Beach profile data for the Elwha River Delta, 2023-11-27

Shoreline topography data were collected using GNSS survey methods, with a differential GPS, typically an AshTech ProMark 200 RTK-DGPS system connected to the Washington State Reference Network, operating in Real Time Kinematic (RTK) mode. Survey data are referenced in the horizontal reference frame to NAD83(2011). Elevations, in meters, are referenced to NAVD88(Geoid09) for all survey data collected before December 2012, NAVD88(Geoid12) for all survey data collected between December 2012 and May 2020, and NAVD88(Geoid18) for all survey data collected subsequently. No conversions were applied to these data to account for variations in horizontal or vertical coordinate system adjustments through time, but an error analysis suggests a standard deviation for the elevations of between 0.03 and 0.05 m across the entire sampling period (2011-2024). All survey data were collected with the GNSS system mounted on a 2.05 m rover pole, held level by a surveyor as a transect line was traced in a cross-shore orientation on the beach. The associated text files include the horizontal (HRMS) and vertical (VRMS) root-mean-square errors estimated by the GNSS system, as well as the RTK-DGPS status reported by the GNSS system at the time each point was collected. Times are referenced to local Pacific time (either PST or PDT).

海岸线地形数据采用全球导航卫星系统（GNSS）测量方法采集，结合差分全球定位系统（differential GPS），通常使用连接至华盛顿州参考网络、工作于实时动态定位（RTK）模式的AshTech ProMark 200 RTK-DGPS系统。测量数据的水平参考系为北美大地坐标系1983（2011版，NAD83(2011)）。高程（单位：米）的参考基准为：2012年12月前采集的数据采用北美垂直基准1988（NAVD88）的大地水准面模型09版（Geoid09）；2012年12月至2020年5月采集的数据采用NAVD88的Geoid12模型；此后采集的数据采用NAVD88的Geoid18模型。未对这些数据进行坐标转换以补偿水平或垂直坐标系随时间的调整差异，但误差分析表明，在整个采样期间（2011-2024年），高程的标准偏差介于0.03至0.05米之间。所有测量数据均通过将GNSS系统安装在2.05米的流动站杆上采集，测量员手持该杆保持水平，沿海滩的跨岸方向追踪样线。相关文本文件包含GNSS系统估算的水平均方根误差（HRMS）和垂直均方根误差（VRMS），以及每个点采集时GNSS系统报告的RTK-DGPS状态。时间参考当地太平洋时间（PST或PDT）。