[time-nuts] Thunderbolt self-survey results...

Neville Michie namichie at gmail.com
Sat Aug 30 19:51:50 EDT 2008

As a microclimatologist I am very aware of the nocturnal inversions  
that occur in the atmosphere.
 From ground level to say 1000 feet the air cools at night forming a  
dense layer. The dielectric
properties of this condition must create apparent thickness beneath  
the satellites.
Whereas there is a balanced triangulation of northing and easting in  
determining lat and long
that will null any atmospheric length effects, there is no way of  
determining the actual altitude
from the apparent altitude caused by extra dielectric layering of the  
atmosphere and ionosphere.
So there is little surprise in variable height data.
What would be interesting is a correlation between apparent height  
error and night minimum
temperature at ground level (air temperature 2 metres from the ground).
cheers, Neville Michie

On 31/08/2008, at 6:15 AM, Mark Sims wrote:

> Besides the wonky geoid,  ionospheric delays (which tend to be  
> poorly modeled and compensated for in single frequency receivers)  
> tend to affect the altitude reading the most.
> You also need to set the cable delay time for best accuracy.
> Also, for a cheap thrill,  run the self survey several times  
> (preferably at the same and at different times of the day) and see  
> how much it varies.  I set my location to the centroid of about a  
> dozen surveys done over three days.
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