Monitoring Shoreline Change

Shorelines are constantly changing, highly dynamic environments. The USGS uses several techniques to measure shoreline change including laser altimetry (surface elevation measurements), shoreline surveying and oblique photography.

LIDAR - Light Detection And Ranging - Laser Altimetry Measurement

In a cooperative research program, US Geological Survey, National Aeronautics Space Administration and National Oceanic and Atmospheric Administration (NOAA) acquire laser altimetry data before and after extreme storms using NASA's Airborne Topographic Mapper (ATM). The ATM is ideal for surveying the topography of beaches. The ATM can survey hundreds of kilometers of coast in a single day with high data densities.

As the aircraft flies along the coast, a laser altimeter scans a several-hundred-meter swath of the earth's surface making an estimate of ground elevation every few square meters (pictured left). Change is determined by comparing pre-storm to post-storm surveys. Airborne scanning laser surveys provide unprecedented data to investigate the magnitude and causes of coastal changes that occur during severe storms. The USGS has acquired LIDAR data for the following National Parks Service Parks and Seashores: Assateague, Canaveral, Cape Cod, Cape Hatteras, Cape Lookout, Channel Islands, Cumberland, Fire Island, Gateway, Golden Gate, Gulf Islands, Padre Island, Point Reyes, and Wright Brothers.

SWASH

The USGS developed the ground-based SWASH (Shoreline Width and Surface Height) system for high-accuracy shoreline position surveying, a powerful new tool for conducting coastal erosion research. The shoreline surveying system extrapolates the position of a visually navigated survey track to the exact location of the target contour. Repeatability tests demonstrate that the system measures shoreline position to better than 1-meter horizontal accuracy, with the capability to survey 70 km of coast during a single low- tide period. The SWASH system is currently being applied to study storm-induced and fair weather shoreline change on beaches in North Carolina and Massachusetts. The most extensive set of measurements are within the Cape Cod National Seashore, where both the short-term impact of storms and the longer seasonal cycle of change has been measured in a continuing survey program initiated in April 1998.

Pictured above: The SWASH system platform is a six-wheel amphibious buggy, approximately 2.4 meters long, with a plastic body, an enclosed canvas cabin, and a cargo bed. It is Max IV manufactured by Recreatives Industries, Inc. of Buffalo, New York. Mounted on a custom frame are four GPS antennas, constituting the Magellen/Ashtech ADU2 array for measuring pitch, roll, and compass orientation, measured to an accuracy of about 0.4 degrees. One of the antennas also serves as the antenna for the Ashtech Z-Surveyor GPS receiver, which in combination with local base stations provides horizontal and vertical position to about 4 cm accuracy.