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This article deals with the large problem of interferometric synthetic aperture. Our analysis begins with the study of transverse distance influence and the orientation of the interferometric baseline. The processing of elevation problem solving relative to the horizontal resolution of conventional synthetic aperture radar has been carried out, including its ambiguity to choose the optimum parameters of the interferometer and thus improve the surface topography. We found out indeed that when we take a picture of the earth's surface at an angle of inclination of the baseline α = π / 4, the best results are obtained. Copyright © 2016 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Sparse antenna arrays with irregularly spaced elements are increasingly being used in large array applications such as radio astronomy and radar. These antenna arrays may consist of hundreds of elements and therefore optimisation of these arrays becomes computationally expensive. This study proposes a novel solution to the problem of null synthesis in such arrays, where nulls are formed in prescribed locations for two-dimensional irregular sparse antenna arrays. The technique is based on a subarray and hybrid synthesis solution, where each subarray spans the entire antenna aperture. Single and multiple null formations with array gain maximisation are considered. The technique's effectiveness is demonstrated using evolutionary optimisation algorithms; however, the basic technique can be used with other optimisation methods. The simulation results presented compare the null synthesis performance with and without subarraying and it has shown that the use of subarray results in improved convergence compared with a direct full array synthesis. Furthermore the technique is appropriate for ready application to parallel computer architectures. [ABSTRACT FROM AUTHOR]

Summary In this short review, we present a self-contained discussion of the image formation properties of the fluorescent confocal microscope. The optical sectioning or depth discrimination property is discussed in detail and new analytic formulae are presented, which relate the optical sectioning strength to the wavelength, numerical aperture and pinhole aperture size in a particularly simple fashion. [ABSTRACT FROM AUTHOR]

Water resources are limited in many areas of the North Slope, Alaska, particularly during winter. Water is used by the oil industry for ice road construction and maintenance, drilling and facility operations, and potable water supplies. The coastal plain between Teshekpuk Lake, in the National Petroleum Reserve-Alaska (NPR-A) and the Colville River has numerous shallow lakes, but further south in the northern foothills of the Brooks Range, and east to the Canning River, lakes are fewer. While many oil and gas lease sales have been conducted, or are proposed, access to the leases may be limited because of the lack of available water for ice road construction. Ice roads are the main means by which exploration is conducted in the Arctic, putting a stress on freshwater bodies that do not freeze to the lakebed in winter. Lakes that do not freeze to the lakebed also serve as overwintering habitat for fish. The purpose of this paper is to report on the potential distribution of water bodies that may provide overwinter water in selected areas from Teshekpuk Lake to the Canning River. The project used synthetic aperture radar (SAR) imagery to search for the presence of water in lakes in March 2006. In the Kuparuk and Canning SAR images, 52 and 61% of lakes were frozen to their beds by March 2006, accounting for 49 and 57% of the lake area in these study regions. Conversely, only 2% of the lakes in the Teshekpuk region were frozen to the bottom by March 2006. Unfrozen water was more available because of deeper and more numerous lakes in the Teshekpuk Lake region (west) than in the Canning River area (east). While only specific SAR tiles were analyzed herein, the method will be a useful tool for land managers who seek to evaluate the potential for ice road construction across the Arctic. [ABSTRACT FROM AUTHOR]

Computed tomography scout view is a mode of operating a CT system. It is generally used to prescribe CT slices and to display slice locations rather than for direct diagnosis. However, we found that a careful study of CT scout view can contribute significantly to the diagnosis. We show seven abdominal, two chest and two head CT, where the study of CT scout view allowed diagnoses to be made that were not readily apparent from the axial slices. [ABSTRACT FROM AUTHOR]

This paper presents an attempt to explore the generation of digital elevation models (DEMs) by radargrammetry from same-side ERS-1/2 synthetic aperture radar (SAR) images. Two ERS-1 and two ERS-2 C-band (wavelength 5·6 cm) SAR images along parallel descending orbits, acquired in 1996 and 1997, are used to form four stereopairs. The test area is western Hong Kong which is dominated by mountains/hills that are largely covered by evergreen-broadleaf trees. The stereopairs covering the same area but with different time intervals (varying from 16 days to 1·5 years) have an intersection angle of 4·5° and a relatively small overlap of 30% (30 km). In addition to the effect of topography, the effect of temporal correlation on the accuracy of the resulting DEMs is also analysed for the first time. From the experimental results obtained in this study, the following conclusions may be drawn: (a) with same-side ERS-1/2 SAR images, an accuracy of 30 to 35 m is achievable; (b) the accuracy of a resulting DEM degrades almost linearly with an increase in slope when the terrain slope is below 30°, and in the areas with slope over 30°, the accuracy of the DEM is significantly degraded and even becomes unacceptable; (c) the worst accuracy is obtained in the foreslope directions and the best accuracy is obtained in the backslope directions; (d) the time interval between two SAR images has no significant effect on the accuracy of the DEM in general; (e) the time interval between two SAR images has no significant effect on the reliability of image matching. [ABSTRACT FROM AUTHOR]

We propose a new quantization method for received synthetic aperture radar (SAR) signals and a quantizer design technique. This method divides the received signal into bandlimited signals by using orthogonal wavelet transforms and quantizes each bandlimited signal by a different quantizer. Employing this method, not only is there a reduction in the computational load for image reconstruction by the SAR fast approximate reconstruction proposed previously by the authors, but the accuracy of the reconstructed image is substantially improved when there are few quantization bits of the received signal, particularly in image reconstruction by the correlation method. In this paper, we design a quantizer for bandlimited signals and demonstrate the effectiveness of the proposed method by computer simulations of image reconstruction. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 1, 87(9): 54–63, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecja.10182 [ABSTRACT FROM AUTHOR]

This article considers Synthetic Aperture Radar and other synthetic-aperture imaging systems in which a backscattered wave is measured from a variety of locations. We focus on the case in which the ground-reflectivity function depends on frequency as well as on position. We begin with a (linearized) mathematical model, based on a scalar approximation to Maxwell's equations, which includes the effects of the source waveform and the antenna beam pattern. The model can also accommodate other effects such as antenna steering and motion. For this mathematical model, we use the tools of microlocal analysis to develop and analyze a three-dimensional inversion algorithm that uses measurements made on a surface and determines the frequency-dependent ground reflectivity. © 2004 Wiley Periodicals, Inc. Int J Imaging Syst Technol 14, 28–34, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.20004 [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]

The frequency-modulated continuous-wave (FM-CW) radar is suitable for detecting objects placed in the near range compared to the pulse radars. This paper considers the principle of the synthetic aperture technique for the conventional FM-CW radar and presents the fundamental detection results of objects placed in the free space. A laboratory measurement is carried out to detect a metallic plate and a pipe in an anehoic chamber using an explored radar system operative in the microwave X-band. This demonstrates the high resolution detection in azimuth direction in the Fresnel region. It is shown that the radar has a potential ability in imaging objects placed in the near range. [ABSTRACT FROM AUTHOR]

Unwanted electromagnetic waves radiated from equipment making use of electromagnetic energy create numerous societal problems. The prevention of these problems has been studied extensively. In this paper, a method for estimating the location of the unwanted electromagnetic waves is studied. Since it is difficult to make the antenna aperture large especially at low frequencies, a search for electromagnetic wave source via a synthetic aperture technique is proposed. In the estimated electromagnetic source distribution by this method, images similar to the antenna sidelobes appear. It is demonstrated by computer simulation that the images can be suppressed by use of the synthetic aperture method with subarrays or use of Mill's cross method. Discrepancies between the true source location and the estimated location have been found in regard to the synthetic aperture length and the geometrical relationship with respect to the aperture center. It has been found that the antenna configuration with the synthetic aperture length of 10 λ can estimate an electromagnetic wave source within 10 λ square with accuracy of less than 1/4 λ square. Therefore this method is sufficiently practical if the location of the source is restricted somewhat. [ABSTRACT FROM AUTHOR]

Imaging using synthetic aperture techniques is a mature technique with a host of different reconstruction algorithms available. Often the same basic algorithm has a different name depending on where the particular algorithm is used, since it may have originated from the medical, nondestructive testing, geological, or remote sensing fields. All this adds to confusion for the nonspecialist. This article gives a short historical precise of active synthetic aperture imaging as it applies to airborne, spaceborne, and underwater remote sensing systems using either radar or sonar, then defines some generic imaging geometry and places all the usable synthetic aperture reconstruction algorithms in a unified framework. This is done by the introduction of mapping operators, which simplify the mapping or reformatting of data from one sampling grid to another. Using these operators, readers can see how strip-map synthetic aperture systems (both radar- and sonar-based) differ from spotlight synthetic aperture systems, how the various algorithms fit together, and how the chirp-scaling algorithm is likely to be the reconstruction algorithm of choice for most future strip-map systems, and just why that should be so. Multilook processing and methods to deal with undersampled apertures using postdetection digital spotlighting are put into the same unified framework, as both of these techniques are frequent adjuncts to synthetic aperture imaging. © 1997 John Wiley & Sons, Inc. Int J Imaging Syst Technol, 8, 343–358, 1997 [ABSTRACT FROM AUTHOR]

A Fourier-transforming coded aperture can be synthesized with a pair of two-dimensional detector arrays, each preceded by a properly designed sequence of two Gabor-zone plates. The coded image falling on one of the arrays corresponds to the cosine transform of the object. The coded image falling on the other array corresponds to the sine transform. Thus the Fourier transform of the object can be formed by using the first coded image as the real part, and the second coded image as the imaginary part, of the Fourier transform. Fourier-transforming coded apertures of this type are capable of producing better resolution than spatial-domain apertures. Although the system described in this article is specifically applied to a gamma-ray camera, such a system is generally applicable to a wide variety of noncoherent imagers. [ABSTRACT FROM AUTHOR]

This article presents a robust motion estimation and correction technique for the realization of synthetic-aperture side-scan sonar imaging. It utilizes the redundancy provided by the multiple-element receiver array configuration. Physical-array subimages are used for the estimation of the motion errors between adjacent receiver positions. Subsequently, the motion errors are formulated in the form of phase perturbations and are corrected accordingly by making adjustments to the wave-field data samples prior to the formation of synthetic-aperture images. © 2005 Wiley Periodicals, Inc. Int J Imaging Syst Technol, 14, 259–261, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.20029 [ABSTRACT FROM AUTHOR]

High-resolution survey of the inside walls of tubular specimens is a unique application of synthetic-aperture composite imaging. This article describes the data acquisition process, 3D motion estimation and compensation, image registration, and superposition for the formation of high-resolution composite images from conventional video sequences. Experiment results from the survey of an oil well are used to demonstrate the capability of the technique. © 2004 Wiley Periodicals, Inc. Int J Imaging Syst Technol 14, 167–169, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ima.20020 [ABSTRACT FROM AUTHOR]