When an object appears towards the radar sensor or goes away from the radar sensor, there is a change in the phase shift of the frequency and from that, the velocity can be inferred.

So, I have two questions.

  1. Is it also possible to find out the velocity "vector" ( ie which direction the object is moving to and not just the magnitude of the velocity of the object )

  2. If the object is neither moving towards the sensor nor away from the sensor ( moving tagentially ) , will there be still a phase shift on the radiated pulse?


1 Answer 1


The answer to your first question is yes if you can resolve the change in bearing or azimuth as well as range in a sequence of measurements, and some variation of a Kalman Filter is used.

The answer to your second question is a lot more interesting because Special Relativity predicts a tangential Doppler shift. One common scenario used in presenting Special Relativity to students, involves two rocket ships flying at different near light speed velocities comparing their clocks.

This may interest you.

H. W. Thim, "Absence of the relativistic transverse Doppler shift at microwave frequencies," in IEEE Transactions on Instrumentation and Measurement, vol. 52, no. 5, pp. 1660-1664, Oct. 2003. doi: 10.1109/TIM.2003.817916 Abstract: An experiment is described showing that a 33-GHz microwave signal received by rotating antennas is not exhibiting the frequency shift ("transverse Doppler effect") predicted by the relativistic Doppler formula. The sensitivity of the apparatus used has been tested to be sufficient for detecting frequency shifts as small as 10-3 Hz which corresponds to the value of (v/c)2 = 5.10-14 used in the transverse Doppler shift experiment reported here. From the observed absence of the transverse Doppler shift it is concluded that either the time dilation predicted by the standard theory of special relativity does not exist in reality or, if it does, is a phenomenon which does not depend on relative velocities but may be a function of absolute velocities in the fundamental frame of the isotropic microwave background radiation. keywords: {Doppler shift;microwave antennas;microwave measurement;33 GHz;absolute velocities;isotropic microwave background radiation;microwave frequencies;relativistic transverse Doppler shift;rotating antennas;time dilation;Doppler effect;Doppler shift;Masers;Microwave antennas;Microwave frequencies;Microwave measurements;Microwave theory and techniques;Receiving antennas;Testing;Transmitting antennas}, URL: http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1240186&isnumber=27804

  • $\begingroup$ So, the radar sensors not only supplies the range ( through the time of flight ), but also the velocity mangitude ( using frequency shift ). Is my understanding correct? To the answer to my second question, actually, the paper quotes a very small resolution. I was more interested in real world applications such as aircrafts, automotive etc. Do you think, object velocity cannot be found because of this transverse doppler effect? $\endgroup$ Jan 31, 2018 at 15:17
  • $\begingroup$ @infoclogged I don't know of any radar that can resolve a tangential component of velocity. The velocity comes from changes in azimuth and range, and sometimes Doppler range rate. There is a possibility of estimating an objects spin. My reading of the paper is that there was a careful effort to measure tangential velocity but couldn't find it. Special Relativity does predict an effect. Why it wasn't resolved is beyond my expertise. I mostly work in SONAR and there, classical Doppler comes from range rate alone. A Police Speed radar just works from the normal component Doppler. $\endgroup$
    – user28715
    Jan 31, 2018 at 17:10
  • $\begingroup$ this explains all - radartutorial.eu/11.coherent/Radial%20Speed.en.html $\endgroup$ Apr 10, 2018 at 13:20

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