The sun-illuminated topographic (shaded relief) image has a 4-m pixel size and was created by vertically exaggerating the topography two times and then artificially illuminating the relief by a light source positioned 45 degrees above the horizon from an azimuth of 0 degrees. In the resulting image, topographic features are enhanced by strong illumination on the northwestward-facing slopes and by shadows cast on southeastern slopes. The image also accentuates small features (relief of a few meters) that could not be effectively shown as contours alone at this scale. Unnatural-looking features or patterns oriented parallel or perpendicular to survey tracklines are artifacts of data collection and environmental conditions.
The data have a weak striping that runs parallel to the ship's track. Some of the striping is the result of poor data return at nadir that appears as evenly-spaced thin speckled lines. Some striping is also due to critical angle effects, where the intensity of return varies as a function of the angle of incidence of the incoming sound on the seafloor (Hughes-Clark and others, 1997).
U.S. Geological Survey, 2006, CAPENORTHSUN_GEO4M_WGS84.TIF: Image of the 4-m Sun-illuminated Topography of the Sea Floor off Eastern Cape Cod (Geographic): Open-File Report 2005-1048, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Science Center, Woods Hole, MA.This is part of the following larger work.Online Links:
- <http://pubs.usgs.gov/of/2005/1048/data/bathymetry/sun_illum/geo/capenorthsun_geo4m_wgs84.zip>
- <http://pubs.usgs.gov/of/2005/1048/data/bathymetry/sun_illum/geo/capenorthsun_geo4m_wgs84.tif>
- <http://pubs.usgs.gov/of/2005/1048/htmldocs/data_catalog.htm>
- <http://pubs.usgs.gov/of/2005/1048/data/bathymetry/sun_illum/geo/>
Poppe, L.J., Paskevich, V.F., Butman, B., Valentine, P.C., Danforth, W.W., Foster, D.S., and Blackwood, D.S., 2006, Geological Interpretation of Bathymetric and Backscatter Imagery of the Sea Floor off Eastern Cape Cod, Massachusetts: Open-File Report 2005-1048, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Science Center, Woods Hole, MA.Online Links:
This is a Raster data set. It contains the following raster data types:
Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitude and longitude values are specified in Decimal degrees.
The horizontal datum used is D_WGS_1984.
The ellipsoid used is WGS_1984.
The semi-major axis of the ellipsoid used is 6378137.000000.
The flattening of the ellipsoid used is 1/298.257224.
(508) 548-8700 x2314 (voice)
(508) 457-2310 (FAX)
lpoppe@usgs.gov
To release a digital map (GeoTIFF image) derived from mulitbeam observations that shows sea floor backscatter intensity (a measure of sea floor texture and roughness) at a spatial resolution of 4 m/pixel.
After the echo sounder data were logged onto the hard disk of the Sun workstation, a suite of processing software developed by the Ocean Mapping Group (www.omg.unb.ca/~jhc/SwathEd.html) was used to correct for artifacts and errors that may have been introduced during data collection. This software also enhanced the corrected data by resolving beam pattern and aspect ratio distortions and by imposing a linear contrast stretch before it generated bathymetric and sidescan sonar image mosaicks in a Mercator projection. All data processing described here is initiated using Silicon Graphics workstations as soon as each acquisition file is closed by the Simrad Mermaid workstation (usually at the end of each survey line). Additional processing was done in the lab to correct for fluctuations in sea level during the survey and for artifacts in the data files that were not corrected in the field (see below).
(2) The processing and editing steps on board the ship were:
(A.) Demultiplex, or unravel, the acquired Simrad data files using RT to generate separate files containing navigation, depth soundings, sidescan sonar backscatter values, and sound velocity information.
(B.) Automatically reject bad data (autoRejectSoundings). For the multibeam soundings, reject data outside expected depth ranges (operator's decision based on nautical chart data); for navigation data, reject fixes with poor GPS statistics.
(C.) Edit the navigation data on-screen using jview to remove undesirable points, including turns at the ends of survey lines.
(D.) Edit the multibeam soundings on-screen using swathed to remove individual anomalous soundings.
(E). Merge tidal information and the corrected navigation back (mergetide and mergenav) into the data files. Tidal information was obtained from predicted tides using the Xtide program <http://www.flaterco.com/xtide/xtide.html>), which generated predicted tides based on the harmonic coefficients for Chatham provided by the Xtide program.
(F.) Map the bathymetric soundings from each processed data file onto a Mercator grid using weigh_grid (a SwathEd utility) with node spacings and scale selected by the operator. The grid file (capenorth.r4) was a floating point binary file.
Person who carried out this activity:
(508) 548-8700 x2274 (voice)
(508) 457-2310 (FAX)
bdanforth@usgs.gov
Data sources produced in this process:
Person who carried out this activity:
(508) 548-8700 x2274 (voice)
(508) 457-2310 (FAX)
bdanforth@usgs.gov
Data sources produced in this process:
Person who carried out this activity:
(508) 548-8700 x2281 (voice)
(508) 457-2310 (FAX)
vpaskevich@usgs.gov
Data sources produced in this process:
Poppe, L.J., Foster, D.S., and Danforth, W.W., 2006, Character and distribution of exposed glaciodeltaic deposits off outer Cape Cod, Massachusetts, and their effects on hydrogeology and benthic habitats: Geo-Marine Letters v. 26, Springer, Germany.
Navigation was by differential GPS.
All collected data were processed and used to produce this dataset.
Are there legal restrictions on access or use of the data?
- Access_Constraints: None
- Use_Constraints:
- Data are not for navigational purposes.
Public domain data are freely redistributable with proper metadata and source attribution. Please recognize the U.S. Geological Survey (USGS) as the source of this information.
(508) 548-8700 x2314 (voice)
(508) 457-2310 (FAX)
lpoppe@usgs.gov
Downloadable Data
Although all data 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.Any use of trade, product, or firm names is for descriptive purposes only and does not imple endorsement by the U.S. Government.
| Data format: | GeoTIFF image, world file, browse graphics and XML and text formatted metadata files. in format TIFF GeoTIFF Size: 0.000 |
|---|---|
| Network links: |
<http://pubs.usgs.gov/of/2005/1048/data/bathymetry/sun_illum/geo/capenorthsun_geo4m_wgs84.zip> <http://pubs.usgs.gov/of/2005/1048/data/bathymetry/sun_illum/geo/capenorthsun_geo4m_wgs84.tif> <http://pubs.usgs.gov/of/2005/1048/htmldocs/data_catalog.htm> <http://pubs.usgs.gov/of/2005/1048/data/bathymetry/sun_illum/geo/> |
| Media you can order: |
DVD-ROM
(Density 4.7
Gbytes)
(format UDF)
|
This image is available as a GeoTIFF image with an accompanying world file. To utilize this data, the user must have an image viewer, image processing or GIS software package capable of importing a GeoTIFF image.
(508) 548-8700 x2314 (voice)
(508) 457-2310 (FAX)
lpoppe@usgs.gov
