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

[Stanley Reynolds]

Thank you both Gerry and Joe , I see I have some reading to do. I would love to say cost is no problem but I do need to keep cost in the hobby range which will effect how large a network and how much labor this project will get. This will mean I need to start small and once I get some results maybe request more help then. If I start small and it turns out I must have a large base line then I can expand to more sites. I'm located in Alabama and would be able to set up several sites in Birmingham,Cullman, and Arley (near smith lake) measured in Google earth that would be 23, 47, and 46 miles apart with Cullman to Arley the shorter distance. For just the feasibility part I could ignore linking the sites and review data by retrieving it physically after the fact. 

My idea would be to have a PC with hard drive record data in two ways, one the stock sensor and GPS time of start and length, the other would be some record of amplitude or wave form via a modified sensor during the same time.

I will post my progress and check for comments here.

----- Original Message ----
From: Gerry Creager <gerry.creager at tamu.edu>
To: TAPR Weather Station SIG Mailing List <wxsig at lists.tapr.org>
Sent: Friday, February 15, 2008 7:43:39 AM
Subject: Re: [wxsig] Array of X1W-4 sensors to detrime direction and distance ?

Sorry!  I got busy with CWOP and "real" work!

I got this back from Joe:
Gerry,
The best I can tell (because I don't see one in the sensors), the 
commercial box does not use any sort of precision timing reference 
oscillator.  They simply have a GPS with 1 pps output to create a 
reference a data acquisition board input.  The sensor's clock is 
adjusted to GPS time and the 1 pps triggers a circuit to generate a 
wide-band pulse.  So, as time goes on, data packets are timestamped with 
GPS time and then the 1pps signal shows up to mark the beginning of the 
second.  Vaisala's system basically detects when the RF amplitude 
exceeds a certain threshold (and matches a lightning source signature to 
reduce false alarms).  The packets are sent near-real time to the main 
server which reads the data from all systems and tries to find a "match" 
in the incoming data streams.  This way, you don't really have to worry 
about a few seconds of internet delay....but, of course, you may delay 
finding a solution...say 15 seconds...from when the flash occurred.

The sensor to server data might look something like this...where the 
data points are time, in nanoseconds from computer GPS time.

He also refers to these articles for the research-inclined:
Journal of Geophysical Research
Correlated high-speed video and radio interferometric observations of a 
cloud-to-ground lightning flash by Vladislav Mazur 1997

JGR again
On the retrieval of of lightning radio sources from time-of-arrival data 
by Wiliam J. Koshak 1996

Back to the grind.  Gotta get some WRF data turned into pictures. Today 
and tomorrow look interesting in Texas for severe weather.

gerry

Timestamp 12/12/07 10:01:20 UTC
5600
1030049
199432942
2932740239

If you collect the data from 3 or more sensors, you just try to find a 
fit...it the Chi squared error exceeds your threshold, throw it out as a 
non-event.
Claims on intracloud lightning with the Houston network are in the 
vicinity of 200m.  NLDN errors, with much larger baselines are on the 
order of 700m.  So, it's very possible to produce an amateur grade 
system, with short baselines, having an accuracy of 1/4 mile with the 
right component selection and software.

I'd really go for multiple sites around a given area...say CLL, HOU, 
AUS, SAT, VCT.  For C-G systems, VLF travels a long way.  A short 3 m 
baseline system would require tremendous timing accuracy  hampered by 
receiver bandwidth and still suffer great errors 100 miles out.


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