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Open-File Report 02-162

Multibeam Mapping of the Los Angeles, California Margin

ArcExplorer Project

Long Beach

Newport Shelf

This Open-File Report contains an ArcExplorer 2.0 project of the Los Angeles Margin multibeam bathymetry and acoustic backscatter imagery. ArcExplorer is a freeware, GIS software package developed by ESRI. This project allows the user to overlay, zoom, pan, and query the Los Angeles Margin multibeam data. Other spatial data in GEOGRAPHIC coordinates can be added to this project.

This ArcExplorer project will only run an a PC running Windows 98/2000/NT.

If the user already has ArcExplorer 2.0 installed on the computer follow the instructions below.

Or download ArcExplorer 2.0 from ESRI.


Download Instructions:

1. Download the laproj.tgz file (10Mb).

2. Laproj.tgz is a bundled and compressed folder containing all the files needed for the ArcExplorer project. Laproj.tgz needs to be uncompressed and unbundled using WinZip or a similar program before opening the project in ArcExplorer. Double click on the laproj.tgz icon. WinZip will start up and uncompress the file resulting in a new file, laproj.tar. Double click on this new icon and WinZip will unbundle the file resulting in a new folder called laproj. Laproj.tgz is 10Mb compressed, 61Mb uncompressed.

2. Double click on the laproj.aep file within the laproj folder to start the ArcExplorer project.

Disclaimer: Downloading files from the Internet can sometimes be problematic. Different web browsers and operating systems act differently. The instructions above may vary from system to system or may not work at all.

One possible problem when downloading the file using Netscape the *.tgz extension automatically changes to *.tar and the file does not uncompress correctly. If this is the case change the *.tar back to *.tgz and uncompress as normal.

Contents of ArcExplorer project

CON50 - 50-meter depth contours from -50 to -900 m generated from the multibeam bathymetry data.

SHADE.TIF> - Shaded-relief TIFF image generated from the multibeam bathymetry data. The illumination azimuth is 300 degrees and the illumination angle is 30 degrees.

BACKSTR.TIF - Gray-scale TIFF image generated from the multibeam backscatter data. The brighter tones indicate stronger acoustic returns off the seafloor (possibly harder surfaces) and the darker tones indicate weaker acoustic returns off the seafloor (possibly sediment). NOTE: The different multibeam sonar systems used for each survey operate at different frequencies resulting in different backscatter intensities, depth of penetration, etc. While pixel values are relative to other values within a survey, pixel values are not relative between surveys. While the backscatter imagery in this ArcExplorer project show the backscatter data from all surveys merged together, the backscatter data are published separately for each survey.


Data Information

Projection: Geographic
Units: Decimal Degrees
Zunits: meters (bathymetry), none (backscatter)
Datum: WGS84
Spatial Resolution: 16 meters



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