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

February 21, 2017

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.