Beach profile data for the Elwha River Delta, 2022-02-14

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).

本海岸线地形数据集采用全球导航卫星系统（GNSS）测量方法采集，所用设备为差分GPS，通常为接入华盛顿州参考网络（Washington State Reference Network）的AshTech ProMark 200型RTK-DGPS系统，以实时动态（Real Time Kinematic, RTK）模式开展作业。所有测量数据的水平参考框架均采用NAD83(2011)坐标系。高程单位为米，2012年12月之前采集的所有测量数据的高程基准为NAVD88(Geoid09)；2012年12月至2020年5月期间采集的数据，其高程基准为NAVD88(Geoid12)；2020年5月之后采集的数据则采用NAVD88(Geoid18)作为高程基准。未针对随时间推移产生的水平或垂直坐标系调整变化对本数据集进行转换，但误差分析结果显示，2011-2024年整个采样周期内，高程的标准差介于0.03至0.05米之间。所有测量数据均通过将GNSS设备安装于2.05米高的流动站测量杆获取，测量员将杆体保持水平，在海滩上沿垂直于岸线的方向布设测线并完成数据采集。配套文本文件包含GNSS系统估算得到的水平均方根误差（HRMS）与垂直均方根误差（VRMS），以及每个测点采集时刻GNSS系统上报的RTK-DGPS工作状态。时间基准采用本地太平洋时间，涵盖太平洋标准时间（PST）与太平洋夏令时（PDT）。