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 Post subject: Sensors in a Sandstorm ?
PostPosted: Tue Jun 14, 2011 6:44 pm 
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Among the bits and pieces of my Samar setting will be rules for sandstorms,
and one of my problems with this subject are the sensors: What can the cha-
racters see on their sensor screens during a sandstorm ?

The sensor types available to them are radar, lidar, infrared and passive elec-
tromagnetic sensors, but not any kind of gravitic sensor. As far as I understand
it, all of their sensors should have their ranges reduced to a few meters at best
and should produce only "drifting snow" on the screens, with the exception of
the passive electromagnetic sensor, which would be mostly useless for naviga-
tion, although it could probably still determine the direction to a strong radio
beacon.

Since I have no real world experience with sensors your input would be most
welcome. :)


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PostPosted: Tue Jun 14, 2011 8:03 pm 
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According to this at least, radar should be pretty much unaffected by sandstorms:
http://www.cassidian.com/cassidian/int/ ... storm.html

(I'd guess it's because the size of the particles is much smaller than the wavelength of the radar).

As for Lidar... we've been able to see ground features with helicopter-mounted Lidar flying through snowstorms (there's a lot of noise to clear up in the air, but the ground returns seem reasonably identifiable). IIRC it's a longer wavelength near-IR laser though, which may make a difference. I'm not sure how well it'd work in a sandstorm though - not as well, I'd imagine. I can ask at work tonight though :).

Lidar can and has been used to detect oncoming sandstorms by firing it off and checking the returns for polarisation or scattering:
http://www.apec-vc.or.jp/e/modules/tiny ... .php?id=23

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PostPosted: Tue Jun 14, 2011 8:14 pm 
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Thank you very much for the informations. :D


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PostPosted: Wed Jun 15, 2011 8:32 am 
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And apparently Lidar probably won't see much past visible in a sandstorm anyway - there'd be too many false returns to make anything useful out of the data. Also, the lidar sensor would get wrecked by the sand too if it left was out in the storm.

(and just to be clear, Lidar isn't just a single laser pointing in a direction and firing a pulse. It's a constantly scanning laser that on a rotating platform that scans the surroundings and builds up a map of the area. But all you get back initially are undifferentiated points, so they'd have to be processed somehow to be useful).

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PostPosted: Wed Jun 15, 2011 12:17 pm 
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Thank you very much again. :D

So the best sensor in case of a sandstorm seems to be a "tuneable" radar,
where the wavelength used by the radar can be adapted to the average size
of the sand particles ...

I think my setting does not have this kind of radar, and I will probably declare
that the standard radar does not do well in a sandstorm, because this gives me
the opportunity to turn the development of such a radar into a research project
for one of the characters.


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PostPosted: Wed Jun 15, 2011 12:54 pm 
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Even if they fix the radar problem, you still have the issue of that huge metal dish sitting out there getting sand-blasted... It might work, but for how long?

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PostPosted: Wed Jun 15, 2011 1:32 pm 
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Right, an important point. It seems they would need a kind of "radome"
of a material which is "transparent" for the radar in both directions and
either very cheap or able to survive more than one sandstorm.


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PostPosted: Wed Jun 15, 2011 2:28 pm 
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Bakelite worked in the real world ... remember the stuff those ugly black telephones were made of in the 1960s.

My grandfather made Bakelite domes for aircraft radar in WW2 (His enlistment was rejected because his job was deemed vital to the war effort).

http://en.wikipedia.org/wiki/Bakelite

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PostPosted: Wed Jun 15, 2011 2:52 pm 
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atpollard wrote:
Bakelite worked in the real world ...

Thank you very much, I like the idea, especially because this seems to be
a material which even a colony without any chemical industry can produce
with comparatively little effort, and which can also be used for lots of other
stuff, especially everyday consumer products. :D


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PostPosted: Wed Jun 15, 2011 5:24 pm 
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http://en.wikipedia.org/wiki/Radar

Lots of interesting stuff there (sandstorms are mentioned under "Clutter" too). While there is short wavelength radar, most of it is rather longer than the average size of sand particles in a storm. I think anything above "X" on the "Frequency Bands" list there shouldn't be too handicapped by being in a sandstorm.

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