[time-nuts] Timing Distribution in Mountainous Terrain
ralph at ralphsmith.org
Sat Sep 11 01:26:40 UTC 2010
On Sep 10, 2010, at 7:44 PM, J. L. Trantham, M. D. wrote:
> I guess I am thinking about this from a user perspective rather than an
> engineering design and implementation perspective. If the requirement is
> aircraft separation, LORAN should be adequate for that, if it was still up.
> You would only have to transmit your position and altitude to a ground
> receiving station that then would relay it to the Center Controllers to be
> displayed on a map along with all the other aircraft.
What you are talking about here is already implemented in ADS-B which is currently being fielded in the US. ADS-B stands for automatic dependent surveillance - broadcast. It is dependent in the sense that the aircraft tells you where it thinks it is. If the aircraft is mistaken or lying you have a problem, although there are ways of validating a report if heard by multiple ground stations.
> However, it seems they want to do this by use of an upside down but
> otherwise 'GPS like method', i.e., the 'satellites' are fixed to
> mountaintops and the aircraft still moves.
Mathematically it is similar, both using multilateration, determining position from knowing the comparative difference in distance between the unknown position and multiple known points. Multilateration, like radar, is an independent surveillance method. The aircraft position is calculated by means external to the aircraft itself. You know where the aircraft is, even if the aircraft doesn't.
> That being the case, what about a fixed, land-line, connection for every
> mountaintop to a central location that broadcasts the time signal, calibrate
> the system using GPS then rely on the central ground station to keep it
As mentioned by others, that can be difficult to do while maintaining the timing tolerances necessary for accurate position determination.
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