Chirp Seismic Shotpoint Navigation every 100 shots in Geographic Coordinates - Lake Mead Survey 2001

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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 2001
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.
Supplemental_Information:
These data were collected as part of USGS field activity 2001-007-FA. Additional information about that field activity is available from https://cmgds.marine.usgs.gov/services/activity.php?fan=2001-007-FA .
  1. How might 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 2001: Open-File Report 02-478, U.S. Geological Survey, Coastal and Marine Geology, Woods Hole Field Center, Woods Hole, MA.

    Online Links:

    This is part of the following larger work.

    Cross, VeeAnn A., and Twichell, David C., 2003, Archive of Seismic-Reflection Data Collected During USGS Cruise Lake Mead 01007 in Lake Mead - Nevada and Arizona, 1-28 April, 2001: Open-File Report 02-478, U.S. Geological Survey, Coastal and Marine Geology Team, Woods Hole Field Center, Woods Hole, MA.

    Online Links:

  2. What geographic area does the data set cover?
    West_Bounding_Coordinate: -114.756065
    East_Bounding_Coordinate: -114.024584
    North_Bounding_Coordinate: 36.484177
    South_Bounding_Coordinate: 36.014389
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
    Beginning_Date: 01-Apr-2001
    Ending_Date: 16-Apr-2001
    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 (6759)
    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 0.0002. Longitudes are given to the nearest 0.0002. Latitude and longitude values are specified in Decimal degrees. The horizontal datum used is North American Datum of 1983.
      The ellipsoid used is Geodetic Reference System 80.
      The semi-major axis of the ellipsoid used is 6378137.000000.
      The flattening of the ellipsoid used is 1/298.257222.
  7. How does the data set describe geographic features?
    lm01_100sht.dbf
    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.
    LINENUM
    Line number assigned to the seismic line along which the shotpoint navigation 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:17143
    EASTING
    The UTM easting position of the shot point. (Source: Software generated.)
    Range of values
    Minimum:702048
    Maximum:767566
    NORTHING
    The UTM northing position of the shot point. (Source: Software computed.)
    Range of values
    Minimum:3989078
    Maximum:4040949

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
    U.S. Geological Survey
    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 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?
    Date: 2001 (process 1 of 5)
    This particular seismic data was acquired with an SIS-1000 chirp subbottom system with the digital data stored on a Triton-QMIPS datalogger. Navigation is updated approximately every 10 seconds and sent to this data logging system. Once the seismic SEG-Y data is separated from the raw data files, the unique navigation points and the shotpoints associated with them are pulled from the header of these seg-y data files. These navigation points reflect the best known position of the acquisition system. In other words, the layback of the instrument is taken into account for the positional fix. *The process date was added as a required element when the metadata was updated in 2026. The process date is an assumption based on the process step itself.
    Date: 2002 (process 2 of 5)
    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. *The process date was added as a required element when the metadata was updated in 2026. The process date is an assumption based on the process step itself.
    Date: 2002 (process 3 of 5)
    These points were then imported into ArcView and saved as a shapefile. *The process date was added as a required element when the metadata was updated in 2026. The process date is an assumption based on the process step itself.
    Date: 2002 (process 4 of 5)
    Since the original navigation was stored in the SEG-Y header in UTM, zone 11, NAD 83 meters, the file was then reprojected to the Geographic Coordinate system using ArcToolbox in ArcGIS 8.1. *The process date was added as a required element when the metadata was updated in 2026. The process date is an assumption based on the process step itself.
    Date: 21-May-2026 (process 5 of 5)
    This metadata file was updated as part of metadata maintenance when added to the web accessible folder. Edits were performed on the original text version of the metadata, then converted to XML. These edits included: Fixed all errors flagged by MP. These included (but are not limited to) adding required elements such as publication place when publisher is provided; added process dates. Additionally, added some DOI online links when possible; added supplemental information with link to the field activity; added USGS Thesaurus and ISO 19115 Topic Category thesauri and appropriate terms in each; renamed “General” thesauri to “None” thesauri; updated the use and access constraints to approved statements; updated the distribution liability to a current approved statement; updated metadata email to a generic email in the event the person leaves the USGS (20260521) Person who carried out this activity:
    U.S. Geological Survey
    Attn: VeeAnn A. Cross
    Marine Geologist
    384 Woods Hole Rd.
    Woods Hole, MA
    USA

    (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 Water Resources, 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.

    Online Links:

    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.

    Online Links:

    Gould, H.R., 1951, Some quantitative aspects of Lake Mead turbidity currents: SEPM Society for Sedimentary Geology Special Publication No. 2, SEPM Society for Sedimentary Geology, McLean, VA.

    Online Links:

    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, issue 2, Journal of Lake and Reservoir Management, London, England.

    Online Links:

    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.

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 navigation was collected with a P-CODE GPS receiver with an assumed accuracy of approximately 10m. Additional error is introduced by undertainty as to the positional relationship between the acquisition system and the navigation antenna. Overall positional accuracy assumed to be 20 meters.
  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 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 No access constraints. Please see 'Distribution Information' for details.
Use_Constraints These data are marked with a Creative Commons CC0 1.0 Universal License. These data are in the public domain and do not have any use constraints. Users are advised to read the dataset's metadata thoroughly to understand appropriate use and data limitations. 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

    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?
    Unless otherwise stated, all data, metadata and related materials are considered to satisfy the quality standards relative to the purpose for which the data were collected. Although these data and associated metadata have been reviewed for accuracy and completeness and approved for release by the U.S. Geological Survey (USGS), no warranty expressed or implied is made regarding the display or utility of the data for other purposes, nor on all computer systems, nor shall the act of distribution constitute any such warranty.
  4. How can I download or order the data?
    • Availability in digital form:
      Data format: shapefile Size: 0.494
      Media you can order: These data were released on DVD that is currently not available online. (format Not documented with the original metadata.)
    • Cost to order the data: None

Who wrote the metadata?

Dates:
Last modified: 02-Jun-2026
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)
whsc_data_contact@usgs.gov
Contact_Instructions:
The metadata contact email address is a generic address in the event the contact person is no longer with the USGS.
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/ofr2002-478/lm01_100sht.faq.html>
Generated by mp version 2.9.51 on Tue Jun 2 16:43:33 2026