Beach profile data for the Elwha River Delta, 2021-07-14

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).

本数据集的海岸线地形数据采用全球导航卫星系统（GNSS）测量方法采集，所用差分GPS（DGPS）设备为AshTech ProMark 200型RTK-DGPS系统，该系统接入华盛顿州参考站网，工作模式为实时动态（RTK）。测量数据的水平参考框架采用北美大地基准1983(2011)（NAD83(2011)）。高程单位为米，其中2012年12月前采集的全部测量数据以北美垂直基准88(大地水准面09)（NAVD88(Geoid09)）为高程基准；2012年12月至2020年5月采集的数据采用北美垂直基准88(大地水准面12)（NAVD88(Geoid12)）；2020年5月之后采集的数据则采用北美垂直基准88(大地水准面18)（NAVD88(Geoid18)）。未针对不同时期水平或垂直坐标系的调整对这些数据进行坐标转换，但误差分析表明，2011至2024年整个采样周期内，高程的标准偏差介于0.03米至0.05米之间。所有测量数据均通过安装在2.05米长流动站杆上的GNSS系统采集，测量人员将杆保持水平，沿海滩上垂直于岸线的方向布设测线并逐点采集数据。配套文本文件包含GNSS系统估算的水平均方根误差（HRMS）与垂直均方根误差（VRMS），以及各测点采集时刻GNSS系统上报的RTK-DGPS工作状态。时间基准采用太平洋本地时间，包括太平洋标准时间（PST）与太平洋夏令时间（PDT）。