2006 Texas Water Development Board (TWDB) Lidar: Aransas and Refugio Counties
This kmz file shows the extent of coverage for the 2006 TWDB Aransas and Refugio counties,
TX lidar data set.
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 Aransas and Refugio Counties, TX (approximately 282 square miles). Multiple returns
were recorded for each laser pulse along with an intensity value for each return.
The data acquisition occurred in missions in 2006. The data was collected by Sanborn
Mapping Company, Inc. for the Texas Water Development Board (TWDB)and the Federal
Emergency Management Agency (FEMA).
Cite this dataset when used as a source.
|Search and Download
|| Distributor information not available
| Point of Contact
Texas Natural Resources Information System (TNRIS)
- Texas Water Development Board (TWDB)
|Data Presentation Form:
|| Digital image
|Dataset Progress Status
|Data Update Frequency:
|| Not planned
||The Aransas and Refugio Counties data set was received from the Texas Water Development
Board (TWDB). It was reviewed by the NOAA Coastal Services Center at the macro level,
which includes checking for format and point characteristics for approximately 5%
of the tiles. In addition, the entire data set is reviewed to establish that bare
earth processing and proper classification of the points has been performed. It does
not include accuracy or data processing (e.g. bare earth quality, flightline mismatch,
feature removal) assessments. Based on the limited review, the data set on average
appeared to be of fair quality. No quantitative accuracy assessment was performed.
||This LIDAR operation was designed to provide a high density set of masspoints within
the defined areas. The data sets are suitable for the development of contours for
use in hydraulic/hydrologic model development, and for assessing environmental impacts.
Typical uses for the data set include: FEMA Flood Plain Map Modernization, DFIRM map
updates, watersheds and other hydro studies per FEMA specifications, county mapping
projects, and flood mitigation assessment.
||2006-06-01 to 2006-06-15
|Spatial Reference System:
|Spatial Bounding Box Coordinates:
|Spatial Coverage Map:
- Digital elevation model
- Digital terrain model
- Surface Model
- Hydrologic Modeling
- Drainage Area
- TNRIS (Texas Natural Resources Information System)
- United States
- Aransas County
- Refugio County
| Use Constraints
|| No constraint information available
|| Fee information not available.
|| Lineage statement not available.
- Sanborn Mapping
- DOC/NOAA/NESDIS/NGDC > National Geophysical Data Center, NESDIS, NOAA, U.S. Department
| Processing Steps
- 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 Aransas and Refugio Counties, TX (approximately 282 square miles). Multiple
returns were recorded for each laser pulse along with an intensity value for each
return. The data acquisition occurred in missions between XXXX, 2006 and XXXX, 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: IMU data is processed using the PosPac V4.2 software by
Applanix Corporation of Richmond Hill, Ontario, Canada. The reflective surface is
derived using the ALS Post Processor software by Leica Geosystems GIS & Mapping Division
of Atlanta, Georgia. 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,
- 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
- The NOAA Coastal Services Center (CSC) 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. CSC performed the following processing to the
data to make it available within the LDART Retrieval Tool (LDART): 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.
- 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 http://www.csc.noaa.gov/digitalcoast/.
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 (http://www.laszip.org/). 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
Metadata Last Modified: 2013-06-11
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