Oceanic sensor networks that gather and communicate superior, real-time data could transform man’s understanding of marine ecology, advance pollution, and disaster management, and inform the various industries that depend on ocean resources. Researchers at KAUST are designing and enhancing underwater wireless sensor networks that could immensely improve present-day ocean sensing equipment.
“Currently, underwater sensors use acoustic waves to communicate data,” explains Nasir Saeed, who is involved in designing a new hybrid optical-acoustic sensor with colleagues Abdulkadir Celik, Mohamed Slim Alouini and Tareq Al-Naffouri. “However, while acoustic communication works over long distances, it can only transmit limited amounts of data with long delays. Recent research has also shown that noise created by humans in the oceans adversely affects marine life. We need to develop alternative, energy-efficient sensors that limit noise pollution while generating high-quality data.”
One alternative is to use optical communication technology instead. However, light waves tend to only travel short distances underwater before they are absorbed. Optical sensors also depend greatly on pointing and tracking mechanisms to confirm they are properly orientated to transmit and receive signals. The team, thus, recommends a hybrid sensor capable of communicating both optical and acoustic signals at the same time. In this way, a data-collection buoy on the water surface can communicate with all the sensors in a network spread out underneath it.
However, marine research requires correct measurements gathered from precise locations, so researchers need to be aware where each sensor is at any particular time. The team made use of mathematical modeling to develop a proof-of-concept localization method.
“Using our technique, the sensors transmit their received signal strength information (RSSI) to the surface buoy,” says Saeed. “For a large communication distance, the sensors use acoustic signals, but if the sensor is within close range of another sensor, it will send an optical signal instead.”
Numerous RSSI measurements for each sensor are gathered by the surface buoy. The buoy then weights these measurements to give preference to the most exact readings before calculating where each sensor is located.
Alouini's and Al-Naffouri's teams suggest that their sensors will require a new energy source instead of depending on short-term battery power. They visualize an energy-harvesting system that powers fuel cells using piezoelectric (mechanical stress) energy or microscopic algae.