Improved imaging approach exploiting early diffractively scattered component of short high frequency pulses propagating through dilute random media with large scatterers

Summary form only given. We consider an approach to imaging involving range measurement with short signals propagating through dilute random discrete-scatterer media with scatterer sizes larger than the wavelength of the incident pulse, such as typical atmospheric clouds in the optical region or rain in the millimeter-wave domain. We demonstrate, through numerical simulations employing the radiative-transfer equation (as well as in terms of simple analytic model describing small angle diffractive scattering component of the propagating pulse), that intensity of a pulse, in addition to a “ballistic” (coherent) contribution and to a long late-time diffusive tail, exhibits also a characteristic sharply rising early-time signal. This early-time component can be attributed to the small-angle diffractive part of the scattering cross-section on medium particles. Correspondingly, it decays with the distance significantly more slowly than the coherent (ballistic) contribution: its attenuation rate is proportional to the large-angle, non-diffractive cross-section, rather than the total cross-section. The sharply rising leading edge of the signal is due to the same physical mechanism of diffractive scattering. We propose to take advantage of the small rise time of the early-time part of the pulse, extract it by means of high-pass filtering, and use as a short signal, providing a high range resolution - typically of the order of several centimeters. We also discuss a possible utilization of longer chirped signals, instead of short pulses. In this case it should be possible to attain by measuring and processing the mutual coherence function for two different observation times (or frequencies), rather than only the field intensity.