| Processing Steps
- System Calibration: Aero-Metric collected data over a previously surveyed area in
Palmer, Alaska. Data was collected at the same settings as this project, using two
intersecting perpendicular lines. Two GPS ground stations were operating on site in
order to minimize GPS error. The data was classified in each line separately for ground
and other common features between lines, such as building roofs. This data was processed
in TerraMatch 8.001 (TerraSolid, Ltd.), to compute corrections for roll, pitch, heading,
and mirror scale. These corrections were applied to the initial processing settings
(.res file). The data was reprocessed to verify the corrections were applied properly.
The corrected data was then compared to ground surveyed measurements in order to check
for any consistent vertical bias. The final step in calibration verified there was
minimal vertical noise due to changes in intensity. This was done by comparing elevations
of points on the airport runway, one point on a runway stripe and another adjacent
point on the pavement.
- Create a smoothed-best estimated trajectory (SBET) of the sensor at a rate of 200
Hz, by integrating the airborne GPS and IMU data. The basis of the GPS coordinates
were computed using NGS OPUS, and were referenced to NAD83 (CORS96) with GEOID06 derived
orthometric heights. The maximum baseline distance for this project was 30 km, the
average base line length was 12 km. The mean GPS positional accuracy for this project
was +/- 0.08 meters.
- Integrate SBET and raw laser data to produce point cloud data in LAS 1.1 format for
each flight line.
- Compute the roll, pitch, heading, and mirror scale correction factors for each flight
line, then apply corrections to the corresponding flight line.
- Automated classification of the bare-earth data from the lidar point cloud using a
series of algorithms customized for the types of terrain encountered in the project.
- Manual classification of any data which appears to be bare-earth but was not properly
classified using the automated methods.
- The shorelines of the lakes and port areas were determined using manual techniques,
starting with digitized shorelines from the orthophotography of the project area.
The lidar points then underwent an intensive manual edit to determine with greater
accuracy the points which represented the water surface. For the final data products
the mean elevation of the water on each lake was used to determine its fixed elevation.
The port areas fixed elevation was determined using the highest water point in the
port data set. This value was found to be 4.72 meters. All points below 4.72 meters
in the port area were fixed to this elevation, as per the contract.
- Create point clouds in LAS 1.1 format for all returns.
- Data verified using survey control points, located throughout the area.
- The metadata was updated for Bounding coordinates, Spatial Reference info using FGDC
- The NOAA Coastal Services Center (CSC) received topographic files in LAS 1.1 format.
The files contained lidar elevation and intensity measurements. The data were received
in projected coordinates of NAD83 UTM6N, meters and were vertically referenced to
NAVD88 orthometric elevations using GEOID06(Alaska). The vertical units of the data
were meters. CSC performed the following processing for data storage and Digital Coast
provisioning purposes: 1. LAS Classifications 11(first return only), 13(first of many
returns), 14(second of many returns), 15(third of many returns), 16(last of many returns)
were all placed into Class 1 (Unclassified) 2. The topographic las files were converted
from Projected Coordinates (NAD83 UTM6N, meters) to Geographic Coordinates (NAD83,
decimal degrees). 3. The topographic las files were vertically converted from orthometric
elevations (NAVD88) to ellipsoidal elevations (NAD83) using GEOID06. 4. The data were
converted to LAZ format.
- 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
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
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
the ellipsoid (either GRS80 or ITRF94), allowing for the ability to apply the most
up to date geoid model when transforming to orthometric heights.