Innovation and development are constant in our work. State-of-the-art equipment and technologies are evaluated and incorporated into our operations, complimenting our internal research and development. To conduct our research, we implement sidescan-sonar, seismic-reflection, and bathymetric systems that use acoustic (sound) energy to remotely sense the sea floor and shallow subsurface in order to define the surficial geology and geologic framework in a given setting. The variety of settings in which we operate dictates that the systems output and receive acoustic energy in a variety of modes and frequencies, thus enabling us to map a defined region of interest at various resolutions and ranges. This use of acoustic energy in ocean exploration has evolved predominantly within the past century. Coincident with the coming of the electronic age, the equipment types developed along unique pathways from basic, but ingenious systems to the elegant and sophisticated systems today. The incentives in these developments are broad, ranging from curiosity, to large-scale exploration of the oceans, as well as war-time needs, resource management, and conservation. To the right, please find a link to a brief history of the use of sound in the marine realm.
Additionally, to properly interpret the geophysical data, ground-truth information is essential, so direct sediment sampling and photography and video of the sea floor are other critical components of our operations. The resultant data must be accurately located to create high-precision mapping products, so state-of-the-art navigational systems are employed during survey operations. The evolution of each type of seismic, sonar, bathymetric, navigation, and ground-truth system is briefly outlined on their respective history pages.
|Two scientists recovering SEABed Observation and Sampling System (SEABOSS) from a deployment in the John Day Reservoir, Columbia River, WA. Image was taken during a USGS research cruise aboard the R/V Estero during 2000.|
A Brief History of the Sea-floor Mapping Group at the WHSC
In the 1970's, when the WHSC was at its inception, sidescan-sonar, seismic-reflection, and bathymetric data were collected and displayed in analog formats, with navigation provided predominantly by LORAN with occasional satellite fixes. There was virtually no photographic imaging of the sea floor and relatively sparse bottom sampling to ground-truth or validate the geophysical data. Early sidescan-sonar records were hand pieced together (mosaicked) and interpretations of both seismic and sidescan-sonar data were performed on paper analog records using colored pencils to represent various horizons and unique surficial acoustic regimes, followed by hand digitizing features that were, in turn, hand drawn on a basemap.
|Composite GLORIA image for Gulf of Mexico. Please see http://coastalmap.marine.usgs.gov/gloria for additional information.|
The mid 1980's ushered in many technological advances in marine geophysical systems, particularly with respect to digital data collection and storage. At that time the USGS, in collaboration with colleagues from the Institute of Ocean Sciences (IOS) in Great Britain, conducted GLORIA (Geologic Long-Range Inclined Asdic) low-resolution reconnaissance mapping of the U.S. Exclusive Economic Zone (EEZ), an area ranging from the U.S. coast to the edge of the continental shelf, out to 200 nautical miles offshore. GLORIA is a digital sidescan sonar system used to map the sea floor, and some of the first digital sidescan sonar mosaics were created from the data set using the USGS Mini Image Processing System (MIPS). The digital GLORIA mosaics cover the area from the continental slope out to the EEZ offshore limits and provide a broad scale view of the sea floor and its surficial characteristics, yielding insight as to active sedimentary processes within the deep-water segment of the EEZ.
Seismic-reflection surveys at that time were limited to use of high-resolution single-channel sparker, boomer, and small airgun systems, later broadening to use of air- and water-gun sources. However, data from those systems were still collected in analog format.
|Fathometer mounted on a sidemount and deployed off Houseboat-200 in Las Vegas Bay, Lake Mead, AZ and NV. The USGS research cruise took place in 2001.|
The late 1980's and 1990's showed tremendous growth as a result of technological advances in high-resolution geophysical systems and computing capabilities. During this period, the USGS Coastal and Marine Geology Program reoriented its priorities from deep-water investigations to shallower water continental shelf studies. Large-scale, reconnaissance GLORIA-type mapping was replaced by more detailed regional geophysical surveys of smaller inner-shelf regions, particularly offshore of urban centers. This period also marked the beginnings of digital data acquisition, which led to improvements in at-sea processing capabilities by enabling near real-time processing of sonar, seismic-reflection, and bathymetric data. In the early 1990's, the WHSC was unique among institutes conducting non-proprietary sea floor mapping in utilizing a Local-Area Network (LAN) to streamline data acquisition, processing, preliminary interpretation and data archival. During this time navigation also improved as Global Position System (GPS) was brought on-line, allowing positioning accuracy to increase by almost an order of magnitude. In the late 1990's, Geographic Information systems (GIS) were incorporated into at-sea operations, enabling integration of a wide-range of geophysical and ancillary data and production of preliminary mapping products in the field.
Although the WHSC began to utilize multibeam swath mapping systems in our research in 1994, it was not until 1999, that the WHSC acquired and integrated an interferometric-sonar system into sea floor mapping operations. This system collects acoustic backscatter (for definition of the terminology, please click on the bathymetry-equipment-swath location) and derives swath bathymetry from the acoustic backscatter. This greatly enhanced our ability to define seabed morphology and geologic framework of a given study area.
Throughout this evolution of geophysical systems, ground-truth capabilities have evolved as well, providing extensive and elaborate sediment sampling and photographic/video documentation. Currently, the WHSC operates an in-house designed SEABedpo Observation and Sampling System (SEABOSS) and a Remotely Operated Vehicle (ROV). Additionally, an Unmanned Surface Vessel (USV) will be integrated into sea floor mapping operations, primarily for work in very shallow water regions (less than 5 m). The USV will be equipped with high-resolution sidescan sonar and seismic-reflection systems and will expand our shallow-water capability.
The WHSC also operates a salt-water resistivity system that detects variations in the conductivity of subsurface water and porous lithologies using a towed electrode cable. The processed resistivity values are combined with seismic-reflection and drill-hole data to develop a three-dimensional conception of the fresh-salt relationships in submarine groundwater (Manheim, Krantz, and Bratton, 2004)
Manheim, F.T., Krantz, D.E., and Bratton, J.F., 2004, Studying ground water under Delmarva coastal bays using electrical resistivity: Ground Water, Special Issue, v. 42, no. 7, p. 1052-1068,