Hydrophones.

Remember Dr. Erin Pettit from Girls on Ice ? She's working on Flask Glacier to the southwest of us right now, but before she left, she asked me and Yuribia Muñoz to help her out with a really cool project.

One of our goals down here is to understand how glaciers work. We're studying them lots of different ways. We put AMIGOS on them, we put GPS stations on them, we take ice cores, we take sediment cores, we look at satellite pictures - you get the idea. But Erin wants to try something else: listening to them.

Some of you may remember that I use sound to measure ocean currents. That's called active acoustics because I send out a sound and listen for the return. This is passive acoustics, where I put a special kind of microphone, called a hydrophone, into the water and listen.

What am I listening for? When ice melts, it makes sounds. It can sound like crackling or popping. When big chunks of ice fall off glaciers (called calving) it can sound like fireworks, at least in the air. Erin and other scientists think that they could use passive acoustic systems to monitor glacial melt rates in areas that are too hard to reach with other instruments.

To test that idea, we are making measurements of sound near any ice we can reach. Our goal right now is to gather preliminary data and also to test the instruments.



Yesterday, we got to go out on the ice again. The biologists took an ice core to look for algae and we used the hole that remained to put the hydrophones in to the water. Clockwise from the left, you can see Yuribia Muñoz, Kim Roe, me, and Laura Grange. We got some good data and identified some problems with one of the hydrophones. It isn't heavy enough, so it's hard to get it through the hole in the ice. Once it's in the water it doesn't fully straighten the wire it's attached to, so we can't be sure exactly how deep it is. We also had some interference on both hydrophones from noises that the ship makes.

It's really important to work out those kinds of problems, even if they sound small and unimportant compared to the complicated equations we use to turn sound from the water into usable data. Scientists need to be able to solve practical problems as well as intellectual ones. Did any of you at DLMS have similar problems with your science fair projects?