Schematic image of ROPOS and its full complement of support equipment used during a deep-water deployment. ROPOS is launched and descends through most of the water column while in the "cage". At about 40 meters above the seafloor it leaves the cage on its tether, which enables ROPOS to work in an area about 100 meters in diameter without moving the ship. The cage houses the tether winch and also serves to isolate ROPOS from the ship's motion. The position of the ROV is found by triangulating on the acoustic transponders, which have been surveyed using the GPS satellite system. Image courtesy of Submarine Ring of Fire 2002, NOAA/OER.