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Antenna height problem?
I’m trying to check out my Trimble 4000sse and ST ground plane antenna TRM14532.00 by doing sessions on local marks that have published GPS data (measured by various organizations), to see how well I match in preparation for doing some GPS On Benchmark submissions. I don’t want to send them questionable data. Things aren’t going well.
The differences from published values are all pretty good. Except … every result has been too high, by an average of over a cm. If there was no height error bias, the chances of results on 4 marks in a row all being high would be 1/16. This is quite discouraging.
I use the Trimble 4-piece measuring rod to find the slant height to the antenna ground plane and subtract a value from a table I computed to get ARP height. I’ve checked that this matches the height from the floor to a straightedge laid across the tribrach adapter. That should be the ARP height above the mark, right?
I can go on trying more published marks, trying to flip tails in this string of heads, but I need any suggestions. What else might be going on?
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Differences are my OPUS-S data minus published value, in cm. The first two are Precise Orbit results, the last two Rapid.
[PRE]
HARN on old concrete post BM
diff my pk-pk Data sheet std dev
North -0.9 0.5 0.15
East 0.0 0.5 0.13
Up +1.1 0.1 0.15DOT OPUS Shared on FENO monument
diff my pk-pk DOT +/-
North 0.3 0.3 0.8
East -0.1 0.7 0.3
Up +2.2 0.8 0.72014 NGS mark
Ellip height from NGS GSVS14 report
diff my pk-pk
up +0.9 0.52014 bluebooked mark
diff my pk-pk Datasheet StdDev
North 0.1 0.8 0.34
East 0.8 0.3 0.29
Up +0.7 2.5 0.6
[/PRE]
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JoeGeodesist sent me an interesting grap. I assume height includes some geoid effects, and ellip ht between two GPS measurements would be better. If my height mismatches looked random, I’d be quite happy.
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