percent cover every 4 to 5 m (depending on vessel speed). The positioning data from the bathymetric survey were postprocessed using Waypoint Grafnav to apply differential corrections with data recorded at the GNSS base station BELI and archived by the WSRN; these data superseded the original positions recorded in real time. The GUI was used to combine filtered sonar data with postprocessed positioning data and orthometric elevations relative to the NAVD88 vertical datum were computed using National Geodetic Survey Geoid12a offsets. The estimated vertical uncertainty of the bathymetric measurements ranged from 2.0 cm to 18.3 cm with a mean of 6.7 cm. Uncertainty in the vertical positions associated with pitch and roll of the survey vessel is unknown. The final point data are provided in a comma-separated text file and are projected in Cartesian coordinates using the Universal Transverse Mercator (UTM), Zone 10 north, meters coordinate system.
Data were obtained to quantify the extent of eelgrass distributions and bathymetry along the natural and urbanized shorelines of Bellingham Bay, WA. These data are fundamental to the USGS Coastal Habitat in Puget Sound Project (CHIPS) to advance models and understanding of the transport and fate of sediment and sediment-bound contaminants. The CHIPS team will use these data to examine the extent that persistent contaminants like PCBs and PAHs that move with fine sediment accumulate and potentially concentrate in important juvenile salmon and estuarine habitats like eelgrass due to the influence of vegetation on sediment trapping. These data are intended for science researchers, students, policy makers, and the public. These data can be used with geographic information systems or other software to identify the distributions of eelgrass and shallow-water bathymetric features.
Additional information about the field activities from which these data were derived are available online at:
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Theme_Keyword_Thesaurus: USGS Thesaurus
Theme_Keyword: bathymetry measurement
Theme_Keyword: aquatic vegetation
Theme_Keyword: GPS measurement
Theme_Keyword: sea-floor characteristics
Theme_Keyword: marine geophysics
Theme_Keyword: single-beam echo sounder
Theme_Keyword_Thesaurus: ISO 19115 Topic Category
Theme_Keyword_Thesaurus: Data Categories for Marine Planning
Theme_Keyword: Bathymetry and Elevation
Theme_Keyword_Thesaurus: Marine Realms Information Bank (MRIB) keywords
Theme_Keyword: Global Positioning System (GPS) observations
Theme_Keyword_Thesaurus: Global Change Master Directory (GCMD)
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Theme_Keyword_Thesaurus: USGS Metadata Identifier
Place_Keyword_Thesaurus: Geographic Names Information System (GNIS)
Place_Keyword: Salish Sea
Place_Keyword: Puget Sound
Place_Keyword: Whatcom County
Place_Keyword: Nooksack River
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