[LINK] limits of technology

Stewart Fist stewart_fist at optusnet.com.au
Tue Dec 12 10:56:34 AEDT 2006

Gordon replied
> The system also doesn't just throw out a number in real time, like a hand held
> GPS. The positioning data and radar data are processed to get results that
> are statistically robust.

I note that the Link Subject line has drifted somewhat.   My original
question was mainly in reference to the whether the scientists were capable
of determining the positional orbits of the satellites that were being used
for measuring GPS and sea levels.

I appreciate that these are two quite different processes, but the both
depend on knowing where one or more satellites are in relationship to the
surface of the Earth (or should that be 'Centre of the Earth') before any
accuracy can be determined.

I'm not sure that 'radar data' that is 'statistically robust' is the same as
'measurement accuracy'

Adam made a similar claim with his GPS being accurate to within 30 cms
providing it was being moved.  But it seems to me that he is not talking
about 'accuracy' so much as 'consistency'.

If all the working GPS satellites within his field of view are being
perturbed by the moon/sun/gravity variation/atmospheric density
combinations, then the readings might be quite consistent, but totally

The same applies, it seems to me, with the interesting discussion about
Differential GPS.

It's a very interesting area of science, and thanks for the contributions.

Yesterday at the RadComm 2006 spectrum conference, I met the Assistant
Director of the Met service responsible for all this satellite measurement
stuff. So later in the week I'll put a whole lot of questions to her by
e-mail, and post the replies on Link.

Stewart Fist, writer, journalist, film-maker
70 Middle Harbour Road, LINDFIELD, 2070, NSW, Australia
Ph +61 (2) 9416 7458

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