Microwave Imaging

Frequency Modulated Continuous Wave (FMCW) radar systems in the millimeter and sub-millimeter range are technologically mature for many applicative fields such as automotive and aerospace industries for imaging and non destructive testing. This work reports on a new implementation of a guided FMCW radar reflectometry unit for sensing and imaging applications. Only a terahertz dielectric waveguide is used for signal transmission between the transceiver module and the sample, thus drastically simplifying the experimental setup. Compared to continuous wave guided systems, one of the main advantages granted by the use of FMCW radars in combination with waveguides, is the differentiation capability between the reflected signals generated along the wave guide as parasitic signals or at its probing end as sensing information and therefore improving the expected signal-to-noise ratio. This innovative approach is demonstrated by using a dielectric hollowcore waveguide integrated with two different radar transceivers; the high-performance, III-V based 100 GHz SynView unit as a reference system and a compact, low-cost, PCB-Integrated, 122 GHz transceiver developed by Silicon-Radar GmbH. Both 3D electromagnetic simulations and raster scans are performed to investigate quantitatively the propagation behaviors including the coupling capabilities, dynamic range limitations, beam profile and induced artefacts of the guided FMCW reflectometry system. The feasibility of a simplified guided terahertz FMCW reflectometry probing unit is proven. The integration of a solid immersion lens at the end of the waveguide is also demonstrated for imaging resolution improvement.

In this paper, we establish the Hermite-Hadamard inequality for r-convex functions. We prove that r-convexity implies s-convexity (0 ≤ r ≤ s). As a result, we obtain a refinement of the Hermite-Hadamard inequality for an r-convex function (0 ≤ r ≤ 1). We also investigate the Hermite-Hadamard inequality for the product of an r-convex function f and an s-convex function g.

Plasma diagnostics is a topic of great interest in the physics and engineering community because the monitoring of plasma parameters plays a fundamental role in the development and optimization of plasma reactors. Towards this aim, microwave diagnostics, such as reflectometric, interferometric, and polarimetric techniques, can represent effective means. Besides the above, microwave imaging profilometry (MIP) may allow the obtaining of tomographic, i.e., volumetric, information of plasma that could overcome some intrinsic limitations of the standard non-invasive diagnostic approaches. However, pursuing MIP is not an easy task due to plasma’s electromagnetic features, which strongly depend on the working frequency, angle of incidence, polarization, etc., as well as on the need for making diagnostics in both large (meter-sized) and small (centimeter-sized) reactors. Furthermore, these latter represent extremely harsh environments, wherein different systems and equipment need to coexist...

The 1-D single-view multifrequency electromagnetic inverse scattering problem, or inverse profiling, is addressed to provide effective means for plasma diagnostics, taking into account the dispersive properties of such a medium. To this aim, first-order linearized approaches are considered in light of the renewed possibility to conveniently solve the underlying ill-posed problem through the sparse recovery optimization provided by the prominent compressive sensing theory. The intrinsic theoretical limitation of such a problem when tackled by means of the standard minimum energy solution is discussed, and effective approaches based on sparse recovery are proposed and tested against simulated data that deal with reliable benchmarks for microwave imaging in plasma diagnostics.

Microwave tomography has gained an increasing attention as a tool for breast cancer screening, owing to its ability of providing a quantitative estimation of the electromagnetic features of the human tissues. In this respect, the design of the experimental setup is a critical issue, since it may affect the complexity of the involved inverse scattering problem and therefore the reliability of the screening. Aim of this communication is to propose some guidelines to properly set the matching fluid. These are derived with reference to an one dimensional simplified breast model, which does not take into account the high heterogeneity of a real female breast. Hence, a preliminary numerical assessment of their effectiveness against three-dimensional anthropomorphic phantoms is given.

Reconstruction of inhomogeneous dielectric objects from microwave scattering by means of quantitative microwave tomography is a nonlinear, ill-posed inverse problem. In this paper, we employ the Huber function as a robust regularization approach for this challenging problem. The resulting reconstructions both in 2D and 3D from sparse data points for piecewise constant objects are encouraging. The reconstructions of more complex permittivity profiles from breast phantom data indicate potential for use in biomedical imaging.

Reconstructing complex permittivity profiles of dielectric objects from measurements of the microwave scattered field is a non-linear ill posed inverse problem. We analyze the performance of the Huber regularizer in the application, studying the influence of the parameters under different noise levels. Moreover, we evaluate the whole approach on real 3D electromagnetic measurements. Our focus is on reconstructions from relatively few measurements (sparse measurements) to speed up the reconstruction process.

Reconstruction of inhomogeneous dielectric objects from microwave scattering is a nonlinear and ill-posed inverse problem. In this paper, we develop a new class of weakly convex discontinuity adaptive (WCDA) models as a regularization for quantitative microwave tomography. We show that this class includes the Huber regularizer and we show how to combine these methods with electromagnetic solvers operating on the complex permittivity profile. 2D reconstructions of objects from the Institute Fresnel database and experimental data at a single frequency demonstrate the effectiveness of the proposed regularization even when employing far less transmitters and receivers than available in the database.

In this paper, a wideband antenna is proposed for ultra-wideband microwave imaging applications. The antenna is comprised of a tapered slot ground, a rectangular slotted patch and four star-shaped parasitic components. The added slotted patch is shown to be effective in improving the bandwidth and gain. The proposed antenna system provides a realized gain of 6 dBi, an efficiency of around 80% on the radiation bandwidth, and a wide impedance bandwidth (S11 < −10 dB) of 6.3 GHz (from 3.8 to 10.1 GHz). This supports a true wideband operation. Furthermore, the fidelity factor for face-to-face (FtF) direction is 91.6%, and for side by side (SbS) is 91.2%. This proves the excellent directionality and less signal distortion of the designed antenna. These high figures establish the potential use of the proposed antenna for imaging. A heterogeneous breast phantom with dielectric characteristics identical to actual breast tissue with the presence of tumors was constructed for experimental ...

Purpose:To assess the feasibility of a method based on microwave spectrometry to detect structural distortions of metallic stents in open air conditions and envisage the prospects of this approach toward possible medical applicability for the evaluation of implanted stents.Methods:Microwave absorbance spectra between 2.0 and 18.0 GHz were acquired in open air for the characterization of a set of commercial stents using a specifically design setup. Rotating each sample over 360°, 2D absorbance diagrams were generated as a function of frequency and rotation angle. To check our approach for detecting changes in stent length (fracture) and diameter (recoil), two specific tests were performed in open air. Finally, with a few adjustments, this same system provides 2D absorbance diagrams of stents immersed in a water‐based phantom, this time over a bandwidth ranging from 0.2 to 1.8 GHz.Results:The authors show that metallic stents exhibit characteristic resonant frequencies in their microw...

A novel microwave imaging approach for early stage breast cancer detection is described. The proposed technique involves the use of an Indirect Microwave Holographic technique employing a patented synthetic reference wave. This approach offers benefits in terms of simplicity, expense, comfort and safety when compared to current mammography techniques. Experimental results using a simulated breast phantom are included to demonstrate the validity of this technique to obtain 2D images. The technique is then extended to demonstrate the possibility of obtaining 3D images by using indirect stereoscopic holographic imaging.

Climatologies of convective precipitation were derived from passive microwave observations from the Special Sensor Microwave Imager using a scattering-based algorithm of Adler et al. Data were aggregated over periods of 3-5 months using data from 4 to 5 years. Data were also stratified by satellite overpass times (primarily 06 00 and 18 00 local time). Four regions [Mexico, Amazonia, western Africa, and the western equatorial Pacific Ocean (TOGA COARE area)] were chosen for their meteorological interest and relative paucity of conventional observations. The strong diurnal variation over Mexico and the southern United States was the most striking aspect of the climatologies. Pronounced morning maxima occurred offshore, often in concavities in the coastline, the result of the increased convergence caused by the coastline shape. The majorfeature of the evening rain field was a linear-shaped maximum along the western slope of the Sierra Madre Occidental. Topography exerted a strong control on the rainfall in other areas, particularly near the Nicaragua/Honduras border and in Guatemala, where maxima in excess of 700 mm month 1 were located adjacent to local maxima in terrain. The correlation between the estimates and monthly gage data over the southern United States was low (0.45), due mainly to poortemporal sampling in any month and an inadequate sampling of the diurnal cycle. Over the Amazon Basin the differences in morning versus evening rainfall were complex, with an alternating series of morning/evening maxima aligned southwest to northeast from the Andes to the northeast Brazilian coast. Areal extent of rainfall in Amazonia was slightly higher in the evening, but a maximum in morning precipitation was found on the Amazon River just east of Manaus. Precipitation over the water in the ITCZ north of Brazil was more pronounced in the morning, and a pronounced land-/sea-breeze circulation was found along the northeast coast of Brazil. Inter-comparison of four years revealed 1992 to be the driest over Amazonia, with about a 23% decrease in mean rain rate compared to the 4-year mean estimated rain rate. The major rain feature of tropical western Africa was found on the west coast-a pronounced overland evening maximum directly between the coast and a high mountain peak, and a morning maximum directly offshore. An intense, localized morning maximum of over 1000 mm month -1 was found at a concavity in the coast laboratory for Atmospheres,

The imaging capabilities achieved from a groundpenetrating radar (GPR) system based on a contactless differential measurement configuration and from a microwave tomographic approach are investigated. The system is made up of two receiving antennas located at different heights and placed symmetrically with respect to the transmitting antenna. The data, obtained as the difference between the signals measured by the two receivers, are processed by means of a microwave tomographic approach, which is based on a linear model of the electromagnetic scattering and is specifically designed for the differential GPR system. The achievable reconstruction capabilities are theoretically investigated and their dependence on the offset between the receiving antennas is taken into account in order to provide hints about the preferable offset. The theoretical analysis corroborates that, in the case at hand, the reconstructed images are affected by a spatial filtering effect and the retrievable spectral content is reduced by "hyperbolas of zeroes," whose occurrence increases with the spatial offset between the two receiving antennas. The effectiveness of the proposed GPR system and of the theoretical analysis is assessed against both synthetic and experimental data.

In this manuscript, we study about dielectric properties of major tissues in the breast within the UWB allocated frequency band. Some tissues mimicking phantoms have been designed and measured using slub-line tool system. The results obtained show good representation for both normal and malignant breast tissues. The tissues phantoms are made from mixture of common materials which are low cost, non toxic and widely available in our daily life.

Microwave imaging for breast cancer detection has attracted growing global attention with a small number of prototypes advancing to the clinical trial stage. This investigation aims to provide an overview of MammoWave, a novel microwave-based imaging system for breast lesion detection and to assess its introduction into the clinical routine and its potential role in future breast screening programs. As a key focus of this work, we will describe in detail the various aspects of the clinical protocol procedure that has enabled us to perform a successful clinical trial. Obtained preliminary results indicate the ability of our device to distinguish breasts with no radiological finding and those with radiological findings, with a sensitivity of 89.6%.

Microwave tomography is a microwave imaging method in which the resolution is not limited by wavelength, but rather by measurement noise and modelling errors. Inversion algorithm is used for obtaining an image from the measured scattered waves. Performance improvement of the inversion algorithm is introduced by approximately modelled antennas as a point, line or plane source. Such modelling of antennas introduces modelling errors. Antenna array in the unshielded measurement chamber will pick up external interference, as well as backscattering of array's own radiation. Multipath occurring in measurement chamber has a large impact on the measurement performance. The wave propagated through the air and reflected from the chamber walls could mask a weaker wave scattered by the object under imaging. Also, a larger number of the antennas improves inversion and gives a more accurate image. This paper proposes a novel design of enclosed measurement antenna array for microwave tomography. To obtain an accurate and efficient antenna model in 3D FDTD, a square spiral wire antenna is used in this design. A metal shield protects the process of measurement from external interference and backscattering. Between the antenna array and the metal shield an absorption wall is introduced, which decreases multipath and partially prevents signal masking. Square spiral wire antennas are overlapped and packed, giving a larger number of antennas in the same space. Enclosed antenna array is modelled in 3D FDTD. Proposed antenna array is compared with solutions found in literature. Comparison is done using metrics relevant for antenna array measurement in microwave tomography.

Monitoring human pressures is the first step in the management of natural ecosystems, as well as a method to evaluate the effectiveness of the applied conservation measures. In this context, five commercial satellite images (QuickBird bundle, SPOT-5 multispectral, Landsat 7 ETMþ, RADARSAT SAR, and ENVISAT ASAR) with various spatial and spectral characteristics have been assessed for their ability to map mussel farms off a coast of northern Greece, where the intensity and uncontrolled expansion of aquacultures is a pressure to a nearby wetland of international importance. The ability to identify the mussel farms on the images from background open water and accurately map these features was tested separately for the two types of mussel farms (pole and long line) present in the study area. The influence of waves on the mussel farms' identification was also investigated. Results indicate that the optimum satellite sensor varied according to mussel farm type, and is not necessarily the one with the highest spatial resolution. Pole farms were identified in all images bearing a spatial resolution superior to 10 m, but were better located and delineated with a high-resolution QuickBird image. Long line farms, on the other hand, were indistinguishable by passive optical sensors, and could only be identified on active microwave images. In addition to this, the findings show that surface waves drastically deteriorate the identification of mussel farms on an ENVISAT image, thus influencing its usefulness for monitoring.

The capabilities of a cylindrical imaging system used in remote thermal sensing and dielectric constant measurements are investigated. The paper presents simulations of absolute and differential reconstructions of bodies within the Born approximation and of stronger diffracting objects. In addi- tion a preliminary experiment is presented.

The second WetNet Precipitation Intercomparison Project (PIP-2) evaluates the performance of 20 satellite precipitation retrieval algorithms, implemented for application with Special Sensor Microwave/Imager (SSM/I) passive microwave (PMW) measurements and run for a set of rainfall case studies at full resolution-instantaneous space-timescales. The cases are drawn from over the globe during all seasons, for a period of 7 yr, over a 60ЊN-17ЊS latitude range. Ground-based data were used for the intercomparisons, principally based on radar measurements but also including rain gauge measurements. The goals of PIP-2 are 1) to improve performance and accuracy of different SSM/I algorithms at full resolution-instantaneous scales by seeking a better understanding of the relationship between microphysical signatures in the PMW measurements and physical laws employed in the algorithms; 2) to evaluate the pros and cons of individual algorithms and their subsystems in order to seek optimal ''front-end'' combined algorithms; and 3) to demonstrate that PMW algorithms generate acceptable instantaneous rain estimates. It is found that the bias uncertainty of many current PMW algorithms is on the order of Ϯ30%. This level is below that of the radar and rain gauge data specially collected for the study, so that it is not possible to objectively select a best algorithm based on the ground data validation approach. By decomposing the intercomparisons into effects due to rain detection (screening) and effects due to brightness temperature-rain rate conversion, differences among the algorithms are partitioned by rain area and rain intensity. For ocean, the screening differences mainly affect the light rain rates, which do not contribute significantly to area-averaged rain rates. The major sources of differences in mean rain rates between individual algorithms stem from differences in how intense rain rates are calculated and the maximum rain rate allowed by a given algorithm. The general method of solution is not necessarily the determining factor in creating systematic rain-rate differences among groups of algorithms, as we find that the severity of the screen is the dominant factor in producing systematic group differences among land algorithms, while the input channel selection is the dominant factor in producing systematic group differences among ocean algorithms. The significance of these issues are examined through what is called ''fan map'' analysis. The paper concludes with a discussion on the role of intercomparison projects in seeking improvements to algorithms, and a suggestion on why moving beyond the ''ground truth'' validation approach by use of a calibration-quality forward model would be a step forward in seeking objective evaluation of individual algorithm performance and optimal algorithm design.

The application of Special Sensor Microwave/Imager (SSM/I) multiparameter satellite retrievals in operational weather analysis and forecasting is addressed. More accurate multiparameter satellite retrievals are now available from an SSM/I neural network algorithm. It also provides greater areal coverage than some of the initial algorithms. These retrievals (ocean surface wind speed, columnar water vapor, and columnar liquid water), when observed together, provide a meteorologically consistent description of synoptic weather patterns over the oceans. Three SSM/I sensors are currently in orbit, which provide sufficient amounts of data to be used in a real-time operational environment. Several examples are presented to illustrate that important synoptic meteorological features such as fronts, storms, and convective areas can be identified and observed in the SSM/I fields retrieved by the new algorithm. The most recent version of the neural network algorithm retrieves simultaneously four geophysical parameters: ocean-surface wind speed, columnar water vapor, columnar liquid water, and sea surface temperature, allowing the knowledge of each variable to contribute directly to better accuracy in ocean surface wind speed retrievals. The neural network wind speed data were recently incorporated as a part of operational Global Data Assimilation System at the National Centers for Environmental Prediction.

This work presents a systematic evaluation of the effectiveness of an air-operated microwave imaging (MWI) system for the detection of arbitrarily oriented thin fractures in superficial bones, like the tibia. This includes the proposal of a new compact, portable setup where a single Vivaldi antenna performs a semi-cylindrical scan of the limb. The antenna is operated in monostatic radar mode, near the skin but without contact, thus ensuring hygiene and patient comfort during the exam. The image is reconstructed using a wave-migration algorithm in the frequency domain combined with an adaptative algorithm based on singular value decomposition which removes the skin artifact taking into account the non-uniform bone profile and tissue cover. The study investigates the system resolution, the robustness of the method to the uncertainty of the permittivity and thickness of the involved tested tissues, as well as the robustness to involuntary patient movement. The experimental validation was performed for the first time on an integral ex-vivo animal leg, with all tissues present, including skin and fur. It confirmed both the effectiveness of the method, and the feasibility of the setup.

Microwave Imaging (MWI) has been studied to aid early breast cancer detection. Current prototypes in more advanced stages of development include both monostatic or multistatic setups. However, multistatic configurations usually include a high number of antennas which consequently require complex and computationally-intensive signal processing algorithms to ensure a good target detection. We previously presented a novel approach using a dielectric lens which reduces the signal processing burden of multistatic setups, while ensuring good spatial resolution. In this paper, we evaluate this novel setup using an anatomically realistic breast phantom and its capability of selecting targets inside the breast. We show a successful detection of the targets using an artefact removal algorithm based on singular value decomposition when the Bessel beam is centered at the target location.

Tropical forest degradation and/or deforestation are issues raising great concern among conservation scientists the world over. In particular, the rate of destruction of tropical forests, through the large extent of commercial logging has attracted a lot of attention. Moreover, many studies and reports i ndicate that this destruction is still increasing, given the rising demand for agricultural land, and wood products from tropical forests, as a consequence of the rising world population. As tropical forest destruction increases, so does the demand for their sustainable management from sections of people with environmental or conservation concerns. Consequently, at both international and national levels, a number of initiatives have come with suggestions of criteria and i ndicators for sustainable forest management determination. However, most of their propositions are still very broad and rarely find appropriate applicability at the forest management unit level. This study looks at some ecological criteria and indicators developed by one such type of organisation in Indonesia, known as Lembaga Ekolabel Indonesia (LEI). The objective of the study is to demonstrate how remotely sensed data could support sustainable forest management by verifying some ecological criteria and indicators for tropical timber certification.

Measurements of sea ice concentration from the Special Sensor Microwave Imager (SSM/I) using seven different algorithms are compared to ship observations, sea ice divergence estimates from the Radarsat Geophysical Processor System, and ice and water surface type classification of 59 wide-swath synthetic aperture radar (SAR) scenes. The analysis is confined to the high-concentration Arctic sea ice, where the ice cover is near 100%. During winter the results indicate that the variability of the SSM/I concentration estimates is larger than the true variability of ice concentration. Results from a trusted subset of the SAR scenes across the central Arctic allow the separation of the ice concentration uncertainty due to emissivity variations and sensor noise from other error sources during the winter of 2003-2004. Depending on the algorithm, error standard deviations from 2.5 to 5.0% are found with sensor noise between 1.3 and 1.8%. This is in accord with variability estimated from analysis of SSM/I time series. Algorithms, which primarily use 85 GHz information, consistently give the best agreement with both SAR ice concentrations and ship observations. Although the 85 GHz information is more sensitive to atmospheric influences, it was found that the atmospheric contribution is secondary to the influence of the surface emissivity variability. Analysis of the entire SSM/I time series shows that there are significant differences in trend between sea ice extent and area, using different algorithms. This indicates that long-term trends in surface and atmospheric properties, unrelated to sea ice concentration, influence the computed trends.

In this article TLS‐ESPRIT [1] will be used to generate two‐dimensional high‐resolution microwave images. To enable the utilization of the 1D algorithm, a two‐dimensional data matrix is decoupled into two one‐dimensional sequences by forming an enhanced data matrix [2]. Pairing of the two 1D estimates is also addressed. To demonstrate the performance of the 2D algorithm, a microwave image was generated for a target measured in a compact range. © 1995 John Wiley & Sons. Inc.

In the paper, "Investigation of histology region in dielectric measurements of heterogeneous tissues," by Porter and O'Halloran, the authors utilize a flexible phantom in a layered material dielectric property analysis to quantify the effective sensing volume of a coaxial dielectric probe. Ostensibly, this test has been used by others to characterize the region for which percent variation in the material composition in front of the probe corresponds to percent variation in the computed effective dielectric properties. By employing a compressible material, the authors fail to isolate features that are attributable solely to the probe, itself, and inadvertently incorporate confounding characteristics associated with the compressible nature of the material. The net effect is to exaggerate the probe's sensing volume which undermines conclusions drawn from the subsequent tissue dielectric property studies.

In the paper, "Investigation of histology region in dielectric measurements of heterogeneous tissues," by Porter and O'Halloran, the authors utilize a flexible phantom in a layered material dielectric property analysis to quantify the effective sensing volume of a coaxial dielectric probe. Ostensibly, this test has been used by others to characterize the region for which percent variation in the material composition in front of the probe corresponds to percent variation in the computed effective dielectric properties. By employing a compressible material, the authors fail to isolate features that are attributable solely to the probe, itself, and inadvertently incorporate confounding characteristics associated with the compressible nature of the material. The net effect is to exaggerate the probe's sensing volume which undermines conclusions drawn from the subsequent tissue dielectric property studies.

This paper reports the results of an experimental campaign carried out in the Central Italy, considering also part of the Tyrrhenian Sea. Integrated precipitable water vapour estimates obtained from measurements of multiple sensors were produced for a period of about one year, with the purpose of validating the corresponding MERIS estimates. The validation is performed both at specific locations and over an extended area, considering ground based instruments (microwave radiometers, GPS receivers, radiosoundings) and satellite borne radiomenters (Special Sensor Microwave Imager Radiometer, ENVISAT Microwave Radiometer).

Vertical wind shear and storm motion are two of the most important factors contributing to rainfall asymmetries in tropical cyclones (TCs). Global TC rainfall structure, in terms of azimuthal distribution and asymmetries relative to storm motion, has been previously described using the Tropical Rainfall Measuring Mission Microwave Imager rainfall estimates. The mean TC rainfall distribution and the wavenumber-1 asymmetry vary with storm intensity and geographical location among the six oceanic basins. This study uses a similar approach to investigate the relationship between the structure of TC rainfall and the environmental flow by computing the rainfall asymmetry relative to the vertical wind shear. The environmental vertical wind shear is defined as the difference between the mean wind vectors of the 200-and 850-hPa levels over an outer region extending from the radius of 200-800 km around the storm center. The wavenumber-1 maximum rainfall asymmetry is downshear left (right) in the Northern (Southern) Hemisphere. The rainfall asymmetry decreases (increases) with storm intensity (shear strength). The rainfall asymmetry maximum is predominantly downshear left for shear values Ͼ 7.5 m s Ϫ1 . Large asymmetries are usually observed away from the TC centers. As TC intensity increases, the asymmetry maximum shifts upwind to the left. The analysis is further extended to examine the storm motion and the vertical wind shear and their collective effects on TC rainfall asymmetries. It is found that the vertical wind shear is a dominant factor for the rainfall asymmetry when shear is Ͼ5 m s Ϫ1 . The storm motion-relative rainfall asymmetry in the outer rainband region is comparable to that of shear relative when the shear is Ͻ5 m s Ϫ1 , suggesting that TC translation speed becomes an important factor in the low shear environment. The overall TC rainfall asymmetry depends on the juxtaposition and relative magnitude of the storm motion and environmental shear vectors in all oceanic basins.

Microwave imaging systems are currently being investigated for breast cancer, brain stroke and neurodegenerative disease detection due to their low cost, portable and wearable nature. At present, commonly used radar-based algorithms for microwave imaging are based on the delay and sum algorithm. These algorithms use ultra-wideband signals to reconstruct a 2D image of the targeted object or region. Delay multiply and sum is an extended version of the delay and sum algorithm. However, it is computationally expensive and time-consuming. In this paper, the delay multiply and sum algorithm is parallelised using a big data framework. The algorithm uses the Spark MapReduce programming model to improve its efficiency. The most computational part of the algorithm is pixel value calculation, where signals need to be multiplied in pairs and summed. The proposed algorithm broadcasts the input data and executes it in parallel in a distributed manner. The Spark-based parallel algorithm is compare...

This paper investigates the influence of noise on a microwave axial tomograph developed by some of the authors for the inspection of dielectric objects. In particular, the impact of the measurement environment is considered and the images obtained from data measured in a controlled and an uncontrolled environment are presented and compared. Moreover, the effects of interference signals are considered. Accordingly, several experimental results are reported and discussed in terms of proper error parameters.

Quantitative microwave imaging employing an ideal Veselago lens is demonstrated using synthetic 2D experiments. Reconstructions of the complex-valued dielectric constant of an arbitrary objectof-interest are obtained from noiseless data using a non-iterative technique. A closed-form Veselago lens Green's function is utilized in the formulation of the problem. The contrast sources corresponding to a single illumination of the object-of-interest is recovered using total-field measurements at several receiver points located in the lens' focusing region. Collecting the field in the presence of the ideal Veselago lens produces well-conditioned matrices for the discretized inverse source problem. The contrast is then directly obtained by first calculating the total-field within the object. Synthetic examples having features as small as λ/25 show that the resolution is only limited by the signal-to-noise ratio of data. Experiments with noisy data reveals that the inversion procedure directly mirrors the noise in the data. Two new filtering processes are introduced based on the truncated Singular Value Decomposition of the data operator and the domain operator involved in the inversion process. These successfully deal with noisy reconstructions. Results show that using the new filtering methods, even with a single illuminating source, outperforms the least-squares method with several illuminating sources.

Quantitative microwave imaging employing an ideal Veselago lens is demonstrated using synthetic 2D experiments. Reconstructions of the complex-valued dielectric constant of an arbitrary objectof-interest are obtained from noiseless data using a non-iterative technique. A closed-form Veselago lens Green's function is utilized in the formulation of the problem. The contrast sources corresponding to a single illumination of the object-of-interest is recovered using total-field measurements at several receiver points located in the lens' focusing region. Collecting the field in the presence of the ideal Veselago lens produces well-conditioned matrices for the discretized inverse source problem. The contrast is then directly obtained by first calculating the total-field within the object. Synthetic examples having features as small as λ/25 show that the resolution is only limited by the signal-to-noise ratio of data. Experiments with noisy data reveals that the inversion procedure directly mirrors the noise in the data. Two new filtering processes are introduced based on the truncated Singular Value Decomposition of the data operator and the domain operator involved in the inversion process. These successfully deal with noisy reconstructions. Results show that using the new filtering methods, even with a single illuminating source, outperforms the least-squares method with several illuminating sources.

We have developed a general framework for modeling gyrosynchrotron and free-free emission from solar flaring loops and used it to test the premise that 2D maps of source parameters, particularly magnetic field, can be deduced from spatially resolved microwave spectropolarimetry data. In this paper we show quantitative results for a flaring loop with a realistic magnetic geometry, derived from a magnetic field extrapolation, and containing an electron distribution with typical thermal and nonthermal parameters, after folding through the instrumental profile of a realistic interferometric array. We compare the parameters generated from forward fitting a homogeneous source model to each line of sight through the folded image data cube with both the original parameters used in the model and with parameters generated from forward fitting a homogeneous source model to the original (unfolded) image data cube. We find excellent agreement in general, but with systematic effects that can be understood as due to finite resolution in the folded images and the variation of parameters along the line of sight, which are ignored in the homogeneous source model. We discuss the use of such 2D parameter maps within a larger framework of 3D modeling, and the prospects for applying these methods to data from a new generation of multifrequency radio arrays now or soon to be available.

We present detailed 3D modeling of a dense, coronal thick target X-ray flare using the GX Simulator tool, photospheric magnetic measurements, and microwave imaging and spectroscopy data. The developed model offers a remarkable agreement between the synthesized and observed spectra and images in both X-ray and microwave domains, which validates the entire model. The flaring loop parameters are chosen to reproduce the emission measure, temperature, and the nonthermal electron distribution at low energies derived from the X-ray spectral fit, while the remaining parameters, unconstrained by the X-ray data, are selected such as to match the microwave images and total power spectra. The modeling suggests that the accelerated electrons are trapped in the coronal part of the flaring loop, but away from where the magnetic field is minimal, and, thus, demonstrates that the data are clearly inconsistent with electron magnetic trapping in the weak diffusion regime mediated by the Coulomb collisions. Thus, the modeling supports the interpretation of the coronal thick-target sources as sites of electron acceleration in flares and supplies us with a realistic 3D model with physical parameters of the acceleration region and flaring loop.

The main purpose of the MIZEX Bulletin series' is to provide a permanent medium for the interchange of initial results, data summaries, and theoretical ideas relevant to the Marginal Ice Zone Experiment. This se ries will be unrefereed and should not be considered a substitute for more complete and finalized journal articles. Because of the si milarit y of the physics of the marginal ice zone in different regions, contributions relevant to any marginal ice zone are welcome, provided they are relevant to the overall goals of MI ZEX . These overall goals are-discussed in Bulletin I (Wadhams et aI., CRREL Special Report 81-19), which desc ribed the research strategy, and Bulletin II (Johannesen et aI., CRREL Special Report 83-12), which out lined the science plan for the main 1984 summer experiment. Copies of earlier or current bulletins ma y be obtained from the Technical Information Branch, USA CRREL. Persons interested in contributing articles to the bulletin should send copies to one of the editors listed below with figures reproducible in black and whi te. Proofs of the retyped manusc ripts will not be sent to the author unless specifically requested.

This dissertation deals with the radiometric calibration of a satellite microwave radiometer known as the TRMM Microwave Imager (TMI), which operated on NASA's Tropical Rainfall Measuring Mission (TRMM). This multi-frequency, conical-scanning, passive microwave, remote sensor measures the earth's blackbody emissions (brightness temperature, Tb) from a low earth orbit and covers the tropics (±35° latitude). The original scientific objective for TRMM's 3-year mission was to measure the statistics of rainfall in the tropics. However, the mission was quite successful, and TRMM was extended for greater than 17 years to provide a long-term satellite rain measurements, which has contributed significantly to the study of global climate change. A significant part of the extended TRMM mission was the establishment of a constellation of satellite radiometer that provide frequent global rainfall measurements that enable severe storm warnings for operational hazard forecast by the international weather community. TRMM played a key role by serving as the radiometric calibration standard for the TRMM constellation microwave radiometers. The objective of this dissertation is to improve the radiometric calibration of TMI and to provide to NASA a new robust, physics-based algorithm for the legacy data processing of the TRMM brightness temperature data product, which will be called TMI 1B11 V8. Moreover, the results of this new procedure have been validated using the double difference techniques with the Global Precipitation Mission Microwave Imager (GMI), which is the replacement satellite mission to TRMM. iv To my God and my parents, I would be nothing without you. To my children Abdulaziz and Khalid, seeing both of you is encouraging me to success.

Antenna design, electromagnetic dispersion, wave propagation, and other electromagnetic phenomena are some of the many computer-based approaches and techniques that are included in the field of computational electromagnetics (CEM). Within the scope of this research, an overview of the ideas, processes, and applications of computational electromagnetics in the investigation and resolution of difficult electromagnetic problems is provided. The purpose of this research is to investigate the fundamental ideas of electromagnetics and the computer modeling approaches that are linked with them. This is accomplished by combining the literature, theoretical frameworks, and applications from the actual world. The research also investigates the application of computational electromagnetics to antenna design. This is a field in which radiation patterns, impedance matching, and antenna designs can be optimized through the use of numerical simulations. Using parametric studies, electromagnetic modeling tools, and optimization approaches, it discusses how to improve antenna performance, reduce interference, and conform to design criteria. Moreover, it explains how to optimize antenna performance. The ethical implications of this study is to enforce the credibility of this field of study to the developmental aspects of electromagnetics in telecom industry and to reflect its significance into an effective deliberation using different techniques as adapted in this project.

Soil moisture is a key environmental variable in the global water, energy and carbon cycles and in environmental assessment and prediction. It greatly affects a broad range of scientific and operational applications in hydrology, climate studies and agriculture. Soil moisture is also a desired input parameter to Numerical Weather Prediction (NWP) models since it controls the land-atmosphere interaction, such as

The Soil Moisture and Ocean Salinity (SMOS) mission was selected in May 1999 by the European Space Agency to provide global and frequent soil moisture and sea surface salinity maps. SMOS' single payload is Microwave Imaging Radiometer by Aperture Synthesis (MIRAS), an L band two-dimensional aperture synthesis interferometric radiometer with multiangular observation capabilities. Most geophysical parameter retrieval errors studies have assumed the independence of measurements both in time and space so that the standard deviation of the retrieval errors decreases with the inverse of square root of the number of measurements being averaged. This assumption is especially critical in the case of sea surface salinity (SSS), where spatiotemporal averaging is required to achieve the ultimate goal of 0.1 psu error. This work presents a detailed study of the SSS error reduction by spatiotemporal averaging, using the SMOS end-to-end performance simulator (SEPS), including thermal noise, all instrumental error sources, current error correction and image reconstruction algorithms, and correction of atmospheric and sky noises. The most important error sources are the biases that appear in the brightness temperature images. Three different sources of biases have been identified: errors in the noise injection radiometers, Sun contributions to the antenna temperature, and imaging under aliasing conditions. A calibration technique has been devised to correct these biases prior to the SSS retrieval at each satellite overpass. Simulation results show a retrieved salinity error of 0.2 psu in warm open ocean, and up to 0.7 psu at high latitudes and near the coast, where the external calibration method presents more difficulties.

In this study two global observational precipitation products, namely the Global Precipitation Climatology Project's (GPCP) community data set and CPC's Merged Analysis of Precipitation (CMAP), are compared on global to regional scales in the context of the different satellite and gauge data inputs and merger techniques. The average annual global precipitation rates, calculated from data common in regions/times to both GPCP and CMAP, are similar for the two. However, CMAP is larger than GPCP in the tropics because: (1) CMAP values in the tropics are adjusted month-by month to atoll gauge data in the West Pacific, which are greater than any satellite observations used; and (2) CMAP is produced from a linear combination of data inputs, which tends to give higher values than the microwave emission estimates alone to which the inputs are adjusted in the GPCP merger over the ocean. The CMAP month-to-month adjustment to the atolls also appears to introduce temporal variations thro...

Emerging dynamic metasurface antennas (DMAs) technology promises to achieve future wireless communications by reducing hardware costs, physical size and power consumption. Especially in the field of radar imaging, they can be used as an effective alternative platform for modern computational imaging; because they can simplify the physical hardware and increase the data acquisition rate. Fourier transform (FT)-based scene image reconstruction techniques are known as cost-effective computing solutions for the imaging system processing unit. However, due to the physical layer compression in DMAs and the fact that they do not produce uniform radiation patterns, the information provided by them is not compatible with Fourier-based techniques and cannot be applied directly. In this paper, we first introduce a 3D near-field bistatic imaging approach using two one-dimensional (1D) DMAs as a panel-to-panel model in a Mills Cross structure. Then, based on the introduced mathematical model, we derive a Fourier-based algorithm for the image reconstruction problem. The proposed algorithm consists of five main steps: pre-processing (to transfer data provided by the transmitter and receiver DMAs to a set of equivalent spatial measurements), applying FTs to the transferred signal, filtering in the Fourier domain, a simplified interpolation, and applying a 3D inverse FT to retrieve scene information. The results of numerical simulations confirm the satisfactory performance of the proposed approach.