Aerial imagery and structure-from-motion data products from UAS survey of the intertidal zone at Lone Tree Point, Kiket Bay, WA, June 2019

An unmanned aerial system (UAS) was used to acquire high-resolution imagery of the intertidal zone at Lone Tree Point, Kiket Bay, Washington on June 5, 2019. This imagery was processed using structure-from-motion (SfM) photogrammetric techniques to derive a high-resolution digital surface model (DSM), orthomosaic imagery, and topographic point clouds. In order to maximize the extent of the subaerially exposed area, the survey was timed to coincide with a spring low tide occurring at approximately 20:19 Universal Coordinated Time (UTC) (13:19 Pacific Daylight Time (PDT)), with a predicted water level of -0.69 meters below mean lower-low water (MLLW) at the Sneeoosh Point NOAA harmonic tide station (station ID 9448576). A total of five flights were conducted for the survey between 19:29 and 20:36 UTC (12:29 and 13:36 PDT). The flights were conducted using a Department of Interior-owned 3DR Solo quadcopter fitted with a Ricoh GR II digital camera featuring a global shutter. The camera was mounted using a fixed mount on the bottom of the UAS and oriented in an approximately nadir orientation. For flights F01, F02, F03, and F04, the UAS was flown on pre-programmed autonomous flight lines at an approximate altitude of 70 meters above ground level (AGL), resulting in a nominal ground-sample-distance (GSD) of 1.8 centimeters per-pixel. The flight lines were oriented roughly shore-parallel and were spaced to provide approximately 70 percent overlap between images from adjacent lines. For flight F05, the UAS was flown manually to acquire imagery over areas not mapped in the previous flights. For all flights, the camera was triggered at 1 Hz using a built-in intervalometer. Before each flight, the camera's digital ISO, aperture, and shutter speed were adjusted for ambient light conditions. Eighteen temporary ground control points (GCPs) were distributed throughout the area to establish survey control. The GCPs consisted of a combination of small square tarps with black-and-white cross patterns and "X" marks placed on the ground using temporary chalk. The GCP positions were measured using post-processed kinematic (PPK) GPS, using corrections from a GPS base station ("SKGT") located approximately 16 kilometers from the study area operated by the Washington State Reference Network (WSRN). This data release presents five data products derived from these surveys which are available for download: 1) an orthomosaic image with a resolution of 2 centimeters per-pixel, 2) a digital surface model (DSM) and a hillshade image with a resolution of 4 centimeters per-pixel, 3) topographic point clouds in LAZ format, 4) the geographic positions of the ground control points, and 5) the raw aerial imagery in JPG format.

2019年6月5日，研究团队使用无人航空系统（unmanned aerial system, UAS）采集了华盛顿州基克特湾（Kiket Bay）孤树角（Lone Tree Point）潮间带的高分辨率影像。本研究采用运动恢复结构（structure-from-motion, SfM）摄影测量技术对该影像进行处理，以生成高分辨率数字表面模型（digital surface model, DSM）、正射影像镶嵌图（orthomosaic imagery）及地形点云。为最大化出露于空气中的潮间带区域范围，本次调查选择在协调世界时（Universal Coordinated Time, UTC）约20:19（太平洋夏令时Pacific Daylight Time, PDT为13:19）的春汛低潮时段开展，对应美国国家海洋和大气管理局（National Oceanic and Atmospheric Administration, NOAA）斯尼乌什角潮汐站（站号9448576）预测的水位较平均低低潮位（mean lower-low water, MLLW）低0.69米。本次调查共开展5次飞行任务，时间跨度为协调世界时19:29至20:36（太平洋夏令时12:29至13:36）。飞行平台为美国内政部（Department of Interior）所有的3DR Solo四旋翼无人机，搭载理光GR II数码相机，该相机配备全局快门。相机通过固定支架安装于无人机底部，成像方向大致为天底指向。对于F01、F02、F03及F04号飞行任务，无人机沿预编程的自主飞行航线飞行，飞行高度约为距地面70米，由此获得的标称地面采样距离（ground-sample-distance, GSD）为1.8厘米/像素。飞行航线大致与岸线平行，相邻航线间的影像重叠率约为70%。对于F05号飞行任务，采用手动操控无人机的方式，以获取此前航线未覆盖区域的影像。所有飞行任务中，相机均通过内置间隔定时器以1赫兹的频率触发拍摄。每次飞行前，均会根据环境光照条件调整相机的数字感光度（ISO）、光圈及快门速度。本次调查区域共布设18个临时地面控制点（ground control points, GCPs）以建立测量控制网。地面控制点由两类标识组成：一是带有黑白十字图案的小型方形防水布，二是使用临时粉笔在地面绘制的"X"形标记。控制点坐标采用后处理动态（post-processed kinematic, PPK）GPS技术测定，校正数据来自华盛顿州参考网络（Washington State Reference Network, WSRN）运营的、距研究区域约16公里的GPS基准站“SKGT”。本次数据发布共提供5类由上述调查衍生的可下载数据产品：1）分辨率为2厘米/像素的正射影像镶嵌图；2）分辨率为4厘米/像素的数字表面模型及晕渲图；3）LAZ格式地形点云；4）地面控制点的地理坐标；5）JPG格式原始航空影像。