Ultrasonically determining flow parameters of a fluid (12) flowing through a passage (14), using far-
field analysis. Includes: (a) acquiring near-field amplitude and
phase change values of
ultrasound waves transmitted (30) into, propagating through, and scattered (32) by, the flowing fluid; (b) determining far-field scattering
amplitude distribution, A(θ, Δf), as two-dimensional function of scattering angle, θ, and
Doppler frequency shift, Δf, from the acquired near-field amplitude and
phase change values; and (c) determining flow parameters (
peak velocity, velocity distribution, flow rate) of the flowing fluid, from the scattering
amplitude distribution. Implementable using ‘clamp-on’ techniques including
ultrasound wave
transmitter and
ultrasound wave
detector array, clamped on, in an oppositely facing configuration, to the passage, for transmitting and detecting ultrasound
waves propagating perpendicular to net flow direction of the flowing fluid. Applicable to different fluids (liquid or / and gas) flowing through different passages (channels, conduits, or ducts) of different types and sizes of processes.