Beach profile data for the Elwha River Delta, 2019-11-29

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).

本数据集为海岸线地形数据，采用全球导航卫星系统（Global Navigation Satellite System，GNSS）测量方法采集，所用设备为差分GPS（Differential GPS，DGPS），典型配置为AshTech ProMark 200 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（Real Time Kinematic，RTK）模式。
测量数据的水平参考基准为NAD83(2011)（北美大地基准1983(2011)）。以米为单位的高程基准设置如下：2012年12月前采集的所有数据采用NAVD88(Geoid09)（北美垂直基准1988(大地水准面09)），2012年12月至2020年5月期间采集的数据采用NAVD88(Geoid12)，2020年5月之后采集的数据则采用NAVD88(Geoid18)。
本数据集未针对随时间推移发生的水平或垂直坐标系调整变化进行任何转换，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。
所有外业测量数据均通过搭载于2.05米高流动站杆的GNSS系统采集：测量员将测量杆保持水平，沿海滩上垂直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系统解算得到的水平均方根误差（HRMS）与垂直均方根误差（VRMS），以及每个点位采集时刻GNSS系统上报的RTK-DGPS工作状态。时间基准采用太平洋沿岸本地时间，涵盖太平洋标准时间（PST）与太平洋夏令时（PDT）。