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OCM Partners, 2023: 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,

Item Identification

Title: 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
Short Name: utexas2002_m13_metadata
Status: Completed
Publication Date: 2006-10-17

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.

Original contact information:

Contact Name: Jim Gibeaut

Contact Org: Bureau of Economic Geology University of Texas at Austin

Title: Research Associate

Phone: 512-471-0344



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).



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 +/-20 deg from nadir; scanning frequency = variable, 28 Hz at the 20 deg 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.


Theme Keywords

Thesaurus Keyword
ISO 19115 Topic Category
None Beach
None Erosion

Temporal Keywords

Thesaurus Keyword
None 2002

Physical Location

Organization: Office for Coastal Management
City: Charleston
State/Province: SC

Data Set Information

Data Set Scope Code: Data Set
Maintenance Note:

None planned, as needed

Distribution Liability:

Any conclusions drawn from analysis of this information are not the responsibility of the Bureau

of Economic Geology or the University of Texas at Austin, the NOAA Office for Coastal Management or its partners.

Data Set Credit: Bureau of Economic Geology, University of Texas at Austin: J. Gibeaut, R. Gutierrez, J. Andrews, T. Hepner, and R. Smyth

Support Roles

Data Steward

CC ID: 691277
Date Effective From: 2006-10-17
Date Effective To:
Contact (Organization): NOAA Office for Coastal Management (NOAA/OCM)
Address: 2234 South Hobson Ave
Charleston, SC 29405-2413
Email Address:
Phone: (843) 740-1202


CC ID: 691279
Date Effective From: 2006-10-17
Date Effective To:
Contact (Organization): NOAA Office for Coastal Management (NOAA/OCM)
Address: 2234 South Hobson Ave
Charleston, SC 29405-2413
Email Address:
Phone: (843) 740-1202

Metadata Contact

CC ID: 691280
Date Effective From: 2006-10-17
Date Effective To:
Contact (Organization): NOAA Office for Coastal Management (NOAA/OCM)
Address: 2234 South Hobson Ave
Charleston, SC 29405-2413
Email Address:
Phone: (843) 740-1202

Point of Contact

CC ID: 691278
Date Effective From: 2006-10-17
Date Effective To:
Contact (Organization): NOAA Office for Coastal Management (NOAA/OCM)
Address: 2234 South Hobson Ave
Charleston, SC 29405-2413
Email Address:
Phone: (843) 740-1202


Currentness Reference: Ground Condition

Extent Group 1

Extent Group 1 / Geographic Area 1

CC ID: 1132925
W° Bound: -95.568694
E° Bound: -93.831419
N° Bound: 29.688483
S° Bound: 28.797218

Extent Group 1 / Time Frame 1

CC ID: 1132924
Time Frame Type: Discrete
Start: 2002-09-18

Spatial Information

Spatial Representation

Representations Used

Vector: Yes

Access Information

Security Class: Unclassified
Data Access Procedure:

This data can be obtained on-line at the following URL:


Data Access Constraints:


Data Use Constraints:

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.

Distribution Information

Distribution 1

CC ID: 743139
Download URL:
File Name: Customized Download

Create custom data files by choosing data area, product type, map projection, file format, datum, etc.

Distribution 2

CC ID: 743140
Download URL:
File Name: Bulk Download

Simple download of data files.



CC ID: 743142
URL Type:
Online Resource


CC ID: 743143
URL Type:
Online Resource

Activity Log

Activity Log 1

CC ID: 691299
Activity Date/Time: 2016-05-23

Date that the source FGDC record was last modified.

Activity Log 2

CC ID: 691298
Activity Date/Time: 2017-11-14

Converted from FGDC Content Standards for Digital Geospatial Metadata (version FGDC-STD-001-1998) using '' script. Contact Tyler Christensen (NOS) for details.

Activity Log 3

CC ID: 718726
Activity Date/Time: 2018-02-08

Partial upload of Positional Accuracy fields only.

Activity Log 4

CC ID: 743141
Activity Date/Time: 2018-03-13

Partial upload to move data access links to Distribution Info.

Data Quality

Horizontal Positional Accuracy:

Selected portions from each lidar data set (last return only) were used to generate a

1m x 1m digital elevation model (DEM). Data estimated to have a horizontal accuracy of 0.01-0.03m from ground surveys using

kinematic GPS techniques were superimposed on the lidar DEM and examined for any mismatch between the horizontal position of

the ground GPS and the corresponding feature on the lidar DEM. Horizontal agreement between the ground kinematic GPS and the

lidar was within the resolution of the 1m x 1m DEM.

Vertical Positional Accuracy:

Ground GPS surveys were conducted within the lidar survey area to acquire ground "truth"

information. The ground survey points are estimated to have a vertical accuracy of 0.01-0.05m. Roads, which are open areas with

an unambiguous surface, were surveyed using kinematic GPS techniques. A lidar data set was sorted to find data points that fell

within 0.5m of a ground GPS survey point. The mean elevation difference between the lidar and the ground GPS was used to estimate

and remove an elevation bias from the lidar. The standard deviation of these elevation differences provides estimates of the lidar

precision. The 2002 lidar data set was determined to have an elevation bias of 0.06m when compared to ground truth. The 0.06m bias

was removed so that mean lidar elevations conform to NAVD88 with an RMSE of 0.103m.

Completeness Report:

Data were edited to remove outliers with ranges above 2200m and below -100m.

Conceptual Consistency:

Not applicable



Air and Ground GPS files from 26102

CC ID: 1132919
Publish Date: 2002-09-18
Extent Type: Discrete
Extent Start Date/Time: 2002-09-18
Source Contribution:

air and ground GPS files | Type of Source Media: digital file

Raw lidar data output from ALTM 1225

CC ID: 1132920
Publish Date: 2002-09-18
Extent Type: Discrete
Extent Start Date/Time: 2002-09-18
Source Contribution:

raw lidar data from ALTM 1225 | Type of Source Media: digital file

Process Steps

Process Step 1

CC ID: 1132921

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 occurred 20020918-20030211.

Process Date/Time: 2002-09-18 00:00:00

Process Step 2

CC ID: 1132922

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.

Process Date/Time: 2003-02-24 00:00:00

Catalog Details

Catalog Item ID: 50121
GUID: gov.noaa.nmfs.inport:50121
Metadata Record Created By: Anne Ball
Metadata Record Created: 2017-11-15 15:24+0000
Metadata Record Last Modified By: SysAdmin InPortAdmin
Metadata Record Last Modified: 2022-08-09 17:11+0000
Metadata Record Published: 2022-03-16
Owner Org: OCMP
Metadata Publication Status: Published Externally
Do Not Publish?: N
Metadata Last Review Date: 2022-03-16
Metadata Review Frequency: 1 Year
Metadata Next Review Date: 2023-03-16