Published online by Cambridge University Press: 18 January 2010
If a radar transmitter and receiver are mounted together in the nose of an aircraft and flown at speed V over flat ground towards a vertical reflector (Fig. 1), then the received signal at the reflector differs in frequency from the transmitted signal by + V/λ (the doppler frequency), where λ is the wavelength of the transmitter. The reflected signal back to the aircraft undergoes a further increase of frequency + V/λ, thus the received signal at the aircraft differs from the transmitted frequency by + 2V/λ. This difference in frequency, referred to as the doppler shift, is proportional to the speed of the aircraft.