The discussion on storm scopes brought a related question to my mine (but different from the other discussion, hence a different thread).
I can imagine how a storm scope would detect the direction of the strike by using multiple antennas. But how would it determine the distance to the strike (hence were to place it on the map)? I imagine that lightening strikes vary hugely in terms of energy, so the strength of the wave can’t the the answer. Obviously triangulation isn’t an answer from a single aircraft.
So how do they do it?
The azimuth is worked out using a multipart antenna – vaguely like the ADF or TCAS does it.
The distance is estimated using the intensity of the signal. Obviously this is unreliable but, as someone rightly said, you don’t fly towards a strike or especially a cluster of them 
I agree with Tom (who is a signal processing expert) in the other thread that the box cannot possibly use timing differences to detect the distance. But what it probably uses is that the spectrum of a small strike differs from the spectrum of a big strike.
I don’t know if that article was referenced in the old thread, but it might be worth reading: http://www.avweb.com/news/avionics/181954-1.html
“My” aeroplane at work has both a weather radar and a stormscope. Within 50NM range or so, the distance and bearing of the lightnings shown on the stormscope usually correlates quite well with the radar display. Above 100NM it shows more a general direction than anything else. If I had to fly on a stormscope alone, I would do everything to stay at least 30…50NM away of the lightning symbols. With a radar, you can safely (more or less…) fly between cells that are no more than 10NM apart. But I would really only do that if there is absolutely no way to fly around the stuff – or if I can visually see the cells.
Thanks guys.
The relevant part of the article linked to by what_next, which explains it beautifully, is this
The real magic of modern sferics is in how they determine the distance to the discharge.
In very broad terms, stored in the electronic brain of a Stormscope and Strike Finder is the electrical signature of a generic thunderstorm discharge. When a live thunderstorm discharge is detected, it is compared to the signature of the one stored in memory. From that basis ranging algorithms are applied, a distance is calculated and a plot is made on the sferic’s display.
The comparison of the detected strike to a generic one is an obvious source of error.
Thanks very much!
