Networked Sensor Swarm of Underwater Drifters

Abstract:

Although coastal waters play a crucial part in the ecosystem and economy, detailed monitoring of these areas has been difficult. This multi-institutional project presents a novel technology, where a large number of autonomous underwater vehicles organize themselves as a swarm, forming a dense four-dimensional spatio-temporal sampling system. The system's unique strength is that it consists of drifters that float with the coastal currents, thereby monitoring phenomena in their own moving frame of reference and allowing for revolutionary sampling densities due to relatively low vehicle cost. To achieve this powerful new technology, the drifter swarm has to operate as an intelligent distributed collective, made possible by the cyber backbone of networked information sharing, location finding and swarm control. By its very nature, a networked drifter swarm is heavily affected by both the physical ocean environment, i.e. the currents, and the challenging underwater propagation medium. The cyber components are designed in way that is tightly matched to these physical factors. In addition to being tightly coupled to the physical world, these cyber challenges are also highly intertwined, necessitating research that is distinctly collaborative. To support underwater communication links, networking protocols, such as time synchronization and retransmission scheduling, have been proposed that are optimized for the specifics of the propagation medium. In addition, position finding algorithms combine local information sharing, sensor data and correlations from current-induced motion behavior. These solutions have been shown to allow for more flexible beacon timing constraints, resulting in better positioning performance, while also foregoing the need for accurate timing or semi-simultaneous receptions. In February and September 2013, two sea trials were conducted, during which a swarm of mini-floats was deployed, showing the correct funtioning of the technology as well as the ability to track the devices underwater. Formation control is being designed for the swarm to self-organize in advantageous configurations by taking advantage the spatio-temporal variability of the current flow field. The resources of the project are also leveraged in various outreach activities. This includes participation in the 'Envision' event organized by the Society of Women Engineers at UCSD over the past three years. Also, these past two summers, PI Jaffe ran a one week workshop on the use of the floats for high school and junior high school teachers who took part in various activities related to the project, including at-sea experiments. In addition to participating in this workshop as well, PIs Schurgers and Kastner are faculty leaders in the COSMOS program; its goal is to expose and motivate young and creative high-school students to various disciplines including computer science and engineering.