Joint-Time-Frequency Gaussian-Chirplet Procesing Of Coherent Ladar Returns From Resolved Vibrating Diffuse Surfaces

摘要

Of the standard JTFT's found in the literature, the Born-Jordan JTFT has been shown to be the best for the suppression of local oscillator laser noise while preserving the target signature in CW coherent ladar applications. The JTFT's are superior to spectrogram algorithms but at the cost of additional computation. Processing of the JTFT image (or spectrogram image) maxima at each time point was found to be superior to processing the centroid at each time point. The centroid calculation is biased toward 0 Hz, particularly at low CNR levels. Sinusoidal-FM processing is degraded by the random location of speckle maxima not being near the frequency excursion maxima points where most of the information lies. Linear-FM homodyne (stretch processing) allows a simple summation in time because all the random speckle maxima lie along two frequencies only, resulting in a robust range estimate nearly unaffected by speckle. The Bom-Jordan JTFT tested allows high frequency and temporal resolution of the target spectra. The well resolved time length of the speckle maxima allow an estimate to be made of the target's spectral width, which is due to the spin rate x cross-range dimension in unresolved target scenarios. Given additional information of one of these parameters, the second can be estimated. Resolved target vibration spectra due to piston and higher order mechanical vibration modes can also be efficiently processed for use in autonomous target identification applications. Finally, we note that the technique of Gaussian-chirplet decomposition of a CW coherent ladar's output signal appears to be about as good, with respect to LO noise suppression and signature fidelity, as the Born-Jordan JTFT. This wavelet-like approach is being studied in terms of target feature extraction and target vibration signature construction. The number of numerical operations appears to be less than that of the various JTFT's depending on parameter settings, but is under investigation.