Trolls that go 'ping'

From: Paul Honigmann (furfur@furfur.demon.co.uk)
Date: Fri 18 Oct 1996 - 22:55:35 EEST


James Frusetta:

>Something I've argued with other GMs (uh, usually
>while playing an Uz PC)
>is whether or not Darksense is "noticed" by other Uz.
>If this is a subsonic "ping" like sonar, wouldn't the
>receivers on other Uz notice it?
...
>To be fair, the arguement I've heard against it
>is that the initial "ping"
>is at a different pitch, and that until
>it "reflects" Uz don't pick it up.
>Any thoughts?

(pause to don pedantic physics hat...)
I haven't been following this thread closely but it is probably relevant
to point out what happens in our own natural world.

Firstly, *sub*sonics wouldn't work well for scanning due to their
wavelength. Subsonic means less than about 10 hertz, so unless the
target is at least 17 metres long you won't see it's reflection.
Besides, subsonic also means (by definition) below the range of normal
hearing, and there's no point emitting a pulse if your race (ie you
yourself) can't hear its reflection...

So, assuming we're talking about supersonics (ie above human hearing
range, or 20,000 Hz +): the same argument about 'above his race's range'
applies, ie if the target Uz can't hear it then neither can the Ping-
emitter.

Next, in New Guinea (well somewhere down that neck of the woods anyhow)
there are some highly evolved bats & insects. The bats appear to have
been so successful with catching insects by sonar that evolution
(selection pressure) left a few very successful strains of insects which
survive v. well compared to their rivals: when they hear a nearby bat
shriek, they themselves either (1) emit a deafening squeak of their own
near the bats' ears most sensitive listening frequency; this quite
deafens the predator and allows insect time to get away; (2) some emit a
squeak at nearly the same frequency as the bat's, but not quite, so the
bat thinks the prey is at the wrong point (due to apparent doppler
shifting of the return squeak) and misses. I think there were 1 or 2
other tactics bugs used but it was a few years ago I read the article in
New Scientist and memory fails.

Point is that targets definitely can hear incoming scanning.

As for the incoming ping being at a different pitch... yeah, often
dolphins (frex) use a very high frequency complex waveform, ie a mix of
frequencies. The US Navy exerimented with Dirac pulse sonar (ie lots of
very high freqs, very short duration pulse of sound) after realising the
dolphins did this and how the backscattered pulse had extra info they
could interpolate just like dolphins: certain materials / textures /
densities reflect certain frequencies better than others. I suspect
there's phase delay info that can be drawn out of the return pulse too
as different frequencies travel at different speeds through water.
However, I doubt the dolphins emit frequencies higher than their race
can hear.

On bats... apparently as they close in on prey the frequency (pitch) of
their squeak goes up. This allows better resolution & greater accuracy
in their strike.

All this makes one wonder about the behaviour of the Crimson Bat. Is it
famed for deep-bellied croaks or can it create supersonic squeaks
capable of bursting eardrums? Is it known for cute cheeping noises as it
approaches feeding time, rising frantically and comically higher and
higher in pitch? Can Uz create a false echo to guide it to its doom by
flying into a cliff? (It is thought dolphins may be able to create sonic
illusions to fool other fish, though it's unproven so far).

Yrs pompously,
- --
Paul Honigmann

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