This project examines the need for underwater ambient noise measurement and experimental validation, highlighting the design and use of Autonomous Underwater Vehicles as a novel and optimal method for the same. An extensive literature survey regarding the current state of noise measurement methods for tropical regions was performed, which also mentions the current state-of-the-art pertaining to AUVs. Furthermore, a flowchart describing the workflow of the project was designed to include the AUV design as well as the data analytics framework. The project is currently focused on AUV design, including both general and hydrophone system design.
- Commercial SONAR technologies are designed for use in the cold, deep waters of the Atlantic and do not fare well in the tropical littoral conditions of Indian Ocean Region (IOR).
- Existing efforts for mapping noise in IOR have been mathematical, or extrapolated data from partial maps. Technology to validate this data is needed.
- AUVs provide great advantages over manned methods like divers and boats, as well as Remotely Operated Vehicles (ROVs); due to their small size, sound-based navigation and autonomous mission and path planning, they can reach areas which would be otherwise inaccessible. (Refer to MH 370 plane crash recovery).
- A sophisticated hydrophone model for noise-source localization, accounting for mathematical modeling of under-sea behavior is also needed.
- AUV design should be split into 3 subsystems: Mechanical, Electrical and Software for modular workflow.
- Mechanical Subsystem recommendations:
- Non-torpedo shaped AUV for better controls.
- Multiple Hulls mounted on a frame for compact housing of various sensors, electronics and actuators.
- Rectangular/Cylindrical hulls made with marine grade aluminium and acrylic.
- Great attention should be given to waterproofing the vessels for protection of circuitry
- Electrical Subsystem Recommendations:
- Multiple modules (PDS, BMS, GPIO and more as needed) to be connected together via CAN to each other and to the SBC for modularity.
- Emergency Protections to be implemented to each subsystem
- Power calculations to be reperformed whenever components are modified from the initial recommendation.
- Software Subsystem Recommendations:
- Software stack should be implemented in multiple levels (Mission Planner, Navigation System, Control System, Device Drivers) (refer Software flowchart)
- Use ROS for device drivers, Gazebo for simulation and Git for version control
- Hydrophone module recommendations:
- Use Acoustic Vector Sensors as they provide hardware advantages over Scalar Hydrophones.
- Algorithms to localize noise sources should be designed through swarm, leader-follower or single AUV arrangements.
- Simulations should be performed, taking into account the marine environment to understand the accuracy of the module.
“AUVs can be designed to carry a range of payloads, including hydrophones. They can be used to record oceanic ambient noise field data. Using AUVs provides an advantage over surface boats as AUVs are not affected by surface waves.”