How does a stormscope/strikefinder actually work?

Dave Jacobowitz wrote:
Okay, this question is just about curiosity and the remote possibility
of an interesting DIY project. I'm an EE, so have the background do
understand (but working in the computer field, may not have the recent
experience to do so.

Just how do lightning detection systems work?

It seems to me that the E/M discharge from lightning is essentially
noise, and so would be rather wide-band. So one could easily detect
that a static discharge had occured by looking for a sudden
simultaneous burst of energy in two or more rather disparate frequency
ranges.

But finding where the discharge was... that seems harder. Clearly, one
filter out one band of frequency and use direction antennas and a
little math to figure out the azimuth to the strike.

So now we have a way to detect a strike and work out its angle
relative to the receiver.

But how do you get distance? All I can think of is having multiple
antennas on the aircraft, separate by some known distance, and using
simply time-domain analysis to convert the relative time of flight to
each of the antennas into a position. This would seem to require at
least three antennas to work, and also would require an uncommonly
precise way of measuring time considering that you can't get antennas
very far away from each other on a light aircraft.

So, how do these devices _actually_work? What frequency ranges do they
work in? How many antennas do they have? How do they determine
distance?

thanks,
Dave Jacobowitz

-- jacobowitz73 --at-- yahoo --dot-- com

You can find a number of websites that can provide a better description
than I can, but the basic concept is that:

1) The intensity of most EM bursts from lightning over a range of
frequencies is such that the strength at a given frequency is
proportional to the strength at other frequencies.

2) Some frequencies suffer very little atmospheric absorption and so
give an unabsorbed measure of the strength of the lightning.

3) Some frequencies are significantly absorbed by the atmosphere.

4) By comparing the unabsorbed frequencies and the absorbed frequencies,
you can make a reasonable guess as to how much atmosphere the EM burst
traversed getting to the receiver, and so can predict how far away the
lightning was.

--
David Rind

Guys,

Thanks for the responses. I was thinking only in terms of the the most
basic first principles of radio propagation, and now I see that that's
probably not a reasonable approach.

Making reasonable assumptions about the relative signal power in
different frequency segments of a lightning strike, and then knowing
something about the attenuative properties of moist air to those
frequency segments, could clearly work, and I don't doubt that's what
airborne lightning detection does.

Of course, now you're in a situation that requires one to know
something about lightning and something about air, but I guess that's
life!

Now I'm really curious to see a spectrogram of several lightning
strikes to see what's predictable about them!

thanks again,
-- dave j, PP-ASEL, no lightning detection on board



David Rind wrote in message ...
You can find a number of websites that can provide a better description
than I can, but the basic concept is that:

1) The intensity of most EM bursts from lightning over a range of
frequencies is such that the strength at a given frequency is
proportional to the strength at other frequencies.

2) Some frequencies suffer very little atmospheric absorption and so
give an unabsorbed measure of the strength of the lightning.

3) Some frequencies are significantly absorbed by the atmosphere.

4) By comparing the unabsorbed frequencies and the absorbed frequencies,
you can make a reasonable guess as to how much atmosphere the EM burst
traversed getting to the receiver, and so can predict how far away the
lightning was.

Guys,

Thanks for the responses. I was thinking only in terms of the the most
basic first principles of radio propagation, and now I see that that's
probably not a reasonable approach.

Making reasonable assumptions about the relative signal power in
different frequency segments of a lightning strike, and then knowing
something about the attenuative properties of moist air to those
frequency segments, could clearly work, and I don't doubt that's what
airborne lightning detection does.

Of course, now you're in a situation that requires one to know
something about lightning and something about air, but I guess that's
life!

Now I'm really curious to see a spectrogram of several lightning
strikes to see what's predictable about them!

thanks again,
-- dave j, PP-ASEL, no lightning detection on board



David Rind wrote in message ...
You can find a number of websites that can provide a better description
than I can, but the basic concept is that:

1) The intensity of most EM bursts from lightning over a range of
frequencies is such that the strength at a given frequency is
proportional to the strength at other frequencies.

2) Some frequencies suffer very little atmospheric absorption and so
give an unabsorbed measure of the strength of the lightning.

3) Some frequencies are significantly absorbed by the atmosphere.

4) By comparing the unabsorbed frequencies and the absorbed frequencies,
you can make a reasonable guess as to how much atmosphere the EM burst
traversed getting to the receiver, and so can predict how far away the
lightning was.