[time-nuts] Some results of PRS10 and Trimble Resolution

[Brooke Clarke]

Hi Björn:

I don't think that's that case.  I live in a small town and hired a 
local surveyor chosen because he's the guy that uses GPS.
He was able to use two GPS receivers separated by say 100 feet and 
connected with a cable to determine an accurate relative bearing between 
his total station and the remote GPS.  I had placed wood stakes at a few 
locations that were very close to Longitude and Latitude points ending 
exactly on the seconds, for example 123:09:50.0W by 39:11:24.0N.  The 
idea was for him to locate the exact points and to locate the house GPS 
antenna.  To do this he needed to go back to his office and post process 
the data.

Since the points I wanted to know about were separated by exactly 1 
second of Lat and 1 second of Lon he just placed his total station a few 
feet from the corner one and shot the other stakes.

It's my understanding the the military has the crypto key needed to use 
the L2 channel to full effect and that's not available to surveyors.  
What surveyors do is record the carrier phase of both the L1 and L2 
signals and resolve the ambiguity in post processing.  There are a 
couple of flavors of post processing.  In one only the data recorded in 
the field is used, in the other the filed data is combined with actual 
data taken at a nearby reference station from the satellites used in the 
field data.  The second method corrects for errors in the ephemeris data 
broadcast by the satellites.

I think what you may be referring to are the differential correction 
methods, either Low Frequency or satellite broadcasts that improve the 
position accuracy of GPS receivers.  But I don't think these can be used 
to improve timing accuracy.

Have Fun,

Brooke Clarke

-- 
w/Java http://www.PRC68.com
w/o Java http://www.pacificsites.com/~brooke/PRC68COM.shtml
http://www.precisionclock.com



bg at lysator.liu.se wrote:

> .  .  .  .
>
>
>Why are dual freq. receivers not used in timing instruments? Ionospheric
>errors are almost removed. Surveyors in every small town on earth are
>routinely getting sub 5cm accuracy in real time. Are not time labs using
>it to transfer their cesium time to each other?
>
>
>--
>
>   Björn
>
>
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