Maintenance Dive on July 16, 2010

David Howitt. and I did a dive at Lime Kiln to achieve three things.  Install a new hydrophone, grounding cable and an underwater video camera.  We did the dive near high tide and managed to to get everything done, which is not always guaranteed on a dive because you're never sure what you will find down there.  We had good support from shore from David King, Kathryn Scurci and Dino.  This was important because we had a bunch of cables and a rope that we had to pull through our protective pipe that runs through the intertidal.  We needed to install a new hydrophone because one of our hydrophones had failed.  We have five hydrophones just off the light house that we are using to record ships and whale calls to try and determine if ship noise is impacting the whale's ability to communicate acoustically.  This replacement hydrophone is one of the ones that we use for calculating the position of the calling whale.  Below is a picture of how we mounted the hydrophone on the stand underwater.  All the underwater pics were taken by David Howitt.

Don't be alarmed by the knife!  I'm not trying to cut any cables, just the ends off a zip tie so that it doesn't bang against a hydrophone.  The hydrophone stand is an old tire filled with concrete, with a PVC pipe sticking out of it so that we can fasten instruments to it.  The long object on the top is our Reson hydrophone, which is our broad band hydrophone that allows us to record sounds over a very broad range of frequencies (pitch).  Although it's hard to see there are another two hydrophones fastened to the PVC pipe below the Reson.  Yes, it's true, we do a lot of our fastening down there with electrical tape.  It is amazing how it sticks to itself, even under water.  That blue thing on the left is the camera we installed on this dive.  It is was a little tricky deciding how to 'frame' the shot from that camera, especially since we couldn't see the shot (you have to view it from the computer on land).  We decided to try and aim it up and back towards land since that way at least we could see the kelp.  We hope that we might be able to record a few orcas swimming past this summer, but we'll see if we get that lucky.  Below is a short clip I took afterward to make sure the camera was working.  Since the currents were picking up you can see how much kelp fronds oscillate in the current.

The grounding wire was installed to try and decrease the amount of hum that you sometimes get from trying to record sound.  This is usually the 60 Hz hum that you get from the power lines, but we also sometimes pick up stuff that isn't really audible underwater, like radio transmissions.  It's amazing how much of a difference having a grounding wire can make.  We attached our grounding wire to a metal pipe to make sure there is plenty of metal exposed to the water to make a good ground.  This is what the setup looked like.

The dive itself went really smoothly and we actually got to see a lot of stuff around us.  Sometimes that is not the case since we are so busy.  This time around, there were a couple of rock fish that didn't seem concerned about us at all.  In fact they almost seemed inquisitive since they watched us feeding cables and rope through the protective pipe from a distance of only thee feet.  Here is a pic of one of them.