Beach profile data for the Elwha River Delta, 2013-11-19

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，简称GNSS）测量方法采集，所用差分GPS系统采用实时动态（Real Time Kinematic，简称RTK）工作模式。2013年之前采集的测量数据通常由麦哲伦（Magellan）ProMark 3型传统RTK-DGPS系统采集，该系统由本地基准站与流动站组成，基准站设于1996年布设的测量控制标记点，其坐标参考基准为NAD83(CORS91)。2013年起，测量数据通常采用与华盛顿州参考网络对接的阿什泰克（AshTech）ProMark 200型RTK-DGPS系统采集。2013年1月至11月采集的测量数据参考基准为NAD83(CORS96)，2013年11月之后采集的数据则采用NAD83(2011)基准。
2012年与2013年测量的高程数据参考基准为NAVD88，推测采用Geoid96大地水准面（测量控制文档未明确指定所用大地水准面）；后续所有测量的高程数据均采用NAVD88(Geoid09)基准。本数据集未针对不同时期水平与垂直坐标系的调整差异进行坐标转换，但误差分析显示，2011至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流动杆的系统采集，测量时需将流动杆保持水平，沿海滩垂直于岸线的方向布设断面并进行测量。
配套文本文件包含GNSS系统估算得到的水平方向均方根误差（Horizontal Root Mean Square，简称HRMS）与垂直方向均方根误差（Vertical Root Mean Square，简称VRMS），以及每个测点采集时刻GNSS系统报告的RTK-DGPS工作状态。时间基准采用本地太平洋时间（PST或PDT）。