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[wxsig] Array of X1W-4 sensors to detrime direction and distance ?

Gerry Creager gerry.creager at tamu.edu
Wed Feb 13 06:16:21 UTC 2008

Using GPS for timing, one could expect 3 relatively closely spaced 
receivers to have common clock locking and be synched to within oh, say, 
20 ns.  More likely, it's much better than that; I'm being conservative.

Getting a baseline off 3 receivers is relatively trivial, and depending 
on the frequency of the impulse one can make some assumptions about 
height... if I understand what I think I've heard.  I've included 
someone with a working knowledge of Vaisala's lightning detection 
technology in the address list.

If one were to do this as a relatively long baseline study, one should 
be able to get significantly better than 1/4 mile resolution, I'd think. 
  Realize that the attitude detection GPS systems can resolve both 
shorter distances and very small angle and direction changes with 
baselines measured in terms of 1-3 meters.


William Beals wrote:
> Stanley:
> Anything based on EMF is going to be pretty tough to measure accurately with
> consumer grade stuff.  Back when I did high speed stuff a good rule of thumb
> was the speed of light is around 1ns per foot, so assuming you want to
> measure something accurately to a quarter mile, all your measurements are
> going to need to be accurate to better than 1300ns or 1.3us.  And--that
> doesn't include the time to get all the signals from the 3+ sensors back to
> a central place to get timed relative to each-other!  
> If (while dreaming) I had been asked to dream up such a system, I'd also
> question if you could accurately relay a detection signal as at the instant
> you detect a bolt and want to send a signal saying you heard it, that
> instant would be a really tough time to send a signal over any band as the
> lightning itself would be trashing most of the spectrum.  I think a better
> bet would be to have really accurate clocks at all 3+ locations, measure a
> time stamp and then send that timestamp non-real-time after the lightning
> hit.  A quick look at Garmin's website shows their OEM receivers give a one
> pulse per second output accurate to 1us, so at least you are getting close.
> I also worry about measurements in terms of 2D vs. 3D space.  If you can
> somehow rationalize lightning as occurring at a point on a 2D plane, 3
> antennas would be fine, but lightning is very much 3D, not a point source of
> noise, nor a simple pulse, so interpreting the data from the sensors may
> involve more than measuring a simple edge time.
> Fun thing to think about...  Especially doped up on antihistamines!
> will
> -----Original Message-----
> From: wxsig-bounces at lists.tapr.org [mailto:wxsig-bounces at lists.tapr.org] On
> Behalf Of Stanley Reynolds
> Sent: Tuesday, February 12, 2008 6:03 PM
> To: TAPR Weather Station SIG Mailing List
> Subject: Re: [wxsig] Array of X1W-4 sensors to detrime direction and
> distance ?
> Some searching turned up this site : www toasystems com
> Some answers but still not sure how practical a simpler solution is, looks
> like they are using at least 3 sensors separated by several KM. 
> I know the US military is using passive sound to locate small arms fire,
> wonder if sound with it's slower speed would make a range and direction
> measurement more practical for a local < 50 feet separation array ? Would
> obviously reduce the detection range vs RF.
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Gerry Creager -- gerry.creager at tamu.edu
Texas Mesonet -- AATLT, Texas A&M University	
Cell: 979.229.5301 Office: 979.458.4020 FAX: 979.862.3983
Office: 1700 Research Parkway Ste 160, TAMU, College Station, TX 77843

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