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.
The SPIRIT system is a spectrally agile IR imaging airborne camera, with the capability to select any of the multiple filters on a frame by frame basis. The implemented solution employs advanced, but proven, technology to meet the objectives, and achieved good spatial and thermal performance in all modes. Sophisticated electronic design has results in a flexible unit, which can respond to the changing requirements of the user. Initial SPIRIT flight trials were undertaken in summer 1998 with more scheduled to continue through 1999. The sensor was installed on to DERA's TIARA research platform, a modified Tornado F2. The flight trials to date have been conducted over a variety of scenarios, collecting spectral data in up to 12 bands, of other aircraft, tanks, and fixed targets. Further ground- based trials, with the sensor mounted on a pan and tilt tracking platform, have been performed on characterized targets and against further air targets. Data from these initial trials are currently being processed to assess whether sufficient spectral information is available to discriminate between target types at militarily significant ranges. Sample hyperspectral imagery form SPIRIT and some results are presented.
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