Could you use the regularity of the window spacing on the train =20
carriages to measure speed by detecting variations in reflected light?

Send a modulated beam across the tracks at the right height and =20
analyse what gets reflected back.

Cheers,
           Robin.


On 27 Oct 2010, at 09:10, "alan.b.pearce@stfc.ac.uk" <alan.b.pearce@stfc.ac=
..uk=20
 > wrote:

>> Camera will be problematic, sub tunnel is dusty and moist,
>
> If it is anything like the London underground, can you measure the =20
> speed
> of the pressure wave of an approaching train?
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>
> --=20
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