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2002 Upper Texas Coast Lidar Point Data, Gulf of Mexico Shoreline in the Northeast 3.75-Minute Quadrant of the Lake Como 7.5-Minute Quadrangle: Post Fay Survey

This data set contains elevation data derived from a lidar survey approximately 300m wide of the Gulf of Mexico shoreline in the Northeast Lake Como quarter-quadrangle on Galveston Island Texas. The geographic extent of the data set is equivalent to the quarter-quadrangle plus 30 meters of overedge. The data is created by combining data collected using an Optech Inc. Airborne Laser Terrain Mapper (ALTM) 1225 in combination with geodetic quality Global Positioning System (GPS) airborne and ground-based receivers. The Bureau of Economic Geology, the University of Texas at Austin owns and operates an ALTM 1225 system (serial number 99d118). This system is installed in a single engine Cessna 206 (tail number N4589U) owned and operated by the Texas State Aircraft Pooling Board. The lidar data described by this document was collected on 18 September 2002 (26102) between 20:34 and 00:08 UTC (actual data collection). Conditions on that day were low clouds at 335m Above Ground Level (AGL), haze, and occasional showers. 99d118 instrument settings for this flight were; laser pulse rate: 25kHz, scanner rate: 26Hz, scan angle: +/-20deg, beam divergence: wide, altitude: 300-490m AGL, and ground speed: 70-106kts. Three GPS base stations, 2 Ashtech and 1 Trimble 4000SSI receivers (backup), were operating during the survey. The three base stations were at the following locations: one 3.5km south of San Luis Pass, one at the Scholes International Airport Galveston, and one on the seawall at Rollover Pass. This data set consists of 1687100 records of x,y, and z values. The data set was generated from a larger data set and includes all valid points within the requested geographic bounds.

Cite this dataset when used as a source.

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    Distribution Formats
    • LAZ
    Distributor DOC/NOAA/NOS/CSC > Coastal Services Center, National Ocean Service, National Oceanic and Atmospheric Administration, U.S. Department of Commerce
    Point of Contact Bureau of Economic Geology, University of Texas at Austin
    Documentation links not available.
    • DOC/NOAA/NOS/CSC > Coastal Services Center, National Ocean Service, National Oceanic and Atmospheric Administration, U.S. Department of Commerce
    • Bureau of Economic Geology, University of Texas at Austin
    • DOC/NOAA/NOS/CSC > Coastal Services Center, National Ocean Service, National Oceanic and Atmospheric Administration, U.S. Department of Commerce
    • publication: 2006-10-17
    Data Presentation Form: Digital image
    Dataset Progress Status Complete
    Data Update Frequency: As needed
    Supplemental Information: The ALTM 1225 has the following specifications: operating altitude = 410-2,000 m AGL; laser pulse rate = 25 kHz; laser scan angle = variable from 0 to +/-20deg from nadir; scanning frequency = variable, 28 Hz at the 20deg scan angle; and beam divergence = 0.2 milliradian (half angle, 1/e). The ALTM 1225 does not digitize and record the waveform of the laser reflection, but records the range and backscatter intensity of the first and last laser reflection using a constant-fraction discriminator and two Timing Interval Meters (TIM). ALTM elevation points are computed using three sets of data: laser ranges and their associated scan angles, platform position and orientation information, and calibration data and mounting parameters (Wehr and Lohr, 1999). Global Positioning System (GPS) receivers in the aircraft and on the ground provide platform positioning. The GPS receivers record pseudo-range and phase information for post-processing. Platform orientation information comes from an Inertial Measurement Unit (IMU) containing three orthogonal accelerometers and gyroscopes. An aided-Inertial Navigation System (INS) solution for the aircraft's attitude is estimated from the IMU output and the GPS information. Wehr, A. and U. Lohr, 1999, Airborne laser scanning - an introduction and overview, ISPRS Journal of Photogrammetry and Remote Sensing, vol. 54, no.2-3, pp.68-82.
    Purpose: The data described in this document are being used to create Digital Elevation Models of the Texas Coast. The DEMs are being used to map the position of the shoreline along the Gulf of Mexico coast of Texas for determining rates of shoreline change following Tropical Storm Fay (September 2002).
    Use Limitations
    • These data depict the elevations at the time of the survey and are only accurate for that time. Users should be aware that temporal changes may have occurred since this data set was collected and some parts of this data may no longer represent actual surface conditions. Users should not use this data for critical applications without a full awareness of its limitations. Any conclusions drawn from analysis of this information are not the responsibility of NOAA or any of its partners. These data are NOT to be used for navigational purposes.
    Time Period: Unknown  to  Unknown
    Spatial Reference System: urn:ogc:def:crs:EPSG::4269 Ellipsoid in Meters
    Spatial Bounding Box Coordinates:
    N: 29.688483
    S: 28.797218
    E: -93.831419
    W: -95.568694
    Spatial Coverage Map:
    • Bathymetry/Topography
    • lidar
    • laser
    • beach
    • topography
    • digital elevation model
    • DEM
    • erosion
    • Gulf of Mexico
    • Texas
    • Galveston Island
    • Lake Como
    Use Constraints No constraint information available
    Fees Fee information not available.
    Source Datasets
    • Raw lidar data output from ALTM 1225
      • Description of Source: Source Contribution: Raw lidar data files. Raw lidar data from ALTM 1225 Source Type: digital file
      • Temporal extent used:  unknown  to 
    • Air and Ground GPS files from 26102
      • Description of Source: Source Contribution: GPS data. Air and ground GPS files Source Type: digital file
      • Temporal extent used:  unknown  to 
    Lineage Statement Lineage statement not available.
    • Bureau of Economic Geology, The University of Texas at Austin
    • DOC/NOAA/NOS/CSC > Coastal Services Center, National Ocean Service, National Oceanic and Atmospheric Administration, U.S. Department of Commerce
    • DOC/NOAA/NESDIS/NGDC > National Geophysical Data Center, NESDIS, NOAA, U.S. Department of Commerce
    Processing Steps
    • Transfer raw ALTM 1225 flight data, airborne GPS data collected at 1 Hz using Ashtech receiver, and ground-based GPS data collected at 1 Hz using Ashtech and Trimble 4000SSI receivers to NT workstation. Generate decimated lidar point file from above three data sets using Optech's Realm 2.27 software. This is a 9-column ASCII data set with the following format: time tag; first pulse Easting, Northing, HAE; last pulse Easting, Northing, HAE; first pulse intensity; and last pulse intensity. View decimated lidar point file to check data coverage (i.e. sufficient overlap of flight lines and point spacing). Compute base station coordinates using National Geodetic Survey's PAGES software. Computed aircraft trajectories for both base stations using National Geodetic Survey's KINPOS software. Coordinates for base stations and trajectories are in the International Terrestrial Reference Frame of 2000 (ITRF2000) datum. Trajectories from both base stations were merged into one. Weighting for trajectory merge is based upon baseline length (distance from base station) and solution RMS. Transformed trajectory solution from ITRF2000 to North American Datum of 1983 (NAD83). Use NAD83 trajectories and aircraft inertial measurement unit data in Applanix's POSProc version 2.1.4 to compute an optimal 50Hz inertial navigation solution. Substitute the aircraft position and attitude information from the inertial navigation solution into Realm 2.27. Extract calibration area data set from lidar point file for quality control and instrument calibration checks. If necessary, use multiple iterations to adjust calibration parameters (pitch, roll, and scale) and reprocess sample data set. Then generate entire lidar point file (9-column ASCII file). Transfer point file from NT workstation to UNIX workstation. Parse the 9-column lidar point file into 3.75-minute quarter-quadrangle components and apply elevation bias correction (determined during calibration step). There are some points in the file that only contain 5-columns. These are points that either the first or last pulse was not recorded. Processing done over 20020918-20030211.
    • The 9-column post-processed data from University of Texas were provided in UTM projection (Zone 15) referenced to NAD83 with vertical elevations in meters referenced to the Geodetic Reference System 80 (GRS80) ellipsoid. The xyz values for the last return were extracted from the 9-column file. The data were converted to geographic coordinates using General Cartographic Transformation Program software developed by the United States Geological Survey. A vertical datum transformation was performed to convert vertical elevations referenced to GRS80 ellipsoid to NAVD88 using National Geodetic Survey (NGS) GEOID99 grids. The data were then converted to a binary format and loaded into the LIDAR Data Retrieval Tool (LDART) database.
    • The NOAA National Geophysical Data Center (NGDC) received lidar data files via ftp transfer from the NOAA Coastal Services Center. The data are currently being served via NOAA CSC Digital Coast at The data can be used to re-populate the system. The data are archived in LAS or LAZ format. The LAS format is an industry standard for LiDAR data developed by the American Society of Photogrammetry and Remote Sensing (ASPRS); LAZ is a loseless compressed version of LAS developed by Martin Isenburg ( The data are exclusively in geographic coordinates (either NAD83 or ITRF94). The data are referenced vertically to the ellipsoid (either GRS80 or ITRF94), allowing for the ability to apply the most up to date geoid model when transforming to orthometric heights.

    Metadata Last Modified: 2013-05-07

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