Bandpass filtering of moving-object laser heterodyne-signals by finite apertures.

Expressions for the frequency power spectral density and power spectral density SNR of a heterodyne detection system are derived assuming the signal radiation field results from a laser illuminated, moving rough object. The calculated spectral density is attenuated at large spectral spread frequencies (resulting from target rotation) by averaging of the high spatial frequency speckle pattern by the finite extent (aperture) of the local oscillator field. Optimum signal detection is obtained only at the Doppler shifted frequency. Spatial anisotropy of the radiation field mutual coherence function precludes exact calculations for arbitrary local oscillator field distributions.

Cross-polarized target signature measurements.

Cross-polarized laser scattering cross sections were measured for twenty-four different paint samples as a function of scattering angle at four visible krypton laser frequencies. The relative magnitudes of the measured cross sections at the four frequencies were used to define a multispectral signature vector for each paint sample. Measured data confirmed the theoretical prediction that the direction of the cross-polarized multispectral signature vector is independent of the scattering geometry.