Sidescan-sonar Tracklines in the Geographic Coordinate System - Lake Mead 2000

Frequently-anticipated questions:

• What does this data set describe?
  1. How should this data set be cited?
  2. What geographic area does the data set cover?
  3. What does it look like?
  4. Does the data set describe conditions during a particular time period?
  5. What is the general form of this data set?
  6. How does the data set represent geographic features?
  7. How does the data set describe geographic features?
• Who produced the data set?
  1. Who are the originators of the data set?
  2. Who also contributed to the data set?
  3. To whom should users address questions about the data?
• Why was the data set created?
• How was the data set created?
  1. From what previous works were the data drawn?
  2. How were the data generated, processed, and modified?
• 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?
  5. How consistent are the relationships among the data, including topology?
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• Who wrote the metadata?

Title:

Sidescan-sonar Tracklines in the Geographic Coordinate System - Lake Mead 2000

Abstract:

A one-week geophysical survey was conducted in the Las Vegas Bay part of Lake Mead during June 1-6, 2000 to acoustically map the surficial sediments and shallow subsurface geology of this part of the lake. The study was done by researchers from the U.S. Geological Survey, Coastal and Marine Geology Program in Woods Hole, MA and the University of Nevada at Las Vegas. The objective was to map the distribution, volume and acoustic character of sediment that has accumulated on the floor of this part of the lake. The need for systematic mapping of this part of the lake's floor is because pollutants associated with surface and groundwater enter the lake through Las Vegas Wash at the head of Las Vegas Bay. Some of the pollutants transported to the lake by this runoff are deposited with the sediments on the lake floor. Understanding the distribution of sediments in the lake is needed to establish an effective monitoring program. The study built upon a geophysical survey conducted by the USGS and UNLV in 1999 that covered the deeper water parts of Las Vegas Bay and Boulder Basin. This year's survey focussed on the shallow water parts of the head of Las Vegas Bay with particular attention being directed at Las Vegas, Gypsum and Government Washes. Of these three Washes, the most effort was put into surveying Las Vegas Wash. This survey was conducted with an Edgetech DF-1000 sidescan sonar, a Knudsen high-resolution chirp subbottom profiling system, a Garmin fathometer, and P-Code GPS navigation. All data were logged digitally.

1. How should this data set be cited?

   Twichell, David C. , and Cross, VeeAnn A. , 2003, Sidescan-sonar Tracklines in the Geographic Coordinate System - Lake Mead 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: -114.874450

   East_Bounding_Coordinate: -114.808870

   North_Bounding_Coordinate: 36.135890

   South_Bounding_Coordinate: 36.114000

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):

      • String (26)

   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 0.000000. Longitudes are given to the nearest 0.000000. 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?

   ssnav_00.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

   A numeric value indicating a line number. Test files collected during the cruise and subsequently used for interpretations are given line numbers in the range of 501-503. This is to differentiate test file 1 from line 1. (Source: VeeAnn A. Cross)

   Range of values
   Minimum:	1
   Maximum:	503

   FILENAME

   Prefix of the filename assigned to each line of sidescan-sonar data collected. (Source: Kenneth F. Parolski)

   Character data set

   SWATH

   The total swath that the sidescan-sonar imagery covers (in meters). (Source: VeeAnn A. Cross)

   Value	Definition
   200m	200 meters

   lengthm

   The length of each line segment in meters. (Source: Software computed.)

   Range of values
   Minimum:	529
   Maximum:	2243

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 02543
   

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

This ArcView shapefile defines the tracklines along which sidescan sonar data was collected.

1. From what previous works were the data drawn?

2. How were the data generated, processed, and modified?

   (process 1 of 4)

   Navigation was acquired by a Hypack navigation system and stored with the Edgetech sidescan sonar data on a QMIPS computer data acquisition system. A unique navigation point was sent to the acquisition system approximately every 10 seconds. Upon extracting the sidescan-sonar data from the acquisition system, the navigation was downsampled to 1 minute intervals.

   (process 2 of 4)

   This 1 minute navigation was then reviewed for errors and sometimes further downsampled to enable the swath of sidescan-sonar imagery to have a smooth track.

   (process 3 of 4)

   This navigation for each line of sidescan data was then combined with all the other lines into an Arc/Info ungenerate format for import into ArcView.

   (process 4 of 4)

   Within ArcView, additional attribute information for each line was added.

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?

   Complete.

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

   These lines represent the lines along which sidescan-sonar image data were collected.

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
   

   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?
   • Availability in digital form:

     Data format:	Size: 0.028

   • Cost to order the data:

Dates:

Last modified: 06-Oct-2003

Metadata author:

VeeAnn A. Cross
U.S. Geological Survey
Marine Geologist
REQUIRED: The city of the address., REQUIRED: The state or province of the address. REQUIRED: The ZIP or other postal code of the address.

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:

• <http://www.esri.com/metadata/esriprof80.html>