2006 Texas Water Development Board (TWDB) Lidar: Brazoria County

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Date that the source FGDC record was last modified.

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

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Data Collection:

Using a LH Systems ALS50 Light Detection And Ranging (LiDAR) system, flight lines of standard density (1.4 meter ground

sample distance) data were collected over areas in Brazoria County, TX (approximately 1428 square miles). Multiple returns

were recorded for each laser pulse along with an intensity value for each return. The data acquisition occurred in 6 missions

between April 9, 2006, April 16, 2006, April 17, 2006, and May 11, 2006 through May 13, 2006. During the LIDAR campaign, the

Sanborn field crew conducted a GPS field survey to establish final coordinates of the ground base stations for final processing

of the base-remote GPS solutions.

Airborne GPS Processing:

Airborne GPS data was differentially processed and integrated with the post processed IMU data to derive a smoothed best

estimate of trajectory (SBET). The SBET was used to reduce the LiDAR slant range measurements to a raw reflective surface

for each flight line. The overlap between flight lines was removed to provide a homogeneous coverage, and the coverage was

classified to extract a bare earth digital elevation model (DEM). Airborne GPS is differentially processed using the

GrafNAV V7.50 software by Waypoint Consulting of Calgary, Alberta, Canada. The PDOP and distance separation is as follows:

1. IMU data is processed using the PosPac V4.2 software by Applanix Corporation of Richmond Hill, Ontario, Canada.

2. The reflective surface is derived using the ALS Post Processor software by Leica Geosystems GIS & Mapping Division of Atlanta,

Georgia.

3. The classification and quality control (QC) of LiDAR data is carried out using TerraScan software by Terrasolid Limited of

Helsinki, Finland.

IMU data Processing:

IMU data provides information concerning roll, pitch, and yaw of collection platform during collection event. IMU information

allows the pulse vector to be properly placed in 3D space allowing the distance from the aircraft reference point to be properly

positioned on the elevation model surface. IMU data is processed using the PosPac V4.2 software by Applanix Corporation of

Richmond Hill, Ontario, Canada.

Reflective Surface Generation:

The reflective surface is derived using the ALS Post Processor software by Leica Geosystems GIS & Mapping Division of Atlanta,

Georgia.

LIDAR Point Classification

The classification and quality control (QC) of LiDAR data is carried out using TerraScan software by Terrasolid Limited of

Helsinki, Finland.

Output LAS Files

The product output of LiDAR data is carried out using TerraScan software by Terrasolid Limited of Helsinki, Finland. LAS Binary,

ascii xyz, and intensity images were created.

The NOAA Office for Coastal Management (OCM) received the files in las format. The files contained Lidar

elevation and intensity measurements. The data was in UTM projection, and NAVD88 Geoid 03 vertical datum. OCM performed

the following processing to the data to make it available within the Digital Coast Data Access Viewer (DAV):

1. The data were converted from UTM coordinates to geographic coordinates.

2. The data were converted from NAVD88 (orthometric) heights to GRS80 (ellipsoid) heights using Geoid 03.

3. The LAS data were sorted by latitude and the headers were updated.