Series_Name: U.S. Geological Survey Geologic Investigations Map
Issue_Identification: I-2589
Publication_Information:
Publication_Place: Woods Hole, MA
Publisher: U.S. Geological Survey, Coastal and Marine Geology Program
Description:
Abstract:
Because of the enormous surrounding population of
Long Island Sound, large inputs of anthropogenic wastes
(e.g. fertilizer and sewage) and toxic chemicals have
produced stresses on the environment of the Sound,
causing degradation and potential loss of benthic
habitats. To examine this problem, we have completed a
surficial geologic map of the western Long Island Sound
sea floor off Norwalk, CT, in an effort to define benthic
habitats and how they are changing with time. This
study area is of special interest because it is affected
by seasonal hypoxia. It covers approximately 60 km/sq
and is located 3-15 km south of the Norwalk Islands in
approximately 16-48 m water depth.
Purpose:
This dataset presents the completed sidescan sonar
mosaic for the study area.
Supplemental_Information:
The sidescan-sonar mosaic reveals six distinctive sea
floor patterns, and when combined with the seismic
data can be used to make some inferences about the
surficial geology. The six patterns include (1) high
acoustic backscatter (light tones), (2) low backscatter
(dark tones), (3) high-backscatter targets interpreted to
be boulders, (4) depressions with high-backscatter floors,
(5) east-west trending high-backscatter stripes with
no apparent relief associated with them, and (6) linear
and curvelinear narrow depressions interpreted to be
trawl marks. Boat wakes and fish are two water column
phenomenon that were observed as well.
Time_Period_of_Content:
Time_Period_Information:
Range_of_Dates/Times:
Beginning_Date: 19931113
Ending_Date: 19931116
Currentness_Reference: Publication Date
Status:
Progress: Complete
Maintenance_and_Update_Frequency: None planned
Spatial_Domain:
Bounding_Coordinates:
West_Bounding_Coordinate: -073.344444
East_Bounding_Coordinate: -073.265272
North_Bounding_Coordinate: +41.068056
South_Bounding_Coordinate: +40.983336
Keywords:
Theme:
Theme_Keyword_Thesaurus: General
Theme_Keyword: USGS
Theme_Keyword: U.S. Geological Survey
Theme_Keyword: Coastal and Marine Geology Program
Theme_Keyword: Long Island Sound Resource Center
Theme_Keyword: Connecticut Geological and Natural History Survey
Theme_Keyword: Connecticut Department of Environmental Protection
Theme_Keyword: University of New Haven
Theme_Keyword: sidescan sonar
Theme_Keyword: digital mosaic
Theme_Keyword: 100-kHz Klein sidescan sonar system
Theme_Keyword: estuary
Theme_Keyword: benthic habitat
Theme_Keyword: hypoxia
Theme_Keyword: sediment distribution
Theme_Keyword: benthic community
Theme_Keyword: surficial geology
Place:
Place_Keyword_Thesaurus: General
Place_Keyword: Long Island Sound
Place_Keyword: Connecticut
Place_Keyword: Norwalk
Place_Keyword: estuary
Place_Keyword: western Long Island Sound
Access_Constraints: None
Use_Constraints:
The U.S. Geological Survey must be referenced as
the originator of the dataset in any future products or
research derived from these data.
Although this derived data set and its lineage dataset
have been used by the USGS, no warranty, expressed or
implied, is made by the USGS as to the accuracy of the
data and/or related materials. The act of distribution shall
not constitute any such warranty, and no responsibility is
assumed by the USGS in the use of these data or related
materials.
The sidescan sonar data were collected using a 100-kHz
Klein sidescan sonar system set to a 100-m range to either
side of the ship's track. These data were logged digitally
on a QMIPS data logger, and were written to tape at 2048
pixels per scan.
Type_of_Source_Media: cartridge tape
Source_Time_Period_of_Content:
Time_Period_Information:
Range_of_Dates/Times:
Beginning_Date: 19931113
Ending_Date: 19931116
Source_Currentness_Reference: Publication Date
Source_Citation_Abbreviation: QMIPS
Source_Contribution:
These data were processed to apply radiometric and
geometric corrections. The processed swaths were
then mapped and digitally mosaicked to complete the
sidescan sonar mosaic for the study area.
Process_Step:
Process_Description:
QMIPS data were processed through a median
filtering routine to suppress speckle noise. Navigation
merged into the header record portion of the data were
plotted and checked. The QMIPS data were exported
for import to the WHIPS processing.
The individual sidescan swaths were processed to
apply a slant-to-ground range correction, shading
correction and striped noise removal. The geometrically
and radiometrically enhanced swaths were then
individually mapped to a user specified scale and
projection.
The individual mapped swaths were imported into
a PCI "pix" database file for digital mosaicking.
The mosaicking procedures included trimming off
unwanted data where two sonar images overlapped,
tone matching the adjacent sonar images if there
are differences, and combining the individual
strips together into a composite image.
Norwalk sidescan sonar mosaic: GEOTIFF image, world file and georeference information
Distribution_Liability:
Although this derived data set and its lineage dataset have
been used by the USGS, no warranty, expressed or
implied, is made by the USGS as to the accuracy of the
data and/or related materials. The act of distribution shall
not constitute any such warranty, and no responsibility is
assumed by the USGS in the use of these data or related
materials.
The sidescan sonar mosaic is available as a
GEOTIFF image with accompanying world file and
georeference report. To utilize this data, the user must
have an image viewer, image processing or GIS
software package capable of importing a GEOTIFF
image. If the georeferencing information cannot be
imported, the user may wish to obtain the georeference
information contained a separate file, georep.txt,
included in the zip file.
