| Description |
This portion of the USGS data release presents bathymetry data collected during surveys performed in Floras Lake, Oregon in June 2018 (USGS Field Activity Number 2018-636-FA). Floras Lake is a coastal lake in southern Oregon that is separated from the Pacific Ocean by sand dunes. It is not influenced by tides, although water levels fluctuate seasonally. Lake bed bathymetry data were collected using two personal watercraft (PWCs) equipped with single-beam sonar systems and global navigation satellite system (GNSS) receivers. The sonar systems consisted of an Odom Echotrac CV-100 single-beam echosounder and 200 kHz transducer with a 9-degree beam angle. Depths from the lakebed to the echosounder were calculated using the digitized acoustic backscatter and sound velocity profiles, measured using a YSI CastAway CTD. Positioning of the survey vessels was determined at 10 Hz using Trimble R7 GNSS receivers. Output from the GNSS receivers and sonar systems were combined in real time on the PWC by a computer running HYPACK hydrographic survey software. Navigation information was displayed on a video monitor, allowing PWC operators to navigate along survey lines at speeds of 2 to 3 m/s. Survey-grade positions of the PWCs were achieved with a single-base station and differential post-processing. Positioning data from the GNSS receivers were post-processed using Waypoint Grafnav to apply differential corrections from a GNSS base station with known horizontal and vertical coordinates relative to the North American Datum of 1983. Orthometric elevations relative to the NAVD88 vertical datum were computed using National Geodetic Survey Geoid12a offsets. Bathymetric data were merged with post-processed positioning data, raw data were examined and soundings adjusted in areas with aquatic vegetation, and spurious soundings were removed using a custom Graphical User Interface (GUI) programmed with the computer program MATLAB. The average estimated vertical uncertainty of the bathymetric measurements is 5 cm based on manufacturer-reported accuracies of the survey equipment. However, the effect of aquatic vegetation on the vertical accuracy of the bathymetric measurements is unknown. The final point data from the PWCs are provided in a comma-separated text file and are projected in cartesian coordinates using the Universal Transverse Mercator (UTM), Zone 10 North, meters coordinate system. [More]
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