[time-nuts] Positional accuracy of the M12+T

[Dr Bruce Griffiths]

Hal Murray wrote:
>> A spherical error volume is a crude approximation, actually it  is an
>> ellipsoidal with  as the height error is usually significantly  larger
>> than the other positional errors which also may have different  rms
>> errors.
>>     
>
> Why is the height error usually larger?  Is that just geometry?  Do I get 
> good height data if there is a satellite close to overhead?
>
>
>   
Hal

Yes its just geometry.
A small variation in height doesn't affect the slant range to a 
satellite as much as similar variations along the other 2 axes.
The slant range to a satellite near the zenith is most sensitive to 
variations in height and it is less sensitive to variations along the 
other 2 axes.
However one needs to know the position along the other 2 axes reasonably 
accurately as well in order to solve for the receiver clock errors.
The "optimum" satellite geometry when all factors are taken into account 
results in the height error being much larger than the errors along the 
other 2 axes.

Bruce