Glory Holes

Near Nova Scotia, a DIDSON works in a glory hole – a hole nine meters deep and 25 meters by 50 meters in size. Equipment is placed in the bottom of glory holes to protect it from icebergs which scour the bottom.
A glory hole wall periodically caves and makes the water zero vis and the video screens blank.
The lens-based sonar provides a sufficient vision feedback to allow work to continue during these turbid periods.

Courtesy of Oceaneering