FFT-based cross-covariance processing of optical signals for speed and length measurement

The National Optics Institute has developed an optical velocimeter composed of two parallel laser beams for measuring perpendicularly the speed and the length of vehicles. The system must be capable of measuring speeds varying from 0 to 150 km/h in both directions with an accuracy of 1%. This paper focuses on the algorithms and signal processing aspects of the system. The speed is measured by estimating the time delay using an FFT-based cross-covariance method between the signals generated by the optical velocimeter. The length is estimated using the speed and the time window corresponding to the entire vehicle. The measurement algorithm has been implemented to run in real time on a C31 DSP and a 486 processor.