[time-nuts] Alternative to GPS?
jimlux at earthlink.net
Wed Oct 6 16:39:18 UTC 2010
Arthur Dent wrote:
> Jim-“You could look at the data from things like OTH-B
> radar (Over the Horizon-Backscatter) to get a feel for this.”
> Zoom in on N45° 10.300 W069° 51.600 on GoogleEarth.
> I’ve driven to this area on some of the dirt roads that run
> through this area. As I understand it, this project isn’t dead,
> just dormant. I’d hate to have to pay their electric bill!
Ah yes.. the big transmitter in Maine:
There are things other than wind that cause disruptions in surface wave
patterns that are detectable by looking at scattered signals. And some
of those things are of strategic interest, so I suspect that research
Orbiting sensors like QuikScat and similar scatterometers filled the
"get winds over the open ocean" role quite nicely. QS sort of failed
last year (the antenna doesn't spin), but there is a European orbiting
scatterometer that provides similar data.
And, there is work on using scattered GPS signals (e.g. if you fly a
receiver, you can make a form of bistatic radar)
There's also a company, in Australia, as I recall, that makes a bistatic
OTH HF radar for surveillance near a coast (but still over the horizon).
That one is much smaller, both physically, and cost-wise, and makes
use of modern signal processing, too.
The performance specs of this latter is what I was really thinking
about, because they're presumably claiming to locate targets with
precisions at km resolution or finer, which is still a pretty big time
uncertainty 1000m=3us, but, at least there's a fair amount of (open)
literature on how to drive the uncertainty down using HF.
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