Adam Jalanzaman
according to new paper Published in Nature Communications. The system can capture color images of distant submerged objects, even in dark environments, transmit data wirelessly for real-time monitoring of underwater environments, aid in the discovery of new rare species, and monitor ocean currents, pollution or commercial and military operations.
We already have a variety of methods for taking underwater photos, but according to the authors, “most marine and oceanic organisms have not yet been observed.” This is partly because most current methods require connectivity to ships, underwater drones, or power plants for power and communications. Non-contact methods must include battery power, which limits its lifespan. While it is in principle possible to harvest energy from ocean waves, underwater currents, or even sunlight, adding the equipment to do so would result in a much larger and more expensive underwater camera.
So the MIT team set out to develop a solution for a battery-free wireless imaging method. The design goal was to reduce the hardware required as much as possible. Because they wanted to keep power consumption to a minimum, for example, the MIT team used inexpensive imaging sensors available for use. The trade-off is that these sensors only produce grayscale images. The team also needed to develop a low-power flash, since most underwater environments don’t get much natural light.
SS Afzal et al., 2022
It turns out that the solution to both challenges is to combine red, green, and blue LEDs. The camera uses the red LED to illuminate the location and captures that image with its sensors, then repeats the process with the green and blue LEDs. The image may appear black and white, according to the authors, but the three colors of light from the LEDs are reflected in the white portion of each image. Thus, a color image can be reconstructed during post-processing.
“When we were kids in art class, we were taught that we can create any color using three primary colors,” Co-author Fadel Adeeb said:. “The same rules apply to the color images we see on our computers. We just need red, green, and blue, those three channels, to build color images.”
Instead of a battery, the sensor relies on piezo acoustic backscattering for very low-power communications after encoding image data into bits. This method does not need to generate its own audio signal (as with sonar, for example), and instead relies on modulating the reflections of underwater sounds to transmit data one bit at a time. This data is captured by a remote receiver capable of retrieving the modified patterns, and then the binary information is used to reconstruct the image. The authors estimate that their underwater camera is about 100,000 times more energy efficient than its counterparts and can run for weeks.
Naturally, the team built a proof-of-concept prototype and ran tests to prove their method worked. For example, imagine the pollution (in the form of plastic bottles) at Keyser Pond in southeastern New Hampshire, as well as the African starfish (Protorster Linkley) in a “controlled environment with outdoor lighting”. The resolution of this last image was good enough to capture the various tubercles along the starfish’s five arms.
SS. Best et al, 2022
The team was also able to use the wireless underwater camera to monitor the growth of an aquatic plant (Aponogeton ulvaceus) over several days, discovering and locating visible beacons often used for underwater tracking and automated manipulation. The camera achieved high detection rates and high location accuracy up to a distance of about 3.5 meters (about 11.5 feet); The authors suggest that longer detection ranges can be achieved with higher-resolution sensors. Distance is also a factor in the camera’s energy harvesting and communication capabilities, according to tests conducted at the Charles River in eastern Massachusetts. As expected, both of these vital capabilities diminish with distance, although the camera manages to transmit data up to 40 meters (131 feet) from the receiver.
In summary, “the wireless, inexpensive, and fully integrated nature of our method makes it a desirable approach for massive ocean deployments,” the authors wrote. Scaling up their approach requires more advanced and efficient transducers, as well as high-power underwater acoustic transmission. It is also possible to use existing grid networks of buoys on the ocean’s surface, or networks of underwater robots such as Argo buoys, to operate power-collecting cameras remotely.
“One of the most exciting applications of this camera for me personally is in the context of climate monitoring,” Adeeb says. “We are building climate models, but we lack data for more than 95% of the ocean. This technology can help us build more accurate climate models and better understand the impact of climate change on the underwater world.”
DOI: Nature Communications ، 2022. 10.1038 / s41467-022-33223-x (About DOIs).