2006 Maryland Department of Natural Resources Lidar: Caroline, Kent and Queen Anne Counties

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Maryland Department of Natural Resources requested the collection of LIDAR data over Kent, Queen Anne and

Caroline Counties, MD. In response EarthData acquired the data from March 18 through April 6, 2006 using its aircraft

with tail number N62912. LIDAR data was captured using an ALS50 LIDAR system, including an inertial

measuring unit (IMU) and a dual frequency GPS receiver. An additional GPS receiver was in constant operation over

a published control point set by EarthData at the base of operations airport which is a secondary Airport Control

Station. During the data acquisition, the receivers collected phase data at an epoch rate of 1 Hz. The use of the

Airport base station ensured that all data capture was performed within 50 miles of a base station. The solutions

from Kent, Queen Anne and Caroline counties were found to be of high integrity and met the accuracy requirements

for the project. These accuracy checks also verified that the data meets the guidelines outlined in FEMA's Guidelines

and Specifications for Flood Hazard Mapping Partners and Appendix 4B, Airborne Light Detection and Ranging

Systems.

Airspeed - 140 knots

Laser Pulse Rate - 52700 kHz

Field of View - 40 degrees

ScanRate - 30 Hz

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

Earthdata International was contracted to provide LIDAR mapping services in the area of Caroline, Kent, and Queen

Anne's Counties, Maryland. Earthdata subcontracted the ground survey tasks to TerraSurv, Inc. The Global

Positioning System (GPS) was used to establish the control network.

The horizontal datum was the North American Datum of 1983, CORS adjustment (NAD 1983 CORS). The vertical

datum was the North American Vertical Datum of 1988(NAVD 1988).

There were a total of 27 stations occupied for this project. There were 19 new LIDAR control stations, 2 temporary

GPS base stations, 3 existing NSRS control stations, 2 CORS stations, and 1 airborne GPS base station used by

the flight crew. The network was observed in a radial configuration. A base receiver was established on a random

point and run throughout the observations in each area. Due to the large area covered, multiple base locations

were used. The temporary base stations were tied to the CORS and NSRS control stations.

| 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 LAS 1.0 format and also converted to ASCII

8. The point cloud data were also delivered in LAS 1.0

format and also converted to ASCII.

EarthData utilizes a combination of proprietary and COTS processes to generate intensity images from

the lidar data. Intensity images are generated from the full points cloud (minus noise points) and the pixel

width is typically matched to the post spacing of the lidar data to achieve the best resolution.

The following steps are used to produce the intensity:

1) Lidar point cloud is tiled to the deliverable tile layout.

2) All noise points, spikes, and wells are deleted out of the tiles.

3) An EarthData proprietary piece of software, EEBN2TIF is then used to process out the intensity values of the lidar.

At this point, the pixel size is selected based on best fit or to match the client specification if noted in the SOW.

4) The software then generates TIF and .TFW files for each tile.

5) ArcView is used to review and QC the tiles before delivery.

The NOAA Office for Coastal Management (OCM) received the files in las and ASCII format. The data were in

Maryland State Plane Projection, NAVD88 vertical datum and the vertical units of measure were meters. OCM performed

the following processing to the las data to make it available within Digital Coast:

1. The data were converted from Maryland State Plane 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.