Last week I was back in Scapa Flow with the intention to scan some of the wrecks, including the Grumman Wildcat JV751 that is now lying in 34m of water:-
https://sketchfab.com/models/97dd210e333349288b8819d3f1a0408f
The technique is called photogrammetry (some of you may remember the Westland Wessex I scanned last year?) and its great for capturing an accurate representation of what lies on the seabed.
Lost from the deck of HMS Trumpeter on the 2nd of December 1944 when the steam catapult malfunctioned, JV751 ended up in the Flow. The pilot E.E. Ames was rescued but the airframe was (not surprisingly) written off.
The airframe has been damaged by fishing activity and the ravages of salt water. Full story here:-
From the model it is possible to derive what is called an orthophoto – a huge single image with enough detail to see close detail – you can seen an example here:-
The Shipwreck Project have been researching an aircraft crash site in Weymouth Bay. Hours in the archives have yielded much of the story, and we are planning to scan and document the site in the New Year – update to follow as and when.
By: grahame knott - 16th November 2016 at 11:36
Hi Graham Simon asked me to reply to this however it can get a bit involved so if you require any more information by all means message me.
GPR uses electro-magnetic waves and will not work in salt water due to its high conductivity. Radar has a good range in air because it is non conductive.
GPR will work to some extent in fresh water due to its low conductivity.
The best way to carry out sub seabed survey is to use a sub-bottom profiler, (shallow seismic) system which generally uses a narrow beam high source level acoustic pulse.
Echo’s are returned from layers or objects of different density much like medical acoustic scanning.
Depth of penetration can be very variable dependent on bottom type (density) but on muddy bottoms you can expect to see several metres down. Frequency of burst is usually around 4Khz and can be simple Carrier Wave(CW) or a chirp.
Chirp allows better Transmit/Receive correlation and thus smaller returns can be detected and hence greater penetration can be resolved.
In water depths over 20 meters attenuation in the water column has significant effects (beam spread and attenuation) and it is best to resort to towing a weighted body with the transducers on it rather than deploying on a pole over the side of the ship.
www.theshipwreckproject.com
By: Graham.A - 15th November 2016 at 14:55
Simon, can Ground Penetrating Radar be used from a ship to see what is under the seabed?
Or are there other methods of being able to see under the mud?
I ask because quite often the wreck settles and gets covered, so there is a much smaller target to find, just wondering if GPR would be a helpful tool for locating wrecks and seeing the true extent of what remains.
Cheers
By: Paul - 15th November 2016 at 10:05
Just looked at some of your other work.
What an excellent way of recording what is there.
Well done.
By: D1566 - 15th November 2016 at 06:23
Excellent – looking forward to the next one 🙂
By: Rocketeer - 14th November 2016 at 21:50
Fantastic! Thanx for sharing. Excellent work
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November 14, 2016 at 8:52 pm