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Sorry for being late in providing more information but the life of a prof is a 
busy one, well, at least for me. You want to determine a height difference of 
a few metres at the same location with an accuracy of hopefully 10%. If the 
height difference is 3 metres, say. then you are looking for 30 cm, one 
sigma. Then you will need to make carrier-phase measurements using a 
survey-grade GNSS (GNSS = global navigation satellite systems, including GPS, 
GLONASS, etc.) receiver and process them using either the precise point 
positioning technique or double-differencing with respect to a reference 
station. I think pseudorange measurements are just too noisy to give you the 
desired accuracy even in differential mode.

Attached are a few slides from my external Differential GNSS Course (to be 
given next in Nashville in September at the ION meeting). The first shows the 
different kinds of positioning available with GNSS, then horizontal and 
vertical positioning accuracies with standalone pseudorange measurements 
(like those used by handheld receivers) but as determined at some FAA 
monitoring stations, then WAAS-corrected position accuracies using the same 
stations.

To get back to celnav, I will have to determine the height of my eye when I go 
to the Big Island of Hawaii a couple of weeks from now at a house up from 
Kona with a nice view of the Pacific. I'll do some GPS height averaging but 
as I'm just taking my plastic Davis sextant, I'm not looking for high 
accuracy, just a bit of fun, to break up the monotony of sitting around the 
pool. ;-)

-- Richard Langley




On 2013-04-10, at 3:45 PM, Marcel Tschudin wrote:

>
> @ Richard Langley
>
> I noticed from your contributions and publications that you seem to be
> more deeply involved in the subject of GPS. May I therefore ask you:
> Do you have an idea on the sort of accuracy one may "generally" expect
> when measuring with GPS at the same location (few tenths of meter
> distance) height *differences* between about 2 and 5 m ? Would it be
> possible to measure at the two locations the height and obtain their
> difference to about +/- 20% or even better to e.g. +/- 10% and what
> type of equipment would this require?
>
> Thanks in advance for some hints.

[[rest snipped]]

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| Richard B. Langley                            E-mail: lang@unb.ca         |
| Geodetic Research Laboratory                  Web: http://www.unb.ca/GGE/ |
| Dept. of Geodesy and Geomatics Engineering    Phone:    +1 506 453-5142   |
| University of New Brunswick                   Fax:      +1 506 453-4943   |
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