Underwater Optical Wireless Communications Sensor Links for Monitoring of Fragile Ocean Environments

Ocean sensing is vital for monitoring aquatic life and ecosystem health. Sensing systems are often deployed for months at a time to collect and store data. However, long-term monitoring systems have storage limits, a high penalty for failure, and periodic redeployment. Real-time sensors combat these issues, allowing for live monitoring of ocean conditions. A real-time ocean monitoring unit consists of a sensor, a data link, and a base station – this paper will focus on the data link aspect in a proposed system that is suitable for delicate ocean environments, like coral reefs or coastal shallows.

Existing links use acoustic waves or wired connections at the physical layer. However, wired links can cause physical damage to fragile ecosystems, and noise generated from acoustics can have adverse effects on wildlife. These effects include hearing loss and behavior changes in fish, as well as stranding in whales [1]. Marine life are crucial to the health of coral reefs – an acoustic sensing network would have a detrimental impact on the vitality and longevity of these environments. In order to provide a safer, less invasive solution, this paper proposes using underwater optical wireless communications (UOWC) as an economic and effective replacement for wires and acoustics.

At the physical layer, the proposed system uses an array of 468 nanometer wavelength blue light emitting diodes modulated with Manchester-encoded on-off keying. A commercial-off-the-shelf silicon PIN photodiode receives and relays data to be processed on a Raspberry Pi single board computer. The design is also modular; each layer functions independently and can easily evolve with changing technology and user requirements. The system can transmit multiple high definition images every minute from a reef floor to the surface of the water. If deployed as a link to a passive sensor, the system can stream constant measurements. Thus, the proposed design enables monitoring of delicate ocean environments using UOWC. Non-disruptive ocean monitoring is crucial for creating a sustainable relationship between the scientific community and nature - UOWC is a promising candidate.

[1] C. Peng, X. Zhao and G. Liu, "Noise in the Sea and Its Impacts on Marine Organisms", International Journal of Environmental Research and Public Health, vol. 12, no. 10, pp. 12304-12323, 2015.