Geophysical / GPR surveys

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shaggybfc
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Geophysical / GPR surveys

Post by shaggybfc » Sat Jan 27, 2018 6:16 pm

Hello all,
Does anybody have any experience of using Geophys or GPR surveys? if so, how good are they and how much does it cost? I'm looking to have one completed on some land, approx 1/2 acre.
The reason:- I know that there are some coins - a significant amount, (and some brass hand bells), buried somewhere in this garden. Unfortunately, I don't know the exact location. I was invited onto the land today to search. It turns out the land is very heavily contaminated - appears to be a 1950's dumping ground. I've tried with an Ace 250, but I'm finding it very difficult to discriminate, with significant signals showing all over the place. The owner of the garden does not want me to dig up all his lawn, but we have dug some test holes. These have shown, brass bed parts, large aluminium items, but no coins.
So I was wondering if a proper survey could identify a large 'metal' mass under the surface? Or, is there any other suggestions to try and pin point large quantities of metal - other / better machines?

Thanks for reading and any advice.
Andi


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Re: Geophysical / GPR surveys

Post by Stillburning » Sat Jan 27, 2018 6:52 pm

I cant help with how good it would be at finding coins but I had a days geophys done at one of my fields, cost £200 and covered about 7000m2, that included the field work, downloads and mapping (half an acre is about 2000m2).

A few months ago I was invited to detect just under a acre round a half timbered thatched manor house dating back to the 1550's, unfortunately it was heavily contaminated with foil and whilst on a field I would have cleared it to see if anything better underneath as most of the area was lawn it wasnt an option.

Have you considered pushing rods into the ground - may get past the coins but not the bells, or even dowsing?

Sounds like an interesting project, let us know how you get on ::g
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Re: Geophysical / GPR surveys

Post by Mega B » Sat Jan 27, 2018 6:58 pm

A tough detecting scenario,GPR either hiring or buying one is alot of money but of course it also depending on how much coins that you are looking at and also the possible value of these coins,it all boils down to the reward to effort and cost ratio.If the landowner has stipulated that you cannot dig the lawn up then accurate pinpointing of the target is vital,but then what machine do you use ??

The machine that could possibly used is a twin box detector,these not only give you depth but dont detect small items as such which can be used as a form of discrimination for your needs.They mainly will pick up larger targets and as you have mentioned alot of coins then i am assuming these would be in a container of some form rather than scattered.

Of course you have not mentioned what type of coins that you have in mind or even if its just a myth which it could be of course,but if its just a tin of old viccy pennies in the hoard then its not wworth the effort as such,but if its a 100% reliable type of information that it could be a substantial amount of say gold sovereigns or other desirable coins then its well worth the effort and with just a 1/2 acre of land should be easy to locate the target.My way of thinking is that i would use my twin box or even a Pulse machine for this specific job but its all finally down to the 'reward to effort and cost' ratio.

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Re: Geophysical / GPR surveys

Post by local hero » Sat Jan 27, 2018 7:24 pm

Another method you could use to avoid digging holes in the lawn is;
After detecting a find, set a pinpointer to say one inch and use a screwdriver or something similar to winkle out the find, doing as little damage as possible to the lawn.
Only retrieve finds from the depth you have set the pinpointer to, this could let you survey what is close to the surface.

The pinpointer should show the length of the object.

Holding the detector high should show large objects.

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Re: Geophysical / GPR surveys

Post by shaggybfc » Sat Jan 27, 2018 11:46 pm

Mega B wrote:
Sat Jan 27, 2018 6:58 pm
A tough detecting scenario,GPR either hiring or buying one is alot of money but of course it also depending on how much coins that you are looking at and also the possible value of these coins,it all boils down to the reward to effort and cost ratio.If the landowner has stipulated that you cannot dig the lawn up then accurate pinpointing of the target is vital,but then what machine do you use ??

The machine that could possibly used is a twin box detector,these not only give you depth but dont detect small items as such which can be used as a form of discrimination for your needs.They mainly will pick up larger targets and as you have mentioned alot of coins then i am assuming these would be in a container of some form rather than scattered.

Of course you have not mentioned what type of coins that you have in mind or even if its just a myth which it could be of course,but if its just a tin of old viccy pennies in the hoard then its not wworth the effort as such,but if its a 100% reliable type of information that it could be a substantial amount of say gold sovereigns or other desirable coins then its well worth the effort and with just a 1/2 acre of land should be easy to locate the target.My way of thinking is that i would use my twin box or even a Pulse machine for this specific job but its all finally down to the 'reward to effort and cost' ratio.
Thanks guys, appreciate the feedback.
well, is it a myth? The land is the garden of a house that my parents used to live in back in the 1950's. About 18 years ago, before my father died, he told me that the people next door to them had died and their family came to clean out the house, said to my dad "take what you want and scrap / burn what you don't, we've taken everything we want"... so as people did back then, they took everything,,, including 10ish large old glass sweet jars full of 'coins'. and the set of hand bells - these were actually hidden behind a wallpapered alcove. When my parents moved out in 1960, he dug a hole and buried the rubbish they didn't want to take, including these jars and a set of brass hand bells. Now this could be totally made up, as he was suffering at the time with dementia. The coins could be, Roman or even simply lead sack seals. I'm sure my father would not have known anything about ancient coins, hence would not have seen any value. They were farmers, the people next door were farmers, so who knows what they could have ploughed up - a Roman Villa and fort within 1/2 mile of the house....
Coins scattered? I assume he either placed them into the hole or threw them in, either way, they'd be in one place.
I've tried to look for dips and hollows in the ground, the ground is not level with many - this is where we dug some test holes (after getting the good signals), recovering the junk.

Stillburning, which company did you use for the geophy survey, I could talk with them to seek their recommendations?

Sounds like a fantasy, I know but I just need to know now.

Andi
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Re: Geophysical / GPR surveys

Post by Easylife » Sun Jan 28, 2018 12:09 pm

Well if it is true the he would not have dug a hole any deeper than he had to just to dispose of the items, certainly not the effort of going into the clay layer. So any detector should give a banging response to a large metallic item or group of them. I would carefully dig a neat plug and use a sheet for the spoil, that way there would be no noticeable disturbance to the lawn. If you prove this method to the landowner then they may be reassured and allow you to dig. An intriguing story. :)
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Re: Geophysical / GPR surveys

Post by chip » Sun Jan 28, 2018 12:48 pm

Any idea on how much rubbish he buried? and Did he bury all the rubbish he did not want in one large pit or did he spread it around in several?
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Re: Geophysical / GPR surveys

Post by Dave The Slave » Sun Jan 28, 2018 1:42 pm

Very intriguing !
Would going for the brass bells give less signals rather than going for the coins, which may or may not be next to the bells. Does your detector give a number reading for brass or a certain tone ?
Would a satellite image of the garden show any ground disturbance ?
A geo ref side by side map may show up any alterations to the property garden boundaries since the 60`s.
Good Luck ::g
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Re: Geophysical / GPR surveys

Post by Stillburning » Sun Jan 28, 2018 5:16 pm

shaggybfc wrote:
Sat Jan 27, 2018 11:46 pm

Stillburning, which company did you use for the geophy survey, I could talk with them to seek their recommendations?

Andi
I used Archeoscan as they as very close to me in Gloucester ::g
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Re: Geophysical / GPR surveys

Post by shaggybfc » Mon Jan 29, 2018 11:42 am

chip wrote:
Sun Jan 28, 2018 12:48 pm
Any idea on how much rubbish he buried? and Did he bury all the rubbish he did not want in one large pit or did he spread it around in several?
Thanks Chip. The area is loaded with rubbish. Lots of ferrous signals that I can discriminate out, but also lots of nice top end signals, Aluminium, copper, brass etc. I dug 4 test pits that returned cracking signals. One gave an oval brass bed knob (and then what looked like the whole bedstead, with springs - but this was not coming up easily), another gave a large mangled aluminium plate, another a large piece of copper tune, and finally a lump of lead in a pile of old bricks / building rubble. This was over a fairly large area, so I'm guessing he didn't bury it all together or this was an accumulation over many years. I did say the owner that the bed area looked the most promising, being household items.
Andi
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Re: Geophysical / GPR surveys

Post by shaggybfc » Mon Jan 29, 2018 11:52 am

Dave The Slave wrote:
Sun Jan 28, 2018 1:42 pm
Very intriguing !
Would going for the brass bells give less signals rather than going for the coins, which may or may not be next to the bells. Does your detector give a number reading for brass or a certain tone ?
Would a satellite image of the garden show any ground disturbance ?
A geo ref side by side map may show up any alterations to the property garden boundaries since the 60`s.
Good Luck ::g
Dave.
Thanks Dave,
I have just bought a cheap brass bell off ebay, to bury and test the response. I have the Garret Ace 250, so there is a scale on it. My experience with the detector is limited, as most of the signals I get are ferrous, so low end 8-|
I have looked at the satellite images, but they don't go into that much detail, same as the LIDAR.

my next step plan is:
set up a test bed at home with a jar of modern coins, some old bronze pennies and this bell and other brass items, to set the machine to discriminate everything other than these items, then go back to conduct a further, more 'scientific' survey... and at the same time speak to the Geophys company suggested by Stillburning...
Watch this space...
Andi
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Re: Geophysical / GPR surveys

Post by Easylife » Mon Jan 29, 2018 12:52 pm

I am not sure that a test bed will help much as most large metallic items will just give a much higher reading than small items of the same metal. The only way to find out if they are there for sure would be to dig everything unfortunately. A sweet jar full of coins is going to give a belting unmissable response. :D
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Re: Geophysical / GPR surveys

Post by Mega B » Mon Jan 29, 2018 1:11 pm

What type of coins are supposed to be in these jars or containers ?? if its been mentioned that they could be say gold coins ie sovereigns etc as theses had only been buried in the last sub 100 years then of course it would be game on as they say.But if the coins involved had been only low value coinage like Viccy pennies and low value silver coins like shilling then one would have too thing is all the effort worth it.

But my opinion of digging a test patch with a jar of coins and the odd bell would be a pointless exercise in my mind,especially trying to discriminate out such large targets.

These targets if all buried together should give such a banging signal even on the lowest value detector and although the field or garden is about 1/2 acre then you should be able to locate the actual target pretty easy and then do a foot print search in pinpointing mode and this should give you a indication on the target area size,i cannot see that the person burying these target would spread them around over multiple target locations within the garden,and also i doubt that they would be buried deep either.Process of elimination that someone had a few jars of coins and a few old handbells would dig them relatively close to the surface.

Even with a ACE250 you should be able to locate these items,why go to all the bother of getting a GPR survey done is a little over the top at the moment.If it was a suspected deep roman gold hoard and you had reasonable good data and history that could back the gold hoard up then yes a GPR would be a way forward,i could basically do the same type of survey with my TW-5 twin box machine and that would have a very good chance of locating the actual jars and bells.
Last edited by Mega B on Mon Jan 29, 2018 1:35 pm, edited 1 time in total.

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Re: Geophysical / GPR surveys

Post by shaggybfc » Mon Jan 29, 2018 1:30 pm

Easylife wrote:
Mon Jan 29, 2018 12:52 pm
I am not sure that a test bed will help much as most large metallic items will just give a much higher reading than small items of the same metal. The only way to find out if they are there for sure would be to dig everything unfortunately. A sweet jar full of coins is going to give a belting unmissable response. :D
Thanks,
OK, a test bed is out of the question then. looks like I'll have a nice bell to polish :-L
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Re: Geophysical / GPR surveys

Post by shaggybfc » Mon Jan 29, 2018 1:42 pm

Mega B wrote:
Mon Jan 29, 2018 1:11 pm
What type of coins are supposed to be in these jars or containers ?? if its been mentioned that they could be say gold coins ie sovereigns etc as theses had only been buried in the last sub 100 years then of course it would be game on as they say.But if the coins involved had been only low value coinage like Viccy pennies and low value silver coins like shilling then one would have too thing is all the effort worth it.

But my opinion of digging a test patch with a jar of coins and the odd bell would be a pointless exercise in my mind,especially trying to discriminate out such large targets.

These targets if all buried together should give such a bagging signal even on the lowest value detector and although the field or garden is about 1/2 acre then you should be able to locate the actual target pretty easy and then do a foot print search in pinpointing mode and this should give you a indication on the target area size,i cannot see that the person burying these target would spread them around over multiple target locations within the garden,and also i doubt that they would be buried deep either.Process of elimination that someone had a few jars of coins and a few old handbells would dig them relatively close to the surface.

Even with a ACE250 you should be able to locate these items,why go to all the bother of getting a GPR survey done is a little over the top at the moment.If it was a suspected deep roman gold hoard and you had reasonable good data and history that could back the gold hoard up then yes a GPR would be a way forward,i could basically do the same type of survey with my TW-5 twin box machine and that would have a very good chance of locating the actual jars and bells.
Thanks Mega B. I am expecting the coins and bells to be buried together, in the same hole. The coins,,, who knows what they are, I'm not expecting them to be gold, at best late Roman at worst, so lead sack seals,,, but they were described as coins, that my old man didn't see any value in. (he was a grunt, so I'd not expect him to have known anything about older coins.

Thanks for the offer to survey the land for me ;)) ;)) ::g are you local to Warwickshire? :))

I'm going to see if I can get back to the garden in the next couple of weeks, to do a better survey. I've only been detecting for a month, so don't really know what to expect from really large / good finds. If it's bronze, it has a higher 'ping' than iron... if there is lots of bronze, is it the same 'ping' or different. I've never heard any difference in volume of the 'ping'

thanks
Andi
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Re: Geophysical / GPR surveys

Post by Easylife » Mon Jan 29, 2018 9:10 pm

Large iron will sound good, try your detector on a car wheel for the big hit. :))
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