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In article <39AD144A.7394215D@caregroup.harvard.edu>, David Rind >How does a Stormscope know the range to a lightning strike? >(Ive never used one, but I understand it has this capability.) >I can see how it can figure out the direction of the strike. Some other answers have given you the general idea. The original Stormscopes calculated range purely by signal strength (based on some "typical" lightning bolt paradigm). The weaker the signal, the further away it was. It wasnt too bad, but the problem of course is that not all lightning bolts are the same. This lead to "radial spread" -- a strong bolt would appear closer than it really was, and a weaker one would appear further away. What you got on the display was a "line" leading off in the direction of the cell. Early units just covered a "sector" as having activity anyway, so you didnt really see the spread. Later units were covered by "marketing" which touted this as a feature -- "Well, if its are REALLY strong cell then you want to stay further away anyway, right?" All newer Stormscopes and Strikefinders are classed as "series II" Sferics, with a substantial amount of compute power inside. It was discovered that, although a lightning discharge generates RF over a large frequency range, different parts of that frequency range are attenuated at different amounts over distance. So what they do now is map a fairly broadband spectrum of energy in the discharge. By comparing this profile (shape) to a "standard" discharge they get a much better feel for distance, regardless of amplitude. Additional examination of this profile is also used (together with bearing data) to isolate cloud/ground lightning from cloud/cloud discharges. The latter are generally NOT plotted on the display, even though they may be counted on the display as "activity." jmk ----------------------------------------------- James M. Knox TriSoft ph 512-385-0316 1109-A Shady Lane fax 512-366-4331 Austin, Tx 78721 trisoft@texas.net ----------------------------------------------- |
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