2010 USGS/NASA Experimental Advanced Airborne Research Lidar (EAARL): Chandeleur Islands, Louisiana (Bare-Earth)

A bare-earth digital elevation map (also known as a Digital Elevation Model, or DEM) of a portion of the Chandeleur Islands, Louisiana, was

produced from remotely sensed, geographically referenced elevation measurements cooperatively by the U.S. Geological Survey (USGS) and the

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 surveyed easily 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, St. Petersburg Coastal and Marine Science Center, St. Petersburg, FL

Title: Computer Scientist

Phone: 727 803-8747 (x3026)

Email: anayegandhi@usgs.gov

The purpose of this project was to produce highly detailed and accurate bare-earth digital elevation maps of a portion of the Chandeleur

Islands, Louisiana, 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 GEOID09 model). Each file contains data located in a 2-kilometer by 2-kilometer tile,

where the upper-left bound can be assessed quickly through the filename. The first 3 numbers in the filename represent the left-most UTM

easting coordinate (e###000) in meters, the next 4 numbers represent the top-most UTM northing coordinate (n####000) in meters, and the last

2 numbers (##) represent the UTM zone in which the tile is located (for example, be_e123_n4567_16).

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.

A footprint of this data set may be viewed in Google Earth at:

https://noaa-nos-coastal-lidar-pds.s3.amazonaws.com/laz/geoid18/1066/supplemental/2010_USGS_NASA_EAARL_Lidar_Chandeleur_Islands_Louisiana.kmz

LAS

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, GEOID09.

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

or its partners.

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

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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.

The U.S. Geological Survey and National Aeronautics and Space Administration request to be acknowledged as originators of this data in future

products or derivative research.

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 centimeters 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," which corresponds to a cell value of -32767 meters in the GeoTIFF file. 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. This metadata file is generalized; each data file on this DVD has its own corresponding

metadata file.

Each file contains data located in a 2-kilometer by 2-kilometer tile where the upper-left bound can be assessed quickly through the filename.

The first 3 numbers in the filename represent the left-most UTM easting coordinate (e###000) in meters, the next 4 numbers represent the top-most

UTM northing coordinate (n####000) in meters, and the last 2 numbers (##) represent the UTM zone in which the tile is located (for example,

be_e123_n4567_16).