Doug,
   For a "ground-pinger": make a fitting to attach a bicycle pump to the 
screw cap on a large plastic (one liter?) soda-pop bottle.  Bury the 
bottle down to the neck (or deeper) and pump until the bottle fails.  (I 
don't know how much pressure these things will stand.)
   It might be better to weaken (say by scoring) the bottom so the push 
is vertical rather than horizontal (as when the side fails). 
Alternatively, the sides could be reinforced by wrapping with duct tape.
   This scheme meets your criteria except the "multiple impact" and 
possibly the "ping instead of thump" but it's hard to beat for cheap.
   A glass bottle might be more ping-like but would leave a hazardous 
residue.  Bottles made of a brittle plastic (e.g., polystyrene or 
methyl-methacralate) might be better that the usual.
   It would be easy to try (but not by me).
   I considered pumping water instead of air but air would give greater 
impact because the stored enrgy is much greater.  That's why pressure 
testing of high pressure gas tanks (e.g., oxygen) uses water rather than 
a gas.

   Another scheme:introduce a standard spark plug into a pop-bottle just 
below the neck.  Run two wires (thru a rubber stopper in the neck or a 
screw cap) into the borrom of the bottle into an inch or so of water. 
Bury the bottle.  Pass current (for a predetermined time)thru the water 
which fill the bottle with oxygen and hydrogen (the mixture will be 
stoichiometric).  Fire a spark thru the plug.  A stoichiometric mix of 
oxygen and hydrogen will detonate, not just burn.  This should give a 
"ping".  I suppose that a blanket should cover the ground above the 
bottle to catch the spark plug.
Bob Barns


Doug Crice wrote:
> For as long as I have been in seismic, people have been trying to build a
> good energy source for engineering seismic studies.  Let me define such a
> device for you experimenters out there.
> 
> 1) A person ought to be able to carry it around
> 2) It needs reasonably high frequency output (ping instead of thunk)
> 3) Build it for $1000 or even $2000 in lots of 10 units, using new
> commercially available and machined parts.
> 4) It should be safe, even when used by students
> 5) There should be no significant regulatory issues (a problem with
> dynamite, the perfect source)
> 6) Operating supplies available in third world countries.
> 7) And last but not least, it needs to work better than a sledgehammer used
> with a seismograph that can stack multiple impacts.
> 
> The in-hole shotgun comes close, but it is possible to shoot yourself in the
> foot, blow your hand off, and in one case, blow your brains out.  The
> associated liability prevents any real company from producing the device.
> Even if you made it impossible to accidentally hurt yourself, under our tort
> system, you would still be liable for intentional injuries.
> 
> Geostuff will be happy to sell the device using our worldwide network of
> contacts, assuming it works and is reliable. Mechanical things tend to self
> destruct.
>  
> Doug Crice          http://www.geostuff.com
> Wireless Seismic            http://www.wirelessSeismic.com
> 12996 Somerset Drive                phone 1-530-274-4445
> Grass Valley,  CA  95945  USA    fax 1-530-274-4446
>  
> 
> 
> I know a gun fired in the ground is not a good source and that's 
> why I included a drop hammer lifted by a bank and dropped back 
> on the rod that is attached to a steel plate that sets on the 
> ground. I may have to use a propane to lift the slide over the 
> piston instead of a blank shot gun shell,
> 
> 
> 
> 
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