While a regular AquaPro uses a single pulse (incoherent) method to calculate water motion, the AquaPro HR uses the pulse-to-pulse (pulse coherent) method. That means the phase difference covariance between emitted and received signals of two pulses are calculated instead of the frequency shift as in the Doppler method. As with all of our other instruments, the water temperature is used to calculate the speed of sound in water, an important parameter to calculate water velocities. The AquaPro HR also records and reports the amplitude and the attitude sensors to process the data.
In the pulse coherent method, two signals must be sent individually, being the second one sent only after the first one has listened. In the end, the phase difference is a direct measure of radial current velocity, as in:
Where V is the radial speed along the beam, is the phase difference between two backscattered signals, c is the speed of sound, is the transmitted frequency and is the time lag between two consecutive pulses. As it deals with the phase and not the frequency shift, when the phase difference goes beyond the range, it introduces the possibility of phase ambiguity.