Darksense & Dolphins

From: James Frusetta (gerakkag@wam.umd.edu)
Date: Thu 30 Jan 1997 - 17:39:52 EET


Thomas Doniol-Valcroze posts Good Stuff on sonar:

> A dolphin can use its sonar out of the water, or even through the
> surface. However, the different speeds of the sound waves in and out
> of the water can cause some mistakes about evaluating distances for
> example. I think a troll standing close to a lake can perfectly "scan"
> the lake and see how deep it is, but he will need some training to
> avoid mistakes.
This is because the return angle is off, refraction at the edge of
water/air, yes? (Sorry: my last science class was a long time ago).

> As a matter of fact, the differences in the sound speed between air
> and water make the "water sonar" a lot more efficient than the "air
Yah -- I think Sea Trolls are described as having darksense approaching
that of the mistress race trolls. Is echolocation "specialized" depending
on whether or not it's an aerial or sea-going critter? Can a bat use sonar

if it's swimming? (Can a bat swim!:) If dolphins can use echolocation out
or in of water, I assume so...

> That also means that using sonar through mist or rain is more
> efficient than dry air.
Interesting! Suggesting the trolls who worship Orlanth have at least _one_
good reason...

> The great thing about sonar is that, using it, you can "see" *inside*
> anything you're looking at. Just like the scanning done on a pregnant
I like your point about seeing inside a pregnant troll -- raises the
interesting question of _when_ the Curse of Kin sets in. The trolls
should know the minute those babies are going to be trollkin.

A question -- how much control over "density" does echolocation have?
Obviously, the dolphin is not "seeing" the water -- it's tuning the
presence of water out. If a troll "looks" in someone's stomach, I assume
it's "tuning" out the darksense return from the surface of the skin,
there. So is it possible to "turn" this up more, and tell if some one has
a broken bone? I suspect maybe the uzuz could, but not the dark trolls.
Has there been work done on, for lack of a better term, how "thick" or
dense an object a dolphin can "look" through?

Or, rather than "tuning" something out, is it more a case of looking at
how the return from that surface skin is different? A full belly gives the
return a different character, of some sort?

> - - About Density: I don't know about the Gloranthan physics of course,
> but in RW, density of materials has an effect on the sound speed. That
> means a dolphin can recognize different coins just by recognizing the
> density of metal it's made of.
_In_teresting. Something like this is mentioned in Trollpak, the troll's
ability to tell metals apart. You've explained this nicely!

> Orcas, sperm whales and belugas, among others, can use their sonar as
> a weapon: they send a very strong sound wave against their prey, and
> can stun or even kill it that way! (the target has to be of limited
> size, though, like a salmon for example).
> It it a lot more difficult to use sonar that way in the air, but in a
> fantasy world, it certainly has a potential MGF.
Definitely an uzuz power, IMO. Perhaps uzko can quest for this power.
Sea trolls probably use it the way you describe. I'd heard of this before
- -- can aerial critters use it? Are there species of bats that do something
similar -- stun insect prey?

> Hmm... I hope I was not too technical (and boring) on this.
Not at _all_! I've done some reading on this, but you're making the points
much clearer and understandable. Thanks!

Quick question -- what's the level of "background noise" that ceteceans
can handle? I'd read that bats, for example, had a lot of trouble in

lab environments so "noisy" that they couldn't distinguish their
echolocation returns from the noise. I'm wondering if this isn't a
(slightly) effective technique against the uz, in war: the Yelm army
smashes spears on their shields, raps their armor, etc., to confuse the
trolls. Probably couldn't make enough noise to do much more than annoy
them, though. Might help explain why trolls dislike smiths, too (a forge
may well be "noisy" enough, with all the metal impacts, to screw with
darksense). And suggests a favored tactic of the dwarves -- when the troll
assault wave pours in, set off gunpowder blasts to confuse their
darksense, then counterattack while their ears (or other sonar recepticle
organ) are ringing....

I'm also curious -- are there examples of echolocation "glare"? (I've been
writing up something along these lines). A critter that gives off a strong
blast of subsonic sound to repel enemies, but to defend rather than to
attack, like the orca? Perhaps not RW, frex, if echolocation is a device
primarily used by predators (which it seems to me, from what I know), but
maybe in Glorantha...

James Frusetta

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