Increasing the accuracy and resolution of coastal bathymetric surveys

The development of coastal sediment budgets and models for sediment transport and shoreline change require bathymetric surveys with vertical resolution and accuracy of 5 cm or better. Horizontal resolution and accuracy need to be at least 10 cm to quantify bedforms and bars.Sleds are probably the most accurate, widely used system for nearshore surveys, but their contact with the bottom limits their speed, spatial resolution. and ability to operate in many situations. Boat-based echo sounder surveys can achieve a higher spatial resolution and can operate where sleds cannot, but waves, tides, and other water-levelfluctuations as well as boat dynamics and variations in the speed ofsound in water can greatly limit their accuracy. Problems related toa survey sled's contact with the bottom cannot be overcome; therefore, echo sounder surveys must be improved. The newly developed high-accuracy, high-resolution bathymetric surveying system (HARBSS) is designed to overcome the confounding effects of changing vessel draft, waves, and tides on depth soundings and to eliminate the need for measuring and modeling water level for a particular survey. The system combines Global Positioning System (GPS) receivers, an electronic motionsensor, a digital-gyro compass, a digital-analog echo sounder, a conductivity. temperature-depth probe (CTD), a computer, and custom software. The GPS antenna, compass, and motion sensor are aligned with the echo sounder's transducer. Using a bias-free phase solution from the GPS data (X,Y,Z accuracy of better than 1 cm), attitude informationfrom the motion sensor, and heading information from the compass, the position and aim of the transducer is determined for each sounding.The CTD provides data to calculate the speed of sound. Using the above data, the sounding depths and horizontal locations of sounding points are corrected in X, Y, and Z with respect to an Earth-centered ellipsoid. In constant and uniform speed-of-sound conditions, HARBSS can provi [ABSTRACT FROM AUTHOR]