• What is LIDAR Beach Mapping Data?
• Collecting Beach Mapping Data
• Traditional Beach Surveying vs. LIDAR Beach Mapping

LIDAR beach mapping data are a remotely sensed data set collected with a Light Detection and Ranging (LIDAR) sensing instrument. Currently, this technology is being used by National Oceanic and Atmospheric Administration (NOAA), NASA, and United States Geological Survey (USGS) researchers to document topographic change along shorelines. These data are collected with aircraft- mounted lasers capable of recording elevation measurements at a rate of 2,000 to 5,000 data points per second and have a vertical precision of 15 centimeters (6 inches). After a baseline data set has been created, follow-up flights can be used to detect shoreline changes. To view a reference list on emerging remote sensing technology, please visit the General Data Resources section of the CD-ROM.

Collecting Beach Mapping Data

The laser beam itself does not move. However, there is a small folding scan mirror mounted to the LIDAR sensing instrument, which can be rotated. The mirror has a 30-degree tilt and rotates so that the laser beam takes elevation measurements in an elliptical area approximately 300 meters (1000 feet) wide.

The LIDAR sensing instruments only collect elevation data. To make these data spatially relevant, the positions of the data points must be known. A high-precision Global Positioning System (GPS) antenna is mounted on the upper aircraft fuselage. As the LIDAR sensor collects data points, the location of the data are simultaneously recorded by the GPS sensor. After the flight, the data are downloaded and processed using specially designed computer software. The end product is accurate, geographically registered longitude, latitude, and elevation (x,y,z) positions for every data point. These "x,y,z" data points allow the generation of a digital elevation model (DEM) of the ground surface.

Beach mapping data sets cover an area from the low water line inland approximately 300 meters (1000 feet). Flights are planned to ensure the most elevation points can be collected at the lowest tide for the largest area possible. The aircraft flight path is generally parallel to the beach. Four passes are flown over each section of the beach. Two of these passes are flown so the center of the swath is over the sand/water interface. The other two passes are flown over the center of the sand/development interface.

A flight will generally last four hours. Weather conditions must be monitored. The flights cannot be flown during times of rain or fog as the water vapor in the air could cause the laser beams to scatter and give false readings. Additionally, the plane cannot fly during times of high winds as the returned laser pulse will not be recorded correctly.

Traditional Beach Surveying vs. LIDAR Beach Mapping

The LIDAR airborne laser beach mapping data set featured on this CD-ROM is currently being evaluated for its utility in mapping elevations and shoreline change on North Carolina beaches. The LIDAR data referenced on this CD-ROM are derived from an aircraft remote sensing technique used to gather coastal topographic measurements.  This technique provides coastal resource managers the opportunity to gather regional, high spatial resolution coverage of beach elevations with high vertical and horizontal accuracy.  Using LIDAR data to collect shoreline topography is proving to be faster and less costly than traditional beach surveying methods.  Many coastal states may benefit from this technology, as shoreline measurements are needed to determine erosion rates, setback lines, and sand volume needs for beach nourishment projects.  Shoreline change measurements can also help coastal resource managers measure the effects of jetties, groins, seawalls, and the effectiveness of beach nourishment projects. For more information about LIDAR data, click here.
 
 

Beach Survey Team	Resulting Survey Data

Using traditional beach survey methods, data are collected in a transect seaward from a benchmark. To cover a large area of beach using traditional beach surveying methods, it takes many person hours. Conversely, remotely sensed LIDAR data could potentially provide a more cost-effective, efficient means of collecting topographic information as long as sub-tidal data are not needed. Furthermore, the data set collected is extremely dense, accounting for topographic changes along the entire beach rather than just along transect lines. Comparisons of LIDAR survey data to standard GPS survey methods agree to within a random error of approximately 15 centimeters (6 inches) ("An Assessment of NASA's Airborne Topographic Mapper Instrument for Beach Topographic Mapping at Duck, North Carolina"). The error is due to the limits of the GPS technology used by both survey methods.
 
 

Airborne Topographic Mapper	Survey Transect Line Overlain on LIDAR Data