Have you noticed differences in detection depth with varying soil moisture?

Jim Hemmingway

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Jan 26, 2008
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Hello Everyone,

With the purchase of some new metal detectors last spring, I put in a test plot just for the heck of it. The soil is a brown clay with maybe an inch max of topsoil overburden. The F-75 ground balance is currently at 84ish and magnetite at 0.1%. The ground balance (GB) with the MXT is at 81ish (I include this for the many folks who own this model).

Under normal dry conditions, on a 10-inch deep nickel (a real nickel composition pre-1981 Canada nickel) the F-75 will easily give a solid two-way signal with a few inches of air space to spare between the coil and the ground surface. Even in the frozen winter conditions of a month ago, it was still pretty much the same good signal, maybe a bit less.

Now the ground where the 10-inch nickel is buried has thawed mostly and is really wet. The wetness probably goes down most of the way. I know this because the garden is adjacent to it, and its always wet down to about a foot at this time of the year.

Checking this 10-inch nickel today, I could just get a not-so-solid two way signal with no room to spare. That’s with the coil swinging back and forth about an inch above the ground. I figure there is about a two-inch loss of depth capability under these wet conditions.

Meanwhile, a 10-inch copper penny buried further up the yard at a higher elevation, under the trees where the ground is much drier but still damper than usual….is giving a slightly improved signal.

As an aside, I’ve always figured all my detectors achieved better depths over our fresh water sand beaches that were always wet at any depth.

A friend from down south sent me a copy of his soil analysis, performed by a leading metal detector manufacturer. It’s interesting because although it’s tougher ground than mine (iron oxides...type not stated in report), when dry it can be ground balanced and decent depths can be had. However, when wet, ground balance is not nearly as effective, and the ground is hard for a signal to penetrate. In fact, the analysis engineer states that there is a world of difference between that soil when dry as compared to when it’s wet. It would seem that somehow the wet conditions “activate” the iron oxides in the soil similar to the way wet conditions affect salt areas….so states the report. Interesting stuff don’t you think?

Does anyone else monitor their test plot signal responses over varying moisture conditions?

Have you noticed differences in depth results? Patterns over time?

Jim.
 

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Michigan Badger

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Oct 12, 2005
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No, can't say that I ever thought of this Jim.

Very interesting reading.

Please share more.

I've always thought wet ground meant deeper finds but again I never really checked. It just "seemed" to me I was going deeper in the wet spring.

I went out today for a 1st try of the F70. Wow, was that a learning experience! (see review).

Thanks,

Badger
 

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Jim Hemmingway

Jim Hemmingway

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Greetings Badger,

"I've always thought wet ground meant deeper finds but again I never really checked. It just "seemed" to me I was going deeper in the wet spring."

Me too MB. And I still generally do feel that I get better depth in the spring in most areas, at least it "seems" that way. I'd like to think that over the years we'd get a pretty fair idea about our own turf.

But then too, I rarely hunt places where the ground is pretty much saturated with water. The observations I posted above indicate there are moisture conditions that do have a negative affect on depth of recovery in some soil types (aside from salt areas). How much moisture is a good question.

Maybe others can give us their experience on the subject.

Thanks MB, I'd like to see your review. Hope all went well ;D

Jim.
 

thompy

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Feb 19, 2005
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like you stated Jim i would imagine i depends on mineralization and the types, i seam to get more depth with the moisture but perfer the dryer grounds where i know alot or iron resides, i run 2 tone and seem to always get the low tone on iron in one direction of my sweep, with the high moisture content its easy to get fooled with the square nails. generally targets are 5" or less in this area with a gravel base below the topsoil. GB 87 to 89 low Fe
 

Lowbatts

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Still torn on this one.
Is the ground more compact when frozen or when thawed and soaked?

Does the thawing result in some expansion? Maybe an inch or more on a 10 inch target?

I know of spots in the park near my house where I get easily repeatable 7 to 8 inch targets when the ground is frozen, wait until it's thawed and cannot find the targets then, especially early thaw time when the ground is soaked as it is now.

All the deepest targets I've ever dug (12+ inches) were in dry ground where any moisture was only top inch or less and damp at best, not wet.
 

deepskyal

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Maybe it's not so much the wetness of the soil that has changed your depth, but the soil movement from the freeze/thaw cycle. Maybe that nickle has shifted position in the ground and is on more of a tilt now from when it was burried flat.....

Just a thought.

Al
 

Michigan Badger

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This really is a fascinating subject.

I've seen this discussed many times before but this is one of the few done more objectively.

I hope it keeps going.

I'd like to work out my own testing area. I was thinking of simply soaking down some coins in the test garden and leave the others bone dry this summer. I could just leave the hole out there over them for hours. Our ground is very sandy and water goes down fast. I could test a spot near the buried coins to make sure the soil is soaked and then see how they compare to the dry soil planted coins.

I like my coin gardens to also include some coins buried by or under small trash (nails).

Badger
 

Michigan Badger

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deepskyal said:
Maybe it's not so much the wetness of the soil that has changed your depth, but the soil movement from the freeze/thaw cycle. Maybe that nickle has shifted position in the ground and is on more of a tilt now from when it was burried flat.....

Just a thought.

Al

That's a good point.

This is why some glue or epoxy coins to the ends of wooden dowels and after making a hole with a pipe they place them down into the ground. This way the coin never shifts.

In the U.K. they have a name for this process but I can't recall it just now.

It's a superior way to plant coins for testing because it doesn't disrupt the natural composition of the soil as much as digging a big hole with a trowel.

I started using it back in 1983 as I recall and it's a great way to test coin depth and mineralization at a new site.

Badger

P.S. This website shows another more accurate way of planting coins for tests. It also shows how to make your own pinpointer and a cute liittle BFO detector.
http://www.matni.com/Arabic/Metal Detector/metal detectors.htm
 

Don in SJ

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I am not sure moisture or lack of will change detection depth, however I am fairly certain it enhances the signal of the target. My most recent example was a week ago Saturday, we just had 10 inches of snow rapidly melt, the ground was not frozen underneath and frost heave is not a factor here. But, I got 3 Large Cents in a tight area that I hit just two weeks before and I hit those exact spots very slowly with my XS and I was just amazed and so was my son with his CZ70 at all the signals we were getting.

The ground was very wet where on the previous hunts it was almost as dry a punk. so I for one believe signals are at minimum enhanced by the high moisture content over bone dry dirt.

Don
 

Tin Nugget

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Jan 11, 2007
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Now you did it, you got me thinking. I do know the black clay soil around here swells when it gets wet as my back door jams at the top when it rains enough, and yes I know this also means a foundation issue, however, if water can make the soil expand enough to lift a cement slab with a house on it I am wondering what it does in the yard. Using Jim's suggestion, I am going to use the dowel rods with coins adhered. I will do a twin test, one set under cover and the other in the open. Not so much looking at detection depth but at soil movement. I will put one 15" deep with an inch of the dowel above ground and another at say 5 or 6 inches deep with an inch above ground. I will try to wait for rain but may water the area myself. This should show me if the ground actually rises when wet. If the shallow dowel has the full inch showing after rain and the deep dowel has less than the inch above ground showing, that would tell me that the ground does rise when wet. no change in coin depth on the shallow coin because it rose with the ground, however, since the deep coin remains in dry dirt and the top six or so inches of dirt is wet and has risen or expanded leaving the coin at the original depth. This could also explain why a coin at 8 or 10 inches comes in well but after a rain, if the water did not reach the coin, it would now be deeper and give less of a signal. By how much I don't know but it sounds like a decent experiment. I am sure different soil types react differently but this hard digging black clay is what I have to work with here. Hope this makes sense, if not, I think I have it right in my head. ;D ;D ;D
 

deepskyal

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http://en.wikipedia.org/wiki/Fluid_statics

Yep...someone opened a can of worms alright... :icon_study:

But I never heard that dowel thing...glad you brought that up. I never had a test garden because basicalyl, I can be lazy about digging hole and burying coins. But dowels...that sounds easy enuf.

That idea of trying to gauge the water pressure with the dowels sticking up just might work...I think anyhow. That link isn't too long of a read but water moving a coin isn't out of the question.

Al
 

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Jim Hemmingway

Jim Hemmingway

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Jan 26, 2008
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Thanks everyone for sharing your views here. There were a number of valid points raised, some which surprised me...just didn't think of them. Good stuff, here’s a bit of a summary if you’re interested….

So far, most of us have zeroed in on the idea of water (rainfall/snowmelt) having a physical effect on the soil. The idea of excessive moisture expanding soil/or causing upward movement seems reasonable. A result could well be that deeper coins in clay matrix might not be affected by water, thus staying put while the soil above swells and rises. It seems to me that wet ground expands/swells compared to dry ground. That factor alone could answer why my 10” nickel could hardly be detected recently. But there’s more too…

We know that freezing water will expand in the form of ice. Hence it would be logical to deduce frozen ground expands. This factor did not seem to affect the nickel signal a month ago. But then, the nickel should not have been affected by frost alone since frost does penetrate more than the depth of the nickel. It would move relative to the soil. Seems to make sense…

Some of us raised the idea of frost/thaw upheaval resulting in much the same effect. We all see the effect of frost leaving the ground. My driveway is the first indicator, along with my backyard fence gate…both become elevated at this time of year. The driveway is at least 2 inches higher than in summertime. I know this because it’s normally at an even elevation with the poured concrete garage floor. That two inches difference would also explain why I cannot presently get much of a signal on the 10” nickel.

Deepskyal made the further insight that such physical soil movement could even offset the coins placement. Seems like a possible explanation too. Thompy makes a further point about unreliable iron ID/disc under moist conditions compared to dry conditions. So it’s not all about depth either….

A number of us made the observation that some amount of moisture in the soil enhances our detection depth. But I wonder about real tough soil conditions that can be encountered, for example in Virginia, northern Alabama, and North Carolina to name a few. How do these soils react to a good rainfall? I suspect my own soil reacts poorly with too much moisture.

Lowbatts seemed fairly sure about his ground in relation to coin signals falling off over wet ground. Well, I'd like to hear more if anyone can give their views.

Last thing, I like the dowel idea for setting coins and measuring ground elevation changes, but won't the frost grab on to the dowel and move it too?

Thankyou everyone, Jim.
 

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