[Q] Strikefinder Theory of Operation

Group-

I'm curious how Strikefinder technology works. Yes, I know some of
the basics, but what's curious to me is the ability of this device to
estimate range and direction to/from a lightning strike.

What I know thus far is the following:

1. Lightning is nature's version of an impulse function (time
domain), and thus it has wide bandwidth (frequency domain).
2. Strikefinder technology originated, I think, because it was
observed that lightning strikes showed up as noise in ADF units.
3. Strikefinder technology operates, I think, as a specialized AM
receiver that attempts to interpret energy bursts as lightning
strikes.

O.K., now I'm getting on the fringe of my knowledge. Yes, I'm an
electrical engineer, so don't be afraid to dive deep into details. I
just hadn't considered theory of lightning detection before and
curiosity is getting to me. I'm wondering:

1. How does Strikefinder technology estimate range and direction to a
lightning strike (my original question)?
2. If Strikefinder technology operates in the AM band, why?
(Lightning contains many other frequency components from which to
choose.)
3. How are range and direction to/from lightning strikes determined?
(I know that up to around 1/2 wavelength, E and H fields are not in
phase. Does the Strikefinder use "Near Field" characteristics to
estimate range?)

Thank you in advance for your input.

-David

On Sep 16, 4:02 pm, wrote:

1. How does Strikefinder technology estimate range and direction to a
lightning strike (my original question)?

Direction is measured using ADF technology, with an internal magnetic-
heading sensor to compensate for the aircraft's heading changes
without a connection to any other instrument.

2. If Strikefinder technology operates in the AM band, why?

Plenty of strong static bursts (sferics).

3. How are range and direction to/from lightning strikes determined?

Exact range determination would require triangulation using two or
more sensors over a wide baseline. All single-sensor lightning
detectors on the market (as far as I know) make a rough range estimate
by assuming that all lightning bolts are of the same intensity and
applying the inverse-square law to derive distance; this can lead to a
large range error for a single bolt and radial 'stretching' of the
storm cell when there are numerous strikes from a cell. The display
therefore has to be interpreted very cautiously and should be used for
avoidance, not penetration of a line or area of cells.

The Strikefinder web site (http://www.insightavionics.com/manuals.htm)
has PDF files of their manuals; look at page 34 of the user's guide to
see an example of cell stretching.

the strikefinder wasnt designed to find lightning strikes.
what was actually designed was the Automatic Direction Finder (ADF)
which would point a needle toward a distant am radio transmitter.
one of the ADF's weaknesses is the annoying habit of pointing toward
any transmission source on the frequency.
lightning broadcasts intensively on all frequencies during the strike
so the adf swings toward the lightning for the moment that it is
transmitting.
a bright chap designed an adf with a display that could process the
spurious transmissions and display their direction on a screen.

cunning serendipity.
Stealth Pilot

I happened to be working a college job for a company (Smythe Research
Associates) in San Diego that had a contract to study lightning back in the
early '60s. From that, Ryan Avionics (somewhere in Ohio) built on our
research and did the original Stormscope and from that, the Strikefinder
folks back in upstate New York did some further refinements.

Smythe found that there was an energy peak somewhere around 50 kHz. from
most lightning. Not ALL lightning, just most. The nice thing about
examining the spectrum surrounding 50 kHz. is that it is quiet. There is
nothing else there. Ryan/Stormscope took advantage of that phenomenon and
centered their detection system on 50 kHz.

Strikefinder took it a step further and said that they wanted to look at ALL
frequencies from below 50 kHz. to well above the broadcast band (and I'm not
sure at all that there isn't a bandstop filter for the broadcast band to
keep you from "detecting" the rockcrusher "clear channel" AM transmitter
when you are close to it). How far is "well above"? That is a very closely
guarded secret from the Strikefinder folks.

The detection system uses the old sense/loop technology from the ADF using a
single E-field "whip" (plate) antenna and the classic crossed-loop H-field
antenna(s) with the expected 90° phase difference between the two. By a
clever digital manipulation of this phase difference, you can tell fairly
precisely the direction of the lightning strike relative to the nose of the
aircraft. Some of the more advanced models of lightning detectors have a
built in magnetic reference so that if the aircraft nose moves, the display
moves along with it.

As to range, there are several methods, some of which depend on the
reflection of that hewmongous pulse of electromagnetic energy from the
surface of the earth bouncing from earth to ionosphere and back again,
creating a double pulse train from each stroke. Again, using digital signal
processing from multiple echoes you can create a "pseudorange" fairly
accurately.

Nearly as accurate, and nowhere as complicated is to "assume" a value for
radiated power from the average lightning stroke and simply do a range
predicated on the peak detected strength of the received lightning pulse.
Some will be stronger and some will be weaker, which is why all of them
don't fall directly on top of one another but form a circular pattern
perhaps twenty miles in diameter on the display. Again, microprocessors can
massage the data to toss out the responses at the one-sigma point and only
give those responses that fall in the expected range.

Now as to the practicality. I've flown a Strikefinder for almost a thousand
hours. It has YET to give me a false indication and it has YET to give me
an incorrect bearing and distance (within expected error) on a really nasty
set of cells.

Google "storm detection" and "73 magazine". Wayne Green's bunch of bandits
came up with some pretty simple and accurate ways of detecting lightning
that the average ham could build and use with an XY oscilloscope display.

Jim

--
"If you think you can, or think you can't, you're right."
--Henry Ford



wrote in message
ps.com...
Group-

I'm curious how Strikefinder technology works. Yes, I know some of
the basics, but what's curious to me is the ability of this device to
estimate range and direction to/from a lightning strike.

What I know thus far is the following:

1. Lightning is nature's version of an impulse function (time
domain), and thus it has wide bandwidth (frequency domain).
2. Strikefinder technology originated, I think, because it was
observed that lightning strikes showed up as noise in ADF units.
3. Strikefinder technology operates, I think, as a specialized AM
receiver that attempts to interpret energy bursts as lightning
strikes.

O.K., now I'm getting on the fringe of my knowledge. Yes, I'm an
electrical engineer, so don't be afraid to dive deep into details. I
just hadn't considered theory of lightning detection before and
curiosity is getting to me. I'm wondering:

1. How does Strikefinder technology estimate range and direction to a
lightning strike (my original question)?
2. If Strikefinder technology operates in the AM band, why?
(Lightning contains many other frequency components from which to
choose.)
3. How are range and direction to/from lightning strikes determined?
(I know that up to around 1/2 wavelength, E and H fields are not in
phase. Does the Strikefinder use "Near Field" characteristics to
estimate range?)

Thank you in advance for your input.

-David

The Strikefinder does not make the assumption that all strikes are
equal. It does a transform on the incoming signals and determines
distance by a top-secret dispersion technique.

There isn't a pot or adjustment in the thing. It is broadband,
looking
at a wide range of frequencies. That way, things like broadcast
stations don't affect it. Flying over Loran transmitters or WWV
with many kilowatts at 60KHz will cause interference, but you have
to be very close.

The big problem is dealing with multiple strikes. The SF discards
strikes that are corrupted by multiples... so sometimes it doesn't
paint every strike. If there is even one, you should sit up.

I've learned that azimuth is very accurate. Distance accuracy
will vary some depending on the ground characteristics. In dry
country, it tends to paint things too far. Near the ocean I've
noticed that cells paint closer than actual. It must have to
do with ground conductivity.

With any spark detection device, you should be flying in directions
where there aren't dots anyway, so the exact ranging doesn't
become a problem.

Bill Hale



On Sep 17, 10:05 am, "RST Engineering"
wrote:
I happened to be working a college job for a company (Smythe Research
Associates) in San Diego that had a contract to study lightning back in the
early '60s. From that, Ryan Avionics (somewhere in Ohio) built on our
research and did the original Stormscope and from that, the Strikefinder
folks back in upstate New York did some further refinements.

Smythe found that there was an energy peak somewhere around 50 kHz. from
most lightning. Not ALL lightning, just most. The nice thing about
examining the spectrum surrounding 50 kHz. is that it is quiet. There is
nothing else there. Ryan/Stormscope took advantage of that phenomenon and
centered their detection system on 50 kHz.

Strikefinder took it a step further and said that they wanted to look at ALL
frequencies from below 50 kHz. to well above the broadcast band (and I'm not
sure at all that there isn't a bandstop filter for the broadcast band to
keep you from "detecting" the rockcrusher "clear channel" AM transmitter
when you are close to it). How far is "well above"? That is a very closely
guarded secret from the Strikefinder folks.

The detection system uses the old sense/loop technology from the ADF using a
single E-field "whip" (plate) antenna and the classic crossed-loop H-field
antenna(s) with the expected 90° phase difference between the two. By a
clever digital manipulation of this phase difference, you can tell fairly
precisely the direction of the lightning strike relative to the nose of the
aircraft. Some of the more advanced models of lightning detectors have a
built in magnetic reference so that if the aircraft nose moves, the display
moves along with it.

As to range, there are several methods, some of which depend on the
reflection of that hewmongous pulse of electromagnetic energy from the
surface of the earth bouncing from earth to ionosphere and back again,
creating a double pulse train from each stroke. Again, using digital signal
processing from multiple echoes you can create a "pseudorange" fairly
accurately.

Nearly as accurate, and nowhere as complicated is to "assume" a value for
radiated power from the average lightning stroke and simply do a range
predicated on the peak detected strength of the received lightning pulse.
Some will be stronger and some will be weaker, which is why all of them
don't fall directly on top of one another but form a circular pattern
perhaps twenty miles in diameter on the display. Again, microprocessors can
massage the data to toss out the responses at the one-sigma point and only
give those responses that fall in the expected range.

Now as to the practicality. I've flown a Strikefinder for almost a thousand
hours. It has YET to give me a false indication and it has YET to give me
an incorrect bearing and distance (within expected error) on a really nasty
set of cells.

Google "storm detection" and "73 magazine". Wayne Green's bunch of bandits
came up with some pretty simple and accurate ways of detecting lightning
that the average ham could build and use with an XY oscilloscope display.

Jim

--
"If you think you can, or think you can't, you're right."
--Henry Ford

wrote in message

ps.com...



Group-

I'm curious how Strikefinder technology works. Yes, I know some of
the basics, but what's curious to me is the ability of this device to
estimate range and direction to/from a lightning strike.

What I know thus far is the following:

1. Lightning is nature's version of an impulse function (time
domain), and thus it has wide bandwidth (frequency domain).
2. Strikefinder technology originated, I think, because it was
observed that lightning strikes showed up as noise in ADF units.
3. Strikefinder technology operates, I think, as a specialized AM
receiver that attempts to interpret energy bursts as lightning
strikes.

O.K., now I'm getting on the fringe of my knowledge. Yes, I'm an
electrical engineer, so don't be afraid to dive deep into details. I
just hadn't considered theory of lightning detection before and
curiosity is getting to me. I'm wondering:

1. How does Strikefinder technology estimate range and direction to a
lightning strike (my original question)?
2. If Strikefinder technology operates in the AM band, why?
(Lightning contains many other frequency components from which to
choose.)
3. How are range and direction to/from lightning strikes determined?
(I know that up to around 1/2 wavelength, E and H fields are not in
phase. Does the Strikefinder use "Near Field" characteristics to
estimate range?)

Thank you in advance for your input.

-David- Hide quoted text -

- Show quoted text -

Could you elaborate on what kind of transform it is doing and how it could
determine distance by dispersion?

Not contradicting you, just don't understand.

Jim

--
"If you think you can, or think you can't, you're right."
--Henry Ford


" wrote in message
ups.com...


The Strikefinder does not make the assumption that all strikes are
equal. It does a transform on the incoming signals and determines
distance by a top-secret dispersion technique.

RST Engineering wrote:

Snip

As to range, there are several methods, some of which depend on the
reflection of that hewmongous pulse of electromagnetic energy from the
surface of the earth bouncing from earth to ionosphere and back again,
creating a double pulse train from each stroke. Again, using digital signal
processing from multiple echoes you can create a "pseudorange" fairly
accurately.

Nearly as accurate, and nowhere as complicated is to "assume" a value for
radiated power from the average lightning stroke and simply do a range
predicated on the peak detected strength of the received lightning pulse.
Some will be stronger and some will be weaker, which is why all of them
don't fall directly on top of one another but form a circular pattern
perhaps twenty miles in diameter on the display. Again, microprocessors can
massage the data to toss out the responses at the one-sigma point and only
give those responses that fall in the expected range.

Now as to the practicality. I've flown a Strikefinder for almost a thousand
hours. It has YET to give me a false indication and it has YET to give me
an incorrect bearing and distance (within expected error) on a really nasty
set of cells.

I can't find a reference now, but I thought one of the other refinements
made by Strikefinder was to use dispersion as a means for distance
measurement.

Matt

"RST Engineering" wrote in message
...
Could you elaborate on what kind of transform it is doing and how it could
determine distance by dispersion?

Not contradicting you, just don't understand.

Jim

Did you happen to read the links about strikefinders when there was a thread
about how strikefinders work, a month or so back?

There were some great explanations, that were provided. What you asked, and
more, was explained.
--
Jim in NC

No, I must have missed it. Was it in this newsgroup? If so, it went right
by me and that would be strange, since I did a fair amount of work writing
about strikefinder, stormscope, and other detection stuff for my column. I
also have a library of the articles written in 73 about lightning detection.

Jim

--
"If you think you can, or think you can't, you're right."
--Henry Ford

"Morgans" wrote in message
...

Did you happen to read the links about strikefinders when there was a
thread about how strikefinders work, a month or so back?

There were some great explanations, that were provided. What you asked,
and more, was explained.
--
Jim in NC

"RST Engineering" wrote in message
...
No, I must have missed it. Was it in this newsgroup? If so, it went
right by me and that would be strange, since I did a fair amount of work
writing about strikefinder, stormscope, and other detection stuff for my
column. I also have a library of the articles written in 73 about
lightning detection.

Might have been the R.A.Piloting group.

As much as I hate finding threads, I'll see what I can do.

One article stands out in my mind, in particular. It told of the different
frequencies of the strikes it looks for, and how cloud to ground and cloud
to cloud strikes have a different signature, and how some strikefinders do
or do not look for them. On second thought, it might have been more about
how ground based systems look for them, to be sent on to other assets for
aviation.
--
Jim in NC