PSNERP FY03 bathymetric lidar data

On this disk are final data from the September-October 2003 survey of the saltwater nearshore of the City of Seattle, WRIA9 (south King County, including Vashon and Maury Islands), the Lofall reach of Hood Canal, and Skagit Bay. Note that coverage of these areas is incomplete: voids range from minimal (City of Seattle, Lofall) to extensive (Skagit Bay).

These data were acquired by the Joint Airborne Laser Bathymetry Technical Center of Expertise (JALBTCX), using the new SHOALS 1000 instrument. Derivative products (classified data points, grids, images) on this disk were produced by Ralph Haugerud of the U.S. Geological Survey from the survey data acquired by JALBTCX.

For further information about these data, please contact

Ralph Haugerud
rhaugerud@usgs.gov
206-553-5542

Eddie Culpepper
Eddie.Culpepper.Jr@sam.usace.army.mil
251-690-3487

Haugerud and Culpepper are preparing a final report, to be available online, that will include the data on this disk as well as a revised Report of Survey, an analysis of data quality, documentation of the processing used to classify points, and documentation of the rules used to interpolate from surveyed points to a continuous surface with no-data areas. In the interim, please cite these data as follows:

Information in the area-specific directories, the draft Report of Survey, and the information in the xyzc directory except for the point classification: JALBTCX, written communication, 2004

Information in the composites and tiles directories, and the point classifications within the xyzc directory: R.A. Haugerud, U.S. Geological Survey, written communication, 2004

Disk contents

city_of_seattle/

City of Seattle data, as received from JALBTCX.

Includes lidar data, aircraft trajectories, digital images, and metadata. Most data are in Washington State Plane north coordinates, datum NAD83, vertical datum NAVD88. Digital RGB images, located in the images subdirectory, were acquired with a down-looking camera during lidar data acquisition. They are accompanied by world files that position the images in the UTM10 coordinate system. Note that the images are not rectified.

lofall/

Lofall data, as received from JALBTCX.

skagit/

Skagit Bay data, as received from JALBTCX.

wria9/

WRIA9 data, as received from JALBTCX.

report_of_survey/

Draft Report of Survey as received from JALBTCX

xyzc/

ASCII files of lidar data points. Reformatted, sorted and classified by Haugerud. Format is

    easting northing elev time date classification     1230000.13 179166.98 -27.56 17:10:04.944036 2003271 G     1230000.50 179487.88 -50.03 17:10:06.047652 2003271 G     1230000.63 179814.94 -62.63 17:10:07.210224 2003271 G

    easting (first 10 characters) and northing (characters 12 - 21) are Washington State Plane North zone feet
    elev (characters 24 to 29) is in feet, referenced to NAVD88
    time (characters 31 to 45) is hours:minutes:seconds
    date (characters 48 to 54) is YYYYDDD
    classification is a single-character code with values of
      G   ground or bottom
        N not-ground, not-bottom (e.g. trees, structures, piers, boats)
    B blunder (points with too-low values, perhaps because of multiple reflection)

Points are sorted into tiles with maximum dimensions of 10,000 ft X 10,000 ft. The file name corresponds to the position of the southwest corner of the tile. That is, file x123y017.xyzc contains points with X-coordinates (eastings) greater than or equal to 1,230,000 and less than 1,240,000 and Y-coordinates (northings) greater than or equal to 170,000 and less than 180,000.

Points were classified with a combination of the 'despike' code described by Haugerud and Harding (2001; see https://pugetsoundlidar.org) and hand editing. The goal of classification was to identify survey points on not-ground objects such as boats and floating docks (N) so that they could be ignored when constructing a bottom model for environmental analysis, and to flag survey points that are too deep and clearly unreal (B). With a few exceptions, an effort was made to NOT flag points that appear to be not-ground because of survey errors, such as some higher-than-average points in areas of swath overlap. For most tiles, classification of upland points was perfunctory and is clearly unsatisfactory; much better coverage of the upland areas is available from the Puget Sound Lidar Consortium.

tiles/

Zipped e00 (ESRI export format) files of Arc-Info grids. Two grids are presented for each XY tile. "be" grids are built only from points classified as "G". "ff" grids are built from all points. For many of the tiles, the be and ff grids are identical, or nearly so.

Grids are in Washington State Plane North coordinate system, with 6-foot cells. Z values are 4-byte floating point numbers, datum NAVD88. Six foot cells strongly oversample the lidar data (nominal point spacing of 4 meters) but are used for compatibility with high-resolution topography from the Puget Sound Lidar Consortium. Grids were built by constructing a TIN and then sampling the TIN at regular intervals using the Arc TINLATTICE command.

composites/

Large-area composite "be" grids:

    sea_n    Seattle north of Elliot Bay. Merged with upland lidar topography from the Puget Sound Lidar Consortium

    sea_s    Seattle south of Elliot Bay. Merged with upland lidar topography from the Puget Sound Lidar Consortium

    wria9_n    northern part of WRIA9

    wria9_s    southern part of WRIA9

    lofall    Lofall reach of Hood Canal, extending along the SE shore from Salisbury Point to a point about 5 miles SW

    skagit    Skagit Bay

For each composite there is a corresponding TIFF image with world file. Note that on the images the blue-to-green color transition is at Z=0 NAVD88, not at MLLW.

Grids and images are in Washington State Plane North coordinate system.

This directory also includes grid n88-mllw. This low-resolution grid provides the offsets necessary to convert the grids on this disk, except for those of the Skagit Bay area, to MLLW vertical datum. To, for example, convert the SEA_N grid to MLLW datum, use the following ArcInfo GRID commands:

Grid: setwindow SEA_N Grid: setcell SEA_N /* necessary to force output to 6-ft cells /* not the 300-ft cells of grid n88-mllw Grid: SEA_NMLLW = SEA_N - N88-MLLW

n88-mllw was derived from datum translations given by NOAA's VDatum tool (https://chartmaker.ncd.noaa.gov/bathytopo/vdatum.htm). At present VDatum for Puget Sound does not provide translations as far north as Skagit Bay, thus n88-mllw does not extend to Skagit Bay.

14 July 2004