alexi_drago
Graduate Poster
- Joined
- Oct 2, 2006
- Messages
- 1,353
I did raise the possibility of a rapid change in the distance between the aircraft and the ground producing a Doppler effect that may affect the radio altimeter in my questions to Dennis Cimino. I suspect that the tracking capability specified for the radio altimeter is that rate of change rather that the speed of the aircraft, but I don't know enough about how radio altimeters work.
You could be right there Warren, it doesn't make sense to me that the tracking capability would be affected by the speed of the aircraft and from the quote below it seems that the tracking capability could be affected by rapid changes in altitude AGL.
Frequency Modulated Continuous Wave (FMCW) Radar
It is also possible to use a CW radar system to measure range instead of range rate by frequency modulation, the systematic variation of the transmitted frequency. What this does in effect is to put a unique "time stamp" on the transmitted wave at every instant. By measuring the frequency of the return signal, the time delay between
transmission and reception can be measure and therefore the range determined as before. Of course, the amount of frequency modulation must be significantly greater than the expected Doppler shift or the results will be affected.
http://www.fas.org/man/dod-101/navy/docs/es310/cwradar/cwradar.htm

None of his sycophants bothered to tell him that the aircraft would also hit the mountain if the Tracking Capability were based on forward speed (according to his interpretation), even at 250 KIAS. DUH!