November 29, 2012

Christian Doppler - Birthday November 29, 1803

Today, we remember the mathematician and physicist Christian Doppler who was born on this day November 29, 1803.  Doppler proposed that the observed frequency of a wave depends on the relative speed of the source and the observer.  The Doppler effect occurring with sound waves was verified in 1845 by Buys Ballot.

Christian Doppler

Amateur radio operators encounter the Doppler effect (or Doppler shift) when working with satellite transmissions.  Satellites travel at very high speeds relative to a terrestrial observer -   The Doppler shift is particularly pronounced at the higher VHF and UHF bands.  The Doppler shift in satellite communications is also a function of the flight path.  An approaching satellite is shift higher in frequency.  As the satellite passes directly over the observer the frequency shift is zero.  Then as the satellite moves away from the observer the frequency shifts lower.