Soil Density

Well I think this is the 4th thread I've started in the last 24 hours. Hope I'm not overdoing it.

A reply from Tom regarding the potential characteristics of the soil at my location got me to wondering about something. All other things being equal, how much can soil density affect depth of detection? The soil here is very compact. Digging post holes is not fun, I can tell you from experience. Even today when I was burying that clad dime I had to stand on my sharpshooter shovel to get down a foot or so and we've had a good bit of rain lately. In other words if two locations were to share exactly the same mineralization numbers but one site had 25% denser soil than the other, would depth of detection be affected.

The electrical characteristics of soils is a science all its own. A GOOD detector engineer should have a broad understanding of soils and how they effect detector performance.... Fortunately First Texas has one of the best in that regard.

Tom

One fact from my area. Soil density prevents coins from sinking very deep. I've got a few places where you can find silver dimes less than two inches deep. While others with very nice grass the same coins might be 6-7 inches deep. But back to your question, I don't have an answer, but would think the density wouldn't have any major effect on the detection depth, at least for me in my area (red clay area of Virginia)

Jackpine Wrote:
-------------------------------------------------------
> The electrical characteristics of soils is a
> science all its own. A GOOD detector engineer
> should have a broad understanding of soils and how
> they effect detector performance.... Fortunately
> First Texas has one of the best in that regard.
>
> Tom

You're right Tom. It is a science of which I don't have a great deal of knowledge. Tom or one of the engineers at Fisher could probably answer my question off the top of his head.

markg Wrote:
> But back to your question, I don't have an answer,
> but would think the density wouldn't have any
> major effect on the detection depth, at least for
> me in my area (red clay area of Virginia).

You may be right Mark. Intuitively though, I would think, that higher density soil means more minerals in any given volume. In other words a 10 inch deep x 4 inch diameter cylinder of soil in one location might contain the same mineral content as a 12 inch deep x 4 inch diameter cylinder of soil at a site with a lower soil density. Accordingly, the site with the higher mineral density would suffer more detector signal attenuation per inch of soil and a corresponding detection depth loss.

Purely conjecture. I can't defend this with scientific data since I don't have any formal education on the subject. If true though, it could possibly be one factor that explains differences in detector performance from one individual to another. It might also help explain the air gap phenomena of the F75 LTD in boost mode. In air the signal is largely not attenuated so you can raise the coil until detector field geometry limits the signal. Can't go deeper with the target though because that means more signal attenuation which is the limiting factor as you go deeper.

Correct.

And it is mineralization that is the trump-card for attenuation. Here... in areas of Florida.........some soils are very dense (hard packed).....and some soils are aerated/low density. No minerals in either case. This does not affect depth in any way. Now..........if mineralization were to come into play.........yes........the more mineralization per cubic inch; subsequently, the more EM attenuation incurred.

NASA-Tom Wrote:
-------------------------------------------------------
> Correct.
>
> And it is mineralization that is the trump-card
> for attenuation. Here... in areas of
> Florida.........some soils are very dense (hard
> packed).....and some soils are aerated/low
> density. No minerals in either case. This does not
> affect depth in any way. Now..........if
> mineralization were to come into
> play.........yes........the more mineralization
> per cubic inch; subsequently, the more EM
> attenuation incurred.

Thanks Tom. Good to have your confirmation on this. I've got to remember to take this into account when I hear F75 LTD reports indicating better performance than I am seeing with mine. Ordered your dvd yesterday and looking forward to what I'll learn there.

I found this to be exactly the case in some areas in Ohio, Tenn and Georgia in that hard packed red stuff. Factoring more mineralization per cubic inch of soil makes perfect sense. I only assumed that this was the case where iron oxide mineralization with high compaction ratio was causing shallow detection depth.
This heavy worst case scenario has a type of over all masking effect. I can tell a difference in the tones and response from my detector (CZ3D) with regards to depth. The coins that I would hear in the hard pan even while shallow at 3-4 inches sound to me like they are 8-10" in the neutral ground, comparatively. Luckily the targets are mostly shallow in these areas.
Target extraction is a time consuming back breaker in hard pan. It does make you wonder about the deeper layers and what may be lurking there.

I've noticed that when some of these areas become wet it then becomes even more difficult to deal with and depth becomes even more shallow. I'm guessing that moisture causes suspension of the salts and minerals ? Tom, would you care to elaborate on this ?


Grant







NASA-Tom Wrote:
-------------------------------------------------------
> Correct.
>
> And it is mineralization that is the trump-card
> for attenuation. Here... in areas of
> Florida.........some soils are very dense (hard
> packed).....and some soils are aerated/low
> density. No minerals in either case. This does not
> affect depth in any way. Now..........if
> mineralization were to come into
> play.........yes........the more mineralization
> per cubic inch; subsequently, the more EM
> attenuation incurred.

dgc Wrote:
-------------------------------------------------------
> NASA-Tom Wrote:
> --------------------------------------------------
> -----
> > Correct.
> >
> > And it is mineralization that is the trump-card
> > for attenuation. Here... in areas of
> > Florida.........some soils are very dense (hard
> > packed).....and some soils are aerated/low
> > density. No minerals in either case. This does
> not
> > affect depth in any way. Now..........if
> > mineralization were to come into
> > play.........yes........the more mineralization
> > per cubic inch; subsequently, the more EM
> > attenuation incurred.
>
> Thanks Tom. Good to have your confirmation on
> this. I've got to remember to take this into
> account when I hear F75 LTD reports indicating
> better performance than I am seeing with mine.
> Ordered your dvd yesterday and looking forward to
> what I'll learn there.


Take a sampling of your ground and put it in a large glass jar of water to see how it layers out. This might tell you why it remains hard to dig in even when damp/wet. Perhaps fine silt and fine clays?

Around here we have mostly sandy loam soils and its easy digging whether wet or dry. The best depths I have seen are on Lake Michigan beaches comprised of large grained quartz sands. The larger grains allow more moisture to be held in suspension and when well packed allows great depth with a few detectors that like that kind of condition.

Tom

Jackpine Wrote:


> Take a sampling of your ground and put it in a
> large glass jar of water to see how it layers out.
> This might tell you why it remains hard to dig in
> even when damp/wet. Perhaps fine silt and fine
> clays?

> Tom

Thanks for the tip Tom. Ill do just that and see what the layers look like.

Grant............water in (esp) highly mineralized ground will conductively/electrically 'activate' the ground. No minerals.........this is a 'depth gain' attribute. No iron trash.........this is a attribute. Lots of iron and/or mineralization.......and it's a problem....up to...and including 'shut down'.