Recovery : AWAC buried in Soft Mud

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Recovery : AWAC buried in Soft Mud

Posted by spikey at August 02. 2006
Dear All:

I deployed a AWAC on a s/steel frame with concrerte weights. This was attached by rope to a concrete sinker 200 kg at a distance of approximately 4 metres, which in turn was attached to two buoys.

Three months later, the buoys were cut. Due to heavy siltation and a soft mud seabed, we have a zero visibility underwater. We have tried finding the sinker/ profiler with divers, but with no luck.

The AWAC stopped pinging two week ago (assumption). Is there any efficient way to locate the poor AWAC? <img src=:(" />

Help needed!

Recovery : AWAC buried in Soft Mud

Posted by spikey at August 04. 2006
The AWAC itself will keep working until the battery falls below 8 V.  The output signal is strong (200 dB ref 1 microPascal or so) but highly focused.  Given how instruments can cross interfere if you are not careful, the high source level should  make it easy to hear the AWAC with a broad band transducer that covers the 1 MHz range.  You should be able to pick up the signal at least 50 m away.  Or so I would think.  Anybody out there with some experience in this?   <img src=:(" />

- Atle Lohrmann

PS If the rope to the buoys floats maybe you can see it with the echo sounder?

Recovery : AWAC buried in Soft Mud

Posted by spikey at August 05. 2006
Artle - I am very interested in the technology of locating an ADCP using something that can pick up the ADCP output, so any info on that would be appreciated.  However since the batteries are probably dead by now, that will not help spikey's situation.

spikey - more information would be helpful, such as water depth and project location.  I am also not sure of the methods the divers may have used.  A circle search around deployment point is what we use to locate moorings, even in zero visibility.  With the bottom type you describe, you may need to use a chain or weighted cable or line that can sink into the bottom enough to snag on the mooring.  You could sweep the bottom with a chain held apart by one large or 2 small boats, or even with 2 divers.  The chain should sink into the soft mud and hopefully grab your lost gage.  Another idea is to do a search with side scan sonar or metal detectors.

Let me note that concrete loses 45% of its weight in seawater (64/140) so you need about twice as much concrete weight in air as you would lead or metal weights.  

I can sympathyze, as we lost instument moorings offshore SE Florda due to the 2004 hurricanes.  However, my moorings using long using ss pipes jetted into the bottom have survived major hurricanes.

Recovery : AWAC buried in Soft Mud

Posted by spikey at August 07. 2006
Dear Lee

I suppose what is needed is something like a"DolphinEar" that downmixes the 1 MHz sound down into the audible band.  Hmmmm....., not very difficult to make if there is a market <img src=;)" />  The problem is not really to detect the sound (which is quite strong) but to find some easy way to transmit the information to the operator.

I am going to check around - I believe we have customers who have used hydrophones to find current profilers that have gone missing.  

Best regards, Atle

Recovery : AWAC buried in Soft Mud

Posted by spikey at August 08. 2006
Hi, I have tried to locate a 307 KHz ADCP with a hydrophone. I had to make a coil in the receiver that had resonance around this frequency. I adjusted the frequency response in water using another ADCP configured the same way. I first used a simple (wide) hydrophone and after I heard a 'click' (broadband...) I changed to a more projected hydrophone and got almost shot by the headphones. The depth was 110 m. I then swept up the frame with a homemade 'thing' on a wire. It took a little while. But if it is not pinging anymore I suggest using a sidescan or a simple mesotech if it is shallow. If the position is well known I would just go on sweeping, it usually works but may ofcourse take a while... good luck

Recovery : AWAC buried in Soft Mud

Posted by spikey at August 09. 2006
Dear All:

Thanks for all the help. Since the battery was dead, and the AWAC no longer pinging, we used divers to find the AWAC. Bingo, we found it after 2 days of search.

We will be making some design for a better AWAC frame comprising of an Acoustic Release Buoy.

Cheers,  <img src=:D" />  <img src=:)" />

Recovery : AWAC buried in Soft Mud

Posted by spikey at August 11. 2006

Glad to hear that you found it!  I know the feeling of relief.... <img src=:)" />

- Atle Lohrmann

Recovery : AWAC buried in Soft Mud

Posted by spikey at June 07. 2007
Sorry to join late. Actually if the battery is dead, you can use Magneto Meter to swath on the deployed area. This is what usual surveyor does to detect buried pipeline or sub-bottom cable. <img src=:D" />

Re: Recovery : AWAC buried in Soft Mud

Posted by Stone Mcgee at December 20. 2019

This means which one thing that we lost and gt back by some tricks and working method this is a great way. The one way to recover something is by increasing arielle to get the coding you will put these codes into the bar and its work.

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