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5 September 2000 Signal tracking technique for laser radar sensors
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This paper describes a signal processing technique that has been developed for a vibration-sensing laser radar. The sensor has successfully acquired data from moving objects. Vibrations on the surface of the object can be induced by internal machinery and, when stationary, would normally be seen as modulations about a fixed carrier frequency. Thus a straightforward demodulation technique can be used to identify any important vibration characteristics. However, for a moving object, the laser transmit frequency is Doppler-shifted upon reflection by an amount proportional to the object's velocity resolved along the line-of-sight of the sensor. Therefore, the carrier frequency of the return signal is not known and the range of frequencies that it could occupy is large in comparison to the bandwidth of the modulations. The algorithm locates the carrier frequency within some large range (typically tens of Megahertz) and generates a synthetic mixing signal that allows the carrier to be down-shifted to baseband. Tracking is performed using a series of Kalman filters on all likely signal candidates and the synthetic mixing signal is made up of the set that scores highly in terms of carrier-to- noise ratio, for example. Following the mix, the resultant signal is decimated so that modulations corresponding to the surface vibration can be studied. This paper illustrates the signal tracking technique applied to a number of real data sets and discusses the benefits of using a predictive method.
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Harvey Lewis, Brendan Ruck, Mark Bernhardt, Paul H. Evans, Peter N. Randall, and Meryl Welch "Signal tracking technique for laser radar sensors", Proc. SPIE 4035, Laser Radar Technology and Applications V, (5 September 2000);

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