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Old October 30th 11, 10:19 PM posted to sci.geo.satellite-nav,rec.aviation.ifr
Alan Browne
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Posts: 18
Default PRN133 ranging now useable for SoL, at non precision approachlevel

On 2011-10-30 16:44 , macpacheco wrote:
Since PRN133 was set healthy for WAAS corrections, its ranging was
kept at NM (Not Monitored) level, preventing its use for safety of
life applications, however in the last few days, its ranging improved
to UDRE 50 meters, which allows it to contribute for non precision
approaches.

With this improvement now all 3 WAAS satellites have ranging useable
for navigation. The other two WAAS satellites usually work at UDRE 7.5
meters which allows it to contribute even to precision approaches.

In contrast, GPS satellites normally operate at 3 meters UDRE, the
best accuracy WAAS allows any ranging source to achieve.

PRN133 has been performing at UDRE of 50 with some degradation to 150.

This is most useful in South America since PRN133 has the best view of
South America of all GEOs, and with a WAAS compatible receiver capable
of tracking two SBAS GEOs, you would effectively get two extra GPS
satellites.


I suppose at least you can use 133 for integrity information for the
rest of the satellites - at least those visible and monitored in N.A.

But the WAAS differential correction would not be applied in S.A. and
the range error from 133 would pollute GPS-only nav solutions in any
case - fine for terminals and en-route only.

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