Chirp Seismic Shotpoint Navigation every 100 shots in Geographic Coordinates - Lake Mead Survey 2000

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Frequently-anticipated questions:

What does this data set describe?
    Title:
    Chirp Seismic Shotpoint Navigation every 100 shots in Geographic Coordinates - Lake Mead Survey 2000
    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 should this data set be cited?

    Twichell, David C. , and Cross, VeeAnn A. , 2003, Chirp Seismic Shotpoint Navigation every 100 shots in Geographic Coordinates - Lake Mead Survey 2000:.

    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, Woods Hole Field Center, Woods Hole, MA.

  2. What geographic area does the data set cover?

    West_Bounding_Coordinate: -114.876823
    East_Bounding_Coordinate: -114.737250
    North_Bounding_Coordinate: 36.135924
    South_Bounding_Coordinate: 36.081648

  3. What does it look like?

  4. Does the data set describe conditions during a particular time period?

    Beginning_Date: 01-Jun-2000
    Ending_Date: 06-Jun-2000
    Currentness_Reference: ground condition

  5. What is the general form of this data set?

    Geospatial_Data_Presentation_Form: vector digital data

  6. How does the data set represent geographic features?

    1. How are geographic features stored in the data set?

      This is a Vector data set. It contains the following vector data types (SDTS terminology):

      • Entity point (1614)

    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 0.0001. Longitudes are given to the nearest 0.0001. 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?

    lm00_100sht
    ArcView shapefile attribute table (Source: ESRI)

    FID
    Internal feature number. (Source: ESRI)

    Sequential unique whole numbers that are automatically generated.

    Shape
    Feature geometry. (Source: ESRI)

    Coordinates defining the features.

    EASTING
    The UTM easting position of the shot point. (Source: software generated)

    Range of values
    Minimum:692808
    Maximum:716830
    Units:meters

    NORTHING
    The UTM northing position of the shot point. (Source: software generated.)

    Range of values
    Minimum:3988421
    Maximum:4002759
    Units:meters

    LINENUM
    Line number assigned to the seismic line along which the shotpoint navigatin point falls. (Source: data processor)

    character set

    SHOT
    The seismic shot number corresponding to that point. (Source: software computed)

    Range of values
    Minimum:1
    Maximum:7061

Who produced the data set?

  1. Who are the originators of the data set? (may include formal authors, digital compilers, and editors)

  2. Who also contributed to the data set?

  3. To whom should users address questions about the data?

    David C. Twichell
    U.S. Geological Survey
    Oceanographer
    384 Woods Hole Rd.
    Woods Hole, MA 02543-1598

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

Why was the data set created?
This ArcView shapefile is used to enable correlation between the seismic-reflection profiles and the sidescan-sonar imagery, geologic interpretation, and other features represented 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?

    (process 1 of 6)
    This particular seismic data was acquired with a Knudsen chirp subbottom system with the data stored digitally on a laptop computer running the Knudsen system software. The navigation is stored in a separate file from the seismic SEG-Y data.

    (process 2 of 6)
    The shot point navigation for each line of seismic data was reformatted and combined into a single file. Since the navigation stored is in geographic coordinates, the X and Y positions were converted to UTM coordinates using PROJ.

    Data sources used in this process:

    • Evenden, 1990, Cartographic Projection Procedures for the UNIX Environment -- A User's Manual: Open-file Report 90-284

    (process 3 of 6)
    The Knudsen system does not necessarily start each seismic file with shot 1. Since the SEG-Y data files were being processed so that each file started with shot 1, these navigation files needed to have the same correction. This way the shotpoint navigation will correspond to the plotted SEG-Y data.

    (process 4 of 6)
    The shot point navigation for each line of seismic data was combined into a single file and then resampled using DigiRule's GeoCad program to a shot interval of 100. The beginning and ending shot of each line was maintained.

    (process 5 of 6)
    These points were then imported into ArcView and saved as a shapefile.

    (process 6 of 6)
    These UTM shapefiles were then reprojected to the Geographic Coordinate system using ArcToolbox in ArcGIS 8.1

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?

  3. How accurate are the heights or depths?

  4. Where are the gaps in the data? What is missing?

    These data represent shotpoint navigation for all the chirp seismic lines collected on this cruise.

  5. How consistent are the relationships among the observations, including topology?

    These data have been checked to remove obviously erroneous data points.

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.

  1. Who distributes the data set? (Distributor 1 of 1)

    David C. Twichell
    U.S. Geological Survey
    Oceanographer
    384 Woods Hole Rd.
    Woods Hole, MA 02543-1598

    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?

    These data were prepared by an agency of the United States Government. Neither the United States government nor any agency thereof, nor any of their employees, make any warranty, expressed or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed in this report, or represents that its use would not infringe privately owned rights. Reference therein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. Any views and opinions of authors expressed herein do not necessarily state or reflect those of the United States government or any agency thereof. Although all data published in this report have been used by the USGS, no warranty, expressed or implied, is made by the USGS as to the accuracy of the data and related materials and/or the functioning of the software. The act of distribution shall not constitute any such warranty, and no responsibility is assumed by the USGS in the use of this data, software, or related materials.

  4. How can I download or order the data?

Who wrote the metadata?
Dates:
Last modified: 04-Feb-2003

Metadata author:
VeeAnn A. Cross
U.S. Geological Survey
Marine Geologist
384 Woods Hole Rd.
Woods Hole, MA 02543-1598

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)

Metadata extensions used:

Generated by mp version 2.7.3 on Mon Oct 06 12:11:19 2003