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#11
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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 |
#12
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"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. |
#13
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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? |
#14
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Dave Jacobowitz wrote:
I do believe that ground-base strike measuring equipment used for forecasting and storm tracking can better isolate the position of lightning strikes -- but in that case, they *do* have the luxury of spreading out their sensors. Now *that* would be a terrific use for mode-S: cooperative weather analysis. - Andrew |
#15
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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 |
#16
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"Andrew Gideon" wrote in message
online.com... 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. I've yet to see any reference that indicates that the devices actually do filter out cloud-to-cloud lightning. So far, all we've got to go on is a Usenet post. 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. First, I have no idea why you say that "static discharge occurs after the storm is already worth avoiding". Lightning is a very good indicator of *active* thunderstorms, exactly the sorts of storms you'd want to avoid. Secondly, storms can appear quickly true, but it's not like one's going to engulf you in an instant. Solutions based upon drop size/density (ie. RADAR) would appear to be more useful in that regard. They are sometimes useful, sometimes not. Consider, for example, that it is entirely possible to have heavy rain, perfectly safe to fly in without a thunderstorm. Also consider that radar suffers from attenuation (heavy rain hiding even heavier rain farther away), while lightning detection does not. So...is it really safe to fly in the clouds with naught but spherics for weather? I haven't had a chance to use them myself, so I can't answer that question first-hand. However, those who ought to know say that lightning is actually a much better predictor of thunderstorm strength, and of whether what's out there is a thunderstorm at all (of course) than rainfall is. Lightning detectors sure seem to be the standard equipment preferred in places like Florida, and they seem popular elsewhere at all, for those frequently dealing with thunderstorms (embedded or otherwise). 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. Turn it on. Stay away from the strikes. I understand your hesitance to just cruise right on into developing thunderstorms without knowing ahead of time how well the Strikefinder works. But I'd have to say you're at least in a better position than most of us to report on how well they work. If I had a plane available to rent with a Strikefinder installed and lived somewhere that isolated thunderstorms happened with any frequency, I would take that opportunity to go out flying when one or more isolated thunderstorms are around, and see what the Strikefinder says. You don't need to get very close at all for the Strikefinder to tell you what it sees. Compare the information from the Strikefinder against that from the Nexrad radar information (available for pretty much everywhere in the US to anyone with an Internet connection), and see for yourself whether you think the Strikefinder does a reasonable job of highlighting the dangerous storms. Pete |
#17
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First, I have no idea why you say that "static discharge occurs after the storm is already worth avoiding". Lightning is a very good indicator of *active* thunderstorms, exactly the sorts of storms you'd want to avoid. I think he (or she?) means that the storm becomes worth avoiding =before= static discharge happens. So, there is a window of development of storms that the stormscope does not cover. I don't know whether this is true or not, but I think that is what was being said. There are certainly "almost thunderstorms" that it's best to fly around. Jose -- (for Email, make the obvious changes in my address) |
#18
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"Teacherjh" wrote in message
... I think he (or she?) means that the storm becomes worth avoiding =before= static discharge happens. So, there is a window of development of storms that the stormscope does not cover. I don't know whether this is true or not, but I think that is what was being said. A developing storm won't necessarily show rain either. Falling rain occurs during the mature and dissipating stages of thunderstorm development, and while water droplets may be present during the developing stage (being lifted by the updraft), there may not necessarily be enough to show up on radar as a significant storm. I agree that his statement might have meant what you said, rather than what I thought it meant. But I still don't see how it would imply 'spherics devices are inferior for detecting thunderstorms. Also, while I'm not positive, if I recall correctly lightning is present in any thunderstorm where turbulence and strong updrafts are present, regardless of the stage of development. In other words, lightning is a very good indicator of what kinds of thunderstorms should be avoided. There are certainly "almost thunderstorms" that it's best to fly around. No doubt...but I haven't seen anything that would suggest a Stormscope or Strikefinder wouldn't identify those storms. Pete |
#19
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"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 |
#20
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"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 |
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