Tomographic Image Reconstruction From Laser Radar Reflective Projections

Abstract

Image reconstruction from projections has been extensively developed in the medical field. For example, Computer Assisted Tomography (CAT) scanners measures the absorption of X-rays along ray-projections through a slice of a body. Applying reconstruction algorithms to these projection measurements leads to two or three-dimensional distribution of the mass density. We have applied similar methods which demonstrate image reconstruction from reflective projections obtained with laser radars. These baseband SAR techniques can be applied to any N-dimensional measurements resulting in reconstructions of N 1-dimensional images. For example, two-dimensional range-Doppler or angle-angle images taken from several views can be reconstructed into three-dimensional images. Shown in this paper, two-dimensional images have been reconstructed from one-dimensional range-time-intensity (RTI) data, Doppler-time-intensity (DTI) data, or a combination of both types of laser radar measurements. Typical RTI measurements can be obtained with either coherent linear FM waveforms, or with incoherent short pulse waveforms. In the DTI case, a cw waveform is sufficient and leads to true narrow-band imaging. We have applied these methods to both computer simulated data and field measurements, at both 10.6 μm and 0.53 μm wavelenghts, using various test targets.