By John P. Mello br>
Sonar (sound navigation and ranging) has been around since the beginning of the 20th century, but it didn’t enter the third dimension until the beginning of the new millennium. That’s when a University of Rhode Island professor, one of his graduate students and the student’s mother founded Providence-based FarSounder.
The company uses technology developed over a 10-year period by Prof. James Miller at URI’s Ocean Engineering and Ocean Technology Center. For the first time in the 100-year-old history of sonar, the technology allows a ship to see what’s ahead of it underwater in three dimensions and in real time. Early adopters of the technology have been luxury yachts and ecotourist adventure vessels, but this spring the company received a $99,940 grant from the U.S. Department of Homeland Security to develop a 3D sonar underwater threat detection system.
PBN recently spoke with Matthew Zimmerman, a founder and vice president for engineering of FarSounder, about the firm’s technology.
PBN: What’s the difference between 1D, 2D and 3D sonar?
ZIMMERMAN: A traditional one-dimensional sonar is like an echo-sounder or fish finder. It looks straight down and tells you how deep the water is that you just drove over.
A two-dimensional sonar points forward and tells you the range and the angle of something in front of you, but not the depth.
With 3D sonar, we’re able to give you range, angle and depth. That allows us to say this portion of the water is safe, this portion of the water is dangerous, and we can give you that information about what’s in front of the vessel before you have to make a navigational decision.
PBN: What were some of the challenges confronting you as you developed this technology?
ZIMMERMAN: Working in shallow water was very difficult. We had to figure out a way to operate even in those conditions, because shallow water is where a system like ours is most important. You can hit something in deep water, but most accidents are caused by hitting things on the sea floor. We spent many years trying to figure out how to do that successfully.
If you have a two-dimensional sonar, you really can’t tell the difference between reflections from waves at the surface and rocks on the bottom and things in the middle of the water. That’s why those systems are not successful for navigation.
Our three-dimensional approach allows us to distinguish, through spatial classification techniques, between those classes of objects. The difficulty in working in three dimensions is figuring out a way to display all that information to the user.
We think we solved that problem. If you’ve had experience using a radar, you should be able to use our system with very little trouble.
PBN: Why is it significant that you can create your 3D picture with a single ping in two seconds?
ZIMMERMAN: We actually have a new release of the software that has a one-second update rate. The speed of sound in water is very slow. It’s only about 1,500 meters per second. That means it would take one second to hear the echo off something 750 meters away. If we had to use 20 or 50 pings to build an image, we’d have to wait 20 seconds or 50 seconds just to see it. Doing it in one ping allows us to build the image in real time.
PBN: What is the “water depth barrier,” and how does your technology break it?
ZIMMERMAN: The water depth barrier is a barrier for other technologies. Our system can map the sea floor in front of a vessel to a minimum of eight times the depth of water that we’re operating in. But beyond that, we can still detect things floating on the surface, rocks coming off the sea floor and things floating in the water column up to a quarter of a mile.
PBN: Do you have to modify your technology for your project with the Department of Homeland Security?
ZIMMERMAN: Yes. We’re reconfiguring the technology for another application. The new application is a swimmer and diver detection system. To do that, we’re developing a new hardware sensor and we’re modifying our software to include better classification techniques. In many ports and harbors, there are many things that look like swimmers and divers acoustically – such as manatees or porpoises or seals. Obviously, those aren’t threats to the port environment and our system needs greater classification capability to separate threats from non-threats and alert the user only when there is something that’s a threat.
PBN: Some sonars have been controversial in recent times because they’ve been linked to threats to marine wildlife. Is your technology a threat to wildlife?
ZIMMERMAN: We’ve constantly strived to build a system that does not affect marine wildlife. The bad things heard about sonar have been caused by very loud, very low-frequency sonars used by the Navy for hunting submarines at distances of hundreds of kilometers. Our system is very quiet and very high frequency. Great whales can’t hear us at all, and we’re quieter than a dolphin when it does its own sonar. We are in the same frequency range but quieter than many of the existing one-dimensional echo sounders that are on every ship around the world.