- Woolpert, Inc.
- DOC/NOAA/NOS/CSC > Coastal Services Center, National Ocean Service, National Oceanic
and Atmospheric Administration, U.S. Department of Commerce
- DOC/NOAA/NESDIS/NGDC > National Geophysical Data Center, NESDIS, NOAA, U.S. Department
| Processing Steps
- Block 7(partial) and 8 - Using an Optech Gemini LiDAR system, 152 flight lines of
high density data, at a nominal pulse spacing (NPS) of 1.5 meter (1.0 meters for Floyd
and Dearborn Counties)and Blocks 5, 6, and 7(partial) - Using Leica ALS LiDAR systems,
219 flight lines of high density data were collected, at a nominal pulse spacing (NPS)
of 1.5 meter. Multiple returns were recorded for each laser pulse along with an intensity
value for each return. A total of thirty (30) missions were flown January 31, 2012
December 13, 2012. Eleven (11) airborne global positioning system (GPS) base stations
were used in support of the LiDAR data acquisition. 248 ground control points were
surveyed through static methods. The geoid used to reduce satellite derived elevations
to orthometric heights was Geoid09. The horizontal datum used for this survey is North
American Datum 1983 (NSRS2007), Indiana State Plane Coordinate System, East Zone,
and expressed in US Survey Feet. The vertical datum used for this survey is North
American Vertical Datum 1988 (NAVD88), and expressed in US Survey Feet. 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.
System Parameters: - Type of Scanner = Optech Gemini - Data Acquisition Height = 7,380-feet
AGL - Scanner Field of View = 20 degrees - Scan Frequency = 32 Hertz - Pulse Repetition
Rate - 100.0 Kilohertz - Aircraft Speed = 150 Knots - Swath Width = 5374 feet - Number
of Returns Per Pulse = Maximum of 4 - Distance Between Flight Lines = Varies. System
Parameters: - Type of Scanner = Leica ALS50-II / ALS60 / ALS70 - Data Acquisition
Height = 7800 feet AGL - Scanner Field of View = 40 degrees - Scan Frequency = Varies
- Pulse Repetition Rate - 99 Kilohertz - Aircraft Speed = Varies - Swath Width = 5678
feet - Number of Returns Per Pulse = Maximum of 4 - Distance Between Flight Lines
- The Optech Gemini and Leica systems' LiDAR system calibration and performance is verified
on a periodic basis using Woolpert's calibration range. The calibration range consists
of a large building and runway. The edges of the building and control points along
the runway have been located using conventional survey methods. Inertial measurement
unit (IMU) misalignment angles and horizontal accuracy are calculated by comparing
the position of the building edges between opposing flight lines. The scanner scale
factor and vertical accuracy is calculated through comparison of LiDAR data against
control points along the runway. Field calibration is performed on all flight lines
to refine the IMU misalignment angles. IMU misalignment angles are calculated from
the relative displacement of features within the overlap region of adjacent (and opposing)
flight lines. The raw LiDAR data is reduced using the refined misalignment angles.
- Once the data acquisition and GPS processing phases are complete, the LiDAR data was
processed immediately to verify the coverage had no voids. The GPS and IMU data was
post processed using differential and Kalman filter algorithms to derive a best estimate
of trajectory. The quality of the solution was verified to be consistent with the
accuracy requirements of the project.
- The individual flight lines were inspected to ensure the systematic and residual errors
have been identified and removed. Then, the flight lines were compared to adjacent
flight lines for any mismatches to obtain a homogenous coverage throughout the project
area. The point cloud underwent a classification process to determine bare-earth points
and non-ground points utilizing "first and only" as well as "last of many" LiDAR returns.
This process determined bare-earth points (Class 2), noise (Class 7), water (Class
9) ignored ground (Class 10), unclassified data (Class 1), overlap points (Class 12),
and bridges (Class 13). The bare-earth (Class 2 - Ground) LiDAR points underwent a
manual QA/QC step to verify that artifacts have been removed from the bare-earth surface.
The surveyed ground control points are used to perform the accuracy checks and statistical
analysis of the LiDAR dataset.
- Breaklines defining lakes, greater than two acres, and double-line streams, wider
than 100 feet (30.5 meters), were compiled using digital photogrammetric techniques
as part of the hydrographic flattening process and provided as ESRI Polyline Z and
Polygon Z shape files. Breaklines defining water bodies and streams were compiled
for this task order. The breaklines were used to perform the hydrologic flattening
of water bodies, and gradient hydrologic flattening of double line streams. Lakes,
reservoirs and ponds, at a nominal minimum size of two (2) acres or greater, were
compiled as closed polygons. The closed water bodies were collected at a constant
elevation. Rivers and streams, at a nominal minimum width of 100 feet (30.5 meters),
were compiled in the direction of flow with both sides of the stream maintaining an
equal gradient elevation. The hydrologic flattening of the LiDAR data was performed
for inclusion in the National Elevation Dataset (NED).
- The NOAA Coastal Services Center (CSC) received the files in las format. The files
contained Lidar elevation and intensity measurements. The data were in Indiana State
Plane projection east (1301) in feet and NAVD88 Geoid 09 vertical datum. CSC performed
the following processing to the data to make it available within the Digital Coast:
1. The data were converted from State Plane coordinates to geographic coordinates.
2. The data were converted from NAVD88 (orthometric) heights to GRS80 (ellipsoid)
heights using Geoid 03. 3. The high and low error outlier elevations were removed
and variable length records (vlr) were removed. 4. The LAS data were sorted by latitude
and the headers were updated. 5. Originally classed points as bridges (classification
13) were moved to ASPRS class 17 (bridge deck). 6. The data were converted to LAZ
- 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.