Increasing societal pressures on the U.S. continental shelves adjacent to dense population centers have brought to light the lack of accurate base maps in these areas. Existing bathymetric maps and random sidescan sonar surveys are either not accurate enough or do not provide the coverage necessary to make policy decisions. Until the mid 1990s, it was not financially prudent nor technically efficient to map the shallow shelves. However, the availability of high-resolution multibeam mapping systems now allow efficient and accurate mapping of the continental margins. In 1996 the U.S. Geological Survey began a large-scale seafloor mapping campaign on the continental shelf and slope adjacent to Los Angeles, CA. The first survey used a Kongsberg Simrad EM1000 (95 kHz). The survey continued in 1998 by mapping the slope and proximal basins from Newport to Long Beach, CA, using a Kongsberg Simrad EM300 (30 kHz). The area was completed in May 1999 by mapping the entire shelf adjacent to Long Beach, CA using an EM3000D (a dual-headed 300-kHz system). The mapping used both INS from the vehicle motion sensor and DGPS to provide position accuracies of ~1 m. All the data were processed in the field in near realtime using software developed at the Univ. of New Brunswick. Because of the different systems used and the range of water depths, the spatial resolution of the processed data varies from <0.5 m on the inner shelf to 8 m on the basin floors.
Perspective overviews of backscatter draped over bathymetry reveals a host of geological features unknown to exist in this area. These features include shallow, linear gullys, barchan dunes, small-scale bedforms in shallow troughs, major canyon system complexes, large- and smallscale mass movements, faults, and large areas of outcrop. The effects on sediment transport of man-made features, such as sewer outfall pipes and dredge-disposal fields, are clearly delineated on the new maps. The maps provide the fundamental base maps for studies as varied as those involving benthic habitats, marine disposal sites, sediment transport, and tectonic map
Journal or Conference Title
Shallow Water Survey Conference (SWS)
Oct 20 - Oct 23, 1999
Gardner, James; Clarke, J.E. Hughes; Mayer, Larry A.; Kleiner, Art; and Paton, Mark, "Mapping a Continental Shelf and Slope in the 1990s: A Tale of Three Multibeams" (1999). Shallow Water Survey Conference (SWS). 829.