Stephen,

Sounds like an interesting project. Unfortunately I can't help you much. I
would think three geophone would do the job if the sensors can pick up the
impact offer the local ground noise.

I'm CC'ing this message to the Public Seismic Network mailing list. Maybe
someone on the list can help you. 

PSN'ers please send any info directly to Stephen Hertig at
shertig@........... and CC the list, since he is not on this mailing list.

Regards,
Larry Cochrane
Redwood City, PSN

At 10:02 AM 5/25/00 -0500, Stephen Hertig wrote:
>
>Dear Mr. Cochrane
>
>I am researching how to calculate low-mass (like baseballs), impact surface
>locations on a grass field (2D only, X & Y's) in a relatively small area
(100 x
>300 m)  using vibration sensors or geophones and PC-based, real-time data
>recording.
>
>The software and programming is very much in the public domain and I'm
assuming
>it can be worked out, but it's the general hardware parameters that have me
>perplexed (out of my field) at this stage.
>
>I'm not sure how many geophones I'll need or what fequency response would
best
>be suited for these measurements.  As the area is small the low-mass,
hense low
>energy impacts may not be a problem, but the signal to noise ratio is a
concern.
>However, I've got no feel if this is assumption is close to reality or
>equivalent to the energy (db) distance ratios of earthquakes, but that is the
>current analog I'm using to try to build a prototype system to record
these xy,
>impact locations.  Although I suspect as all I need are s-wave, first
arrivals I
>may be able to detect and calculate the "epicenter" (+/- about 1/m???)
from at
>least 3 senors and hopefully be well above any noise. If more than 3
senors are
>needed to record the events in this area (e.g., sensor has to be closer to
the
>impact than about 100 yds to see signal above noise) then I suspect things
get
>really complicated/expensive in terms of the A/D device and new modified
>multi-channel (3+) software needed.
>
>Do you think this can be done with only 3 sensors (i.e. Channels)?
>
>If so what type/parameters of senors would you suggest? (i.e. geophone
frequency
>response, vertical or horizontal spring orientations. Is horizontal better
for
>just s waves?)
>
>If not any comments on a alternate system setup? or others to ask these
>questions?
>
>
>You can blame your great web page(s) for this request, and thank you very
much
>for taking time
>for any consideration or comments.
>
>Sincerely,
>Steve Hertig, geologist
>shertig@..........
>
>
>
>
>
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