2004 Harrison County, Mississippi Lidar Mapping

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EarthData Aviation. was contracted by EarthData International to collect ALS-40 Lidar data over Harrison

County, Mississippi. The project site was flown on March 8th and 9th 2004 using a Horizons, Inc. aircraft with tail number

N97HC. 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 11,100 feet above mean terrain, at an average airspeed of 120 knots. Sensor

pulse rate was set at 20 kHz with a field of view of 45 degrees and a rate of 11.0 Hz. Average swath width of the collected

raw lines is 9,112.7 feet. Point spacing was 5 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 Gulfport airport. Recorded digital data was

shipped via external hard drive to the production facility for processing. During airborne data collection, an additional 46

GPS control points were established throughout the airport. 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.

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

Waggoner Engineering in contract to EarthData International established at total of 9 survey points within

Harrison County, MS.

| 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 9001compliant 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 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.

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

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

8. Project data was clipped to a 500-meter buffer outside of the official project boundary.

The NOAA Office for Coastal Management (OCM) received LAS files containing the bared-earth elevation and intensity

data from URS. OCM performed the following processing on the data to make it available within the Lidar Data Retrieval Tool

(LDART):

1. The data were projected from MS State Plane coordinates to geographic decimal degrees using the General Cartographic

Transformation Package.

2. The data were sorted based on latitude.

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

ellipsoid elevations using Geoid 03.