Summary

The PASS is an efficient instrument that takes advantage of its strengths of utilizing the light where it travels the best i.e. the air. And the sound, where the sound travels extremely well, i.e. in the water. The system has a LASER that throws a beam of light, which gets absorbed at the surface of the water and is then converted into sound waves. These sound waves further travel through water and get reflected from the underwater objects and reach the instrument above where they are converted into electrical signals. This reception of the reflected sound waves takes place through extremely sensitive sensors called transducers. Then PASS also has intelligent algorithms that jot down the received sound signals as pieces of a jigsaw puzzle and produce the required 3-D image of the corresponding underwater object.

Description

Stanford Engineers combine light and sound to curate the latest airborne technology see underwater.

How wonderful would it be, if we look clearly at the life and ecosystems under the water and that too without diving? Yes, the near future holds such great possibilities.

Scientists at Stanford, have successfully engineered a method to capture images of ocean beds. They achieved this with a brilliant combination of light and sound waves. Though, there are many sophisticated instruments like satellites and airplanes to capture images of the earth and its landscapes. But there is no way until now to capture images and to see the global water beds from the air. The technology, scientists have developed is known as the PASS, i.e. the Photoacoustic Airborne Sonar System.

So, what do we have now?

Currently, we have technologies of the Camera, Radar, and even the LIDAR. But they are relatively inefficient in touching the extreme depth of ocean beds to gather information. And scientists have been able to capture only 5% of the ocean’s environment until now. So, the idea of acquiring images of beneath the water from an airborne system, could be the latest technology to see underwater. And it would reach the untapped ocean depths, take a quick biological survey and also search for the debris or wreckages of the ships on a larger scale.

So, how does the PASS function?

PASS is an efficient instrument and takes advantage of properties of both light and sound waves. The light travels the best in air, while sound travels the best in water. Thus, the system combines these two properties, to produce a photoacoustic effect. PASS has a LASER that throws a beam of light, which gets absorbed at the surface of the water. And is then converted into sound waves that further travel through water and touch underwater objects. The waves are then reflected from these objects and reach the instrument above, where they are converted into electrical signals. Reception of these reflected signals takes place through extremely sensitive sensors called transducers. PASS also has intelligent algorithms that jot down the received signals as pieces of a jigsaw puzzle. And produces the required 3-D image of the corresponding underwater object.

Need to develop the latest airborne technology to see underwater

The earth’s surface has nearly 70% oceans, and scientists have only been able to get high-resolution images of only a small fraction. Thus, the need to have an advanced system was even more pressing. Aidan Fitzpatrick, electrical engineer at Stanford and Ajay Sanghavi have burnt midnight oils to come up with such an idea. And Brutus Khuri Yakub, an electrical engineering professor at Stanford University contributed to engineering some of the PASS’s instruments. And the U.S. Office of Naval Research and the Advanced Research Projects Agency-Energy (ARPA-E) supports the entire project.

Energy Loss

When light and sound waves travel, they suffer loss of energy. Sound waves, especially cannot transmit from air to water or vice versa without suffering a loss of 99.9 percent. Here, researchers have also produced sound waves underwater with the help of lasers to compensate for the loss. Thus, preventing the loss of sound energy twice. Another technical barrier was the refraction of light and also the refraction of sound. Scientists mitigated these issues with the help of image reconstruction algorithms. These algorithms correct all of the bending of waves when they travels back to the air from the water to produce a clear 3-D image.

Instances for the loss of energy

Aidan tells that electromagnetic radiation is a broader term for many radiations like microwave, light and the radar, put together. And all of these energy forms lose energy strength while traveling from one physical medium to another, with mechanism being a little different for the sound waves. For instance, the light doesnot reach the deep ocean beds and hence they are darker. Also a cellphone that uses electromagnetic radiation, does not catch signals while underwater. It happens due to loss of energy or energy drop.

Hence the process of imaging inside of water bodies is much different from the process used to map land bodies. The sonar systems seem to be inefficient, because of huge costs and being incapable of hunting a larger chunk of area. Thus an airborne system to capture images and gather information from under the water without losing much energy, was required.

PASS- the idea and its future.

The idea for the PASS is similar to a project that captures images of underground roots of plants. Thus analogically, the Photoacoustic Airborne Sonar System combines light and sound to seep through the air-water junction and fetch, the unseen.

The future

PASS has a very promising future compared to the existing sonar systems which peep through thousands of meters in the water. And scientists are certain about the fact that it will touch similar depths and will be of much more significance. Though they have tested PASS only for a volume of water comparable to a huge fish tank. But, Fitzpatrick wishes to accept the challenge of taking the PASS to the flowing waters and test it there. He also reveals that the instrument to be used for the aerial survey would be either a helicopter or a drone and is expected to fly at least tens of meters above the water surface. Thus making the PASS an extremely powerful invention for mankind.

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Sonali Singh