The invention is a liquid volume-flow meter suitable for measuring extremely turbulent flow. The meter comprises a measuring chamber formed as a pipe having a wall of transparent material fitted inline with an existing pipe of similar diameter, whereby the detector has minimal effect upon the operation of an existing installation. The meter further comprises an optical velocity array for measuring the speed of liquid flowing within the measuring chamber and an optical area sensor for measuring the area within the measuring chamber occupied by liquid flowing. The optical area sensor comprises a plurality of arrays including a backscatter reflection array to estimate the height of liquid within the measuring chamber and at least one further correction array to correct the estimation made by the reflection array. Each array comprises an optical emitter and an optical detector that operate through the transparent wall of the measuring chamber.

Methods and apparatus for operating an ultrasonic flow meter to accurately estimate the average flow velocity in a pipe when the meter has at least one failed chord and one non-failed chord. The method partitions the velocity range into a number of consecutive, non-overlapping "bins," where separate bins are maintained for each chord and each flow direction. Each bin stores a chord proportion value and, in some embodiments, a chord velocity value. The bins are initialized with pre-selected values and, during normal operation, updated, or trained, based on the measured velocities. When a chord fails, and there is at least one non-failed chord, an estimated proportion value for each non-failed chord is generated using the values stored in the bins. The estimated average flow velocity is then calculated by dividing the summation of the measured flow velocities, from the non-failed chords, by the summation of the estimated proportions.

A method and apparatus for measuring particle motion using electromagnetic radiation uses beams of radiation modulated with a distinct frequency and/or phase. A particle traversing these beams scatters a portion of the radiation. Scattered radiation, which retains its modulation information, is then detected, and a cross-correlation technique is used to quantify the particle's motion, for example, particle velocity.

A method and apparatus for measuring particle motion using electromagnetic radiation uses beams of radiation modulated with a distinct frequency and/or phase. A particle traversing these beams scatters a portion of the radiation. Scattered radiation, which retains modulation information, is then detected, and a cross-correlation technique is used to quantify the particle's motion, for example, particle velocity.