Abstract
The exploration of submerged karst networks by underwater robots requires the development of specific equipment such as an acoustic obstacle detection system to ensure the safety of the robots against any collision, to help it to navigate and to collect data for the mapping of the caves. The confined nature of the environment, its complex walls and the turbidity of the water are constraints that have made commercial underwater systems unsuitable. Therefore, it was necessary to develop our own system: the acoustic shield. In parallel, in order to collect information on the water quality during the exploration, we studied the feasibility of a system of characterization of the turbid waters by acoustic attenuation measurement at different frequencies from 1.5 MHz to 16 MHz. This second system will be also a complement to the acoustic shield by informing it on the level of turbidity, so that the detection system can know its effective detection range. Therefore, we have studied and developed two systems. For the system of characterization of suspended sediments, we made the choice of a simplified theoretical model. We proceeded to characterize different types of sediments by proposing a simplified experimental approach for which the results showed an efficiency in the estimation of the size and concentration of suspended sediments. For the obstacle detection system, we designed and developed all the data acquisition system including sensors, signal conditioners and microcontroller integrating an algorithm for sensor management and reconfiguration, based on a real-time operating system in order to make the system autonomous and intelligent. We tested this acoustic detection system with different sensor distributions in front of irregular rocky surfaces, similar to karst walls. The results showed a high capacity of adaptation of the system to the morphological variations. Moreover, it was able to ensure an almost total coverage of the tested area ranging from 0.25 m to 1.5 m with an angular range from -7.5° to +7.5°.