comparative detection distance tests (VLF vs PPM)

[Willy Bayot]

Hi,

This is an extensive test result table comparing the detection distance of meteorites of various types and weights between a White's Spectra V3 set in 'meteorite search' mode and a PPM.

It clearly shows that the maximum detection distances are much larger with the PPM for not only the ferrous types like the siderites but also the Chondrites H, L and LL.
It is true that the Achondrites are not detected but they are neither by the VLF .

This test has been reported here on a french-speaking forum:
http://meteorites.superforum.fr/t38....vlf-spectra-v3

It is also to be noted that a VLF or a PI only detect the targets right under their coil at the published distance while the PPM detects them even on both sides of its sensor. If the distance of detection of a given target is one meter, it will be detected at one meter deep but also at one meter on each side of the sensor path. This means that the sensor of a PPM has NOT to be swing'ed which makes the survey much more comfortable.

Just as a reminder, look at this web site to find a good PPM with a very reasonable price tag:
http://users.skynet.be/fa352591/index.htm

Willy

[Krzychu_]

Hi!
Very interesting presentation.
Unfortunately, for some reason I can't go to http://users.skynet.be/fa352591/index.htm. What specific PPM magnetometers and what are the sensitivities of the equipment used to obtain these results?

Regards,

Kris

[walesto]

Hi,
Unfortunatelly this link (
http://meteorites.superforum.fr/t38....vlf-spectra-v3
) is no longer valid.
Does anyone have copy of those results?
I have PPM and recently I had opportunity to check it with 6-7kg iron meteorite at depth 1,1m. Unfortunatelly no significant reaction could be noticed, while VLFdetector on static mode was able to give very, very low signal.
Best regards,
Tomek

[ivconic]

Hi,
Unfortunatelly this link (
http://meteorites.superforum.fr/t38....vlf-spectra-v3
) is no longer valid.
Does anyone have copy of those results?
I have PPM and recently I had opportunity to check it with 6-7kg iron meteorite at depth 1,1m. Unfortunatelly no significant reaction could be noticed, while VLFdetector on static mode was able to give very, very low signal.
Best regards,
Tomek

Fortunately Willy Bayot is still here. We had recent dispute, so i can tell.
So he can answer on this.
Until than; i will try to answer.
Magnetometer is not metal detector. You can't behave with it like it is metal detector.
Freshly put target in soil is not presenting any kind of "magnetic anomaly" or other words; it has no time to develop any kind of magnetic anomaly.
Especially in freshly disturbed soil when you break the Earth magnetic field flows by digging, burring and messing around.
What you have to do is to leave target for a while, few weeks or even several months. Mostly depending on target's magnetic features.
Each magnetometer is a story of its own, relating to handling and adjusting.
So i guess Willy would be most competent person here to give you most proper guidelines.
What i am most certainly sure about, is that any magnetometer will easily "detect" 6-7kg meteorite at depth 1.1m.
With condition that such meteorite must have magnetic features.
In the past when i made several EPE Becker's magnetometers; i did lot of filed testings.
Old rusty iron piece, 12x4cm, "detected" very easily at 75cm in soil. With "progress bar scale" full signal.
But it was genuine piece of iron, present there in soil for very long time. We approximated it to 3-4 century BC.
...
Usual mistake made by layman is to try to use magnetometers like ordinary metal detectors.
Therefore the fails and lack of any results.

[walesto]

Hi,
Thank you for your reply.
When we were testing detection by magnetometer, meteorite was still untouched in soil, laying there for over at least 700 years. There was done only outrop in which it was visible. And when we were sure that it is meteorite we tried to verify my PMP. There were noticed maybe just few nT and rather of only possitive anomaly and it was very, very difficult to distinguish it of false sygnals (there were some variations because of neighborhood of high voltage lines).

Some time ago one of my collegues has told me that Iron-Nickel meteorites give weaker response to magnetometer than typical man made iron. Is it true???
I could not believe it, but now, after opportunity to see it on burried mass (detected by frame PI) I became confused.

Almost 2 years ago I was doing researches using PMP and as you said - magnetometer is not a metal detector so I didn't notice anomalies just walking and searching for them, but anomalies were revealed after doing approx. 1500 measurements in a grid every 60cm.

I have described my results in a short conference abstract:

http://www.hou.usra.edu/meetings/lpsc2018/pdf/1644.pdf

So you can see how anomalies were recognized.

I will be grateful for any further comments and advices in this subject (comparing detection of iron using PMP vs other metal detectors).

Best Regards,
Tomek

[ivconic]

Very interesting PDF article, thanks for pointing on it.
Unfortunately i can't tell much on meteorite hunting experiences.
Except from what i heard from others.
As for PPM; i never had chance to see it in alive and try to work with it.
Also all about it i read in articles.
But from Willy's skim explanations over the emails; i got the impression that it is "slow scanning" high resolution magnetometer.
He suggested me (insisted) on 20 and more samples per second , in order to provide higher resolution and better accuracy.
Knowing this; i presume it is "slow scanning" and it takes time to move over the cells in matrix.
Natural iron-nickel alloy sounds a bit strange to me, must admit.
And if it is true; than nickel is the cause of bad detection, for sure.
What i can tell here is probably nothing new. I can only justify that magnetometers are powerful tools to locate ancient settlements made of baked clay, bricks also pottery.
Here we usually hunt for such finds. Ancient underground facilities, tombs, bunkers.
And when we speak on Ancient Rome and later Byzantine period; than the pottery is most significant indicator that can be caught with magnetometers.