DETAILED BEACH SURVEYING WITH RTK-GPS

Real-time kinematic global positioning systems (RTK-GPS) have been widely adopted by coastal researchers for the purpose of monitoring coastal change, but survey design is not standardized and the technology's potential has been underutilized in the investigation of questions requiring 3-dimensional topographic information. Most researchers use the equipment to measure widely-spaced profile lines and/or some proxy of the “shoreline” for comparison with older maps and aerial photos. Not only is the selection of this datum prone to error, but the limited spatial coverage of these methods severely restricts the range of applications for which the data can be used.

Detailed beach topography can be measured efficiently and accurately with the adoption of a survey design and data collection strategy similar to what was used for monthly beach surveys over a 2-year period on Shackleford Banks, NC. With a Trimble 4700 system mounted on an all-terrain vehicle (ATV), 6-11 alongshore lines were measured at breaks in slope on a complex beach while cross-shore tie-in lines measured in areas selected for their morphological representativeness further increased data density. This resulted in the collection of 30,000 to 80,000 data points on the beach of this 15-km long island during each typical 4-day survey period. RTK-GPS was also used to establish survey control point coordinates and frequent tests ensured the accuracy and precision of surveyed measurements. Kriging in ESRI's ArcMap produced detailed, accurate and flexible maps that were used to calculate and visualize changes in morphology and volume, as well as to derive and compare any desired datum or profile. LIDAR data were processed in the same way and analyzed in conjunction with the GPS data.

RTK-GPS is becoming increasingly user-friendly and widespread in its use, while scientists, government agencies, and the public are increasingly concerned with better understanding the ways in which our coastlines are changing. Carefully designing surveys will allow these data to be more useful for a multitude of applications.