2007 USGS/NPS/NASA Experimental Advanced Airborne Research Lidar (EAARL): Northern Gulf of Mexico Barrier Islands

A bare earth elevation map (also known as a Digital Elevation Model, or DEM) of the northern Gulf of Mexico barrier islands and Naval

Live Oaks was produced from remotely sensed, geographically referenced elevation measurements cooperatively by the U.S. Geological

Survey (USGS), the National Park Service (NPS), and the National Aeronautics and Space Administration (NASA). This data set provides the

those bare earth elevation measurements of the barrier islands in the following counties:

St. Bernard in LA, Harrison and Jackson in MS, Mobile and Baldwin in AL, and Escambia and Santa Rosa in FL.

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

managers with a useful tool to make management decisions regarding land development.

Original contact information:

Contact Name: Amar Nayegandhi or John Brock at USGS

Contact Org: Jacobs Technology, contracted to USGS

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 northern Gulf

of Mexico barrier islands for use as a management tool and to make these data available to natural resource managers and research

scientists.

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Unprocessed Lidar data are not in a format that is generally usable by resource managers and scientists. 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 (CMG) Program has developed custom software to convert unprocessed 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 Advanced

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

algorithms are used to convert unprocessed waveform Lidar data acquired by the EAARL to georeferenced spot (x, y, z) returns for

"bare earth" topography. These data are then converted to the North American Datum of 1983 and the North American Vertical Datum of 1988

(using the GEOID 03 model). The files are in the Quarter-Quad tiling format and are named after the U.S. Geological Survey Alpha

Quarter-Quad naming convention ('QQ_naming_convention.doc'). 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 variables measured by EAARL are: distance between aircraft and GPS satellites (m), attitude information (roll, pitch, heading in

degrees), scan angle (degrees), second of the epoch (sec), and 1-ns 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 herin 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;

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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.

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

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

and vertical elevation accuracy of +/-15 cm for the topographic surface. Quality checks are built into the data-processing software.

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

Elevations of the DEM are vertically consistent with the point elevation data, +/-15 cm.

Several regions of the dataset are labeled as "No Data", which corresponds to a cell value of -32767 m in the LAS 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.

Each file contains data located in USGS 24K Quarter Quadrangle tile and are named after the USGS Alpha Quarter Quad naming convention.

AAOOOaoq, where AA is the positive whole number component of the latitude. OOO is the positive whole number component of the longitude

(zero-padded to a width of 3); a is an alpha character a-h designating which quad in the degree of latitude; where a is closest to 0 minutes

and h is closest to the next full degree. Each represents 1/8 of a degree; o is a numeral 1-8 designating which quad in the degree of

longitude, where 1 is closest to 0 minutes and 8 is closest to the next full degree. Each represents 1/8 of a degree; q is an alpha

character a-d designating which quarter in the quad, where a is SE, b is NE, c is NW, and d is SW. Each quarter-quad is 1/16 of a degree

in latitude and 1/16 of a degree in longitude.