Holographic Doppler Imaging of Rotating Objects

Abstract

The Doppler frequency shift of coherent light reflected from rotating objects is used to obtain one-dimensional resolution much greater than the classical limit for aperture limited imaging systems. The Doppler information is processed by using the temporal and spatial filtering properties of modulated-referencewave holograms. The holographic reconstruction is a superresolved image. Resolution improvements greater than 200 times the classical limit were obtained at good signal-to-noise ratios.

Ultrawideband coherent noise lidar range-Doppler imaging and signal processing by use of spatial-spectral holography in inhomogeneously broadened absorbers

“…Multichannel Doppler filtering is performed in parallel by combining the spectral domain processing with a Doppler compensator afforded by acoustooptic techniques 25 or simply by a piezomirror, which rotates around an axis with constant angular speed, which yields different spatial speeds, resulting in different compensating Doppler frequency at different radius. 26 When a reference light beam illuminates the rotating mirror, different portions of the beam will pick up different Doppler shifts with a linear dependence of velocities on position, resulting in an array of Doppler-compensated reference bins. Since the lidar signal is a random-noise waveform, the range-delayed and Doppler-shifted lidar returns interfere with the array of the compensated Doppler bins, and build up accumulated SSH gratings at the spatial positions, where the Doppler shifts are compensated, but wash out at other locations.…”

“…2. However, other schemes may work as well, such as a tilting mirror 26 or a resonant peizoelectroacoustic modulator array. 35 In this configuration, the two AODs, driven by the same rf chirp, with one device reverse imaged onto the other, and operated in conjugated orders, can produce a modulation of a transmitted beam by an array of Doppler shifts.…”

Waveform design for low frequency tomography

“…The study of tomography (tomo Greek for "a section", "a slice", or "a cutting") as a medical diagnostic tool began in the 1920s and 30s with research being conducted in several locations, culminating (penultimately) with the Computerized Axial Tomograph technique in the early 1960s (Nobel Prize in 1979) and subsequent explosive medical imaging advances. Radio frequency and radar applications began to emerge in the mid 1970s to early 1980s describing angle-Doppler and synthetic aperture processes that produce high resolution images [1][2][3][4][5]. Mensa [6] first describes the image process in the context of tomography followed shortly by extension from monostatic to bistatic geometry [7].…”