[gurps] [VEHICLE] of the week 731 ? Planetary Defense Battery

[Onno Meyer]

Anthony replied to me:

> > I'm not so sure. There is talk about ladar for ASW or fish finding, and 
> > that -1 would kill those applications ...
> 
> Most fish swim pretty close to the surface, and using ladar for ASW is 
> about wake-finding, not direct detection.

http://www.janes.com/extracts/extract/juws/juws1952.html

Mines don't leave wakes, and most do not swim close to the surface,
either. 

http://books.google.de/books?id=AYRqVix7uScC&pg=PA662&lpg=PA662&dq=asw+ladar+OR+lidar+OR+laser&source=web&ots=YdrQ4QPMy4&sig=i-TltE1UmX4_Q1rSMFpfIFS6Pp8&hl=en&sa=X&oi=book_result&resnum=9&ct=result

This source suggests a depth of 50 to 70 m. Call it 0.1 miles, to allow for a
safe flight altitude, and the -8 from VE means you need a scan rating of 13
to detect a standard-size target. That would mean a nominal range of 2 
miles. Sounds low, even for a prototype system, since subs are larger 
than tanks or jets, but we're in the right ballpark. 

On the other hand, -1 per yard would mean a nominal range around 70
million miles, certainly a no-go.

OTOH, the following paragraph seems to suggest wave detection for 
mines below 30m, so I might be wrong ...