"Blunkett u-turn on data privacy plans"

[Brian Morrison]

On Mon, 3 Mar 2003 10:19:51 +0000, Brian Beesley wrote:

>It will be very interesting to see how badly affected these applications will 
>be affected when the US "detunes" GPS for military reasons during the 
>forthcoming attempt to singe Saddam's moustache.

Since Selective Availability was turned off in May 2000, the US has
clearly perfected 'theater'-wide jamming of GPS and hence does not need
to turn on SA again.

The original reason for SA was to make artillery counter battery fire
more difficult for an enemy, there aren't many other applications where
short term accuracy matters that much, position averaging avoids much
of the SA effect over longer time periods. But when you need to know
the exact relative position and distance of the enemy's guns to fire
back at them, SA was very good at making that vector wander about at
random.

Of course, the friendly military can make use of the P(Y) code on the
L2 frequency which is not perturbed but is protected by crypto.


-- 
Brian Morrison                                       bdm@fenrir.org.uk
              do you know how far this has gone?
               just how damaged have I become?
                                      'Even Deeper' by Nine Inch Nails