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Subject: TWL: RE: Chart/WAAS accuracy
From: Jim Donohue (jim_donohue@XXX.XXX)
Date: Thu Jan 02 2003 - 23:11:14 EST
The obvious place where one wants all the accuracy one can get is repeating
a prior path in either forward or reverse. Depending on the circumstances
WAAS may or may not be sufficient. I would love to have sub meter including
altitude though that is a way off yet. Coming out of the marina in the fog
one went into in the clear is a good example...I will take all the accuracy
I can get. Know a vessel lost on Minerva reef because he tried a different
exit than entrance.
There are also anchoring situations in Coral where 3 meters is much better
than 6. One wants to drop the hook in the middle of the sand...and not on
the coral. It is difficult even if you can see sometimes.
The common thread in these needs is repeatability. Even if the charts are
no good you can go back where you once where.
The satellite configuration is presently overfilled and could well meet all
objectives if less than full. There appears little danger of significant
loss of accuracy. I, for one, will however be much happier when the euro
satellites provide full redundancy and increased accuracy.
WAAS was never contemplated for CAT III landings. Only the lesser
approaches. LAAS and something still to be defined are needed for CAT III.
It will come though.
I will stop looking for more accuracy when it is good enough to mow my
lawn...what..about 8 years from now?
Jim
>
> At the moment WAAS is undergoing trials and two satellites are in place.
> Visibility may not be adequate in the higher latitudes such as
> the PNW; nor
> will it be good if terrain blocks the line of sight.
> Tucked into a sheltered cove surrounded by tall trees, or worse,
> high hills
> may well mean the two WAAS satellites are not visible.
>
> Now add to that the information that the authorities have
> acknowledged that
> some of the older satellites are degrading and the process of geting
> replacements installed will be delayed.
>
> In other words you are simply kidding yourself that a WAAS
> equipped receive
> will guarantee safer anchoring as compared to an orodinary GPS.
>
> In fact if this is the only thing you rely on when anchoring out, please
> don't invite me to stay onboard ovenight.
>
> And if you are using something else as well why is this even being
> discussed.
> Cheers
>
> Arild
>
>
>
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