|INTRODUCTION - Autonomous Underwater Vehicle|
Underwater exploration using Unmanned Underwater Vehicles (UUVs) is nowadays becoming a crucial tool both for industrial and scientific needs. UUVs were first developed in early 1960's by the US Navy in order to carry out deep-sea rescue and recovery operations. Since then UUVs have progressed significantly, representing nowadays the platform of choice for interacting with the underwater environment. The main reason behind their success is the absence of the human operator inside the vehicle which proved to decrease drastically the cost of the operations while increasing both reliability and human safety.
The UUVs offer countless possibilities for scientists in fields like biology, geology, oceanography, seafloor mapping and archaeology, offshore platform inspection and maintenance, monitoring of human activities that impact the environment, and rapid recovery and investigation after maritime disasters (such as in the case of the Prestige tanker accident). The vast majority of commercially available UUVs are remotely operated (ROV). They are connected to the surface by an umbilical cable that provides communication and power. A specialized human operator is needed to send commands to the ROV while receiving feedback from the sensors mounted on vehicle. The requirement for specialized operators on regular basis could prove costly for repetitive or extended missions, and it is out of reach from small research groups or administrations that could benefit from having imagery data for their study sites. Moreover the use of ROVs in specific applications is restricted due to the presence of the umbilical cable.
Autonomous Underwater Vehicles (AUVs) were designed to overcome the limitations imposed by the ROVs. They are designed to be deployed, carry out a predefined set of tasks and return to a pre-established recovery point. In the last few years a series of research centers (MIT, WHOI, ISR) and commercial companies have put great effort in developing feasible solutions for AUV architectures. Despite steady progress, AUV design still represents an open issue, mainly due to the limitations on the range/precision of the sensors and control architectures, among other factors. Furthermore, the absence of the umbilical cable imposes strong power availability constraints that ultimately limit the range of AUV operation. This reason is behind current AUV designs that employ a torpedo shape to decrease drag, thus increasing speed and range.
We propose the development of an AUV system intended for detailed colour mapping and monitoring of extended seafloor areas. The proposed modular design is compatible with a wide range of potential applications in the fields of habitat mapping, geological surveying and archaeological site exploration. Emphasis will be put in applications that can benefit from close range benthic sensing using optical and acoustic imagery. As pointed out above, a typical mission will comprise a survey over a region of interest. The vehicle will be capable to autonomously perform a predefined trajectory resorting to an acoustic positioning system complemented with internal inertial navigation sensors. The tracks will ensure full coverage of the benthos while flying at low altitude, acquiring visual and acoustic data, in addition to other environmental parameters that may be gathered with additional sensors (i.e., temperature, turbidity). The data will be geo-referenced, providing the possibility to carry out additional surveys of the same region in later missions. This represents an important aspect if one needs to track the evolution of the seabed morphology over time. The capability of routinely performing missions and detecting changes in the benthos has not yet been demonstrated. The development of the proposed platform and associated data geo-registration algorithms is expected to contribute decisively towards this goal.