An optical flow sensor determines the velocity of a moving flow of air or other gas utilizing a plurality of photodetectors spaced apart in a direction parallel to the direction of gas flow. An optical beam is transmitted across the flowing gas and falls upon the photodetectors. Scintillations that occur in the flowing gas due to eddies and particulates in the gas are detected in all of the photodetectors, but at slightly different times due to the longitudinal separation of the photodetectors in the direction of gas flow. The output signals of the photodetectors are conditioned and amplified and transformed to digital form. Temporal cross correlation analysis is then performed on the digitized signals in a digital signal processor. A time differential between signals from the different photodetectors is then calculated electronically. The velocity of gas flow is then determined by dividing the spatial distance of separation between adjacent photodetectors by the time difference at which the same scintillation event is detected by each photodetectors.