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The Doppler effect (also Doppler shift) is the change in the frequency of a wave in relation to an observer who is moving relative to the source of the wave. [ 1 ] [ 2 ] [ 3 ] The Doppler effect is named after the physicist Christian Doppler , who described the phenomenon in 1842.
The magnitude of the shift is a function of the wavelength of the signal and the angular velocity of the antenna: S = r W / λ Where S is the Doppler shift in frequency (Hz), r is the radius of the circle, W is the angular velocity in radians per second, λ is the target wavelength and c is the speed of light in meters per second. [13]
Doppler Effect: Change of wavelength and frequency caused by motion of the source. The formula for radar Doppler shift is the same as that for reflection of light by a moving mirror. [3] There is no need to invoke Albert Einstein's theory of special relativity, because all observations are made in the same frame of reference. [4]
That is, where () is the maximum Doppler spread or, maximum Doppler frequency or, maximum Doppler shift given by = with being the center frequency of the emitter. Coherence time is actually a statistical measure of the time duration over which the channel impulse response is essentially invariant, and quantifies the similarity of the channel ...
A disadvantage of FDOA is that large amounts of data must be moved between observation points or to a central location to do the cross-correlation that is necessary to estimate the doppler shift. The accuracy of the location estimate is related to the bandwidth of the emitter's signal, the signal-to-noise ratio at each observation point, and ...
Doppler shift with source moving at an arbitrary angle with respect to the line between source and receiver. The analysis used in section Relativistic longitudinal Doppler effect can be extended in a straightforward fashion to calculate the Doppler shift for the case where the inertial motions of the source and receiver are at any specified angle.
Three common methods are used to calculate the Doppler shift and thus the water velocity along the acoustic beams. The first method uses a monochromatic transmit pulse and is referred to as "incoherent" or "narrowband". The method is robust and provides good quality mean current profiles but has limited space-time resolution.
Pulse-Doppler processing: Echoes originating from a radiated burst are transformed to the spectral domain using a discrete Fourier transform (DFT). In the spectral domain, stationary clutter can be removed because it has a Doppler frequency shift which is different from the Doppler frequency shift of the moving target.