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

[Evyn MacDude]

On Thu, Oct 30, 2008 at 2:08 PM, Anthony Jackson <ajackson at iii.com> wrote:

> Evyn MacDude wrote:
>
>  Anthony, it all depends on your wave length,  There are sensors that can
>> detect subs from orbit. Power and gross coverage are the limiting factors.
>>
>
> They don't do it by seeing through seawater (to the extent it's actually
> possible, which is unclear and probably classified, it likely involves
> detection of wakes or thermal plumes, neither of which is a targeting
> sensor). Pure water has its greatest transparency in the 400-500 nm range,
> at which point it absorbs about 2% of light per meter, and it probably takes
> about 30% absorption to get a -1 to perception rolls, so we're talking -1
> per 15 meters. Seawater is rarely perfectly clear, actual values are
> probably -1/10 for clear ocean water, on the order of -1/meter for average
> coastal water.


Naw the plume and the wake hump detection is yesterdays news. I don't
remember the wavelength regime, but the technique was in the Synthetic
aperture set, and it wasn't a direct lookdown view. And it was definitively
not in realtime, there was significant processing overhead involved with the
process.

There are lots of neat things you can see from orbit, if, and this is a
major if, you invest the time to process the information you gather. What
you can detect from the instant look is neat, but only the tip of the
iceberg.

-- 
Evyn