2003 Oahu Coastline Lidar

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Horizons Inc. was contracted by EarthData International to collect ALS-40 Lidar data over the coastal area of

Oahu, Hawaii. The project site was flown on October 21 and November 1, 8, 24, 27, and December 7, 2003, using aircraft 2636P.

Lidar data was captured using an ALS-40 Lidar system, including an inertial measuring unit (IMU) and a dual frequency GPS receiver.

Lidar was obtained at an altitude of 1,524 meters (5,000 feet) above mean terrain, at an average airspeed of 110 knots. Sensor pulse

rate was set at 20,000 Hz with a field of view of 20 degrees and a scan rate of 19 Hz. Average swath width of the collected raw

lines is 537 meters. Point spacing was 2 meters. Lidar data was recorded in conjunction with airborne GPS and IMU; the stationary

GPS receiver was positioned over a control point located at the airport. Recorded digital data was shipped via external hard drive

to the production facility for processing. During airborne data collection, an additional GPS receiver was in constant operation

over a published National Geodetic Survey (NGS) control point at Honolulu Airport. The coordinate value for temporary control point

"PHNL" was determined by a network adjustment to CORS stations EHN1 and HNLC, both of which were tied to the project control

network. During the data acquisition, the receivers collected phase data at an epoch rate of 1 Hz. All GPS phase data was post

processed with continuous kinematic survey techniques using "On the Fly" (OTF) integer ambiguity resolution. The GPS data was

processed with forward and reverse processing algorithms. An adjustment was made to the ellipsoid height of the published point by

Terrasurv to reflect Local Tidal Elevation. The results from each process, using the data collected at the airport, were combined

to yield a single fixed integer phase differential solution of the aircraft trajectory.

| Source Geospatial Form: Model | Type of Source Media: Firewire Drive

Kevin Chappell, of Terrasurv and under contract to EarthData International established 30 ground control

points along the coastline of the island of Oahu and within a blocked area around Honolulu where the 2005 flight was flown. The

points were surveyed using GPS for both vertical and horizontal coordinate values. The horizontal datum used was the North American

Datum of 1983 (Pacific Plate Fixed Realization, epoch 2002.0). The vertical datum used was a Local Tidal Datum.

| Source Geospatial Form: Diagram | Type of Source Media: Electronic mail system

EarthData has developed a unique method for processing lidar data to identify and remove elevation points falling

on vegetation, buildings, and other aboveground structures. The algorithms for filtering data were utilized within EarthData's

proprietary software and commercial software written by TerraSolid. This software suite of tools provides efficient processing

for small to large-scale, projects and has been incorporated into ISO 9001 compliant production work flows. The following is a

step-by-step breakdown of the process.

1. Using the lidar data set provided by EarthData, the technician performs calibrations on the data set.

2. Using the lidar data set provided by EarthData, the technician performed a visual inspection of the data to verify that the

flight lines overlap correctly. The technician also verified that there were no voids, and that the data covered the project limits.

The technician then selected a series of areas from the data set and inspected them where adjacent flight lines overlapped. These

overlapping areas were merged and a process which utilizes 3-D Analyst and EarthData's proprietary software was run to detect and

color code the differences in elevation values and profiles. The technician reviewed these plots and located the areas that

contained systematic errors or distortions that were introduced by the lidar sensor.

3. Systematic distortions highlighted in step 2 were removed and the data was re-inspected. Corrections and adjustments can

involve the application of angular deflection or compensation for curvature of the ground surface that can be introduced by crossing

from one type of land cover to another.

4. The lidar data for each flight line was trimmed in batch for the removal of the overlap areas between flight lines. The data

was checked against a control network to ensure that vertical requirements were maintained. Conversion to the client-specified

datum and projections were then completed. The lidar flight line data sets were then segmented into adjoining tiles for batch

processing and data management.

5. The initial batch-processing run removed 95% of points falling on vegetation. The algorithm also removed the points that fell

on the edge of hard features such as structures, elevated roadways and bridges.

6. The operator interactively processed the data using lidar editing tools. During this final phase the operator generated a

TIN based on a desired thematic layer to evaluate the automated classification performed in step 5. This allowed the operator

to quickly re-classify points from one layer to another and recreate the TIN surface to see the effects of edits. Geo-referenced

images were toggled on or off to aid the operator in identifying problem areas. The data was also examined with an automated

profiling tool to aid the operator in the reclassification.

7. The final DEM was written to an ESRI grid format (.flt).

8. The point cloud data were also delivered in LAS format.

The NOAA Office for Coastal Management (OCM) received LAS files containing the point cloud elevation data from Earth

Data, Inc. OCM performed the following processing on the data to make it available within the Lidar Data Retrieval Tool (LDART):

1. Variable length header records were added to the LAS files to identify projection, datum and sort order.

2. The LAS files were sorted by latitude.

For data management purposes, the Office for Coastal Management converted the data from NAVD88 elevations to

ellipsoid elevations using Geoid 99.