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| From: | gisela.noci |
| Subject: | RE: [Paparazzi-devel] RE: distance measurement for landing. |
| Date: | Thu, 12 Nov 2009 19:39:25 +0200 |
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The radalt link is in fact NOT UWB; it is
a conventional radalt, at microwave frequency, and works by varying the frequency
of the transmitted pulse, and then looking at the difference in frequency of
the transmitted pulse and the received pulse. The phase shift is in essence
measured and the range calculated. This is the classic Doppler effect. Also,
the implementation is by its very nature large, heavy and power hungry, maybe
10watts at least. UWB is the transmission of a single, very
fast ( less than 1 nanosecond) pulse, and then detecting is reflected return an
measuring the time it took to go and come back; exactly the same as ultrasound
ranging, except the transmission is at ‘light speed’ . If you have good
oscilloscope and are an electronics hobbiest, you can put together a simple
demonstrator; however, to do autoland with one requires it to be far more
accurate, etc. Regarding the webcam solution, fine for
very short range (1 or 2 meters), will not work in bright light ( CCD will
saturate) and suffers the same problem as the ultrasound; poor reflectivity of
the signal from the ground surface. ‘Real’ laser rangfinders use a high energy
pulse of laser light, in the order of 10s of watts, sometimes even 100s of
watts, for very short periods, also in the nanosecond or sub-nanosecond range.
The rest is the same as for UWB, it is simply a time of flight measurement of
the pulse to reach and reflect of a target, back to the source. High energy is
needed because of poor ground reflectivity….As I said some mails ago, no magic
bullet here..Yet….. Joe From:
address@hidden
[mailto:address@hidden On Behalf Of Sergey Lukin Hi guys, |
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