1999 Post Hurricane Dennis NOAA/USGS/NASA Airborne LiDAR Assessment of Coastal Erosion (ALACE) Project for the US Coastline

This data set includes data collected in 1999 after Hurricane Dennis and before Hurricane Floyd along the outer banks of North Carolina. Laser beach mapping uses a pulsed laser ranging system mounted onboard an aircraft to measure ground elevation and coastal topography. The laser emits laser beams at high frequency and is directed downward at the earth's surface through a port 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 aircraft travels over the beach at approximately 60 meters per second while surveying from the low water line to the landward base of the sand dunes.

Original contact information:

Contact Org: NOAA Office for Coastal Management

Phone: 843-740-1202

Email: coastal.info@noaa.gov

This data was collected as part of an effort to map beach topography and assess beach change along the US coastline.

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This data set was collected with a LIDAR (LIght Detection And Ranging) instrument designed and developed by the Observational Sciences Branch (OSB) of NASA at the Wallops Flight Facility in Virginia. The instrument, originally designed for mapping ice sheets in Greenland, is called the Airborne Topographic Mapper or ATM. The ATM II (the latest version), operates with a Spectra Physics laser transmitter, which provides a 7 nanoseconds long, 250 microjoules pulse at a frequency-doubled wavelength of 523 nanometers in the blue-green spectral region. The laser transmitter can function at pulse rates from 2 to 10 kilohertz (kHz). The laser system with a separate cooling unit weighs approximately 45 kilograms (kg) and requires approximately 15 amperes of power at 115 volts. The transmitted laser pulse is reflected to the surface of the earth with the aid of a small folding mirror mounted on the back of a secondary mirror of a rotating scan mirror assembly mounted directly in front of the telescope. The scan mirror, which is rotated at 20 hertz, is comprised of a section of round aluminum stock, machined to a specific off-nadir angle. A scan mirror with the off-nadir angle of 15 degrees was utilized, producing an elliptical scan pattern with a swath width equal to 50 percent of the approximately 700-meter aircraft altitude. The reflected laser pulse is transmitted to a photo-multiplier assembly that consists of a lens, a narrow bandpass filter, and a single photomultiplier tube. Note: The Spatial Reference section of this document may lack fully FGDC-compliant information regarding projection parameters (i.e., Central meridian, false Northing, etc.). The State Plane or UTM Zone will be supplied, and the corresponding parameters can be found in Appendix C of: Snyder, John, 1987, Map Projections, a Working Manual (U.S. Geological Survey Professional Paper 1395): Washington, U.S. Government Printing Office.

This data was collected for the purposes of research. Any conclusions drawn from analysis of this information are not the responsibility

of NOAA, the Office for Coastal Management, or its partners.

This data can be obtained on-line at the following URL: https://coast.noaa.gov/dataviewer. The data set is dynamically generated based on

user-specified parameters.

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None

This data was collected for the purposes of research. Any conclusions drawn from analysis of this information are not the responsibility of NOAA or the Office for Coastal Management. This data is likely to contain returns from the water surface and vegetation. No processing has been done to remove returns from water or vegetation. 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.

Raw elevation measurements have been determined to be vertically accurate to within 15 cm. Processing steps (datum conversion, projection, grid interpolation, etc.) introduce additional error factors which have not been tested at the time of this publication.

The ATM LIDAR elevation points are known to be horizontally accurate to +/- 0.8 meters at an aircraft altitude of 700 meters.

The ATM LIDAR elevation measurements have been found to be within +/- 15 centimeters of each other in successive and overlapping

passes of the same area. In comparisons of LIDAR data for a small geographic region with various ground surveys the differences

are between +/- 15 to 20 centimeters. The accuracy of the majority of the data is estimated to be consistent with the above

stated results. At this time, there has been no large scale verification of the data.

All elevation data points that appeared to be within a reasonable vertical range were retained, and other points were thrown away.

This filtering process was performed 'by eye'.

Not applicable