2 meter unenhanced GeoTIFF Sidescan-Sonar Mosaic of Virgin Basin - Lake Mead, Nevada (VBASIN_UNGEOG.TIF, geographic)

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Frequently anticipated questions:

What does this data set describe?

Title:
2 meter unenhanced GeoTIFF Sidescan-Sonar Mosaic of Virgin Basin - Lake Mead, Nevada (VBASIN_UNGEOG.TIF, geographic)
Abstract:
Lake Mead is a large interstate reservoir located in the Mojave Desert of southeastern Nevada and northwestern Arizona. It was impounded in 1935 by the construction of Hoover Dam and is one of a series of multi-purpose reservoirs on the Colorado River. The lake extends 183 km from the mouth of the Grand Canyon to Black Canyon, the site of Hoover Dam, and provides water for residential, commercial, industrial, recreational, and other non-agricultural users in communities across the southwestern United States. Extensive research has been conducted on Lake Mead, but a majority of the studies have involved determining levels of anthropogenic contaminants such as synthetic organic compounds, heavy metals and dissolved ions, furans/dioxins, and nutrient loading in lake water, sediment, and biota (Preissler, et al., 1998; Bevans et al, 1996; Bevans et al., 1998; Covay and Leiker, 1998; LaBounty and Horn, 1997; Paulson, 1981). By contrast, little work has focused on the sediments in the lake and the processes of deposition (Gould, 1951). To address these questions, sidescan-sonar imagery and high-resolution seismic-reflection profiles were collected throughout Lake Mead by the USGS in cooperation with researchers from University of Nevada Las Vegas (UNLV). These data allow a detailed mapping of the surficial geology and the distribution and thickness of sediment that has accumulated in the lake since the completion of Hoover Dam. Results indicate that the accumulation of post-impoundment sediment is primarily restricted to former river and stream beds that are now submerged below the lake while the margins of the lake appear to be devoid of post-impoundment sediment. The sediment cover along the original Colorado River bed is continuous and is typically greater than 10 m thick through much of its length. Sediment thickness in some areas exceeds 35 m while the smaller tributary valleys typically are filled with less than 4 m of sediment. Away from the river beds that are now covered with post-impoundment sediment, pre-impoundment alluvial deposits and rock outcrops are still exposed on the lake floor.
  1. How might this data set be cited?
    Twichell, David C., and Cross, VeeAnn A., 2003, 2 meter unenhanced GeoTIFF Sidescan-Sonar Mosaic of Virgin Basin - Lake Mead, Nevada (VBASIN_UNGEOG.TIF, geographic): Open-File Report 03-320, U.S. Geological Survey, Coastal and Marine Geology Program, Woods Hole Coastal and Marine Science Center, Woods Hole, MA.

    Online Links:

    This is part of the following larger work.

    Twichell, David C., Cross, VeeAnn A., and Belew, Stephen D., 2003, Mapping the floor of Lake Mead (Nevada and Arizona): Preliminary discussion and GIS data release: Open-File Report 03-320, U.S. Geological Survey, Reston, VA.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -114.633747
    East_Bounding_Coordinate: -114.358236
    North_Bounding_Coordinate: 36.181256
    South_Bounding_Coordinate: 36.063916
  3. What does it look like?
    http://pubs.usgs.gov/of/2003/of03-320/htmldocs/icons/vbasinun.jpg (JPEG)
    Browse image showing overview of Virgin Basin sidescan-sonar mosaic.
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 01-Apr-2001
    Ending_Date: 26-Apr-2001
    Currentness_Reference:
    ground condition
  5. What is the general form of this data set?
    Geospatial_Data_Presentation_Form: remote-sensing image
  6. How does the data set represent geographic features?
    1. How are geographic features stored in the data set?
      This is a Raster data set. It contains the following raster data types:
      • Dimensions 6510 x 12366 x 1, type Pixel
    2. What coordinate system is used to represent geographic features?
      Horizontal positions are specified in geographic coordinates, that is, latitude and longitude. Latitudes are given to the nearest 0.000018. Longitudes are given to the nearest 0.000022. 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.
  7. How does the data set describe geographic features?
    Band_1
    Information unavailable from original metadata. (Source: Information unavailable from original metadata.)
    ObjectID
    Internal feature number. (Source: ESRI) Sequential unique whole numbers that are automatically generated.
    Entity_and_Attribute_Overview:
    The pixel value represents the DN return value of the sidescan-sonar system. A high value (ie 254) indicates a highly reflective lake floor surface, while a low value (ie 0) indicates low reflectance.
    Entity_and_Attribute_Detail_Citation: U.S. Geological Survey

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)
    • David C. Twichell
    • VeeAnn A. Cross
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
    David C. Twichell
    USGS
    Oceanographer
    384 Woods Hole Rd.
    Woods Hole, MA

    508-548-8700 x2266 (voice)
    508-457-2310 (FAX)
    dtwichell@usgs.gov

Why was the data set created?

This sidescan-sonar imagery is used to map the morphology of the lake floor and determine the extent of sediment distribution on the lake floor.

How was the data set created?

  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
    Date: Unknown (process 1 of 11)
    Sidescan sonar imagery was collected using a Datasonics SIS-1000 sidescan sonar system and logged to a Triton QMIPS data logging computer.
    Date: Unknown (process 2 of 11)
    The digital sidescan data were then processed and mapped to provide proper geographic locations of features identified in the imagery. The processing steps included subsampling the raw sidescan data using a median filtering routine to suppress speckle noise and reduce file size, and corrrect for slant-range distortion, signal attenuation, and dropped sonar lines using XSonar (Danforth et al., 1991). After these processing steps, the imagery was mapped into its proper geographic location using techniques summarized by Paskevich (1996). Individual sidescan swaths were mapped with each pixel geographically positioned at a resolution of 2 m/pixel. Due to the difficult nature of working in a lake environment, XSonar was modified by Danforth to incorporate the ability to exclude portions of the imagery from the beam angle correction routine. This enabled the stark contrast between highly reflection rock outcrops and fine-grained sediment deposits to be preserved. This enhancement was not available in 2001 when the data were collected, so the data were reprocessed in 2001. Processing the data up to this point was done be VeeAnn Cross.
    Date: Unknown (process 3 of 11)
    Non-overlapping swaths were then brought into the remote sensing software package PCI. The techniques for generating the composite digital sidscan mosaic are summarized by Paskevich (1992). Processing of the data from this point on was done by David C. Twichell.
    Date: Unknown (process 4 of 11)
    Because of the close relationship of the imagery to the topography of the lake, a shaded-relief image generated from the DEM with the 10m contours burned into it was imported to PCI and the sidescan-sonar image strips were georeferenced to it. Misalignments based on the ground control points that were selected between the sidescan-sonar imagery and the DEM after georeferencing were less than 20m in all areas of the lake except a small section of Black Canyon and part of Boulder Canyon.
    Date: Unknown (process 5 of 11)
    The mosaic then had a linear stretch applied to the data to reduce the valid data range from 0-255 to 0-254. When mapped on a white background, the background can be made transparent in the GIS without affecting the data.
    Date: Unknown (process 6 of 11)
    Once the mosaics were completed, noise and areas of no data were trimmed from the fringes of the completed mosaic. The lake shoreline as defined by the U.S. Bureau of Reclamation was used to trim noise and nodata areas that fell beyond the limits of the lake.
    Date: Unknown (process 7 of 11)
    The UTM projected image was the reprojected to Geographic coordinates using BlueMarble's Geographic Transformer software. Transform parameters used a resolution of 2m/pixel and a central latitude of 36N.
    Date: 14-Nov-2016 (process 8 of 11)
    Edits to the metadata were made to fix any errors that MP v 2.9.34 flagged. This is necessary to enable the metadata to be successfully harvested for various data catalogs. In some cases, this meant adding text "Information unavailable" or "Information unavailable from original metadata" for those required fields that were left blank. Other minor edits were probably performed (title, publisher, publication place, etc.). Added online link to the data in the identification section. Added online link to the data in the distribution section. Both geographic and a planar coordinate system were present, the planar one was removed. The metadata date (but not the metadata creator) was edited to reflect the date of these changes. The metadata available from a harvester may supersede metadata bundled within a download file. Compare the metadata dates to determine which metadata file is most recent. Person who carried out this activity:
    U.S. Geological Survey
    Attn: VeeAnn A. Cross
    Marine Geologist
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2251 (voice)
    508-457-2310 (FAX)
    vatnipp@usgs.gov
    Date: 20-Jul-2018 (process 9 of 11)
    USGS Thesaurus keywords added to the keyword section. Person who carried out this activity:
    U.S. Geological Survey
    Attn: VeeAnn A. Cross
    Marine Geologist
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2251 (voice)
    508-457-2310 (FAX)
    vatnipp@usgs.gov
    Date: 18-Nov-2019 (process 10 of 11)
    Crossref DOI link was added as the first link in the metadata. Person who carried out this activity:
    U.S. Geological Survey
    Attn: VeeAnn A. Cross
    Marine Geologist
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2251 (voice)
    508-457-2310 (FAX)
    vatnipp@usgs.gov
    Date: 08-Sep-2020 (process 11 of 11)
    Added keywords section with USGS persistent identifier as theme keyword. Person who carried out this activity:
    U.S. Geological Survey
    Attn: VeeAnn A. Cross
    Marine Geologist
    384 Woods Hole Road
    Woods Hole, MA

    508-548-8700 x2251 (voice)
    508-457-2310 (FAX)
    vatnipp@usgs.gov
  3. What similar or related data should the user be aware of?
    Bevans, H.E., Goodbred, S.L., Miesner, J.F., Watkins, S.A., Gross, T.S., Denslow, N.D., and Choeb, T., 1996, Synthetic organic compounds and carp endrocrinology and histology, Las Vegas Wash and Las Vegas and Callville bays of Lake Mead Nevada: Water-Resources Investigations 96-4266, U.S. Geological Survey, Reston, VA.

    Bevans, H.E., Lico, M.S., and Lawrence, S.J., 1998, Water quality in the Las Vegas Valley area and the Carson and Truckee River basins, Nevada and California, 1992-1996: Circular 1170, U.S. Geological Survey, Reston, VA.

    Couvay, K.J., and Leiker, T.J., 1998, Synthetic organic compounds in water and bottom sediment from streams, detention basins, and sewage-treatment plant outfalls in Las Vegas Valley, Nevada, 1997: Open-File Report 98-633, U.S. Geological Survey, Reston, VA.

    Gould, H.R., 1951, Some quantitative aspects of Lake Mead turbidity currents: SEPM Special Publication No. 2, Society of Economic Paleontologists and Mineralogists, Tulsa, OK.

    LaBounty, J.F., and Horn, M.J., 1997, The influence of drainage from the Las Vegas Valley on the limnology of Boulder Basin, Lake Mead, Arizona-Nevada: Journal of Lake and Reservoir Management v. 13.

    Paulson, L.J., 1981, Nutrient management with hydroelectric dams on the Colorado River: Technical Report #8, Lake Mead Limnological Research Center, Department of Biological Sciences, University of Nevada, Las Vegas, Nevada.

    Preissler, A.M., Roach, G.A., Thomas, K.A., and Wilson, J.W., 1998, Water resources data, Nevada, water year 1998: Water Resources Data Nevada NV-98-1, U.S. Geological Survey, Reston, VA.

How reliable are the data; what problems remain in the data set?

  1. How well have the observations been checked?
  2. How accurate are the geographic locations?
    The ship was navigated with P-CODE GPS. The towfish was deployed at approximately the same depth each day, with little variation during the course of the survey. Therefore range to fish values are assumed consistent and accurate.
  3. How accurate are the heights or depths?
  4. Where are the gaps in the data? What is missing?
    All imagery necessary to map the lake floor was used.
  5. How consistent are the relationships among the observations, including topology?
    All these data were collected with the same sidescan-sonar towfish. The majority of the data comprising this mosaic was acquired at a 1500m total swath width. In some small areas, data gaps were filled with data collected at a 750m total swath width. However, in each case, the data were resampled to a 2 m pixel size.

How can someone get a copy of the data set?

Are there legal restrictions on access or use of the data?
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. 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.
  1. Who distributes the data set? (Distributor 1 of 1)
    David C. Twichell
    USGS
    Oceanographer
    384 Woods Hole Rd.
    Woods Hole, MA

    508-548-8700 x2266 (voice)
    508-457-2310 (FAX)
    dtwichell@usgs.gov
  2. What's the catalog number I need to order this data set? Downloadable Data
  3. What legal disclaimers am I supposed to read?
    Although these data have been used by the U.S. Geological Survey (USGS), U.S. Department of the Interior (DOI), no warranty expressed or implied is made by the U.S. Geological Survey as to the accuracy of the data. 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 imply endorsement by the U.S. Government.
  4. How can I download or order the data?
  5. What hardware or software do I need in order to use the data set?
    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.

Who wrote the metadata?

Dates:
Last modified: 08-Sep-2020
Metadata author:
VeeAnn A. Cross
U.S. Geological Survey
Marine Geologist
384 Woods Hole Rd.
Woods Hole, MA

(508) 548-8700 x2251 (voice)
(508) 457-2310 (FAX)
vatnipp@usgs.gov
Metadata standard:
FGDC Content Standards for Digital Geospatial Metadata (FGDC-STD-001-1998)
This page is <https://cmgds.marine.usgs.gov/catalog/whcmsc/open_file_report/ofr2003-320/vbasin_ungeog.tif.faq.html>
Generated by mp version 2.9.50 on Tue Sep 21 18:20:19 2021