ROTARY LASER-GPS SHORELINE MAPPING

Beach mapping and surveying are conducted using a rotary laser level and laser detector, a 7.5 meter stadia rod, and a hand-held real-time sub-meter global positioning system (GPS) receiver. Using this methodology, beach surveying becomes a one-man task since no manning of the rotary laser is required. In addition, multiple beach profiles can be conducted simultaneously. User-defined GIS attributes are recorded into the GPS unit at each data point. A rotary laser level provides a laser-beam horizontal datum plane, which is referenced to a known elevation. A laser detector is affixed to the top of a stadia rod, which is then raised until it intercepts the laser beam. Point elevation is determined by subtracting rod height from laser beam elevation. Point position and Geographic information system (GIS) attributes are recorded as a file in the GPS unit. Multiple data points are useable to produce beach profiles, contour maps, and volumetric changes. GIS attributes can be used to define terrain, record location of sedimentary structures and sediment grain characteristics, and flora/fauna observations, for example. To date, multiple beach surveys using this method have been conducted on Folly Island and Dewees Island, South Carolina. A LASERMARK® LM 2000 self-leveling rotary laser and a LASERMARK® LD-400 laser detector provide a reference elevation datum plane. Manufacturers printed specifications for the rotary laser claim a vertical accuracy of 0.16 centimeters measured at a distance of 30.5 meters. Maximum range is 610 meters. Laser detector beam detection sensitivity is listed in manufacturers printed specifications as +/- 0.75 millimeters when selected to the fine setting. Rotary laser vertical error was measured at 15-meter intervals to a maximum distance of 305 meters. Maximum vertical error at 305 meters was found to be 0.91 centimeters. A Thales MobileMapper CE® GPS computer provide position data while recording GIS attributes. Manufacturers Published data claims real-time sub-meter accuracy when the GPS receiver is corrected with a WAAS or RTCM signal.