| Description |
This portion of the USGS data release presents topography data collected during surveys performed in the Columbia River littoral cell, Washington and Oregon, in 2020 (USGS Field Activity Number 2020-622-FA). Topographic profiles were collected by walking along survey lines with global navigation satellite system (GNSS) receivers mounted on backpacks. Prior to data collection, vertical distances between the GNSS antennas and the ground were measured using a tape measure. Hand-held data collectors were used to log raw data and display navigational information allowing surveyors to navigate survey lines spaced at 100- to 1000-m intervals along the beach. Profiles were surveyed from the landward edge of the study area (either the base of a bluff, engineering structure, or just landward of the primary dune) over the beach foreshore, to wading depth on the same series of transects as nearshore bathymetric surveys that were conducted during the same time period. Additional topographic data were collected between survey lines in some areas with an all-terrain vehicle (ATV) equipped with a GNSS receiver to constrain the elevations and alongshore extent of major morphological features. Positioning data from the survey platforms were referenced to a GNSS base station with known horizontal and vertical coordinates relative to the North American Datum of 1983. Differential corrections from the GNSS base stations to the survey platforms were either applied in real-time with a VHF radio link, or post-processed using Trimble Business Center software. Orthometric elevations relative to the NAVD88 vertical datum were computed using National Geodetic Survey Geoid12a offsets. The average estimated vertical uncertainty of the topographic measurements is 4 cm. The final point data are provided in comma-separated text format and are projected in Cartesian coordinates using the Washington State Plane South, meters coordinate system. Due to equipment and staffing issues associated with the global pandemic, topographic surveys performed at the southern portion of the Clatsop Plains sub-cell (lines 71 to 101) and North Beach sub-cell took place several weeks prior the corresponding bathymetric surveys. [More]
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