Beach profile data for the Elwha River Delta, 2023-05-25

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).

本数据集的岸线地形数据采用全球导航卫星系统（GNSS）测量方法采集，使用差分GPS设备完成观测，典型配置为AshTech ProMark 200型实时动态差分GPS（RTK-DGPS）系统，该系统接入华盛顿州参考站网，并工作于实时动态（RTK）模式。所有测量数据的水平参考基准为北美大地基准1983(2011)（NAD83(2011)）。高程单位为米，2012年12月前采集的全部数据以北美垂直基准1988（大地水准面09，NAVD88(Geoid09)）为垂直基准；2012年12月至2020年5月间采集的数据以北美垂直基准1988（大地水准面12，NAVD88(Geoid12)）为基准；2020年5月之后采集的数据则采用北美垂直基准1988（大地水准面18，NAVD88(Geoid18)）作为垂直基准。未对上述数据进行任何转换以抵消不同时期水平或垂直坐标系调整带来的影响，但误差分析结果显示，2011-2024年整个采样周期内，高程数据的标准差介于0.03米至0.05米之间。所有测量数据均通过搭载于2.05米高流动站杆的GNSS系统采集，测量人员需保持杆体水平，沿海滩上的垂直岸线方向完成测线追踪。关联的文本文件包含GNSS系统估算的水平均方根误差（HRMS）与垂直均方根误差（VRMS），以及每个测点采集时刻GNSS系统上报的RTK-DGPS状态信息。时间基准采用太平洋当地时间，分为太平洋标准时间（PST）与太平洋夏令时间（PDT）。