sferic detection and localisation with DSP

phunky.data@caramail.com (phunkyman) wrote in message news:<e435cb3e.0403302331.700519c7@posting.google.com>...
> Hello,
>
> I know the existense of these 2 sferics detectors but i don't succeed
> in finding how they really work! If you have an idea?!
> You say they measure intensity to determine distance, but how are they
> linked?
> I looked at many sferic project but nothing is really close to what i
> must do.
> 
> Thanks.

As Ray indicated, a look at the applicable patents should shed some
light on their techniques.

Maurice Givens

phunkyman wrote:
> Hello,
> 
> 
>>I think you'll need a basic understanding of the issues, even if you can
>>rely on others to work out the details for you. Without that, you could
>>find yourself proposing the electronic equivalent of a tunnel to China
>>as a practical project.
> 
> 
> Don't worry, i have a basic understanding as i'm student in
> electronics and data processing. But i can't know everything so
> sometimes i need to ask help to other ones. Moreover, "mixing" ideas
> is a good thing i think.
> 
> 
> 
>>You understand, I hope, that a baseband signal to be sampled may have no
>>significant component as high as half the sample rate. You must arrange
>>that either by sampling at a frequency more than twice the signal's
>>highest, or by filtering the signal to remove any components higher than 
>>half the sample rate. All sorts of signals appear on an antenna,
>>including UHF television. Even if there were a converter sensitive
>>enough to use signals as weak as those typical of antennas, it would
>>need to be preceded by  filter.
> 
> 
> Don't worry again! I know the nyquist criteria and i know that i will
> recieve many different signals with many different frequencies on the
> antenna. I'll make a filter that's for sure.

When you wrote of connecting an antenna directly to an ADC, I took you
at your word.

>>A major source of uncertainty and noise will be power-line harmonics and
>>impulse noise. (Spark plugs are miniature lightning generators.) I've
>>never played with this, except once using an audio amplifier and a
>>long-wire antenna to hear whistlers on a loudspeaker. The most involved
>>part was an analog comb filter to remove 60 Hz and its harmonics that I
>>borrowed, and whose design I didn't understand. As for the rest, the
>>brain is a good noise filter. I doubt that the occasional whistler would
>>have been noticeable on an oscilloscope. The eye, while far better than
>>anything I can program, is not as good a filter for that sort of
>>material as the ear.
> 
> 
> 
> I can confess i didn't think about power-line harmonics! Thanks to
> remind me this thing. But maybe it won't be critical as the device
> must be handheld, so i'll just have to get far from power-line
> devices.
> 
> 
>>To digitize your signal, I imagine that you will want at least 12 bits,
>>and to make the acquisition less than maximally fussy, you will probably
>>want a 14-bit converter; 13 bits plus sign. If the smallest step of such
>>a converter represents a small multiple of the expected noise over the
>>band, then full scale will be in the order of volts. The electric fields
>>you want to characterize are at most a few microvolts per meter. In
>>addition to a filter, you need either an amplifier or an antenna larger
>>than the local zoning code is likely to permit.
> 
> I'm sorry i don't understand "local zoning code"? Anyway, tell me if i
> understand well what you meant : i must amplify the signal recieved on
> the antenna because this one has a voltage which is too weak; is that
> right? If it is, don't worry again i thought about it.

"Zoning code" was sort of a joke that obviously didn't fly. If your ADC
wants five volts and the field strength is 10 microvolts per meter, a
bare antenna -- at 100% efficiency -- would need to be 500 kilometers
long. It's hard to get permits for structures like that.

> Do you think we can calculate the distance of the storm from the
> voltage of the signal recieved on the antenna? In fact, does the
> amplitude of the sferic signal is greater when the storm is near than
> when it's far? If it does, i could calculate the distance this way,
> but the issue would be to know how the amplitude of the signal and the
> distance are related? What do you think about that?

For any given strike, the amplitude of the signal greater in nearer
antennas. The signal amplitude is highly dependent on the energy in the
strike, and that varies greatly. You can't tell how far a star is merely
from its brightness. Stars like Cephid variables are a special case. I
don't know of anything comparable for lightning.

If I remember, distance is best estimated from the sweep rate of the
whistler. A whistler is the result of atmospheric dispersion operating
on an impulse -- the lightning stroke. The greater the distance, the
more the impulse's component frequencies are dispersed in time.

I used a gold-leaf electrometer to predict storms. The electrometer was
on a downstairs windowsill, connected by a wire in a glass tube to a
"contact plate" near the roof line. the vertical electric field was a
good predictor of thunderstorm activity. 500 V/meter on a clear day
could rise to more than 10,000 V/meter an hour before a storm.

Jerry
-- 
Engineering is the art of making what you want from things you can get.
�����������������������������������������������������������������������

Intensity alone is going to give a pretty poor range resolution.  Lightning
is a fairly good approximation to an impulse.  By looking at the dispersion
and attenuation of frequencies in the impulse response and knowing from
empirical measurement the properties of the atmosphere, you can make a
better estimate of the range than you can on intensity alone.  Look for the
patents by both companies.

phunkyman wrote:

> Hello,
>
> > There are 2 sferics detectors (asmiuth and range) that I know of that
> > are commercially available. I believe they are using orthogonal
> > antennas for angle of arrival and a measure of the intensity to
> > determine distance.  The use of frequency-dependent wave velocity is
> > interesting.  You might want to see if you can get information on what
> > they are doing for signal conditioning.  The companies are B. F.
> > Goodridge and Strike Finder.  Also, take a look at the research being
> > done on the Sferics Project.  I can't remember which university is
> > doing this, but a Google search should show it.
>
> I know the existense of these 2 sferics detectors but i don't succeed
> in finding how they really work! If you have an idea?!
> You say they measure intensity to determine distance, but how are they
> linked?
> I looked at many sferic project but nothing is really close to what i
> must do.
>
> > Good luck,
>
> Thanks.

--
--Ray Andraka, P.E.
President, the Andraka Consulting Group, Inc.
401/884-7930     Fax 401/884-7950
email ray@andraka.com
http://www.andraka.com

 "They that give up essential liberty to obtain a little
  temporary safety deserve neither liberty nor safety."
                                          -Benjamin Franklin, 1759

Hi,

> Intensity alone is going to give a pretty poor range resolution.  Lightning
> is a fairly good approximation to an impulse.  By looking at the dispersion
> and attenuation of frequencies in the impulse response and knowing from
> empirical measurement the properties of the atmosphere, you can make a
> better estimate of the range than you can on intensity alone.  Look for the
> patents by both companies.

I thought i could determine the distance from the dispersion
phenomenon. That was my first idea. But according to what i understand
about lightning em signals, the dispersion only acts with signals
called tweeks. And as tweeks are sferic signals which have traveled
over more than 1000 kms and as i must design a lightning detector
which will give the distance of a storm producing at 500 kms max, i
can't use tweeks signals. So i must detect sferic signals and
determine the distance from these ones.
I thought i could do it from the intensity but apparently many people
say it's not reliable. I thought strike alert or other commercial
detectors do it this way but i have no info about that. I searched for
patents, as you advised, but i don't succeed in finding them!

Thanks.

No more people can help me?

phunky.data@caramail.com (phunkyman) wrote in message news:<e435cb3e.0404010049.709b82a0@posting.google.com>...
> Hi,
> 
> > Intensity alone is going to give a pretty poor range resolution.  Lightning
> > is a fairly good approximation to an impulse.  By looking at the dispersion
> > and attenuation of frequencies in the impulse response and knowing from
> > empirical measurement the properties of the atmosphere, you can make a
> > better estimate of the range than you can on intensity alone.  Look for the
> > patents by both companies.
> 
> I thought i could determine the distance from the dispersion
> phenomenon. That was my first idea. But according to what i understand
> about lightning em signals, the dispersion only acts with signals
> called tweeks. And as tweeks are sferic signals which have traveled
> over more than 1000 kms and as i must design a lightning detector
> which will give the distance of a storm producing at 500 kms max, i
> can't use tweeks signals. So i must detect sferic signals and
> determine the distance from these ones.
> I thought i could do it from the intensity but apparently many people
> say it's not reliable. I thought strike alert or other commercial
> detectors do it this way but i have no info about that. I searched for
> patents, as you advised, but i don't succeed in finding them!
> 
> Thanks.

phunky.data@caramail.com (phunkyman) wrote in message news:<e435cb3e.0404070627.2a0b3543@posting.google.com>...
> No more people can help me?
> 

As I said earlier, look for the sferics project at one of the
universities using the Google search engine.  I typed in sferics
project, and the FIRST entry was labeled SFERICS RESEARCH PROJECT with
the URL

http://www.theramp.net/sferics/

Here they give a complete explanation, drawings for the hardware,
source for the software, etc.  Use the search engine!!


Maurice Givens