NWDTW 2024

A combined point cloud of about 85.6 million points was collected during 27 scans of a section of the western shoreline along the Shinnecock Peninsula of Suffolk County, New York, to document baseline geospatial conditions during July and October 2022 using a scanning total station. The three-dimensional accuracy of the combined point cloud is assessed to identify potential systematic error sources associated with the surveying equipment and the novel methodology used to collect and field-register (data are oriented and aligned in real time) point cloud data. The accuracy of the combined point cloud was assessed in terms of relative and absolute reference frames. Relative accuracy provides a measure of error within the local coordinate system and is determined by combining the uncertainty associated with the position of the scan station (the point being occupied by the scanning total station during the scan), the uncertainty associated with the position of the network control points, and the uncertainty associated with the laser of the scanning total station. Assessment of the absolute accuracy includes these three potential error sources combined with the uncertainty associated with the geodetic coordinates to which the local control network is referenced. The combined overall relative horizontal and vertical accuracy of the point cloud is 0.0156 and 0.0241 meter, respectively, at the 95 percent confidence level; the combined overall absolute horizontal and vertical accuracy of the point cloud is 0.0374 and 0.0733 meter, respectively, at the 95 percent confidence level.
A second survey was conducted during March 2023 following a substantial erosion event associated with (unnamed) Winter Storm “Elliot” (weather channel assigned this unofficial name). A bare-earth digital elevation model was then created of “pre-storm” (1st survey) and “post-storm” (2nd survey) conditions. The pre-storm, bare-earth DEM, was then compared with the post-storm DEM to detect topographic (and shallow bathymetric) change along the western shoreline and determine areas/features that are most susceptible to erosion during a major coastal storm event. The distribution and magnitude of erosion and deposition, and potential volume changes, will be disseminated in a USGS scientific report.

The California Water Science Center’s Estuarine Hydrodynamics team works in the Sacramento-San Joaquin River Delta (the Delta) and faces two main challenges with tying water level to datum. Challenges include: 1) long distances between land and gage infrastructure on pilings in the river (sometimes ~300m+). This makes it virtually impossible to use traditional leveling techniques. 2) land movement. The Delta is comprised of human-made levee systems that are susceptible to significant movement due to the organic soils of the region. Couple this with the movement of a given gage’s piling and it becomes extremely time consuming and costly to determine the accuracy of the water level’s data tied to datum.
The solution? Automate static GNSS surveys on every gage every week. We use a single board computer (SBC), GNSS Survey Grade Receiver, cellular modem, and datalogger to conduct a 12-hour static survey once per week. Once the survey is complete, the SBC packages the raw data, converts those data to a format the National Geodetic Survey’s Online Position User Service (OPUS) can ingest and then sends the converted file off to the USGS sFTP server as well as OPUS. Once the OPUS corrections have been made, we receive an email containing the corrected data and metadata and can then relate those data to our water level with much more confidence.