2008 USGS/NPS/NASA Experimental Advanced Airborne Research Lidar (EAARL): Assateague Island National Seashore

This is a bare earth data set that was collected 24-25 March 2008 along the shoreline of the Assateague Island National Seashore in

Maryland and Virginia. The data falls in these counties: Worcester (MD) and Accomack (VA). A footprint of the data coverage may be

viewed at: ftp://ftp.coast.noaa.gov/pub/crs/beachmap/kmzs/USGS_Assateague_Island_National_Seashore_Lidar.kmz

ASCII xyz point cloud data were produced from remotely sensed, geographically referenced elevation measurements cooperatively

by the U.S. Geological Survey (USGS), the National Park Service (NPS), and National Aeronautics and Space Administration (NASA).

Elevation measurements were collected over the area using the NASA Experimental Advanced Airborne Research Lidar (EAARL); a pulsed

laser ranging system mounted onboard an aircraft to measure ground elevation, vegetation canopy, and coastal topography. The system

uses high-frequency laser beams directed at the Earth's surface through an opening in the bottom of the aircraft's fuselage.

The laser system records the time difference between emission of the laser beam and the reception of the reflected laser signal in

the aircraft. The plane travels over the target area at approximately 50 meters per second at an elevation of approximately 300 meters.

The EAARL, developed by NASA at Wallops Flight Facility in Virginia, measures ground elevation with a vertical resolution of 15 centimeters.

A sampling rate of 3 kilohertz or higher results in an extremely dense spatial elevation dataset. Over 100 kilometers of coastline can be

easily surveyed within a 3- to 4-hour mission. When subsequent elevation maps for an area are analyzed, they provide a useful tool to

make management decisions regarding land development.

Original contact information:

Contact Name: Amar Nayegandhi

Contact Org: Jacobs Technology, U.S. Geological Survey, FISC, St. Petersburg, FL

Title: Computer Scientist

Phone: 727-803-8747 (x3026)

Email: anayegandhi@usgs.gov

The purpose of this project was to produce a highly detailed and accurate bare-earth digital elevation map of the Assateague

Island National Seashore in Virginia and Maryland for use as a management tool and to make these data available to natural resource

managers and research scientists.

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Raw lidar data are not in a format that is generally usable by resource managers and scientists for scientific analysis. Converting

dense lidar elevation data into a readily usable format without loss of essential information requires specialized processing.

The U.S. Geological Survey's Coastal and Marine Geology Program (CMGP) has developed custom software to convert raw lidar data

into a GIS-compatible map product to be provided to GIS specialists, managers, and scientists. The primary tool used in the conversion

process is Airborne Lidar Processing System (ALPS), a multi-tiered processing system developed by a USGS-NASA collaborative project.

Specialized processing algorithms are used to convert raw waveform lidar data acquired by the EAARL to georeferenced spot (x, y, z) returns

for "first surface" and "bare earth" topography. the zero crossing of the second derivative (that is, detection of local maxima) is used

to detect "first surface" topography, while the trailing edge algorithm (that is, the algorithm searches for the location prior to the

last return where direction changes along the trailing edge) is used to detect the range to the last return or "bare earth".

Statistical filtering, known as the Random Consensus Filter (RCF), is used to remove false bottom returns and other outliers from the

EAARL topography data. The filter uses a grid of non-overlapping square cells (buffer) of user-defined size overlaid onto the original

point cloud. The user also defines the vertical tolerance (vertical width) based on the topographic complexity and point sampling

density of the data. The maximum allowable elevation range within a cell is established by this vertical tolerance. An iterative

process searches for the maximum concentration of points within the vertical tolerance, and removes those points outside of the

tolerance (Nayegandhi and others, 2009). These data are then converted to the North American Datum of 1983 and the North American

Vertical Datum of 1988 (using the GEOID03 model).

The development of custom software for creating these data products has been supported by the U.S. Geological Survey CMG Program's

Decision Support for Coastal Parks, Sanctuaries, and Preserves project. Processed data products are used by the U.S. Geological

Survey CMG Program's National Assessments of Coastal Change Hazards project to quantify the vulnerability of shorelines to coastal

change hazards such as severe storms, sea-level rise, and shoreline erosion and retreat.

The LAS grid is encoded with a 1 meter resolution. The input parameters for the Random Consensus Filter were:

grid cell size (buffer) = 6 meters x 6 meters; vertical tolerance (vertical width) = 50 centimeters.

The variables measured by EAARL are distance between aircraft and GPS satellites (meters), attitude information (roll, pitch,

heading in degrees), scan angle (degrees), second of the epoch (seconds), and 1-nanosecond time-resolved return intensity waveform

(digital counts). Z value is referenced to orthometric elevations derived from National Geodetic Survey Geoid Model, GEOID03.

Although these data have been processed successfully on a computer system at the U.S. Geological Survey,

no warranty expressed or implied is made regarding the display or utility of the data on any other system, nor shall the act of

distribution imply any such warranty. The U.S. Geological Survey shall not be held liable for improper or incorrect use of the

data described and (or) contained herein. Reference herein to any specific commercial product, process, or service by trade name,

trademark, manufacturer, or otherwise does not constitute or imply its endorsement, recommendation, or favoring by the United

States Government or any agency thereof.

Any conclusions drawn from the analysis of this information are not the responsibility of NOAA, the Office for Coastal Management or

its partners.

Unclassified

None

This data can be obtained on-line at the following URL: https://coast.noaa.gov/dataviewer;

None

Users should be aware that temporal changes may have occurred since this data set was collected and some parts of this data may no

longer represent actual surface conditions. Users should not use this data for critical applications without a full awareness of its

limitations.

Microsoft Windows XP Version 5.1 (Build 2600) Service Pack 2; ESRI ArcCatalog 9.2.2.1350

The expected accuracy of the measured variables is as follows: attitude within 0.07 degree, 3-centimeter nominal ranging accuracy,

and vertical elevation accuracy of +/-15 centimeters for the topographic surface. Quality checks are built into the

data-processing software.

Raw elevation measurements have been determined to be within 1 meter in horizontal accuracy.

Elevations are vertically consistent with the point elevation data, +/-15 centimeters.

Several regions of the dataset are labeled as "No Data". These "No Data" areas are a result of the survey not covering a particular

region, optical water depth of greater than 1.5 Secchi disc depths, or the manual removal of lidar processing artifacts.

Unknown