Magnometers - Why such a big differene in price ?

[barnhse]

I am wondering if you really get what you pay for?

I have been searching for a buried safe for over 2 years.
The top of the safe is 3X3 feet square.
It is buried 25 feet in a wet, salty marsh with a high concentration of hematite and some iron ore rocks and some slag.
Hence, my Pulse Induction metal detector has way too manny hits, and other detectors don't have enough depth and other methods won't work in the salty, hematite, wet soil.

My best guess is to use a magnetometer in grid patterns.

I am wondering why the huge variance in prices.
1) For the low end in price, I found an Earth Magnetometer Model EM2 magnometer on eBat for about $800.
2) For the next bump in price, I found was to rent a G-858 MagMapper, but could not get insurance for a week to cover the rental (no insurance company would do it, as it is aa $20,000 magnometer). (I spoke with tech support, and they said even with a G-858 the odds of finding my target would be only like 80%)
3) The next bump in price is some $10,000 magnometer.

Would I be wasting my money with the $800 EM2 magnometer in such a harse environment trying to go so deep?

 

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[Carl-NC]

I looked at the EM-2 and was pretty impressed with the resolution. Typical Earth field is 50uT and it has 1nT resolution. It looks to be a single-sensor mag, most mags used for searching have 2 sensors arranged as a differential and commonly called a gradiometer. A gradiometer can be used like a metal detector, a single-sensor cannot unless your target signal is overwhelmingly strong.

IMO, the EM-2 would do the job but you will probably want to use it to grid-map the area. Ideally, it should have built-in data logging and you could download the data into a mapping program and automagically see the the results. Doesn't look to have data logging, which means you'll need to manually write down the results and then enter it into the mapping program.

 

[BillA]

I had one of those Dalton (?) things, then a Geometrics 858, and then their cesium mag
Indeed you do get what you pay for
80% seems not so bad (what is YOUR confidence level?)
find someone who has one and pay them for a couple of days of gridding
Bill

 

[BillA]

talk wit Geometrics, they have a rental dept but they also know the ´local' operators who can make you a map
Bill

 

[barnhse]

talk wit Geometrics, they have a rental dept but they also know the ´local' operators who can make you a map
Bill

Hi BillA, and Carl-NC,

I just happend to re-check my post here, I missed any emails I got saying anyone replied to my original post here.
Very sorry.
I was not ignoring you.

I would love to find someone with a Geometrics mag and pay them for a couple of days of gridding.
Looking for someone, I posted on my local treasure hunting group, but no one has anything.
Darn.

Regarding the EM-2, I don't mind manual logging.
I contacted AlphaLab, Inc. to see if they would rent their cheap Earth Magnetometer Model EM2.
To my surprise, you can rent an Earth Magnetometer Model EM2 for a month for $260 (plus shipping) and the rental can be applied to purchase price if you decide to buy it.
I will start saving my loose change.

 

[cactusman]

Magnetometers are specialized tools, that's part of the reason for the price, and yes, you get what you pay for.

A 3X3 safe is going to be a tough target at 25 feet. My Schonstedt can pick up a well casing at 15 feet, so they can locate ferrous objects at great depth, but it seems that the length of the target is more important than the surface area, as magnetometers are picking up the magnetic signal from the target, and the size of the target is the key factor in the magnetic field it has generated (thanks to the earth's magnetic field). If the safe was say 3X6 you could probably locate it at 25 feet, maybe.

Try renting a unit, or perhaps buy a used one, and do some grid searching -- the potential reward would warrant the price. If you go used, you could always resell it and recover most of your money, so that's my suggestion. -- Either way, good luck with your search!

 

[barnhse]

Magnetometers are specialized tools, that's part of the reason for the price, and yes, you get what you pay for.

A 3X3 safe is going to be a tough target at 25 feet. My Schonstedt can pick up a well casing at 15 feet, so they can locate ferrous objects at great depth, but it seems that the length of the target is more important than the surface area, as magnetometers are picking up the magnetic signal from the target, and the size of the target is the key factor in the magnetic field it has generated (thanks to the earth's magnetic field). If the safe was say 3X6 you could probably locate it at 25 feet, maybe.

Try renting a unit, or perhaps buy a used one, and do some grid searching -- the potential reward would warrant the price. If you go used, you could always resell it and recover most of your money, so that's my suggestion. -- Either way, good luck with your search!

Hey Cactusman,

If the safe is 3X3X4 feet cubed, where the bottom is 24 feet down (the top being "only" 20 feet down), do you think a Schonstedt would find it?
If so, is there a place to rent a Schonstedt?
I see on Amazon that a Schonstedt GA-52Cx sells for around $800. Which is bit more than the wife will allow on my "foolishness".
Would hematite soil and/or iron ore rocks effect a a Schonstedt's readings?

Thanks

 

[cactusman]

Hey Cactusman,

If the safe is 3X3X4 feet cubed, where the bottom is 24 feet down (the top being "only" 20 feet down), do you think a Schonstedt would find it?
If so, is there a place to rent a Schonstedt?
I see on Amazon that a Schonstedt GA-52Cx sells for around $800. Which is bit more than the wife will allow on my "foolishness".
Would hematite soil and/or iron ore rocks effect a a Schonstedt's readings?

Thanks

That's a great question. I would say it is possible that hematite and iron ore could distort the magnetic field of the safe, as they would have smaller magnetic fields of their own, if they are large enough.

As for the Schonstedt GA-52Cx picking up a 3X3X4 feet cubed safe at 20 feet, I would honestly say it's iffy, but if you can get access to one, you can certainly try it. If I were you I would look at simply renting one -- call contractor supply stores and ask them if they rent magnetic locators, like the ones surveyors use to find property stakes, and often large hardware stores have one or two available to rent. -- The Schonstedt GA-52Cx is probably the most common one around.

 

[barnhse]

That's a great question. I would say it is possible that hematite and iron ore could distort the magnetic field of the safe, as they would have smaller magnetic fields of their own, if they are large enough.

As for the Schonstedt GA-52Cx picking up a 3X3X4 feet cubed safe at 20 feet, I would honestly say it's iffy, but if you can get access to one, you can certainly try it. If I were you I would look at simply renting one -- call contractor supply stores and ask them if they rent magnetic locators, like the ones surveyors use to find property stakes, and often large hardware stores have one or two available to rent. -- The Schonstedt GA-52Cx is probably the most common one around.

Hey Catcusman,

Hematite is everywhere where I am searching.
In fact, if I dig a hole and stick my pin pointer in the hole, it always goes off.
If I stick my pin pointer in a pile of dirt I just dug up, it always goes off.

I am interested if a magnetometer will even work in such an environment.
What do you think?

 

[BillA]

I am not Catcusman, but I will offer an opinion. A fancy gradiometer with the appropriate software and a good grid should show exactly where the safe is (if there, eh?). A magnetic analomy map will show just that, with a trashy/noisy background you will need a more sensitive mag.
Get a mag stick and dig some holes, cheap anyway.
Bill

 

[barnhse]

I am not Catcusman, but I will offer an opinion. A fancy gradiometer with the appropriate software and a good grid should show exactly where the safe is (if there, eh?). A magnetic analomy map will show just that, with a trashy/noisy background you will need a more sensitive mag.
Get a mag stick and dig some holes, cheap anyway.
Bill

Hi BillA,

So very sorry, I didn't mean to leave anyone out.
Any information and opinions are very valuable to me.

I have a good grid.
What equipment do you suggest?

With all the information that I have already posted, do you think the EM-2 would do the job?

Thanks again!

 

[BillA]

sorry, no exp with the EM2
me, I would never get (back) into manual logging just from the precision aspect
you are looking for an independent exploration geologist, try Geometrics for some leads
Bill

 

[Carl-NC]

Barn, you're gonna half to spend some money to find out. No one can possibly answer your question without having tested things under the conditions you speak of. Personally, I'd borrow/rent a mag and test on a similar safe first, not buried of course. Ironically, I used to have one about that size.

If this lost-safe-story comes from a treasure magazine or one of those 'old west' magazines, then the money you spend is "for entertainment purposes only." Otherwise, it might be a worthwhile venture.

 

[barnhse]

Thank you BilllA and Carl-NC.

I will start saving my loose change.

Spending some money for entertainment value is not really lost money.

 

[99thpercentile]

I know this post is old, but I would like to make a few points about magnetometers.

Magnetometer surveys for geophysics always use two sensors, this is so that you can remove the diurnal drift of the magnetic field. There are two ways to accomplish this. One way is to use a gradiometer setup, which is typically two magnetometers that separated by a distance vertically. Another way is to have one magnetometer set up as a base station at a fixed location and the second moving magnetometer is the one used to find targets. The data files from each sensor are merged into a single file based on time and then the subtracted difference is the data that is gridded.

Gradiometers have another advantage in that the design also removes large scale changes on the site and focuses on shallow differences. This makes them useful to find compact shallow targets, but not very useful to find deep targets.

A cheap fluxgate graiometer like the Schonstedt or any other unit designed to locate survey markers would not be an effective tool to find a target at 25 ft depth. You would want a good geophysical magnetometer such as Geometrics, Scintrex, GEM Systems, QuSpin. These sensors have noise floors of less than 0.01 nT. For large areas you would log the magnetometer data along with GPS data. Here is an example figure of data I collected over an abandoned well head with a QuSpin QTFMv2 sensor, another unit as the base station, an RTK GNSS receiver on the rover, and an RTK GNSS base station. I don't have any good examples over safes at 25 ft as I haven't personally looked for one.

A rule of thumb from Sheldon Breiner's "Application Manual for Portable Magnetometers" is that a total field magnetometer can find a buried car at 50 ft depth.

Breiner, S., 1973. Applications Manual for Portable Magnetometers.