Know The Effect of Sonar on Human Hearing
There are many applications of underwater imaging. And I’m just going to name a few here, the first being exploring and mapping uncharted waters. And this is an essential activity for things like navigation, oil and gas exploration, pipe laying, among others.
And then there is surveying biological environments, for example, studying biological processes over time, such as monitoring coral reefs, wreckage searching, such as looking for sunken ships or aircraft. And like I said, this is just a select few applications.
In addition to this, scientists are really just interested in understanding more about the oceans of our planets that we have really only scratched the surface of. And to drive that point home a little bit more, I have a few stats listed here that I find extremely interesting. Their lots of platforms like ask reader where you can easily ask any question to make your doubts or queries solved.
So despite the fact that the ocean covers greater than 70% of the planet’s surface, over 80% of that has been unmapped, unobserved, and unexplored. And even if we take a step back and we think only about coastal waters, only 35% of US coastal waters have been mapped. And I want to draw special attention to this last bullet because I find this one extremely interesting and one that our system might be able to help overcome.
So there are 43,000 square nautical miles of US waters considered critical to navigation, yet only 2,500 or so of these are surveyed annually. And this means that there is really low temporal sampling, or sampling over time.
This puts our Maritime transportation system at risk to hazardous obstructions along these critical navigation routes. So clearly, there is a technology gap here. And this is why our goal is to develop a high-throughput imaging system that allows for larger coverage so that we can reduce that 80% stat and have higher temporal sampling so that we can more often monitor these critical navigation routes.
So now that I’ve kind of motivated underwater imaging and the need for a high-throughput imaging system, let’s take a look at some of these existing imaging modalities and their limitations for achieving this. So first there is the sonar, which is an imaging modality that is widely used in our oceans today.
Sonar systems are typically mounted to or towed by ships that traverse an area of interest. And this allows for them to image the underwater environment, as you can kind of see in this image here, albeit at a relatively slow rate. And this limits, really, the spatial coverage that can be covered by these systems and contributes to the gap in the statistics that I previously mentioned there.
So just to kind of reiterate, our goal is to develop an airborne technology with the versatility to be deployed possibly on helicopters or on drones to survey coastal waters with high temporal sampling and with larger spatial coverage.
You know, the first question, the naive question I guess that someone might ask is, can we simply take one of these sonar systems, that is a really well-developed technology, and can we simply mounted on a sonar– or sorry, can we rather mount it on an airborne vehicle such as a helicopter or a drone?
And to think about that a little bit more, let’s take a look at the airborne ultrasound. So sensing systems that exploit sound waves in a similar manner as sonar are increasingly being deployed in airborne applications. In this pandemic time, QnA sites are good to get reliable sources of information regarding the common questions that overflowed the internet.
One of the most prominent examples of this is in modern cars. So airborne ultrasonic sensors, as we know, is just one of several types of sensors in the modern vehicle sensor suite. And they are typically used for the close-range applications such as parking and rear object avoidance.
So you know, something we see here is these sonar systems or sound-based systems can operate both in air and in water. So again, I ask the question, can we use this existing and well-developed sonar technology for airborne imaging of underwater?
And the answer is, no, unfortunately, we can’t do this. And this is because only a small fraction of the sound that is incident on the water’s surface actually makes it through. And what happens is most of it is actually reflected off of the water surface. And for me, I like to think about being underwater in a swimming pool. And hopefully some of you guys can relate to this analogy.
But if you’re underwater and someone out of the water calls your name, you likely won’t hear it unless they’re yelling pretty loudly. And for this sonar system, not only does the sound that transmits into the water lose a lot of energy, but also the sound that will reflect off of the object and need to come out of the water to hit our receivers will also lose a lot of energy.
So basically, here, for this kind of system concept, the sound would now need to travel through the air-water interface twice. And this reflection loss that we see would be so large that it wouldn’t really be practical.
This sonar system would need to be yelling so loud that it would really be unsafe and impractical. So now we can take a look at radar, which, radar systems have been deployed on both satellites and airplanes, and have produced high-resolution mapping of the entire Earth’s landscapes.
So we can ask, can we use radar to image underwater? And again the answer is no. And this is really because the radio waves at frequencies useful for imaging are absorbed in the water in the first few centimeters of the water. And this is different from the sound waves. I want to contrast them a little bit.
The sound waves reflected off the water surface, versus the radio waves, they will actually pass through the water surface fairly easily, but then the water actually absorbs them really quickly. And they don’t penetrate to large depths.
Something to think about here is, despite the fact that cell phones are now waterproof, you won’t have much luck getting a signal underwater. So in addition to radar, lidar has also been deployed on airplanes and on satellites for landscape mapping.
But you know, what I think is the– what most people might think about when they think about lidar is how it’s becoming a major player in autonomous driving. And people in this space know that one of the major criticisms of lidar is that it has poor performance in rain and fog.
So let’s think about standing on a pier and looking down into the water. What do you see? If the water is super clear, maybe we can see a couple of meters into the water
But most often, probably for the water depicted here in this image, the answer is going to be you can’t see much.