Beach profile data for the Elwha River Delta, 2015-03-24

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GPS（Differential GPS, DGPS）工作于实时动态（Real Time Kinematic, RTK）模式。
2013年之前采集的数据通常采用麦哲伦ProMark 3传统RTK-DGPS系统（即本地基准站与流动站架构）完成采集，基准站架设於1996年布设的测量控制点标志上，测量控制点坐标参考基准为北美大地基准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的阿什泰克ProMark 200 RTK-DGPS系统采集；2013年1月至11月间采集的测量数据参考基准为北美大地基准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年测量的垂直数据参考基准为北美垂直基准88（North American Vertical Datum 1988, NAVD88），推测采用大地水准面96（Geoid96），因测量控制文档未明确指定大地水准面模型。后续所有测量的垂直数据参考基准均为采用大地水准面09（Geoid09）的北美垂直基准88（NAVD88(Geoid09)）。
未针对随时间推移发生的水平或垂直坐标系基准调整对本数据集进行坐标转换，但误差分析结果显示，在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米高流动杆上的GNSS系统采集，测量时需保持流动杆水平，沿海滩垂直于海岸方向布设的断面线进行点位追踪。
配套文本文件包含GNSS系统估算得到的水平均方根误差（Horizontal Root-Mean-Square Error, HRMS）与垂直均方根误差（Vertical Root-Mean-Square Error, VRMS），以及每个点位采集时刻GNSS系统上报的RTK-DGPS工作状态。所有时间均参考本地太平洋时间，含太平洋标准时间（PST）与太平洋夏令时（PDT）。