| 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 Matagorda County, TX (approximately 1139 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, 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: 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