Review of Autonomous Undersea Vehicle (AUV) Developments 
Instrument rack - The instrument rack consists of two cylindrical benthic chambers and an 
oxygen microprofiler mounted to a titanium vertically-moveable rack on the front of the ROVER 
frame. This assembly can be slowly lowered and raised with two titanium lead screws mounted 
vertically on both sides. 
Two acrylic transparent benthic chambers are mounted on either end of the instrument 
assembly. A bottom leading edge of thin, teflon-coated titanium reduces the force required to 
push the chambers into the sediment and eliminates adhesion of sediment to the chamber wall. 
A stirring bar, centrally mounted in each chamber, is driven by a pressure-compensated stepper 
motor via a magnetic coupling. This stirring assembly moves vertically on three titanium guide 
rods powered by a drive motor and a fine-scale lead screw. In the "up" position, the stirring 
assembly leaves a large hole in the chamber top, allowing the chamber to purge during insertion 
into the sediment. In the "down" position, the stirring assembly seals against an O-ring on the 
top plate of the benthic chamber. 
The oxygen-sensing system for each benthic chamber consists of a polarographic oxygen 
sensor and a flow cell. The oxygen sensor for each chamber on the ROVER is mounted in an 
external flow cell and is alternately exposed to chamber and ambient water using a pump and 
valve system. The ambient reference measurement is necessary to correct for long-term drift in 
the oxygen sensors and provides a direct comparison between chamber-water oxygen 
concentration during the incubation and stable oxygen concentration in the ambient bottom 
water. The flow-cell sample water is transferred by a DC motor-driven pump to the flow cell 
through plastic capillary tubing. A 3-position slider valve is used to switch the water supply to 
the flow cell from chamber to ambient, and this valve is under the control of the benthic chamber 
controller. A 1-liter Niskin bottle is mounted vertically on the instrument rack near one of the 
benthic chambers to take a water sample for dissolved oxygen analysis at the end of the last 
incubation. Closure of this bottle is triggered by a burn-wire release via the central controller. 
At each new measurement site, the instrument rack is lowered to place the oxygen microprofiler 
sensors just above the sediment and the benthic chambers ~6 cm into the sediment. The 
oxygen microprofiler is mounted on the instrument rack between the two benthic chambers. 
This microprofiler can accept up to 12 oxygen (or other) microsensors and four resistivity 
sensors that are arranged in a circular pattern on a plate that is mounted beneath the 
microprofiler-controller electronics cylinder. The titanium controller housing and electrodes are 
lowered stepwise toward the sediment surface by a fine-scale, DC-motor-driven lead screw (1 
mm pitch). The resistivity sensors detect the sediment-water interface as a change in resistivity 
and allow the microprofiler controller to determine the sensor penetration depth into the 
sediment. Feedback from the resistivity sensors sets the system to profile an additional 
programmable distance into the sediment, and readings from each oxygen sensor are recorded 
at 0.5-mm increments. When the microprofiler completes the oxygen measurements to the 
programmed depth, the unit is retracted from the sediment. Oxygen sensor outputs from the 
benthic chambers and microprofiler are digitized and then transferred to the central controller for 
storage on a disk drive. 
34 
