Beach profile data for the Elwha River Delta, 2017-09-19

Data were collected using GNSS survey methods, with a differential GPS operating in Real Time Kinematic (RTK) mode. Data from prior to 2013 were typically collected with a Magellan ProMark 3 traditional RKT-DGPS system (i.e. local base station and rover), with the base station sited on survey control markers installed in 1996, with survey control coordinates referenced to NAD83(CORS91). Starting in 2013 survey data were typically collected with an AshTech ProMark 200 RTK-DGPS system connected to the Washington State Reference Network. Survey data collected between January and November 2013 are referenced to NAD83(CORS96), and after November 2013 to NAD83(2011).
Vertical data for surveys in 2012 and 2013 are referenced to NAVD88, presumably using Geoid96 (the survey control documentation does not specific a geoid). For all subsequent surveys the vertical data are referenced to NAVD88(Geoid09). No conversion 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 elevation data of between 0.03 and 0.05 m across the entire sampling period (2011-2018).
All survey data were collected with the GNSS system mounted on a 2.05 m rover pole, held level 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).

本数据集采用全球导航卫星系统（Global Navigation Satellite System, GNSS）测量方法采集，所用差分全球定位系统（Differential GPS）运行于实时动态（Real Time Kinematic, RTK）模式。2013年之前的测量数据，通常采用麦哲伦ProMark 3型传统RTK-DGPS系统采集（即配置本地基准站与流动站），基准站架设於1996年布设的测量控制标记之上，测量控制坐标参考北美大地基准84（CORS91）[NAD83(CORS91)]。自2013年起，测量数据通常采用连接至华盛顿州参考网络的AshTech ProMark 200型RTK-DGPS系统采集。2013年1月至11月间采集的测量数据参考北美大地基准84（CORS96）[NAD83(CORS96)]，2013年11月之后采集的数据则参考北美大地基准84（2011）[NAD83(2011)]。
2012年与2013年的测量高程数据参考北美垂直基准88（NAVD88），推测采用大地水准面96（Geoid96）（测量控制文档未明确指定所用大地水准面型号）。后续所有测量的高程数据均参考北美垂直基准88（大地水准面09）[NAVD88(Geoid09)]。本数据集未针对不同时期水平或垂直坐标系的调整差异进行坐标转换，但误差分析显示，2011-2018年整个采样周期内，高程数据的标准差介于0.03至0.05米之间。
所有测量数据均通过安装于2.05米高GNSS流动杆上的系统采集，测量过程中保持流动杆水平，沿海滩横向（即与岸线垂直的方向）布设断面轨迹。
配套文本文件包含GNSS系统估算的水平均方根误差（Horizontal Root Mean Square Error, HRMS）与垂直均方根误差（Vertical Root Mean Square Error, VRMS），以及每个测点采集时刻GNSS系统报告的RTK-DGPS工作状态。时间采用本地太平洋时间（含太平洋标准时间PST与太平洋夏令时PDT）。