COMBINING SIDE-SCAN SONAR, SUBMERSIBLE ROVS, AND UNMANNED AERIAL VEHICLES FOR UNDERWATER INSPECTIONS AND BATHYMETRIC MAPPING OF AN INACTIVE QUARRY NEAR CLAYTOR LAKE, VIRGINIA

Hydrographic surveying, which measures and describes physical features underwater, plays a vital role in some types of mining, construction, inspection, and environmental protection. Due to the challenging environment, underwater data acquisition often depends on remote sensing. One of the most frequently used techniques is sound navigation and ranging (sonar). When combined with unmanned vehicle technology, both aerial and submersible, detailed and informative maps and models can be produced.

A combination of side-scanning sonar, a submersible remotely operated vehicle (ROV), and unmanned aerial vehicles (UAVs) were used to survey an inactive flooded quarry owned by Salem Stone Corporation near Radford, Virginia. Like many inactive mines, machinery and tools were left behind and the owners were interested in locating them. A GPS enabled side-scan sonar unit was attached to a small boat and piloted across the quarry in a grid like pattern. This supplied sufficient depth data and sonar imagery to create a bathymetric map and to identify the locations of numerous quarry structures and features. To supplement these findings, a submersible ROV and UAVs were used to acquire additional images of features identified by sonar.

Each system had its own benefits and limitations. The UAV quickly provided georeferenced imagery over a large area, but was dependent upon water clarity and therefore limited in depth. The submersible ROV provided video imagery for the deeper areas. The ROV, however, does not have GPS and therefore its imagery was not georeferenced. The side-scan sonar compensated for this by providing both GPS locations and depths.

This test study was able to match several quarry structures and features found on the sonar images with their counterparts in both the aerial and submersible unmanned vehicle imagery. That allowed the research group to generate a bathymetric map of the flooded portions of the quarry, which also keyed images of submerged structures and features, including tires, pipelines, fish nests, and more.

These methods could prove beneficial to geoscientists when identifying and locating underwater geologic features. These tools could also help environmental consultants in such activities as infrastructure inspections, mapping underwater hazards, and locating pipeline leaks.