How does a stormscope/strikefinder actually work?

There are two theories about how to determine distance, and there are two
lighning detector companies in the market. Each of them strongly propounds
their theory to be the best.

In either case, the direction is done with an electronic version of the old ADF
goniometer using an e-field sense antenna and an h-field loop antenna.
Combining those two with an appropriate phase shifter gives you a cardioid
pattern with a sharp null. Phase shift until you are in the null and this gives
you heading relative to the loop antenna.

The question is where to look in the spectrum for the noise. In some tests I
did as a very young engineer, we found that the lightning spectrum peaked around
50 kHz. and one of the systems on the market looks very closely around this
frequency. Their algorithms have done a very good job on predicting range by
signal strength averaged over many strikes. Quite accurately.

The other company says that 50 kHz. gives the maximum amount of energy, but that
looking in a rather broad bandwidth gives more accurate results. The actual
number is a trade secret, but my suspicion from the components involved is that
they look in a noise bandwith of a few hundred Hz. but sweep the range from 50
kHz. to somewhere in the 3 MHz. range. As a function of WHAT they hear and
comparing one frequency to another for the same strike, they predict distance.
Quite accurately.

Howzat?

Jim



(Dave Jacobowitz)
shared these priceless pearls of wisdom:




Jim Weir (A&P/IA, CFI, & other good alphabet soup)
VP Eng RST Pres. Cyberchapter EAA Tech. Counselor
http://www.rst-engr.com

Jim Weir wrote in
:

Howzat?

As usual, pretty durn good.

From my conversations with a couple of the BFG guys that worked the "series
I to series II" transition, the first real trick was to accurately
characterize the lightning RF data. In several parts of the country they
put up triangulation systems (ground based). This allowed them to
accurately pinpoint any strikes in area. They then outfitted a couple of
planes and flew them around the outskirts of any storms that moved through.

The result from the planes was the recorded RF broad-spectrum energy
patterns from strikes at known distances. It was from this that they found
that they could do a good estimate of distance by essentially matching the
basic pattern to one of several basic shapes (this is partly how they
exclude cloud-to-cloud) and then comparing the difference between the
"paradigm" shape and what was actually measured.

The rest was just a lot of high-speed (for the time) DSP.

jmk

"James M. Knox" wrote:

It was from this that they found
that they could do a good estimate of distance by essentially matching the
basic pattern to one of several basic shapes (this is partly how they
exclude cloud-to-cloud) and then comparing the difference between the
"paradigm" shape and what was actually measured.

Dumb question time. Why exclude cloud-to-cloud? Wouldn't that type of lightning also
indicate conditions one would wish to avoid?

George Patterson
In Idaho, tossing a rattlesnake into a crowded room is felony assault.
In Tennessee, it's evangelism.

G.R. Patterson III wrote:

"James M. Knox" wrote:

It was from this that they found
that they could do a good estimate of distance by essentially matching the
basic pattern to one of several basic shapes (this is partly how they
exclude cloud-to-cloud) and then comparing the difference between the
"paradigm" shape and what was actually measured.


Dumb question time. Why exclude cloud-to-cloud? Wouldn't that type of lightning also
indicate conditions one would wish to avoid?

Good question. I think the idea that a lightning bolt is an impulse
that excites all frequencies equally at the source. So it shouldn't
matter if it is cloud-cloud or cloud-ground. And, how does a receive
know which is which anyway?

William W. Plummer wrote:

Dumb question time. Why exclude cloud-to-cloud? Wouldn't that type of
lightning also indicate conditions one would wish to avoid?

Good question. I think the idea that a lightning bolt is an impulse
that excites all frequencies equally at the source. So it shouldn't
matter if it is cloud-cloud or cloud-ground. And, how does a receive
know which is which anyway?

I'm stuck on the question "why would I care?" I mean, if I want to avoid a
t-storm, I don't particularly care whether the discharges are to the ground
or within the atmosphere.

This brings me to my main concern about this type of device, at least as I
understand it. Static discharge occurs after the storm is already worth
avoiding. If I'm in the clouds, this seems terribly likely to permit a
storm to suddenly appear much too close.

Solutions based upon drop size/density (ie. RADAR) would appear to be more
useful in that regard.

So...is it really safe to fly in the clouds with naught but spherics for
weather?

BTW, since my club's aircraft are all carrying strikefinders, I'd appreciate
any references to descriptions of how best to leverage these in IFR flight.

- Andrew

"G.R. Patterson III" wrote in
:


Dumb question time. Why exclude cloud-to-cloud? Wouldn't that type of
lightning also indicate conditions one would wish to avoid?

The official answer is "where would you plot it???"

Some of the newer models have a feature that allows you to temporarily
disable the suppression feature. This was in response to pilot requests
(pilots who got tired of seeing a lot of lightning and NOTHING showing up
on the screen).

jmk

"James M. Knox" wrote in message
2...
Dumb question time. Why exclude cloud-to-cloud? Wouldn't that type of
lightning also indicate conditions one would wish to avoid?

The official answer is "where would you plot it???"

What do you mean? You'd plot it where it happens, just as with
cloud-to-ground strikes.

How could that possibly be an "official" answer?

Pete

James M. Knox wrote:

Dumb question time. Why exclude cloud-to-cloud? Wouldn't that type of
lightning also indicate conditions one would wish to avoid?

The official answer is "where would you plot it???"

Azimuth: Where the strike is strongest. Distance: Based upon strength.

Aren't these how strikefinders handle cloud-to-ground strikes?

Some of the newer models have a feature that allows you to temporarily
disable the suppression feature. This was in response to pilot requests
(pilots who got tired of seeing a lot of lightning and NOTHING showing up
on the screen).

Yes, well, that would bug me too laugh!

- Andrew