Why hasn't GPR gone further for Metal Detecting ?

[woodchuck1127]

"GPR is extremely accurate when it comes to locating metallic and non-metallic objects. GPR systems work by sending a tiny pulse of energy into the ground from an antenna. An integrated computer records the strength and time required for the return of reflected signals. Any subsurface variations, metallic or non-metallic, will cause signals to bounce back. When this occurs, all detected items are revealed on the computer screen in real-time as the GPR equipment moves along. Users can even tell from the signal returned whether the feature in question is metallic or non-metallic. " To me you would think this would be the way to go in future metal detecting and maybe use multibeam GPR what do you think ?

 

[slingshot]

Cost prohibitive, probably. I look for some ingenous person to come up with an icon/pixel alternative with perhaps an off color icon to denote metal. Still, we'll have the ferrous/nonferrous problem.

 

[Grilled Scallops]

Try looking at the screens ground radars produce. It's not actually like you're looking into the ground, it's more like you're looking at curves on a graph. There's no chance you'd ever tell a bottle cap from a ring with one, that's for sure. You have to move slowly, they are heavy and expensive.

 

[woodchuck1127]

Well if you look at first Fish finder, first GPS, first generation night scope, or computer and look at them now, compared to what they use to be. I think GPR or echo sounding radar would be next step in a new metal detecting phase.

 

[Tom_in_CA]

Try looking at the screens ground radars produce. It's not actually like you're looking into the ground, it's more like you're looking at curves on a graph. There's no chance you'd ever tell a bottle cap from a ring with one, that's for sure.......

This is correct. The problem with GPR is pixel size. The smallest they can get the pixel size to, is something like 1" across. Hence all items that we md'rs would angle for (rings, coins, etc...) will be ........ doh, 1 pixel! That tells you nothing ! Even things you'd THINK would be tell-tale in shape (like a horseshoe for instance), is nothing but a messy blotch of pixels.

Yet for some reason the misconception seems to exist, that you are magically looking at shapes in the ground, as if it was a TV screen, haha. And even if the day came where the pixel size were 100x better, I think it would still be useless. Like to think you're going to see the difference between a pulltab and a gold ring. Also the moment you add the slightest bit of tilt to any object, (coins, rings, etc...) you can kiss shape showing TID judgements good bye.

Hence what we need is not shape-showing technology. But rather: composition showing. Ie.: when the day comes to when a machine can tell the difference between aluminum and gold, on a size-per-size basis, is the day we'll all get rich digging gold rings till our arms fall off

 

[slingshot]

Try looking at the screens ground radars produce. It's not actually like you're looking into the ground, it's more like you're looking at curves on a graph. There's no chance you'd ever tell a bottle cap from a ring with one, that's for sure.......

This is correct. The problem with GPR is pixel size. The smallest they can get the pixel size to, is something like 1" across. Hence all items that we md'rs would angle for (rings, coins, etc...) will be ........ doh, 1 pixel! That tells you nothing ! Even things you'd THINK would be tell-tale in shape (like a horseshoe for instance), is nothing but a messy blotch of pixels.

Yet for some reason the misconception seems to exist, that you are magically looking at shapes in the ground, as if it was a TV screen, haha. And even if the day came where the pixel size were 100x better, I think it would still be useless. Like to think you're going to see the difference between a pulltab and a gold ring. Also the moment you add the slightest bit of tilt to any object, (coins, rings, etc...) you can kiss shape showing TID judgements good bye.

Hence what we need is not shape-showing technology. But rather: composition showing. Ie.: when the day comes to when a machine can tell the difference between aluminum and gold, on a size-per-size basis, is the day we'll all get rich digging gold rings till our arms fall off

And I still think of my bfo days-how a piece of foil would cause an instant squeal in the audio and other metals a normal increase in the beat rate. There must be some technology to measure the rate a signal reflects off different metals? Although rings have a similar composition to tabs, it seems they would bounce back the signal slower than aluminum.

 

[Tom_in_CA]

Hey there slingshot, what year did you get into the hobby? Was about 1975-ish for me. By that time it was all-metal TR's, and a few early vlf/tr's on the scene. But I do recall seeing some guys still hunting with BFO's at that time. How deep could you get on a coin-sized object with your BFO ?

As for your question: A relative of mine worked as an engineer for Westinghouse military technology division back in the 1990s. One day he showed me an article that had appeared in one of their in-house newsletters. Tech jargon paper meant only to be read by fellow engineers on super technical stuff. The article was about how Westinghouse had been commissioned to to build a device that could tell materials apart. The purpose of the experimentation was, of course, to tell things like explosives, contaminents, etc... It bombarded the test object (still only in the experimental phase at that time) with radiation or xray spectrums of some sort. It was mounted on a bobcat tractor, and the user had to wear a lead suit. They would aim in at a concrete box that had varieties of test objects concealed inside. And the resulting readout would give percentages like XX% lead, XX percent nitrates, XX% steel, and so forth.

At the end of the article was a credit given to a particular lead researcher engineer on that particular project. And inviting any questions to be sent to him. I sent a snail mail letter (this was in the days before email) introducing myself as the such & such relative of coworker so & so ... And asked if such a device could be used to tell the difference between aluminum and gold. I was careful to tell of the dilemma facing md'rs. That : On a size per size basis, aluminum and gold share the same conductive readouts. So .... given a wad of particular foil (or wadded up tab or whatever) versus a gold ring of EXACT SAME TID READOUT on a metal detector, could his device tell which was gold and which was aluminum?

A year went by and I never got an answer. So I forgot all about it. Till one day, the phone rang. The guy was cleaning up his desk, and had found my letter at the bottom of a pile of old papers and such. He said "yes, the machine would tell those items apart". But he said it would cost a million dollars, and have oodles of red tape to get govt. clearances to operate, and you'd have to wear lead suits

That was nearly 25 yrs. ago, so who knows if we're closer today ? I bet there'd be a market, even at insane prices, if you could truly waltz out to parks and dig only gold, while effortlessly passing aluminum. Heck, I'd even be willing to wear a lead suit

 

[attackcat1]

Hmmm sounds like it was putting out some serious radiation of x rays , I don't know if wearing a lead suit would be worth getting cancer. Anyhow you would think that with todays tech advancements GPR would be better