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How can i measure the thickness of ice

How can i measure the thickness of ice.

Is there an easy way either with IR or Laser to do this.

Why :-  It would be far safer to send a robotic car across an ice lake to test if the ice is thick enough for skating - or even in a rescue type operation.

Any answers however lateral and crazy welcome.......

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The mythbusters used some sort of device that used sonar to prove the myth that Hoffa is buried in Giant's stadium as false. I'm not 100% sure how it worked but it is probably similar to what Oddbot said.
So far of the methods discussed I suggest sonic measurements as you best bet. Geologist use similar methods where the fire a modified gun into the ground and measure the echos to create an image of the ground beneath them. I believe that radar is also used but without research I am not sure it is feasable.

I tried shining a laser through a block of glass as an experiment and it indeed gives two beams out.

 

The top of the picture shows the laser through beam.

The bottom of the picture shows the two reflected beams. 

one off the direct surface of the glass, and the other off the back of the glass.

lasersmall.jpg

Yes these are ideal conditions but proves a point that its possible.

NB:- the glass block is a laser cut 3D profil of my "Better-Half"

The problem is ice can be clear or white depending on the oxygen content. Light wont always refract the same given the same thickness.

Gareth's laser is hitting the opposite side (the bottom of the ice) only once. That would account for the first reflection.

The second reflection likely comes from the beam bouncing around inside the block. Likely hitting the left and right sides of the block on the way back out. A sheet of ice would have these extra sides. That second reflection would simply dissipate in the sheet.

Don't count on the second reflection for your measurement. At best, you could measure the angle of the first, compared to the beam going in.

I was careful to align angle the laser so it was a true reflection off the back of the glass block. (so no side wall issues)

The picture is direct through pure crystal glass - no artifacts...........but......

The interesting thing i found too (the glass block i used contains laser formed scars that form a 3D face)  when you align the laser to hit a cluster of the scars then they also reflect laser light back to the surface not random but also in a mirror like way to the surface again (albeit at a low light level and at an angle proportional to the depth).... the plot thickens

 

I think the brute force method would be most reliable. Make the robot do what a human would do. March out onto the ice and drill. If you have a minimum thickness you think is acceptable, drill down to that depth. Then stop the drill from spinning. Now extend the drill and see if you can lift the bot.

If the drill goes down to your minimum thickness (say 15 cm) and then can lift the weight of the bot on the point of the drill without sinking. I'd say you have some pretty solid ice.

Ping - pong with a low frequency sound maybe?

"Ice

It is possible to measure the thickness of ice from one side using appropriate transducers and instruments, either thickness gages or flaw detectors. Applications have included studies of ice buildup on aircraft wings under laboratory conditions, measurement of ice thickness on ponds and lakes, studies of ice buildup in coolers and other industrial processes, and research analysis of elastic modulus and other material properties in glacial core samples. The limitations on ice measurement are typically surface smoothness and the concentration of air bubbles or cracking within the ice. The latter often presents a significant restriction when measuring thick ice buildups, particularly in nature."

Application detail