toring strategies, and other research studies.

Mapping the Sea Floor

Modern oceanographic surveys use remotesensing techniques (sidescan sonar (fig. 1), multibeam echosounding (fig. 2), and high-resolution

seismic-reflection profiling), direct sampling, and

visual observations to characterize the sea floor.

The surveys provide a new, highly detailed view

of the sea floor. In contrast to earlier maps that

were based on widely spaced data, the new digital images are similar in detail to an aerial photograph and show the changes in seabed features

over a wide range of scales. The locations and

effects of human activities, such as waste disposal

and bottom trawling, are often clearly observed.

Sedimentary features, such as bed forms, provide

information about the transport and fate of sediments and pollutants and about the importance of

the underlying geologic structures and the geologic history in controlling the present distribution of surface sediments.

Mapping the Area Offshore of New

York and New Jersey

Sidescan sonar and multibeam systems

emit pulses of sound that reflect off the sea

floor. Features of the sea floor are identified

by the pattern and varying levels of sound

reflected (backscattered) from the sea floor.

One of the most striking characteristics of the

backscatter maps of the New York Bight area

(fig. 3) is the variability in sediment characteristics over scales of tens to hundreds of

meters. Sampling, bottom photography, and

the high-resolution seismic observations show

that the bottom sedimentary environments in

this area range from outcropping rock to

muds. The maps show a complex pattern of

sediment properties that is a result of the

underlying geology, modern processes, and

anthropogenic activities.

The surveys off the New York-New Jersey

area are being carried out by the USGS in cooperation with the U.S. Army Corps of Engineers,

Texas A&M University, the State University of

New York at Stony Brook, the University of

New Brunswick, the Canadian Hydrographic

Service, Wesleyan University (Connecticut),

and Coastal Carolina University.

References Cited

Butman, Bradford, Danforth, W.W

W.C., and Bucholtz ten Brin

1998, Seafloor topographic 

backscatter maps of the Upp

Shelf valley and adjacent sh

of New York: U.S. Geologic

Open-File Report 98–616.

Schwab, W.C., Allison, M.A., Cor

L.L., Butman, B., Bucholtz te

M., Denny, J., Danforth, W.W

Foster, D.S., 1997, Initial resu

resolution sea-floor mapping 

the New York - New Jersey m

area using sidescan sonar: No

Geology and Environmental 

19, no. 4, p. 243–262.

For more information, please co

Bradford Butman

U.S. Geological Survey

Woods Hole Field Center

384 Woods Hole Road

Woods Hole, MA 02543–159

U.S. Department of the Interior

U.S. Geological Survey

USGS Fact Sh

Reprinted N

ing sound to either side of the ships path.

Typical survey swaths (yellow area) are a few

hundred meters wide. Lower: The intensity and

pattern of sound reflected from the ocean floor

provide information on the composition of sediments and the topography. Strong reflections

from boulders, gravel, and the walls of trawl

grooves appear as light tones on this data

record; weak reflections from finer sediments or

shadows behind vertical features are dark. A

composite image, pieced together from multiple

survey strips, provides an image of the sea

floor similar in detail to an aerial photograph. 

is fixed to the ship’s hull, the data ca

georeferenced and surveys can be 

speeds of 15 knots. The multibeam 

vide a new, highly detailed view of t

Used with the permission of the Un

New Brunswick.
20 Km

20m

40m

60m

NEW JERSEY

HUDSON SHELF VALLEY

NEW YORK

LONG ISLA

Fire Island

Areas of Erosion

Areas of Accretion

20

10

10 Km

Figure 3. The USGS has mapped the sea floor in the New York Bight apex and alongthe southern shore of Long Island by using sidescan sonar, and the Hudson Shelf valley and adjacent shelf by using multibeam. This combined backscatter image (red ishigh backscatter and blue is low backscatter) shows a complex pattern of sedimentproperties that is a result of the underlying geology, modern processes, and anthropogenic activity. The backscatter intensity is related to sediment texture, as well asother properties. In general, high backscatter indicates coarse-grained sediment or

Left: Along the southyears old) rocks outcr(bright high-backscattpatterns of coastal chlower sea level about subsequent sea-level the west. These sedimprocesses into a seriethe west of the outcrofrom these ridges maIsland and may influeFrom W.C. Schwab a

Below: Steristics oby drapindepth at at the lefmaterial posal; a with coarHudson Swest; and struction