Miller, B.V., Payne, J.D., Killion III, W.F., and Adams, R.F., 2019, Geophysical surveys and geospatial data for Bob Kidd Lake, Washington County, Arkansas: U.S. Geological Survey data release, https://doi.org/10.5066/P9I4W2P0.
Summary
GNSS Method A benchmark monument was set at each end of the earthen dam in accordance with (U.S. Army Corps of Engineers, 2002). A level II survey (Rydlund & Densmore 2012) was conducted on each monument to establish control. Two 4-hour observations were conducted with a staggered approach for each monument, with one 4-hour session in the morning of the first day and one 4-hour session in the afternoon of the second day. Once elevational control was established, a Real Time Kinematic (RTK) system was set up with base on the monument that had the best observations. Using this system, a point cloud survey was conducted along the top and face of the dam using both a monopod and an All-Terrain Vehicle. A Global Navigation Satellite [...]
Summary
GNSS Method
A benchmark monument was set at each end of the earthen dam in accordance with (U.S. Army Corps of Engineers, 2002). A level II survey (Rydlund & Densmore 2012) was conducted on each monument to establish control. Two 4-hour observations were conducted with a staggered approach for each monument, with one 4-hour session in the morning of the first day and one 4-hour session in the afternoon of the second day. Once elevational control was established, a Real Time Kinematic (RTK) system was set up with base on the monument that had the best observations. Using this system, a point cloud survey was conducted along the top and face of the dam using both a monopod and an All-Terrain Vehicle. A Global Navigation Satellite System (GNSS) receiver was set to “continuous topo” mode to create an elevational model of the dam. Additionally, using the monopod and receiver the location of every electrode in the resistivity survey was georeferenced and a backpack mounted system was used to georeference the frequency domain electromagnetism survey. A single base static survey requires a minimum observation time of 4 hours for each monument, as well as a 4-hour concurrent occupation with other nearby benchmarks with 80 percent of the total observations in the data file to be used and at least 80 percent of ambiguities in the solution should be fixed. The vertical peak-to-peak error should not exceed 0.08 m, and the root mean squared (RMS) error of the solution should not exceed 0.03 m. A Level II also requires a “constrainment” quantity of a minimum of two “2nd order accuracy or better” established bench marks within a 60-km spacing. Surrounding benchmarks in the study, named “NGS V-310” and “Agronomy” were used to satisfy this requirement for this study.
GNSS Data Processing
Using conversion software, RINEX (Receiver Independent Exchange Format) files were created from the raw file or files retrieved from the receiver. Elevations and adjustments are conducted through the National Geodetic Survey (NGS) “Online Positioning User Service" (OPUS) website (https://geodesy.noaa.gov/OPUS/). OPUS used algorithms and scripts and software (PAGES) for the adjustment of GPS ephemerides. OPUS then computed coordinates for the NGS Continuously Operating Reference Station (CORS) network and adjusted the elevation and position coordinates accordingly.
Reference:
Rydlund, P.H., Jr., and Densmore, B.K., 2012, Methods of practice and guidelines for using survey-grade global navigation satellite systems (GNSS) to establish vertical datum in the United States Geological Survey: U.S. Geological Survey Techniques and Methods, book 11, chap. D1, 102 p. with appendixes.
