over control in a reflexive teleoperated mode (automatic collision avoidance). Initial tests of the system in military warehouse environments have demonstrated probabilities of detection well in excess of 0.90 with a very low false alarm rate. The system is being extended to allow the supervision of multiple mobile platforms by one operator.

In the underwater environment, the Advanced Unmanned Search System (AUSS) (Walton et al., 1993; Uhrich and Walton, 1993), developed by the Navy, is a supervisory controlled, broad-area, undersea search system. The remote vehicle is 17 ft long and 31 inches in diameter, weighs approximately 2,800 lb, has an endurance of 10 hr and a maximum velocity of 5 kn, and can operate to depths of 20,000 ft. An acoustic link transmits compressed search data from the vehicle at 4,800 bits/s and sends high-level commands to the vehicle at 1,200 bits/s. The primary search sensor is a side-looking sonar. Electronic still and 35 mm film cameras provide imagery for identification. Depending on the amount of compression desired, sonar and video images take from 20 s to 2 min to transmit. On-board navigation sensors include a forward-looking sonar, a Doppler sonar, gyro-compass, depth sensor, attitude sensors, and rate sensors. In addition, bottom-deployed long-baseline acoustic transponders and ship-based short-baseline acoustic, Loran-C, and global position system (GPS) navigation systems can be used to update the remote vehicle navigation system and to allow the surface support craft to maneuver to maintain the acoustic telemetry link. In a typical scenario, the AUSS system operator commands the remote vehicle to execute a search path and supervises the system by monitoring vehicle position, status, and transmitted imagery. If an object of interest is detected by the operator, the vehicle can be ordered to automatically home in on the object and get higher resolution video imagery for evaluation.

Class 4 Systems: Nontethered, No Telemetry

The final class of systems represents the perceived high ground of mobile robotics research and development. The premium on on-board automation is extremely high, and the remote vehicle carries out its mission without requiring human monitoring or intervention. The human is involved only in programming or specifying the desired high-level behavior of the system and possibly in retrieving mission or sensory data after the mobile robot has returned from an excursion. This means that all sensor regard control, interpretation, and the reasoning required to transit within the environment without collisions must occur on board. Class 4 systems do not need a telemetry connection to their control station and therefore can be highly maneuverable and operate to long distances. Mission duration, like Class 2 and Class 3 vehicles, is still limited by on-board



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