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The normal Radon transform as well as the circular Radon transform are reviewed in this work. Traditionally, the first is linked to computerized tomography and the second is linked to synthetic aperture techniques that are well-established in both, radar, and ultrasound imaging systems. A new method that adapts the ordinary algebraic reconstruction methods to numerically reconstruct an image from its circular Radon transform is presented. To this end, a representation of an image using the unit box functions is employed, this representation facilitates the formation of an exact matrix of coefficients for a linear system to be solved. Regularized least square is used to solve the relatively small systems, and a machine learning approach is used for large systems. Several experiments are conducted for validation of the built system as well the reconstruction of images from their circular Radon transform. [ABSTRACT FROM AUTHOR]

Synthetic aperture radar (SAR) imaging though the Earth ionosphere is subject to distortions due to ionospheric turbulence. We consider the limiting cases of small-scale and large-scale turbulence and characterize the distortions in terms of image blurring and azimuthal shift. It is shown that in the large-scale case, a high level of eikonal fluctuations can coexist with the low degree of image distortions, and that blurring becomes significant at much higher levels of fluctuations than the shift. In the smallscale case, a low level of eikonal fluctuations is a precondition for imaging, while the magnitude of distortions depends on the ratio between the eikonal correlation radius and the length of the synthetic aperture. [ABSTRACT FROM AUTHOR]

This paper presents a technique for improving the internal imaging of a solid object immersed in water using an ultrasonic array. This technique consists in determining the position and shape of a convex object surface using a combination of synthetic transmit aperture (STA) and sign coherence factor (SCF) methods. The SCF attenuates the grating lobe noise. The technique is applied to a cylindrical aluminium object with internal holes simulating defects. The first step is the acquisition of a sequence of STA images with SCF, using a distinct group of adjacent array elements for each image. In the second step, a circle is fitted to the positions of the peak values in each image. Finally, using the Fermat's principle and this circle as the interface between the water and the metallic object, the propagation delays from the array elements to the image grid points may be calculated and used in another STA image. In this final image, the small holes in the cylindrical object can clearly be identified. The effects of the SCF for a large diameter circular reflector are simulated and compared with experimental data. [ABSTRACT FROM AUTHOR]

In this work, signal processing techniques are used to improve the quality of image based on multi-element synthetic aperture techniques. Using several apodization functions to obtain different side lobes distribution, a polarity function and a threshold criterium are used to develop an image compounding technique. The spatial diversity is increased using an additional array, which generates complementary information about the defects, improving the results of the proposed algorithm and producing high resolution and contrast images. The inspection of isotropic plate-like structures using linear arrays and Lamb waves is presented. Experimental results are shown for a 1-mm-thick isotropic aluminum plate with artificial defects using linear arrays formed by 30 piezoelectric elements, with the low dispersion symmetric mode S0 at the frequency of 330 kHz. [ABSTRACT FROM AUTHOR]