<P> Only the radial component of the velocity is relevant . When the reflector is moving at right angle to the radar beam, it has no relative velocity . Vehicles and weather moving parallel to the radar beam produce the maximum Doppler frequency shift . </P> <P> When the transmit frequency (F T (\ displaystyle F_ (T))) is pulsed, using a pulse repeat frequency of F R (\ displaystyle F_ (R)), the resulting frequency spectrum will contain harmonic frequencies above and below F T (\ displaystyle F_ (T)) with a distance of F R (\ displaystyle F_ (R)). As a result, the Doppler measurement is only non-ambiguous if the Doppler frequency shift is less than half of F R (\ displaystyle F_ (R)), called the Nyquist frequency, since the returned frequency otherwise cannot be distinguished from shifting of a harmonic frequency above or below, thus requiring: </P> <Dl> <Dd> F D <F R 2 (\ displaystyle F_ (D) <(\ frac (F_ (R)) (2))) </Dd> </Dl> <Dd> F D <F R 2 (\ displaystyle F_ (D) <(\ frac (F_ (R)) (2))) </Dd>

Where the satellite or aircraft produces or beams a signal towards the object or land