Abstract: The open channel flow meter of the present invention uses a progressive spectral analyzer to increase the efficiency and accuracy thereof. This is accomplished by using a smaller degree fast Fourier transform covering small sections of the span of the sensor. Additional sections of the span are added to the analysis as required to cover the desired velocity range. This approach also allows one to bypass the processing of velocity spans outside the actual site conditions. This allows circuitry which costs less, uses less power, and achieves more precise readings in a shorter time period.