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The visibility samples generated by the synthetic aperture interferometric radiometer (SAIR) under near-field observation conditions contain information about the distance from the target to the instrument. This requires a precise understanding of the target–instrument distance to guarantee imaging quality in near-field SAIR applications. In this paper, we introduce a novel distance estimate approach for near-field SAIR systems, which achieves satisfactory imaging performance in the absence of prior information on target–instrument distance. First, we reformulate the signal model of near-field SAIR from the fractional Fourier transform (FRFT) perspective. This formulation ties the distance that is variable to the visibility function in a straightforward manner, offering an efficient solution for image reconstruction in near-field SAIR. Subsequently, we present an iterative strategy for target–instrument distance estimation based on simulated annealing (SA). In each iteration, the modified average gradient (MAG) of images reconstructed within the FRFT framework is evaluated, and based on the Metropolis criterion, the estimated target–instrument distance is optimally updated iteratively. Finally, the validity and effectiveness of the proposed distance estimation method for near-field SAIR imaging systems are demonstrated through numerical simulation and real experiments. [ABSTRACT FROM AUTHOR]

Drew lesson from the synthetic aperture radar, and made the further processing to the fictitious wave-field data, that was correlation and synthesizing processing. Specifically, developed the traditional mode of processing that mainly based on profiles into a new method,in which, several apertures synthesis with the measure point as the center, lapse point-by-point, finally, multiple coverage was adopted. In hopes to improves the signal-to-noise ratio, highlight the abnormal, improves the resolution and increases the exploration depth. Through the processing of theoretical model data, verified the effectiveness of this method. The different theoretical model processing suggests that related to enhanced synthesis of useful signal, to improve the signal to noise ratio, resolution enhancement effect. The feasibility and validity of synthetic aperture of transient electromagnetic imaging numerical calculation was demonstrated. [ABSTRACT FROM AUTHOR]

In the buried-object search technique using a pulsed radar, the estimation method for the buried-pipe location and the underground propagation velocity of the electromagnetic wave by means of a synthetic aperture method has been studied. In general, the electromagnetic wave attenuates as it propagates m the underground and the amplitude of the received signal often becomes extremely small. Therefore, it has been difficult in the signal processing using the amplitude value to recognize several buried objects at different depths by an identical discrimination standard. To resolve this difficulty, a new zero-crossed synthetic aperture method is developed. In the underground cross-sectional image, the waves reflected from a buried pipe form a hyperbolic pattern dependent on the underground propagation velocity of the electromagnetic wave. By evaluating only the edge of this hyperbolic pattern, the underground propagation velocity of the electromagnetic wave and the location of the buried object are estimated. First, to extract the edge, the amplitude value at the time when the observed signal has a ‘0’ amplitude is replaced with ‘1’ if the phase of the original waveform changes from minus to plus whereas with ‘-1’ if it changes from plus to minus. The amplitude at other time points is replaced with ‘0.’ Subsequently, a synthetic aperture process (addition process) is carried out. Since the absolute value of the amplitude is 1 or 0, it is not necessary to consider the effect of the attenuation of the amplitude due to propagation of the electromagnetic wave as a discrimination reference in the estimation of the location of the buried pipe after the addition process. The location of the buried pipe can be detected accurately. [ABSTRACT FROM AUTHOR]