Metal locators

[CannondaleKid]

With this topic being brought up in the GPSJoe search thread, while it is very relevant to the search thread, I think it can be explored more thoroughly with a dedicated thread.

While many of the first units I came across, including some long distance models, they pretty much required you to be walking in the immediate vicinity of the (in most cases) underground object, immediate being 5-7'.

Many required pounding a spike into the ground and searching in an area around that spike. Well and good, but that only worked when the metal object (pipe, wire, etc.) was, in fact, underground.

So I continued searching and came up with a few sites with further information relevant to this particular searching requirement:
How metal detectors work:
http://whiteselectronics.com/info/field-reports/55.html

A well-known and well respected instrument company that sells products to NASA as well as the military:
Schonstedt Instrument Company
http://www.schonstedt.com/index.cfm?page=indexml

This looks like a good place to check out a wide variety of types of locators:
http://www.kellycodetectors.com/professional/

I haven't had a chance to run through all those listed on the above page, but this one shows the most promise of anything so far:
http://www.kellycodetectors.com/anderson/anderson.htm

If anyone has experience and/or more in-depth knowledge of this type of technology including practical use, Please... by all means, enlighten us.
Anything to assist in the search for Joe is welcome!

[Vaporman]

Upon further research, I don't think that Greenlee that my work rents out will work for this scenario since it's designed with two leads that you connect to the valves wires and then with the wand you walk the yard while doing your best to trace the wire by following the signal...

[nonot]

Not to get your guys hopes down, but metal detectors, radar, and other devices which rely upon electromagnetic forces to work just aren't going to function that well in rocky terrain covered in brush. The rocks and brush are going to scatter, absorb, and reflect the energy, and it's likely that a hiker has very little ferrous metal to help produce a large signature (aluminum is a poor metal at doing that.) If there's iron in the soil...forget about it.

While I'm not in the mining industry, I do know that they have tools to find density differences, which typically involve things like digging a hole, setting off an explosive, and measuring the resulting shock wave - with some fancy math you reconstruct the refraction pattern and figure out where stuff is. (None of which is really applicable to your question, but without some more information on the kelly detectors, those things look like glorified diving rods.)

[JimmyLyding]

Most metal detectors that I'm familiar with are either short-distance devices that are designed to find objects w/ high ferrous content (think coins) or electrical conductors that have marker balls, marker tape, or are enclosed in metallic conduit. The marker balls and tape are designed to indicate the presence of whatever they're marking.
As the Cannondalekid pointed out you're not going to find a device that finds low-ferrous metal (like what's in a wristwatch) from any appreciable distance. A better option to find something that's not on the trail would be the view from a helicopter. I'm not sure if that's already happened, but a bright sunny day could provide the right conditions to see the reflection from a pair of sunglasses or some other reflective object.
Has any group done a "sweep" search where a group of people walk through an area only a few feet apart? I know firsthand how difficult the terrain is in the area, but that may be the best way to cover a particular area.

[CannondaleKid]

A better option to find something that's not on the trail would be the view from a helicopter. I'm not sure if that's already happened...

Yes, SAR had a helicopter in the early days of the search. I have no idea how many chopper search flights were done, but I know Gabriele spent some time up in the air searching. She mentioned to me that it was not an easy task. Not being able to look straight down you must look at some angle less than 90 degrees, and as that angle gets smaller any open areas surrounded by vegetation (esp. trees) are quickly blocked from view. So unless something like constant vertical hi-res filming (and someone to watch it all very carefully after the fact) and flying back and forth in a narrow grid pattern, over and over as well as from as many angles as possible, one simply could not say the area had been "searched thoroughly."

Has any group done a "sweep" search where a group of people walk through an area only a few feet apart?

By superimposing all the search tracks currently posted on HAZ in one view, simply put, no. While some very small areas (the Peeley summit?) may very well have been covered that way, probably 99.9% of the search area has not.

I know firsthand how difficult the terrain is in the area, but that may be the best way to cover a particular area.

As difficult as it might be, you are correct, the most effective search is conducted in sweeps with as many individuals as possible spaced as closely as practical which, in this terrain is nigh on impossible. But as long as we have a number of people still in this, willing to keep on, just because it's against all odds should not stop us from trying.