Digital seafloor images and sediment grain size from the mouth of the Columbia River, Oregon and Washington, 2014

Geo-referenced digital imagery of in-situ seafloor sediments in the mouth of the Columbia River was collected and analyzed to determine median grain size of the surface sediments. Digital imagery of the seafloor was collected with a flying eyeball (Rubin and others, 2007) from the R/V Parke Snavely from September 11 to September 13, 2014 (USGS Field Activity 2014-642-FA). The flying eyeball consists of a standard definition plumbing inspection video camera and LED light ring inserted in a 50 kg wrecking ball. The video camera has a resolution of 480 by 720 pixels with a resolution of 0.009 mm/pixel when the target is flush against the exterior surface of the lens. Sample locations were chosen to allow for the observation of spatial variability of grain size over the length of many large bedforms. The bedforms were identified from a bathymetric survey performed in a previous field effort in 2013 (Gelfenbaum and others, 2015). During survey operations, the flying eyeball was repeatedly lowered to the seafloor with a winch along the transect. The winch was equipped with a conducting cable that transmitted the video signal from the camera to the research vessel in real time where it was recorded with a Sony DV recorder. Positioning of the vessel was determined with an Applanix PosMV and integrated with the digital video recording at 1-Hz intervals using Red Hen Systems (RHS) VMS200 hardware, which encodes the position information on the audio channel of the video tape. In addition to the imagery, surface sediment was collected using a small Ponar, or "grab", sampler at 12 locations throughout the study area. The physical samples were emptied into a tray on the deck of the vessel and observed with the flying eyeball. Approximately 50 g of sediment from each sample was retained and later processed in the lab using a Beckman Coulter laser diffraction analyzer to determine grain-size distributions. Still images were extracted from the videos using RHS IsWhere software, which embeds the images with the positioning information. Images were extracted from the video when the target substrate was flush against the exterior surface of the lens and the LED lights effectively illuminated the sediments. This process was performed for both the in-situ and sediment grab sample video types. The size of sediment in the still images was determined using techniques described in Rubin (2004). An auto-correlation was calculated for each image and a calibration equation relating the auto-correlation coefficient and median sediment diameter was developed using grain-size distributions derived from the laboratory analyzed grab samples. The calibration equation was used to assign median sediment diameter values to the images of the in-situ sediments which do not have a corresponding grab sample (Rubin, 2004; Buscumbe and Masselink, 2008; Barnard and others, 2007). This portion of the data release includes still images collected in the mouth of the Columbia River, a table that includes the image locations and derived mean sediment diameters, and associated metadata.

本数据集针对哥伦比亚河河口的原位海底沉积物采集并分析了地理参考数字影像，以测定表层沉积物的中值粒径。
2014年9月11日至13日，研究团队依托“帕克·斯内夫利号”（R/V Parke Snavely）研究船，使用“飞行眼球”（Flying Eyeball，Rubin等，2007）成像系统采集了海底数字影像，对应美国地质调查局（USGS）野外活动编号2014-642-FA。
该“飞行眼球”系统由一台标清管道检测摄像机与LED环形灯组成，被集成于一枚50kg的破碎球内部。该摄像机分辨率为480×720像素，当拍摄目标紧贴镜头外表面时，空间分辨率可达0.009 mm/像素。
采样点位的选取旨在覆盖大型床形的延伸范围，以观测沉积物粒径的空间变异性。这些床形是通过2013年野外作业获取的水深测量数据识别得到的（Gelfenbaum等，2015）。
野外作业期间，研究团队通过绞车沿测线将“飞行眼球”系统反复下放至海底。绞车配备了传输电缆，可将摄像机拍摄的视频信号实时传回研究船，并通过Sony DV录像机进行录制。
研究船的定位信息由Applanix PosMV系统获取，并通过Red Hen Systems（RHS）VMS200硬件以1Hz频率集成至数字视频记录中，该硬件可将定位信息编码至录像带的音频通道内。
除影像数据外，研究团队还在整个研究区内的12个点位使用小型Ponar抓斗采样器（Ponar grab sampler）采集了表层沉积物样品。
实物样品被转移至船甲板上的托盘内，并使用“飞行眼球”系统进行观测。每个样品留存约50g沉积物，后续在实验室使用Beckman Coulter激光衍射分析仪进行处理，以测定沉积物的粒径分布。
研究人员使用RHS IsWhere软件从视频中提取静态图像，该软件可将定位信息嵌入图像中。当拍摄底物紧贴镜头外表面且LED灯光有效照亮沉积物时，即从视频中截取静态图像。该流程同时适用于原位沉积物和抓斗采样沉积物的视频素材。
静态图像中的沉积物粒径通过Rubin（2004）所述方法进行测定。研究人员为每张图像计算自相关系数，并利用实验室分析抓斗样品得到的粒径分布，建立自相关系数与沉积物中值粒径之间的校准方程。
借助该校准方程，可对无对应抓斗采样样品的原位沉积物影像赋予中值粒径数值（Rubin, 2004; Buscumbe and Masselink, 2008; Barnard and others, 2007）。
本次公开的数据包含哥伦比亚河河口采集的静态图像、包含图像点位及推导得到的沉积物平均粒径的数据表，以及相关元数据。