[time-nuts] Loran, GPS, Lightning, Timing

[Don Latham]

as, ahem, one of the early experimenters of lightning detection, gotta tell
ya, the return stroke risetime is on the order of 1 us. Also, the very
beginning of the waveform, that is the first part of the spike, is connected
with the beginning of the breakdown, hence the location on the ground. 
Subsequent parts of the waveform are due to higher portions of the channel.
Also, there are two polarities of discharge, and the "positive" discharge
gives a waveform that looks like a cloud discharge that does not strike ground
at all. Those seriously interested should get hold of a copy of "Lightning" by
Martin Uman; this is bby now old, but is available inexpensively and will get
you started. The original detectors used wideband crossed loops to get
direction and no time of arrival; well before GPS timing. I hadn't looked into
the "amateur" network!
Vaisala corp has the best USA net, otherwise there is one in Boston and TOA
enterprisesin Florida. U of Washington has a network as well.
Enjoy!  I can tell you after 50 years of dinking with it, Lightning is fun if
ya ain't too close.
Don

Tom Van Baak
>> The first input you need is the exact longitude/latitude of the
>> lightning bolt.
>>
>> The easiest way to do that is with a set of GPS synchronized receivers,
>> aaaand we're back to sqare one!
>
> That's true for ultimate accuracy. But notice how each strike is seen by
> dozens of observers and each observer knows their (fixed) position and has
> their own local (approximate) clock.
>
> So it seems to me it's not unlike how GPS works: with enough samples, it
> should be possible to solve for latitude, longitude, and time of each strike.
> Like running GPS in 3D mode rather than position hold (zero D) mode.
>
> Now the accuracy is clearly not going to be at the nanosecond level. Maybe not
> even microsecond level, since as you mentioned, there are biases and jitter
> and who know what propagation variations.
>
> But over time, you should be able to converge on differential local clock
> measurements. What I'd like to see is the TDEV of this as a common view time
> transfer method. A couple of hops and we could compare UTC(PHK) with UTC(TVB),
> for example.
>
> Perhaps another side effect of their lightning project is that it could create
> dynamic propagation maps using the residuals in their massive database. When I
> first owned WWVB gear I thought I had accurate time. After I got GPS, I
> realized that my WWVB receivers now became accurate Colorado-to-Seattle
> weather stations. As they say, one man's error is another man's signal.
>
> /tvb
>
>
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>


-- 
"The power of accurate observation is commonly called cynicism by those who
have not got it."
 -George Bernard Shaw

Dr. Don Latham AJ7LL
Six Mile Systems LLC
17850 Six Mile Road
Huson, MT, 59846
mail:  POBox 404
Frenchtown MT 59834-0404
VOX 406-626-4304
Skype: buffler2
www.lightningforensics.com
www.sixmilesystems.com