Target High-resolution Image Research Articles

High-resolution neutron imaging of laser fusion targets using bubble detectors

The results of proof-of-principle neutron imaging experiments using bubble detectors are reported. Bubble detectors, which detect neutrons with a spatial resolution as small as 5 μ, were used to image the neutrons from laser-driven compressed deuterium–tritium target plasmas in OMEGA [Boehly et al., Opt. Commun. 133, 495 (1997)]. The results demonstrate that bubble detectors should revolutionize the design of coded aperture neutron imaging systems. Prospects for imaging target plasmas in the National Ignition Facility [Kilkenny et al., Rev. Sci. Instrum. 66, 288 (1995)] with 5 μ spatial resolution in the target plane appear excellent.

High-resolution ISAR imaging of maneuvering targets by means of the range instantaneous Doppler technique: modeling and performance analysis

Very high resolution inverse synthetic aperture radar (ISAR) imaging of maneuvering targets is a complicated task. In fact, the conventional range Doppler (RD) ISAR technique does not work properly when target motions generate terms higher than the first order in the phase of the received signal relative to each scatterer. This effect typically happens when at least one of these situations occur: (1) very high resolution images are required; (2) the target maneuvers; and (3) the target undergoes significant angular motions (roll, pitch, and yaw). A novel ISAR technique, named range instantaneous Doppler (RID), has been proposed for the reconstruction of very high resolution images of maneuvering targets. In this paper, we analytically show that the RID technique works properly when high-resolution ISAR images are required of maneuvering and/or rolling, pitching, and yawing targets; we also quantify the performance improvement of the RID technique with respect to the RD technique. The problem is tackled from an analytical point of view. First, we define a new model of the ISAR received signal that is valid for maneuvering targets, then we derive and compare the analytical expression of the point spread function (PSF) for the two techniques. Furthermore, we perform a statistical analysis to evaluate the improvement of the RID technique versus the RD technique in terms of spatial resolution. Finally, we prove the effectiveness of the RID technique by simulating the imaging process for two different targets: (1) a ship that undergoes roll, pitch and yaw motions and (2) a fast maneuvering airplane.

A new fast method for the reconstruction of 2-D microwave images of rotating objects

In this paper, the problem of microwave imaging of rotating objects is approached from a digital signal processing point of view. Attention is focused on the reconstruction of the two-dimensional (2-D) image of an object obtained by processing complex samples of the continuous wave (CW) signal return received for different object aspect angles covering a 2pi total variation. The effects of a polar sampling of the Fourier transform (FT) of the target reflectivity function on the impulse response of the imaging system are analyzed. A criterion for the choice of the angular sampling interval in order to control the image blurring is given. Finally, a new and fast digital signal processing method for image reconstruction is proposed. This method reconstructs high resolution images of rotating targets illuminated by a CW electromagnetic signal or by a large bandwidth transmitted signal. This algorithm is suitable for processing wideband received signal of targets observed for a large variation of the viewing angle, so it is very attractive for the reconstruction of very high spatial resolution target images in SAR/ISAR systems. To show the performance of the method we finally present and discuss the results obtained by applying the proposed technique on simulated and experimental data.

Multipath effects on ISAR image reconstruction

The effects of specular multipath on the reconstruction of high resolution target image provided by an inverse synthetic aperture radar (ISAR) are investigated. First, a model of the received signal that takes into account the reflections produced by the surface of the Earth is defined, Then, the impulse response of the imaging system used to reconstruct the reflectivity function of the target is evaluated. Finally, the theoretical analysis is validated by some simulation results relative to different motion conditions.

Superresolution of near or far field coherent targets using aperiodic antenna arrays

A technique for obtaining high resolution images of point-like coherent targets using aperiodic antenna arrays is developed. Whereas existing superresolution techniques can be used to image coherent targets located only in the far field of periodic receiving arrays, this technique can be used to obtain high resolution images of targets in the near field also. The key to this technique is the use of multiple transmitters. Completely correlated (coherent) targets are decorrelated by transmitting sequentially from different locations, thereby enabling the use of modern superresolution techniques to estimate the target locations. An expression for estimating the variance of the target locations is derived, and is verified by empirical methods. For the same amount of transmitted power and the same number of receivers, this variance is shown to be an order of magnitude smaller than that of existing superresolution techniques. The practicality of this technique is demonstrated with experimental microwave data.