Abstract

Frequently in longwave (microwave and acoustic) imaging situations arise where the object being imaged is located in the proximity of background producing severe clutter. Examples are airborne/spaceborne downlooking radar and downlooking sonar. The aim of this paper is to demonstrate the capability of a high resolution microwave imaging system in discriminating objects of interest against such severe clutter. The approach is based on a spotlight imaging mode in which spectral, angular, and polarization diversities are utilized to access the 3-D Fourier space of a coherently illuminated microwave scene.1 A brief theoretical review of the principle is presented followed by a description of an experimental microwave imaging facility employed in collecting realistic data of a representative situation: that of a low-flying aircraft. The antennas are positioned as if they were spaceborne looking downward to the target and the ground. Only one 2-D slice of the 3-D Fourier space is obtained; hence the reconstructed image is a projective side view. The reconstructed images show clearly the ability of clutter discrimination. The polarization-enhanced microwave images obtained are comparable visually to high contrast photographs of the scene taken with flashlight illumination. Finally, a proposal for further clutter reduction by a spotlight hopping imaging mode is discussed.

© 1985 Optical Society of America