[time-nuts] Lady Heather survey accuracy

lists at lazygranch.com lists at lazygranch.com
Thu Jan 24 17:16:31 UTC 2013


If you go onto alt.sci.satellite-nav, there are many technical threads about why averaging GPS position readings has its limitations. It isn't like averaging an electronic measurrment where you are filtering random noise. Or maybe it is like an electronic measurement where you have to deal with drift.



-----Original Message-----
From: John Nelson <honeyway at outlook.com>
Sender: time-nuts-bounces at febo.com
Date: Thu, 24 Jan 2013 16:13:36 
To: <time-nuts at febo.com>
Reply-To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Subject: [time-nuts] Lady Heather survey accuracy

I hesitate to ask this question on here since it's perhaps more one for
position-nuts rather than time-nuts. My excuse is that it involves a
Thunderbolt ;-) 

I've been a happy user of a Thunderbolt for a while as an accurate time and
frequency source but until recently I hadn't got round to mounting it in a
proper enclosure with its PSU and finding a permanent home for the result in
the office. Having done so I asked Lady Heather to carry out a 48h
'precision survey' and got a result which although close to that done when I
first acquired the unit was about 10m different. I then carried out two
further surveys which gave similar disparate results.  

LH reports latitude and longitude results to eight decimal places, which in
principle suggests centimetre accuracy. I don't know enough about the finer
points of GPS to know whether this is actually achievable over a 48h period
but the results I'm seeing suggest that it's not.  

So the question amounts to this -- how reliable is the position produced by
LH after a 48h 'precision survey' and what level of accuracy is achievable
in practice? I'm guessing it's more like four places of decimals than eight.


John

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