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deep-water recording

To: <>
Subject: deep-water recording
From: Dave Mellinger <>
Date: Thu, 12 Jan 2006 09:35:32 -0800
Does anyone have experience of recording underwater at depth?  I am
interested in recording at around 100 m in one study, and up to 2 km in

Hello Steve,

I'll assume you're operating from a boat.  To record at 100 m depth, by far the 
simplest thing to do is just to get a hydrophone with a cable 100 m long.  
(Most commercially-available hydrophones will work at 100 m depth, but be sure 
to check!)  Dangle it off the side of the boat, possibly with a weight if the 
hydrophone doesn't sink by itself.  It helps to have some means to stop or 
reduce the up-and-down motion of the cable and hydrophone caused by the rolling 
and pitching of the boat.  Two techniques you can use for this are (1) to 
attach a 1-m long elastic piece (bungee cord, surgical tubing, etc.) at two 
points in the cable 2-3 m apart, so that the elastic bears the weight of the 
hydrophone and you have a large loop of cable out to the side where the elastic 
is; and (2) to run the cable through the center of a flat disk, 30-50 cm in 
diameter, which is attached to the cable and which inhibits any up-and-down 
cable motion.  If you use both of these methods, put the disk b
elow the cable loop.

You might also have a problem with cable strum or vibration, which comes from 
relative motion of the cable and water; this can occur either because wind 
pushes the boat with respect to the water, or because the boat is anchored and 
there is a current.  (Differential currents at different depths can also be a 
problem, but probably not much of one at only 100 m depth.)  If strum is a 
problem, two things you can do are (1) pay out cable as the boat drifts, so 
that the cable down to the hydrophone is not moving relative to the water, and 
(2) use a cable with a faring, which is basically a wrapper of some sort that 
allows it to move through the water without strumming.

Recording at 2 km depth is significantly harder.  You can, of course, use a 
2-km-long cable and proceed as above; you'll also need a hydrophone which works 
at 2 km.  Another option is to use one of the sound-recording systems that have 
been developed for use on whales, seals, etc.  These are compact little (~20 cm 
long) packages that incorporate a hydrophone and other sensors, electronics, 
and a hard disk for the data.  The two I know about are the Bioacoustic Probe 
(or B-Probe), developed by Bill Burgess at Greeneridge Sciences 
(, and the DTAG, developed by Mark 
Johnson and Peter Tyack at Woods Hole Oceanographic Institution 

Good luck,


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