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@ Rchard 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.

Marcel


On Wed, Apr 10, 2013 at 7:32 PM, Richard B. Langley  wrote:
> ________________________________
>
> It would be averaging the effects of measurement (pseudorange) imprecision
> (random over longish time intervals) and multipath (not random and not
> repeatable except for a fixed location with the same satellites one sidereal
> day to the next). And, to a lesser extent, tropospheric delay errors and
> other minor model deficiencies. Two sites, some distant apart, would
> experience different errors although the pseudorange-based DGPS technique
> (such as that supported by the Coast Guard) uses the errors computed at a
> reference station to improve the positions of a rover (in real time).
> -- Richard Langley
>
> On 2013-04-10, at 1:20 PM, Marcel Tschudin wrote:
>
>>
>> Thank you, Brad, for finding this Android app for me. I presume that
>> the 1 m represent an absolute accuracy and that measurements of height
>> differences may possibly attain a higher accuracy. I will give this
>> affordable gadget a try and perform some tests with it.
>>
>> Marcel
>>
>>
>> On Wed, Apr 10, 2013 at 6:28 PM, Brad Morris
>>  wrote:
>> > ________________________________
>> >
>> > Hi Marcel
>> >
>> > There is an app in the Android market called "Precision GPS Pro".  The
>> > cost
>> > is US$0.99
>> >
>> > It claims a 1 meter elevation accuracy after averaging, although they do
>> > not
>> > indicate how long an average you require to achieve that.
>> >
>> > The free version of this app does not do elevation averaging.
>> >
>> > I have not tried this app.
>> >
>> > Brad
>> >
>> > On Apr 9, 2013 6:21 AM, "Marcel Tschudin"
>>  wrote:
>> >>
>> >> ________________________________
>> >>
>> >> In my sunset observations the guesstimates for the HoE of probably not
>> >> better than +/- 20% are indeed a weak point. But how weak? The dip is
>> >> proportional to the square root of the HoE which means that the
>> >> estimated dip error is only half of the estimated HoE error. For the
>> >> average HoE of 3.5m the "normal" dip is 3.3 moa and a 10% error of it
>> >> therefore +/- 0.33 moa. This corresponds in the photo to slightly more
>> >> than one pixel which is 18 seconds of arc.
>> >>
>> >> Frank, you mentioned estimating HoE within about +/-5%. I'm wondering
>> >> whether you would also be able to attain such an accuracy by climbing
>> >> over the rocks as shown in my photo:
>> >>
>> >>
>> >> 
https://mail-attachment.googleusercontent.com/attachment/u/0/?ui=2&ik=b33d2c81ba&view=att&th=13ddab531282f2e7&attid=0.1&disp=inline&realattid=f_hf5h7cfp0&safe=1&zw&saduie=AG9B_P-DvbGAuAxTxtruQd29-avq&sadet=1365502394438&sads=w4N-7jPt0vbdfN6eZHKSEaR8vQ0
>> >> For my average of 3.5 m this would correspond to less than 20 cm or
>> >> what might be more familiar to you to about half a foot.
>> >>
>> >> In order to verify my guesstimates I do indeed consider to perform
>> >> some additional measurements. I'm wondering how good I could measure
>> >> it using GPS and also the Russian version of it. I have no experience
>> >> in using these systems. I understand that I would have to measure both
>> >> levels, eye and sea level and then take the difference. Is there an
>> >> Android application which I could load on my Samsung pad allowing to
>> >> collect measurements over a longer time period which then calculates a
>> >> mean altitude and its standard deviation? What are the sort of result
>> >> one could obtain this way?
>> >>
>> >> Marcel
>> >>
>> >> : http://fer3.com/arc/m2.aspx?i=123477
>> >
>> > : http://fer3.com/arc/m2.aspx?i=123498
>>
>>
>> : http://fer3.com/arc/m2.aspx?i=123499
>>
>
> -----------------------------------------------------------------------------
> | Richard B. Langley                            E-mail: lang---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
> |
> | Fredericton, N.B., Canada  E3B 5A3
> |
> |        Fredericton?  Where's that?  See: http://www.fredericton.ca/
> |
> -----------------------------------------------------------------------------
>
> : http://fer3.com/arc/m2.aspx?i=123500

   

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