Thank you
Ted

--------------------------------------------------
From: 
Sent: Tuesday, June 11, 2013 6:38 PM
To: 
Subject: Re: Water/Laser geophone instrumentation

> From: Ted Channel 
> To: psnlist 
> Sent: Tue, 11 Jun 2013 16:24
> Subject: Re: Water/Laser geophone instrumentation
> 
> Hi All,  Chris your rain gutter idea is very interesting too.  Is there
> a pict illustrating the version of the Cascades used?
> 
> Hi Ted,
> 
> ****Check out :-
> http://cires.colorado.edu/~bilham/tiltmeter.file/Tiltmeters.html
> http://www.geodesy.cwu.edu/instruments/tilt/
> 
> Here is a different question...   Picture a perfectly balanced beam, on
> a centre pivot, just like a see-saw, with two kids of similar mass.
> Would this beam tend to remain fixed during an earthquake?  But I don't
> know if the see-saw, would tend to remain fixed/level as the earth
> isolated during an event.
> 
> ****A see saw may be stable if the hinge at the centre is slightly 
> raised
> above the level of the line joining the centres of mass at both ends,
> giving a pendulum with a large rotational moment of inertia and quite a
> long period. This would not react to vertical motion, but it would
> react a bit to horizontal motions parallel to the beam.
>     If the hinge lies on the line joining the centres of mass at both
> ends, the see saw should not be effected by horizontal motions either, 
> or
> by rotational ones.
> 
>    Regards,
> 
>    Chris
> 
> 
> 
> --------------------------------------------------
> From: 
> Sent: Monday, June 10, 2013 9:51 AM
> To: 
> Subject: Re: Water/Laser geophone instrumentation
> 
>> From: Geoff 
>> To: psnlist 
>> Sent: Tue, 4 Jun 2013 20:13
>> Subject: Water/Laser geophone instrumentation
>>
>>
>> Hello PSN,
>>
>> TWO ideas to play with,
>> I was just playing around with a drink container of water. The
>> container was about 1/3 full. I took a laser pointer and reflected
>> the laser light off the surface of the water. The reflection seemed
>> to exhibit motion related to the water from which it was reflected.
>> NOW,
>> Would it be possible, to use a setup like this, to detect seismic
>> motions ?
>> 1. Tub of water of some design.
>> 2. reflected laser light off the surface somehow.
>> 3. laser light sensor to detect disturbances
>>    down to the nano-meter of motion ??
>> 4. at this moment in time, ignore planes of motion.
>>
>> Hi Geoff,
>>
>> ****I tried something similar using about 12 ft of rainwater gutter
>> flat on the ground with sealed ends, part filled with water. There
>> is a huge system like this in the Cascades. You use a calculated
>> length to 'slop' oscillate from end to end at a given period, but
>> you make the water depth shallow enough to give critical
>> damping. I shone a red semiconductor laser off the centre of the
>> trough at grazing incidence and looked at the fairly strong
>> reflection about 40 ft away on a white wall. I had intended to make
>> a long plastic float and attach a surface silvered mirror to the
> centre,
>> to stop ripples due to air currents and to reduce evaporation, but
>> the quality of the laser beam was so poor that the edges of the spot
>> were all 'bobbly' and unusable. It might work better with a long
>> He/Ne laser tube.
>>
>> In addition, how about an adaptive optics sensor like the
>> astronomers use to detect tornadic or helical winds in the
>> atmosphere ?
>>
>> ****What method do these use and what references do you have ?
>>
>>    Regards,
>>
>>     Chris Chapman
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