THE FEASIBILITY OF DETECTING SHOCK WAVES BY PULSE DOPPLER RADAR

Classical geometric optics estimates of the echo characteristics from both isotropic and directed acoustic shocks are presented together with the detection capability of a typical sensitive pulse Doppler radar (AFCRL Porcupine Doppler) in order to determine the feasibility of detecting large well defined boundaries of refractive index. Both the radar cross-section and the Doppler spectrum of an acoustic shock are sensitive to wind and temperature induced perturbations of the shock surface. For standard deviations in wind and temperature of 0.5 m/sec and 1C, the theoretical values of the maximum radar cross-section and minimum Doppler spectral width of a typical directed shock of 50 meters radius are found to be 0.0008 sq cm and 58 cps respectively. This target cross-section is about 6 dB stronger than the minimum cross-section detectable by the Porcupine radar at a range of only 1.8 kilometers. At this range, the presence of a weak signal may be completely masked by the presence of strong ground clutter signals. Signal processing techniques which improve the mean square to noise ratio and provide sub-clutter visibility are therefore crucial to the success of the experiment. Moreover, the sensitivity of the radar cross-section and the Doppler spectrum to wind and temperature perturbations restricts the experiments to calm conditions. (Author)