Simulating an optical guidance system for the recovery of an unmanned underwater vehicle

Abstract

The underwater environment is hazardous, remote, and hostile. Having a look and interacting in this environment is a challenge for a human supervisor. Moreover, to design an unmanned underwater vehicle (UUV), or evaluate its performance in operation, access to the underwater world is required. A powerful way to visualize the behavior of the vehicle is to create a virtual world with all functionalities of the real world, and to operate the vehicle in this virtual world. This implementation of a virtual laboratory is an excellent way to perform meaningful simulations and complex system testing. In order to study the problem of UUV recovery by a submarine, simulations can be a great help. After the vehicle has finished its mission, it has to proceed to a predetermined rendezvous area to return to the submarine. When the UUV and submarine have detected each other, the recovery begins. The vehicle needs a very accurate guidance mode in order to steer itself to the recovery device. An additional guidance system coupled with a nominal navigation system may be a way to ensure safe vehicle navigation through the flow around the slowly moving submarine. When considering the different technological possibilities concerning the additional guidance system, a functional design approach leads to the choice of an optical technology. The assumptions for the optical guidance mode are that the UUV is fitted with a camera and a high-powered light is located at the edge of the recovery device. The principle is that the UUV tracks the highest intensity light source. A software program was designed, taking into account the physical phenomena occurring during the light propagation under the water, to simulate the kind of images that can be obtained from a camera. Because both camera optics and hydrodynamics response are simulated using high-resolution physics models, this virtual camera provides physically based sensor inputs to the robot software in the laboratory. The image synthesizer module is integrated with an underwater virtual world. A variety of simulations were performed, with varying light sources and positions, to verify proper guidance system operation during different UUV/submarine configurations. The results obtained during the simulations were used to create an optical guidance control mode. All the steps for designing such a simulated guidance system are described in this communication.