Russian River Bathymetric and Terrestrial Topographic Data Collection and Processing
In April 2013, GMA was contracted by the Sonoma County Water Agency (SCWA) to acquire conventional and sonar survey data, Light Detection and Ranging (LiDAR) data, and digital imagery at four project reaches on the Russian River in Northern California. Data were collected for the purpose of developing a detailed digital terrain model (DTM) for each project reach that would support fish habitat modeling being conducted by the SCWA.
Field surveys consisted of both sonar and conventional surveys. The majority of the sonar surveys were completed using a portable multi-channel sweep system. The system was deployed in a 7-channel configuration with 1-meter spacing from a 19-ft Sotar cataraft. In addition to sonar sweep surveys, single-beam sonar surveys were also performed.
Conventional surveys were conducted in areas that were not accessible during the boat based surveys. In general, these areas included the heavily vegetated channel margins, shallow riffles, submerged and emergent boulders, and mid channel bars. The majority of the wading surveys were conducted using a Trimble S6 DR 300+ Total Station.
Detailed accuracy assessments of the LiDAR, Sonar, Wading, and digital imagery data were conducted and followed the guidelines set forth in the National Standard for Spatial Data Accuracy (NSSDA) (FGDC, 1998). Two types of accuracy assessment were carried out, absolute accuracy (the consistency of the data to external and or higher accuracy data sources) and relative accuracy (the consistency of the dataset with itself).
High accuracy topographic mapping of the Russian River study reaches proved to be very challenging due to the thick riparian vegetation that was prevalent in all of the survey reaches. Thick riparian vegetation prevented full penetration of LiDAR in many areas, thereby reducing the overall accuracy. In addition, the riparian vegetation made sonar surveys very challenging due to the constantly changing GPS conditions and spotty coverage. Conventional survey techniques were relied heavily upon to fill in the areas that could not be surveyed with sonar based equipment.