EVALUATION OF BATHYMETRY METHODS FOR MAPPING ELEVATION IN ESTUARIES

Tide flat elevation within estuaries is important for structuring the spatial distribution of many intertidal organisms.  Correct assessment of habitat classification and tide flat elevation relies on precise and accurate positional data, especially at small spatial scales. New advancements in Global Positioning System (GPS) improve location precision and accuracy, but it is uncertain how bathymetric data collected using different GPS systems varies. In Netarts Bay, Oregon, we compared two GPS systems with a Biosonics MX echosounder to survey bathymetry: 1) Differential GPS (DPGS); and 2) Real Time Kinematics GPS (RTK). While DGPS uses satellites to receive correct coordinates from base stations, RTK obtains more precise and accurate positioning by using satellites and a nearby base station to provide real time correction to coordinates. Bathymetry data were interpolated using inverse distance weighting with the ArcGIS 10.3 Geostatistical Analyst toolbox to determine the difference between the two methods. We found that 80% of the area surveyed differed by 30 cm or less when comparing rasters of the two methods, and a mean difference of 21.08 +/- 0.07 cm (mean +/- standard error).  Thus, the choice to invest in RTK GPS or DGPS depends on the order of magnitude of acceptable error for the desired application. Keywords: Technology, Bathymetry, mudflat