2002111914053300FALSE20031006101354002003100610135400{BC3CA17F-AAE1-469E-9FA6-437F87A01021}Microsoft Windows 2000 Version 5.0 (Build 2195) Service Pack 4; ESRI ArcCatalog 8.2.0.700enLake 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.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.David C. Twichell2003tempiceenh_g.tifremote-sensing imageVeeAnn A. CrossEnhanced TIFF Sidescan-Sonar Mosaic East of Virgin Basin - Lake Mead, Nevada: Geographic CoordinatesMapping the floor of Lake Mead (Nevada and Arizona): Preliminary discussion and GIS data releaseDavid C. TwichellVeeAnn A. CrossStephen D. Belew2003Open-File Report03-320U.S. Geological SurveyWoods Hole Field Center, Woods Hole, MA
ground condition2001040120010426None planned-114.368843-114.02320136.20541736.003037-114.368843-114.02320136.00303736.205417GeneralCMGPCoastal and Marine Geology ProgramimagesmosaicOFR03-320Open-File Reportreservoirsidescansidescan sonarTIFFU.S. Geological SurveyUSGSWoods Hole Field CenterGeneralArizonaColorado RiverIceberg CanyonLake MeadLas VegasMojave DesertNevadaUnited StatesVirgin BasinNorth AmericaNONEThe U.S. Geological Survey must be referenced as the originator of the dataset in any future products or research derived from these data.Raster DatasetDavid C. TwichellU.S. Geological SurveyOceanographermailing and physical address384 Woods Hole Rd.Woods HoleMA02543-1598(508) 548-8700 x2266(508) 457-2310dtwichell@usgs.govSynthetic organic compounds and carp endrocrinology and histology, Las Vegas Wash and Las Vegas and Callville bays of Lake Mead NevadaH.E. BevansS.L. GoodbredJ.F. MiesnerS.A. WatkinsT.S. GrossN.D. DenslowT. Choeb1996Water-Resources Investigations96-4266U.S. Geological SurveyWater quality in the Las Vegas Valley area and the Carson and Truckee River basins, Nevada and California, 1992-1996H.E. BevansM.S. LicoS.J. Lawrence1998Circular1170U.S. Geological SurveySynthetic organic compounds in water and bottom sediment from streams, detention basins, and sewage-treatment plant outfalls in Las Vegas Valley, Nevada, 1997K.J. CouvayT.J. Leiker1998Open-File Report98-633U.S. Geological SurveySome quantitative aspects of Lake Mead turbidity currentsH.R. Gould1951SEPM Special PublicationNo. 2Society of Economic Paleontologists and MineralogistsThe influence of drainage from the Las Vegas Valley on the limnology of Boulder Basin, Lake Mead, Arizona-NevadaJ.F. LaBountyM.J. Horn1997Journal of Lake and Reservoir Managementv. 13Nutrient management with hydroelectric dams on the Colorado RiverL.J. Paulson1981Technical Report#8Department of Biological Sciences, University of Nevada, Las Vegas, NevadaLake Mead Limnological Research CenterWater resources data, Nevada, water year 1998A.M. PreisslerG.A. RoachK.A. ThomasJ.W. Wilson1998Water Resources Data NevadaNV-98-1U.S. Geological SurveyMicrosoft Windows 2000 Version 5.0 (Build 2195) Service Pack 4; ESRI ArcCatalog 8.2.0.700tempiceenh_g.tif-114.368843-114.02320136.20541736.0030371-114.368843-114.02320136.20541736.0030371enFGDC Content Standards for Digital Geospatial MetadataFGDC-STD-001-1998local timeVeeAnn A. CrossU.S. Geological SurveyMarine Geologistmailing and physical address384 Woods Hole Rd.Woods HoleMA02543-1598(508) 548-8700 x2251(508) 457-2310vatnipp@usgs.gov20031006http://www.esri.com/metadata/esriprof80.htmlESRI Metadata ProfileISO 19115 Geographic Information - MetadataDIS_ESRI1.0dataset20.20620.206David C. TwichellU.S. Geological SurveyOceanographermailing and physical address384 Woods Hole Rd.Woods HoleMA02543-1598(508) 548-8700 x2266(508) 457-2310dtwichell@usgs.govThese 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.Downloadable Data002file://\\REDHOOK\LMofr\data\sscanimgs\geographic\enhanced\tempiceenh_g.tifLocal Area Network20.206Raster DatasetRasterPixel11227155130.0000220.00001881Upper LeftTRUEPackBits1pixel codesFALSETIFFdecimal degreesdecimal degrees255GCS_WGS_1984D_WGS_1984WGS_19846378137.000000298.257224Decimal degrees0.0000180.000022row and column0.0000220.000018GCS_WGS_19842155130.000022112270.000018120031006Sidescan sonar imagery was collected using a Datasonics SIS-1000 sidescan sonar system and logged to a Triton QMIPS data logging computer.Danforth, W.W., O'Brien, T.F., and Schwab, W.C., 1991, USGS image processing system: near real-time mosaicking of high-resolutoin sidescan-sonar data: Sea Technology, Jan., 1991, p. 54-59.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.Paskevich, V.F., 1996, MAPIT: An improved method for mapping digital sidescan sonar data using the Woods Hole Image Processing System (WHIPS) software: U.S. Geological Survey Open-File Report 96-281, 73p.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.Paskevich, V.F., 1992, Digital mapping of sidescan sonar data with the Woods Hole Image Processing System software: U.S. Geological Survey Open-File Report 92-536, 87p.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.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.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.A root stretch was applied in PCI to the sidescan image to help enhance the features. The root stretch was from 15-220 with resulting values between 0 and 254. This was done so that the white background (255) could be made transparent in the GIS.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.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.All imagery necessary to map the lake floor was used.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.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.Band_1Table256ObjectIDObjectIDOID400Internal feature number.ESRISequential unique whole numbers that are automatically generated.ValueValueInteger000RedRedDouble000GreenGreenDouble000BlueBlueDouble000