Download Data
Arc/Info Export FilesThere are two ARC/INFO export files (.e00) availablefor Lake Tahoe on this CD-ROM; 1. Bathymetry - Depth lt_bathy.e00.gz 2. Backscatter - Digital number (DN) associated with the reflected energyoff the seafloor lt_back.e00.gz
Full Resolution TIFF ImagesThere are three full resolution TIFF images availablefor Lake Tahoe on this CD-ROM. These files can be added to a GIS system by creatinga world file using the information from the Arc/Info Grid Information below. Or these files can be directly opened in many imageprocessing programs such as Adobe Photoshop and Adobe Illustrator. 1. lt_shd.tif.gz: Shaded relief of bathymetry using a multi-directionalhillshading AML ** 2. lt_bathy.tif.gz : Bathymetry 3. lt_back.tif.gz: Backscatter ** Multi-directionalhillshading AML created by Florence Wong, U.S. Geological Survey, MenloPark CA.
Formal Metadata
Download Instructions 1. Download compressed ARC/INFO export and TIFFfiles into drive and/or folder. 2. Uncompress files using decompression program.There are different decompressing programs for specific computer platforms. - UNIX usually has a version of GZIP alreadyunstalled on the system. If not, there are four of the more common GZIPprograms on this CD-ROM (Alpha Dec, SGI, Sparc-Solaris 2.5 and 2.6). Thesecan be found in the top directory of this CD-ROM in the GZIP folder underUNIX. If you are on a different system go to www.gzip.org to findthe GZIP program that will work for you. - Window users may use Winzip to decompressthese files. There is also a freeware Windows version of GZIP on this CD-ROM.This can be found in the top directory of this CD-ROM in the GZIP folderunder Windows. -Macintosh users may use MacGZIP. There is a copy on this CD-ROM. Thiscan be found in the top directory of this CD-ROM in the GZIP folder underMac. |
3. In Arc/Info or ArcView "Import" *.e00file. Use the grid option.
Data Collection Lake Tahoe was mapped between August 2 and August17 1998 using a Kongsberg Simrad EM-1000 Multibeam System hull mounted toC&C Technologies's RV Inland Surveyor. For more information refer toUSGS Open File Report 98-509, The Bathymetryof Lake Tahoe, California-Nevada
Processing Steps 1. Bathymetry and backscatter data processed onSilicon Graphic computer using software developed by the Ocean Mapping Group,University of New Brunswick. (see USGS OpenFile Report 98-509, The Bathymetry of Lake Tahoe, California-Nevada)
2. Processed data downloaded to a Sun Sparc Ultra 2, running Solaris 2.5as an ascii file (longitude, latitude, depth, or backscatter DN value)
3. In Arc/Info 7.1.2 a point coverage is created from the ascii file.
4. Point coverage is projected into UTM projection.
5. Projected point coverage is gridded using IDW (Inverse Distance Weighted)function.
6a. Grid is exported to Arc/Info export (.e00) file.
6b. Grid is converted to a TIFF image using the "Gridimage" command.
7. Both the export and TIFF files are compressed using UNIX version of GZIP.
Arc/Info Grid InformationBathymetry | Cell Size = | 10.000 | | Data Type: | Floating Point | | Number of Rows= | 3416 | | Number of Columns = | 1992 | | | | | BOUNDARY | | | Xmin = | 745374.500 | | Xmax = | 765294.500 | | Ymin = | 4314478.000 | | Ymax = | 4348638.000 | | | | | STATISTICS | | | Minimum Value = | 1400.017 | | Maximum Value = | 1898.999 | | Mean = | 1566.823 | | Standard Deviation = | 161.000 | | | | | COORDINATE SYSTEM DESCRIPTION | | | Projection | UTM | | Zone | 10 | | Datum | WGS84 | | Units | METERS | | Spheroid | WGS84 |
Backscatter | Cell Size = | 10.000 | | Data Type: | Floating Point | | Number of Rows= | 3418 | | Number of Columns = | 1992 | | | | | BOUNDARY | | | Xmin = | 745374.500 | | Xmax = | 765294.500 | | Ymin = | 4314459.000 | | Ymax = | 4348639.000 | | | | | STATISTICS | | | Minimum Value = | 0.00 | | Maximum Value = | 246.800 | | Mean = | 172.595 | | Standard Deviation = | 15.764 | | | | | COORDINATE SYSTEM DESCRIPTION | | | Projection | UTM | | Zone | 10 | | Datum | WGS84 | | Units | METERS | | Spheroid | WGS84 |
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