Use of Lidar in Coastal Studies

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Since 1998, airborne light detection and ranging, or lidar, capabilities have been developed and utilized to support CMHRP research projects and hazard assessments. Lidar is a remote-sensing technique that measures distance to a target by sending out light energy and detecting how long it takes the reflected pulses to return to the sensor. Lidar data provide information about the elevation, shape, and characteristics of Earth's surface. High-accuracy land and seafloor elevation data acquired using CMHRP-developed lidar have improved vulnerability assessments of coastal regions. The elevation data have been used to determine how coastal beaches, dunes, wetlands, and coral reefs changed after storms or other events.

Perspective view of coastal bathymetry looking onshore, St. Thomas, US Virgin Islands

Perspective view of coastal bathymetry looking onshore, St. Thomas, US Virgin Islands, mapped using lidar and depicted with false-color, showing detailed submerged features, including coral reefs. Credit: Xan Fredericks, USGS

Illustration of Airborne Lidar Acquisition Platform

Schematic illustrating elevation data acquisition through a lidar system mounted on a small aircraft. Credit: Betsy Boynton

Pre- and post- Hurricane Sandy elevation maps of Mantoloking, New Jersey

Pre- and post- Hurricane Sandy elevation maps of Mantoloking, New Jersey. At this location, storm surge and waves eroded the beach and dunes and a breach cut through the approximately 250-meter-wide island, destroying houses and roads. Overwash deposition occurred in many areas. Orange and red colors indicate higher elevations while yellow and green colors indicate lower elevations. Credit: USGS

Beach simulation of topography and bathymetry change during a storm.

Beach simulation of topography and bathymetry change during a storm. Pre-storm lidar data can be used to set up elevation grids for the model and post-storm lidar can be used in assessing how well the model performs. Credit: USGS

Applications to coastal vulnerability studies are represented well by the USGS response to Hurricane Sandy, which made landfall along the New Jersey coastline in 2012. USGS collected lidar data along the entire New Jersey coastline to document Sandy's impact. By including lidar data collected before the storm, the CMHRP is able to initialize coastal hazard models, predict coastal change, and document actual changes due to storms or other events. For example, at Mantoloking, New Jersey,  storm surge and waves eroded the beach and dunes, and the 250-meter-wide barrier island was completely breached, destroying houses and roads. Overwash deposition occurred in many areas. The CMHRP's lidar capability was utilized immediately after the storm before the breach had been filled, whereas the photo survey was conducted a few days later after the breach was filled.

East end of Fire Island depicted with airborne imagery and lidar

East end of Fire Island, showing white sandy beaches and marshes, depicted with airborne imagery, and lidar-derived bathymetric features in the estuary behind the island, in the offshore region, and in the channel connecting the estuary to the ocean. Credit: USGS

Lidar surveys of the northern Chandeleur Islands, LA, and Crocker Reef, FL

Lidar surveys of (left) the northern Chandeleur Islands, located in the northern Gulf of Mexico off the coast of Louisiana; and (right) Crocker Reef, a senile (dead) coral reef located southeast of the Florida Keys. Surveys such as these can resolve features of varying spatial scales, while repeat surveys can be used to analyze seafloor change over time. Credit: USGS

Lidar surveys are being used to assess the vulnerability of natural resources. Lidar resolution (approximately 1 m × 1 m) allows a broad range of seabed features to be distinguished at many different spatial scales, such as sand waves, island topography, and reefscapes. The high resolution is achieved rapidly over large distances (when there is sufficient water clarity), leading to efficient and effective resource characterization, particularly in relatively shallow and complex coastal areas, such as reefs and wetlands.