On the signal-to-noise ratio enhancement of the Doppler process

The output signal-to-noise ratio (SNR) of the ultrasound Doppler process, with and without the commonly used sample and hold circuit, is calculated rigorously, and confirmed by experiment. On the basis of this result it is shown that the use of pulsed Doppler processing without increase of the transmitted power enhances the output SNR of a pulse-echo system observing moving particles by the factor f_rT_t, where f_r is the repetition rate of the pulse echo and Doppler systems and T_t is the transit time of the particles across the range cell. If nonlinear losses are significant, then changing to continuous Doppler operation and lowering the peak transmitted power to maintain the average power constant can produce additional improvement in SNR due to reduced non-linear losses in the transducer and the propagation medium, as well as reduced requirements for transducer damping.