Tomographic techniques applied to laser radar reflective measurements

Methods of tomography are applied to laser radar reflective measurements to study remote imaging of macroscopic objects. Techniques to produce 2-D images from I-D data and 3-D images from 2-D data are described, and examples are shown. The data are the received signals from laser radars, resolved in either I-D (range or Doppler) or 2-D (angle-angle) and taken from many viewing directions. Examples are presented of reconstructed images of laboratory test objec1s obtained with infrared and visible laser radars. Each reconstructed image depicts the object's geometric features. Prospects for future applications are discussed. This article describes the application of to-mographic Image-reconstruction techniques to measurements made with laser radar remote sensors. Tomographic methods are used to reconstruct an image from a set of its projections and have been applied to many fields, e.g., radio astronomy and medical imaging [1,2]. Here we use a well-developed technique of tomography to combine laser radar reflective measurements taken from many viewing directions. The result is an image ofthe illuminated obj ect. We discuss the reconstruction of 2-D images from f-D data and the reconstruction of 3-D images from 2-D '< data. This article reviews work reported in more (''c detail elsewhere [3-5]. As in X-ray absorption CAT scans, the goal of 2-D transmission tomography is to estimate the spatial dependence of the absorption of a penetrating radiation-based on a series of 1-D projections of a slice of an object. Transmission tomography utilizes a line of detectors to resolve the absorption characteristics of the object along an axis perpendicular to the line of sight (LOS) of the detector. The signal from each detector is the integrated absorption along the LOS through the object, so that a line of detectors produces a 1-D absorption projection ofthe object. The absorption at each point in the slice can be estimated from a series of such projections measured in angular increments around the object. In the laser radar measurements discussed here, the object is resolved in either range, Doppler (velocity), or angle. The signal in each resolution cell represents the energy reflected off the corresponding illuminated surface of the object. A series of signals along the resolution coordinate produces a reflective projection ofthe object. The goal of reflective tomography is to estimate object surface features based on a set of reflective projections that are measured in angular incre,ments around the object. While the' two types of measurements-transmission and reflective-are fundamentally …