Some sonar techniques.

From: Thomas Doniol-Valcroze (tconrad@orbital.fr)
Date: Thu 30 Jan 1997 - 13:27:51 EET


Greetings all.

James Frusetta:
- ---------------
>any sonar specialists out there?

Well, I'm not really a specialist but I do research on dolphins and
whales, and dolphins do use a very performant echolocation system.

I like all your Uz descriptions of the sonar "feel" of different
objects, and I just wanted to add a few thoughts on this subject.

- - About Water:
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.

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

sonar". Because sound travels at 300 m/s in the air, and at 1500 m/s
in the water. The response time of the sonar is reduced in water, and
it makes it a lot more accurate.

That also means that using sonar through mist or rain is more
efficient than dry air.

- - About Hollowness:
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

woman. A dolphin, as well as a troll, can say if someone is pregnant,
what that person had for dinner, and so on.

IMO, that means that a troll can say if a pregnant female is expecting
trollkins or dark trolls.

- - 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.

That means that, not only you can find a coin buried in the sand at
the bottom of a lake, but you can also say if it's gold or silver.

- - About techniques:
The usual technique for efficient hunters like sperm whales or orcas
is the following:
 First, the hunter scans the whole area using a wide and unaccurate
beam of sound, at low frequencies that can travel very far, that give
him a general idea of potential preys.
 Then, he focuses a narrow beam of higher frequencies on the prey to
receive accurate data about it.

- - Using sonar as a weapon:
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.

Hmm... I hope I was not too technical (and boring) on this.
Anyway, my point was that sonar is an amazing stuff in RW. In a
fantasy world, I think it should be even more so!

Yours, Thomas.

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