Doing anything on a frozen lake can carries some amount of risk. Nevertheless, every year events ranging from car racing to ice skating are held on them. As such, proper safety precautions are needed, the most important of which is ensuring the ice is thick enough to withstand the weight of whatever may be on it. This is done by cutting holes into the ice and measuring its depth in several locations. But this is a dangerous and imperfect process only giving a rough picture of actual thickness. So to solves these problems, a team of students at ETH Zurich made an ice measuring submersible drone. 

The concept of ice measurement employed is, on paper, reasonably simple. When a sonar pulse is sent out, some of the energy will return off the bottom of the ice sheet, but some of it will pass through creating a second return. By measuring the difference in these two returns, the thickness can be calculate with a high degree of precision. Attach the sonar to a submersible and give it a positioning system and you can simply get a thickness map, right? Well, employing theory in practice is a far more complicated prospect as the students soon found out.

The submersible itself is slightly positively botany. It features two concrete ballasts to adjust the center of cavity and six propulsion motors for six degrees of freedom. It’s powered by a NVIDIA Jetson to allow for autonomous operations and a whole host of sensors. Navigation is handled by a variety of sensors, mostly GPS and SBL. The GPS antenna sits in a radome at the top of the submersible, allowing for a strong enough signal for a positional fix when touching the bottom of the ice. SBL works similarly to sonar, where a transmitter on the submarine sends out an audio ping, received by a trio of hydrophones used to calculate the drone’s position.

But does all this complexity really work? Well, mostly. A number of real-world factors greatly compound the submarine’s effectiveness. The signal noise from in the sonar makes accurate measurements nigh impossible with that methodology. As such, the team used a depth based approach, by touching the submarine to the bottom of the ice, and measuring the water pressure and therefore depth, the ice’s thickness can be easily calculated. However, this method too is not without flaws. When snow falls on alpine lakes, it pushes the ice sheet downward, and a new ice sheet can form on top. This top sheet’s layer is what’s most important, but the depth measurement can only take into account the overall sheet’s thickness. Regardless, this was a really impressive first test of the submersible, and we look forward to seeing where it goes from here!

Make sure to check out this autonomous submarine next!