| 摘要 |
A method for estimating the velocity of flow containing a cloud of ultrasound scatterers using time-domain cross-correlation of baseband data. When the scatterers move from one range cell to another between firings, the returning echo signals from adjacent firings will look like time-shifted copies of each other. When the data is basebanded, however, the signals no longer look like time-shifted copies of each other because the baseband process divides the incoming signal into complex quadrature signals. The relative amounts in the real and imaginary parts will be dependent on the relative phase of the incoming signal and the complex mixer, and is therefore range dependent. A scattered signal that may be all real in one firing will have both I and Q components in the next firing when the scatterer has moved by several range cells. This is compensated for by rotating the baseband data for the second firing, prior to cross-correlation, by an angle equivalent to 2 pi times the mixer frequency (of the quadrature demodulator) divided by the sample rate. The correlation lag corresponding to the actual scatterer displacement will be concentrated in the real part of the complex correlation function, and this can be identified using both peak and phase information.
|
