Ultra wide band radar holographic imaging of subsurface targets.

摘要

This report discusses ultra wide band (i.e., 60 ps impulse) radar holography which is a unique technique for imaging subsurface targets with extremely high lateral and depth resolution. The large frequency bandwidth, typically 100%, provides excellent depth resolution and the synthetic aperture optimum lateral resolution of one-half wavelength at the center pulse frequency. Radar impulse holography can simply be described as a multi-frequency detection and imaging technique where the target's broadband time waveform signals are recorded over a defined aperture; decomposed into their discrete frequency components as single frequency holograms, and reconstructed into a composite image. Computer generated holograms are constructed for each frequency component in the 3-dB pulse bandwidth and plane wave angular spectrums computed to provide unique detection analysis with respect to target identification, etc. The hologram at each frequency component in the pulse can be thought of as a diffraction lens for each reflecting point on the target. A complex target consists, of a multitude of points, and the recorded hologram becomes the superposition of these individual diffraction lens. It is a unique diffraction pattern capable of defining the target's image and scattering characteristics in the near- and far-field.