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Ground penetrating radar has been acknowledged as an effective and efficient technique for non-destructive investigation for near-subsurface exploration that is based on the reflection receiver-transmitter of the antenna when hitting buried objects. An accurate interpretation of GPR data is greatly important in locating and mapping underground objects. Although GPR research has achieved remarkable success, the interpretation of GPR raw data highly depends on the reliance of user experts. Further, unexperienced GPR users are subject to error since the hyperbola signatures may resemble each other. Therefore, this work focuses on the development of a 3D reconstruction of the hyperbola signature of underground objects using GPR images for mapping applications. In this study, 3D reconstruction has been developed based on the Synthetic Aperture Focusing Technique, also known as SAFT. At the first stage, the raw input of GPR images was subjected to zero-time correction and background elimination. Next is the projection of each hyperbola signature by means of B-Scan images to create a 3D image. Then, the resultant 3D images were stacked together, and further 3D interpolation techniques were employed on the images. The experimental studies have been done on GPR data using a metal sphere as a sample. The findings of the study highlight that the SAFT method was able to reconstruct the 3D model of the hyperbola signature and exhibit the ability to provide clues about the location of the underground object through the representation of the voxel point of the images. Based on these results, the SAFT technique provides good insight into the 3D reconstruction of hyperbola signatures using GPR images in mapping applications. [ABSTRACT FROM AUTHOR]

The Mosul Dam project was built on weakly, unstable generational land, and when it enters into contact with the water, its properties change. As a result, excess water in several vertical apertures in the dam's body must be observed to warn against the possibility of the dam collapse. A bar scale is used to initially measure the water column depth in the dam apertures. This research proposes a new system using wireless sensors injected as a floated object on the water columns altimeter and sending the water-level values to LoRa-WAN in real-time. This study simulates a new Long Range Wide Area Network (LoRa-WAN) technology to monitor a variety of water levels in Mosul Dam, which is linked to an Internet of Things (IoT) structure that is based on wireless sensor networks (WSNs). A LoRa gateway is employed to transfer these data over it. Alerts will be transmitted by end devices and received by the LoRa WAN, showing the specific end devices position, if the water levels exceed the allowable predetermined level. The network will then take suitable measures. This paper displays a simulation software implementation omnet++ to evaluate the performance of LoRa as an outcome of implementation across the FLoRa framework to simulate monitoring the water level in Mosul Dam. The performance impact of LoRa networks was evaluated on Network Energy Consumed and Packet Delivery Ratio for (1) the number of gateways, and (2) the distance between each end device and the LoRa gateway. Our results demonstrated that optimizing the parameters that impact a LoRa network's performance can convert traditional monitoring to smart monitoring as well as the capability of one LoRa gateway to run up to (1000) end devices. [ABSTRACT FROM AUTHOR]

This paper addresses an automatic adjustment of the Chirp baseband pulse duration for synthetic aperture radar depending on the height of the aircraft that brought the sensor. With this capability, the radar sensor will automatically adjust the duration of the chirp pulse to obtain the optimal signal density in order to obtain a detailed chirp signal. This method also might ease the operation of sensing with a synthetic aperture radar (SAR) system at varying aircraft altitudes. The chirp signal is generated by the DDS method with the load of the memory look-up table using a digital-to-analog converter (DAC) resolution of 14 bit and a frequency sampling of 200 MHz. The results of the simulation tests have demonstrated that the suggested method can produce chirp signals and automatically modify the duration of chirp signals adjusted with aircraft altitude changes between 1 to 1500 meters. [ABSTRACT FROM AUTHOR]

Anak Krakatoa Volcano is a young volcano that appeared in the caldera after the proximal eruption in 1883 from the Krakatoa volcanic complex. currently, Anak Krakatoa Volcano is in the construction phase. Based on measurements by the Center for Volcanology and Geological Hazard Mitigation (PVMBG) conducted in September 2018, it was found that the elevation of the Anak Krakatoa volcano is above 338 m from sea level. From June 25, 2018, until the end of 2019 Anak Krakatoa Volcano experienced a strombolian eruption, this eruption caused deformation on the surface of the Volcano. The research used the Differential Interferometry Synthetic Aperture Radar (DInSAR) method with Sentinel-1A image data from April 2018 to December 2019 which was further validated using volcanic activity released by PVMBG. The results were obtained in the form of deformation value based on Line of Sight (LOS) displacement, and the result of deflation is 0,01 cm to 17,1 cm using cross-section in the area around the crater is deflation in June 2018 to February 2019. [ABSTRACT FROM AUTHOR]

Microwaves are usually in the range of a few to ten centimeters with the wavelengths used by remote sensing radars to monitor Earth's atmosphere. The radar pulse loses energy as they travel in the space at a rate proportional to the beamwidth. The beam spread significantly by the time it reaches the earth. Synthetic aperture radars are the solution to this problem since the outcome will greatly change. Synthetic aperture radars were designed to circumvent natural aperture radar limitations. Such systems obtain a strong azimuth resolution which is not based on the slant but does use small antennas and fairly long wavelengths. [ABSTRACT FROM AUTHOR]

This case study discusses the possibility of using satellite data, instead of ground pluviometric measurements, as input data in modeling a hydrological system. One of the biggest problems in the monitoring process is the determination of floodable areas in order to establish and assess damage and risk management. Also, the maps regarding the floods are a real help to the institutions and to those who intervene in rescuing the population. Unlike optical sensors, synthetic aperture (SAR) radar provides valid measurements by covering high-resolution clouds. [ABSTRACT FROM AUTHOR]

This case study discusses the possibility of using satellite data, instead of ground pluviometric measurements, as input data in modeling a hydrological system. One of the biggest problems in the monitoring process is the determination of floodable areas in order to establish and assess damage and risk management. Also, the maps regarding the floods are a real help to the institutions and to those who intervene in rescuing the population. Unlike optical sensors, synthetic aperture (SAR) radar provides valid measurements by covering high-resolution clouds. [ABSTRACT FROM AUTHOR]

A method of space-based interferometric synthetic aperture radar measurements (InSAR and DInSAR techniques) is designed for obtaining of different types of altitude data for the Earth surface, i.e. terrain heights and surface displacements. Phase noise is an intrinsic random uncorrelated additive process, which complicates data processing in such systems. The experimental study of the linear non-adaptive phase noise filters are studied using the previously developed technique for experimental evaluation of the InSAR processing algorithms effectiveness. The accuracy characteristics for the filters applied to ALOS PALSAR data for areas with hilly and low-mountainous terrain are obtained, and it is shown, that one of the filters gives a slight better results (with less error value) under the equal computational complexity. [ABSTRACT FROM AUTHOR]

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]

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]

Computer technique was developed to simulate basic parameters of spaceborne synthetic aperture radars operating in the pulsed mode. Relationships are obtained and presented that make it possible to calculate dimensions of the antenna aperture, repetition period of the transmitter pulses and their duration, as well as duration of the pulse strobes opening the receiving device input, size of the antenna aperture, radiometric sensitivity and resolution, transmitter pulse power, bandwidth of the signal modulating the carrier frequency, aperture synthesis time and information flow rate. The technique is implemented on a personal computer in the C++ environment. The program menu with windows for input of initial data and output of simulation results is presented displayed in the form of 9 types of parametric dependences of the SAR characteristics on the observation point viewing angle. Technique introduction makes it possible to quickly, conveniently and with satisfactory accuracy perform systematic assessment of the SAR main characteristics choosing the most preferable options in the equipment basic parameter combinations. [ABSTRACT FROM AUTHOR]

The binocular telescope is characterized by the presence of a symmetric and parallel double optical system for each eye separately. It consists of a refractive optical system that contains a set of achromatic lenses and a Porro prism inside a plastic tube. The function of the prism is to reduce the length of the telescope as well as change the optical path of the rays to obtain an image suitable for human vision. The use of this type of telescope is suitable for ground observation due to the engineering nature of the design, as well as the focal lengths used for the lenses and the magnification factor. In addition to the use of lenses for refractive telescopes, it is suitable for ground observation rather than astronomical observation due to the presence of chromatic aberration and the small size of the pupil aperture. This research includes a study of the refracting binary telescope by simulation the design, and the study of its optical properties by using of Zemax program for optical designs. The program provides a set of analysis tools to assess the efficiency of the performance of the telescope when the pupil aperture changes. The results showed the effect of image quality when changing the diameter of the pupil aperture due to the change in the achromatic aberration value. [ABSTRACT FROM AUTHOR]

The article deals with a method of mathematical modeling of input signals of radar systems with synthesizing the aperture of an X-band antenna with the implementation of the method of direct solution of the correlation integral. The solution of the problem of onboard radar input signals simulation based on the polygonal model of objects and underlying surfaces that form the radar scene is presented. The possibility of solving the problem of calculating the scattering fields of triangular elements of a radar scene based on phenomenological models for underlying surfaces and on the basis of physical optics methods for anthropogenic objects is shown. In the used methods of physical optics, the induced electromagnetic field on the surface of an element of the object of the radiophysical scene is calculated through the Fresnel reflection coefficients for the horizontal and vertical polarization of the incident wave, and the reflected secondary field is determined through the Stratton-Chu integral. This approach makes it possible to take into account the surface materials of objects of a radiophysical scene with any types of dielectric and magnetic parameters, which allows to consider the proposed method as a universal tool for modeling input signals of radar systems scattered from objects of different electrophysical properties. Radar images of typical scenes from various underlying surfaces with objects located on them are presented on the basis of mathematical modeling. [ABSTRACT FROM AUTHOR]

The paper copes with a transcritical CO2 refrigeration plant: R744 (CO2) is an economic and natural refrigerant with a negligible impact on the environment and with good thermodynamic and safety properties compared to synthetic ones, and it is a sustainable alternative in commercial refrigeration of retail food. A specific 18 kWt test bench is available and under testing in the lab of the University of L’Aquila. Experimental tests were performed at different external temperatures between 8 °C and 33 °C: first results showed that COP (Coefficient Of Performance) decreases when external temperature grows up. Experimental data made it possible to calibrate a mathematical model of the test rig, useful to evaluate the effect of the possible introduction of new technologies: variation of receiver pressure, intercooled two-stage compression and expander in place of the high pressure throttling valve. All these technologies may be useful to improve plant efficiency and to promote new “green” installations in warmer climates, where food conservation standard in terms of goods cold-chain are increasingly demanding, especially considering EU and Global goals on HFC reduction targets (e.g. EU F-gas regulation - 2014 and Kigali amendment to the Montreal Protocol - 2016). [ABSTRACT FROM AUTHOR]

As they degrade and age, concrete structures are susceptible to the development of multiple defects, such as alkali-silica reaction (ASR). ASR forms a gel that occurs over time between alkaline cement paste and reactive, noncrystalline silica in aggregates [1]. With the continuing extension of the life span of nuclear power plants, it is important to monitor the structural integrity of concrete structures after 40+ years. Compression strength, modulus of elasticity, flexural stiffness, shear strength, and tensile strength are performance characteristics susceptible to the development of ASR. Current methods for monitoring for defects and degradation within thick concrete structures require damaging the concrete. Oak Ridge National Laboratory, in collaboration with the University of Pittsburgh, has developed a nondestructive evaluation (NDE) and reconstruction technique that enables deep-image reconstruction of damaged concrete. The frequency-banded synthetic aperture focusing technique (FB-SAFT) is an augmented SAFT reconstruction that segments the time-series data into different frequency bands using wavelets immediately before performing SAFT reconstructions [2]. This paper presents the NDE instrumentation and reconstruction techniques applied to thick-reinforced concrete structures and concludes with preliminary results. [ABSTRACT FROM AUTHOR]

Cold spray is a solid state coating technology with high deposition rates that is very suitable for large scale applications of additive manufacturing (AM). For quality control of complex parts, laser ultrasonics is particularly attractive due to its non-contact nature and is well adapted to online implementation. In this study, various inspection results performed off-line on metallic parts produced by the cold spray AM process are presented. Laser ultrasonics combined with the synthetic aperture focusing technique (SAFT) is used to detect flaws and through-thickness distributed porosity is investigated using the laser-ultrasonic backscattered signal. Also, laser shockwave is used to characterize bond strength at the interface between the deposition and the substrate. For post heat treatment of cold spray AM metallic parts, laser ultrasonics is used to monitor in real time recrystallization and sintering. Inspection results from either the top layer or the underside of the substrate are reported and discussed. [ABSTRACT FROM AUTHOR]

One-sided non-destructive evaluation (NDE) is widely used to inspect materials, such as concrete structures in nuclear power plants (NPP). A widely used method for one-sided NDE is the synthetic aperture focusing technique (SAFT). The SAFT algorithm produces reasonable results when inspecting simple structures. However, for complex structures, such as heavily reinforced thick concrete structures, SAFT results in artifacts and hence there is a need for a more sophisticated inversion technique. Model-based iterative reconstruction (MBIR) algorithms, which are typically equivalent to regularized inversion techniques, offer a powerful framework to incorporate complex models for the physics, detector miscalibrations and the materials being imaged to obtain high quality reconstructions. Previously, we have proposed an ultrasonic MBIR method that signifcantly improves reconstruction quality compared to SAFT. However, the method made some simplifying assumptions on the propagation model and did not disucss ways to handle data that is obtained by raster scanning a system over a surface to inspect large regions. In this paper, we propose a novel MBIR algorithm that incorporates an anisotropic forward model and allows for the joint processing of data obtained from a system that raster scans a large surface. We demonstrate that the new MBIR method can produce dramatic improvements in reconstruction quality compared to SAFT and suppresses articfacts compared to the perviously presented MBIR approach. [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]

Segmented quartz windows are a concept to build larger windows for receivers that require a closed aperture. Reflection losses are a significant loss factor for such solar receivers. Without any additional measures, the reflection loss can reach about 12%. One important measure to improve transmission is the application of anti-reflective coatings, which is beneficial in any case. Another option is modifying the window geometry, especially the edge surfaces of the glass segments. A certain fraction of the reflection losses are caused by a light-guide effect in the glass body, for rays entering through the front surface. Changing the cut surfaces in a way reducing the light-guide effect can significantly improve transmission of a segmented window. Several possible configurations are evaluated and discussed. The results of ray-tracing simulations verify the improvement. The final selection of the window configuration depends on the optical properties and on mechanical strength, manufacturing and cost considerations. This has to be evaluated for any specific receiver design. [ABSTRACT FROM AUTHOR]

Additive manufacturing provides a unique opportunity to embed defects of known size and shape to produce reference samples for inspection and quality control purposes. This paper reports defect detectability studies with cylindrical additively manufactured cobalt-chromium alloy specimens which contain defects of known sizes and distributions. The specimens were characterized using immersion, synthetic aperture focusing (SAFT), phased array, and nonlinear ultrasonic techniques. Results include detectability, signal to noise ratios, and comparison of results between the methods and what is believed to be the first determination of a non-linearity (beta) parameter for an additively manufactured material. The results indicate that additive manufacturing provides a valuable method to produce reference samples, though additional work is required to validate the shape and morphology of the defects specified. [ABSTRACT FROM AUTHOR]

All commercial nuclear power plants (NPPs) in the United States contain concrete structures. These structures provide important foundation, support, shielding, and containment functions. Identification and management of aging and the degradation of concrete structures is fundamental to the proposed long-term operation of NPPs. Concrete structures in NPPs are often inaccessible and contain large volumes of massively thick concrete. While acoustic imaging using the synthetic aperture focusing technique (SAFT) works adequately well for thin specimens of concrete such as concrete transportation structures, enhancements are needed for heavily reinforced, thick concrete. We argue that image reconstruction quality for acoustic imaging in thick concrete could be improved with Model-Based Iterative Reconstruction (MBIR) techniques. MBIR works by designing a probabilistic model for the measurements (forward model) and a probabilistic model for the object (prior model). Both models are used to formulate an objective function (cost function). The final step in MBIR is to optimize the cost function. Previously, we have demonstrated a first implementation of MBIR for an ultrasonic transducer array system. The original forward model has been upgraded to account for direct arrival signal. Updates to the forward model will be documented and the new algorithm will be assessed with synthetic and empirical samples. [ABSTRACT FROM AUTHOR]

To observe delicate Earth surface continuously, satellite-based monitoring system is required. Especially in tropical region, Synthetic Aperture Radar (SAR) is necessitated considering its ability to penetrate cloud and other atmospheric attenuations. Recent fully polarimetric SAR has been exploited. Nonetheless, this mode of imaging consumes higher amount of energy, which is one of the main issues in satellite-based platform. In this paper, a study exploiting hybrid (also known as compact) polarization is presented. Comparison to fully polarimetric mode of SAR is made using polarimetric decomposition. This research indicates that single signal transmission in hybrid polarization cannot fully replace fully-polarized mode. This suggests that hybrid polarization should be limitedly applied to geobiophysical applications such as biomass or soil moisture estimation. However, for general land cover discrimination and monitoring, hybrid polarimetry is fairly useful. Analysis of transformed divergence on decomposition parameters entropy, alpha angle and anisotropy shows that hybrid polarization successfully discriminates major land cover types with some degrees of confidence. [ABSTRACT FROM AUTHOR]

The study presents a basic framework for structural integrity assessment using synthetic aperture focusing technique and the extended finite element method. Synthetic aperture focusing technique (SAFT) is used to acquire detailed descriptions of three-dimensional flaws in engineering structures. Flaws extracted from SAFT can readily be represented as a surface mesh or a volume mesh. The mesh is integrated into a normal structural finite element model (FEM) via level set method to formulate an XFEM problem. Applying the cyclic fatigue load and solving the problem provides essential quantities for evaluation of the stress intensity factor (SIF), serving as a driven force of crack growth. The crack front is updated using crack growth equations, such as Paris' equation and its variants under cyclic loading condition. The result is considered to be accurate due to the fact that, for one thing it can minimize the uncertainty in quantification of three-dimensional flaws, and for another it provides a highly reliable solution to SIF for any point in the crack front under mixed mode loading conditions. Combination of the two components allows for removal of approximations and over conservativeness in conventional ultrasound based structural integrity assessment. [ABSTRACT FROM AUTHOR]

A method for determining the effective Rayleigh surface wave (RSW) velocity under the probe during a RSW imaging experiment was developed. The synthetic aperture routine can take in polycrystalline data with arbitrary c-axis orientation for each crystal and calculate the total effect that the crystals below the probe has on the response. It relies on calculation of RSW velocity in arbitrary directions for hexagonal crystals by applying numerical methods to the general theory described by several groups using the Stroh formalism. In this paper, the method will be summarized and example will be shown that demonstrate the feasibility of the routine for approximating scans over the surface of samples. Application of the method in the context of material characterization will be discussed. [ABSTRACT FROM AUTHOR]

Improvements in detection and resolution are always desired and needed. There are various instruments available for the inspection of concrete structures that can be used with confidence for detecting different defects. However, more often than not that confidence is heavily dependent on the experience of the operator rather than the clear, objective discernibility of the output of the instrument. The challenge of objective discernment is amplified when the concrete structures contain multiple layers of reinforcement, are of significant thickness, or both, such as concrete structures in nuclear power plants. We seek to improve and extend the usefulness of results produced using the synthetic aperture focusing technique (SAFT) on data collected from thick, complex concrete structures. A secondary goal is to improve existing SAFT results, with regards to repeatedly and objectively identifying defects and/or internal structure of concrete structures. Towards these goals, we are applying the time-frequency technique of wavelet packet decomposition and reconstruction using a mother wavelet that possesses the exact reconstruction property. However, instead of analyzing the coefficients of each decomposition node, we select and reconstruct specific nodes based on the frequency band it contains to produce a frequency band specific time-series representation. SAFT is then applied to these frequency specific reconstructions allowing SAFT to be used to visualize the reflectivity of a frequency band and that band's interaction with the contents of the concrete structure. We apply our technique to data sets collected using a commercial, ultrasonic linear array (MIRA) from two 1.5m x 2m x 25cm concrete test specimens. One specimen contains multiple layers of rebar. The other contains honeycomb, crack, and rebar bonding defect analogs. This approach opens up a multitude of possibilities for improved detection, readability, and overall improved objectivity. We will focus on improved defect/reinforcement isolation in thick and multilayered reinforcement environments. Additionally, the ability to empirically explore the possibility of a frequency-band-defect-type relationship or sensitivity becomes available. [ABSTRACT FROM AUTHOR]

Oak Ridge National Laboratory (ORNL) comparatively evaluated the ability of a number of NDE techniques to generate an image of the volume of 6.5' X 5.0' X 10" concrete specimens fabricated at the Florida Department of Transportation (FDOT) NDE Validation Facility in Gainesville, Florida. These test blocks were fabricated to test the ability of various NDE methods to characterize various placements and sizes of rebar as well as simulated cracking and non-consolidation flaws. The first version of the ultrasonic linear array device, MIRA [version 1], was one of 7 different NDE equipment used to characterize the specimens. This paper deals with the ability of this equipment to determine subsurface characterizations such as reinforcing steel relative size, concrete thickness, irregularities, and inclusions using Kirchhoff-based migration techniques. The ability of individual synthetic aperture focusing technique (SAFT) B-scan cross sections resulting from self-contained scans are compared with various processing, analysis, and interpretation methods using the various features fabricated in the specimens for validation. The performance is detailed, especially with respect to the limitations and implications for evaluation of a thicker, more heavily reinforced concrete structures. [ABSTRACT FROM AUTHOR]

A Synthetic Aperture Microwave Imaging (SAMI) system has been designed and built to obtain 2-D images at several frequencies from fusion plasmas. SAMI uses a phased array of linearly polarised antennas. The array configuration has been optimised to achieve maximum synthetic aperture beam efficiency. The signals received by antennas are down-converted to the intermediate frequency range and then recorded in a full vector form. Full vector signals allow beam focusing and image reconstruction in both real time and a post-processing mode. SAMI can scan over 16 pre-programmed frequencies in the range of 10-35GHz with a switching time of 300ns. The system operates in 2 different modes simultaneously: both a 'passive' imaging of plasma emission and also an 'active' imaging of the backscattered signal of the radiation launched by one of the antennas from the same array. This second mode is similar to socalled Doppler backscattering (DBS) reflectometry with 2-D resolution of the propagation velocity of turbulent structures. Both modes of operation show good performance in fusion plasma experiments on Mega Amp Spherical Tokamak (MAST). We have obtained the first ever 2-D images of BXO mode conversion windows. With active probing, first ever turbulence velocity maps have been obtained. We present an overview of the diagnostic and discuss recent results. In contrast to quasi-optical microwave imaging systems SAMI requires neither big aperture viewing ports nor large 2-D detector arrays to achieve the desired imaging resolution. The number of effective 'pixels' of the synthesized image is proportional to the number of receiving antennas squared. Thus only a small number of optimised antennas is sufficient for the majority of applications. Possible implementation of SAMI on ITER and DEMO is discussed. [ABSTRACT FROM AUTHOR]

In the continuous casting process the avoidance and rapid detection of occurring solidification cracks in the slab is a crucial issue, in particular for the maintenance of a high quality level in further production processes. Due to the elevated temperatures of the slab surface a remote sensing non-destructive tool for quality inspection is required, which is also applicable for the harsh industrial environment. In this work the application of laser ultrasound (LUS) technique during the continuous casting process in industrial environment is shown. The proof of principle of the detection of the centered solidification cracks is shown by pulse-echo measurements with laser ultrasonic equipment for inline quality inspection. Preliminary examinations in the lab of different casted samples have shown the distinguishability of slabs with and without any solidification cracks. Furthermore the damping of the bulk wave has been used for the prediction of the dimension of the crack. With an adapted "synthetic aperture focusing technique" (SAFT) algorithm the image reconstruction of multiple measurements at different positions around the circumference has provided enough information for the estimation of the localization and extension of the centered solidification cracks. Subsequent first measurements using this laser ultrasonic setup during the continuous casting of aluminum were carried out and showed the proof of principle in an industrial environment with elevated temperatures, dust, cooling water and vibrations. [ABSTRACT FROM AUTHOR]

The failure of propulsion components of ships and ferries can lead to serious environmental and economic damage or even the loss of lives. For ultrasonic inspection of such large components we employ mechanized scanning and defect reconstruction using the Synthetic Aperture Focusing Technique (SAFT). We report on results obtained in view of the detection of defects with different inspection techniques. Also, we address the issue of Probability of Detection by reporting results obtained in POD and MAPOD-studies (Model-Assisted POD) using experimental and simulated data. Finally, we show recent results of surface and sub-surface inspection using optical and eddy current techniques. [ABSTRACT FROM AUTHOR]

Above ground storage tanks are required to undergo periodic internal inspections. Because these inspections are hazardous and expensive to conduct from the inside of the tank, there is a keen interest for alternative inspection techniques that can be conducted without removing the tanks from service. Southwest Research Institute® (SwRI®) is currently developing a screening technique that uses magnetostrictive sensor (MsS) guided wave technology and a Synthetic Aperture Focusing Technique (SAFT) to map the condition of a tank floor from the outside of the tank. Preliminary testing was conducted on a mockup constructed to resemble the outer annulus of the tank floor and the attached tank wall. A test procedure was developed where the MsS probe was scanned around the outside circumference of the tank to collect a Bscan array of waveforms. Testing has demonstrated that the inspection technique is effective at detecting both pitting corrosion and broad local corrosion in the outer annulus of the tank floor. [ABSTRACT FROM AUTHOR]

The synthetic aperture focusing technique (SAFT) is an imaging technique commonly used in ultrasonic inspection. In order to apply SAFT to the inspection of austenitic welds, the inhomogeneous anisotropic nature of the weld structure has to be taken into account. A suitable approach to accomplish this, is to couple the SAFT-algorithm with a ray tracing program (RT-SAFT). While SAFT-imaging of cracks in austenitic welds by use of ray tracing has been carried out before, all attempts so far were limited to longitudinal cracks which usually allows a treatment as 2-dimensional problem. In case of transverse cracks, a full 3-dimensional ray tracing is necessary in order to perform a SAFT-reconstruction. In this paper, we give an outline of our attempts to reconstruct images of transverse cracks in austenitic welds, utilizing 3-dimensional ray tracing and a layered structure model derived from an empirical model of grain orientations in welds. We present results of this RT-SAFT on experimental data taken from transverse cracks in different austenitic welds, which show that size and position of the cracks can be estimated with good accuracy, and compare them to images obtained by assuming an isotropic homogeneous medium which corresponds to the application of the classical SAFT-algorithm. [ABSTRACT FROM AUTHOR]

Ultrasonic Synthetic Aperture Focusing Technique (SAFT) reconstruction method is developed to provide high-resolution images of the inspected areas and volumes. The basic idea of the method is to coherently superimpose multiple A-scan measurements, incorporating the phase information of the sampling points. The method involves two major steps: data mapping according to time-of-flight (ToF), and local normalizing. Data mapping refers to the process of mapping each of the sampling points to a three-dimensional grid that represents the geometry model of the object being inspected. The value for each cell of the grid is a summation of all sampling points mapped into the cell. Local normalizing refers to normalizing a selected region of interest (ROI) for defect visualization and quantification. Lab experiments are performed using a 10MHz phased array ultrasonic probe to collect data from a cylinder material block. The method is used to process the experimental data. Using the developed method, spatial resolution of inspection is significantly improved comparing with traditional reconstruction methods. Results indicate that four closely spaced 0.794mm-diameter flat-bottomed holes are clearly identified. [ABSTRACT FROM AUTHOR]

Ultrasonic imaging measurement models (IMMs) are developed that generate images of flaws by inversion of ultrasonic measurement models. These IMMs are generalizations of the synthetic aperture focusing technique (SAFT) and the total focusing method (TFM). A special case when the flaw is small is shown to generalize physical optics far field inverse scattering (POFFIS) images. The ultrasonic IMMs provide a rational basis for generating and understanding the ultrasonic images produced by delay-and-sum imaging methods. [ABSTRACT FROM AUTHOR]

A time domain synthetic aperture focusing technique (SAFT) for flaw imaging of immersed structures with curved surfaces is improved in conjunction with approximate wave solutions, which were obtained in an explicit form by Schmerr (1998). In the improved SAFT, the approximate solutions are used to normalize A-scan waveforms and then the normalized waveforms are superimposed to obtain images with high contrast for a flaw in a structure in curved surfaces. As examples, the proposed SAFT is applied to experimental data for a side drilled hole (SDH) in an immersed round bar. [ABSTRACT FROM AUTHOR]

Advances in technology and theory in 30 years of underwater acoustic signal processing and its applications in China are presented in this paper. The topics include research work in the field of underwater acoustic signal modeling, acoustic field matching, ocean waveguide and internal wave, the extraction and processing technique for acoustic vector signal information, the space/time correlation characteristics of low frequency acoustic channels, the invariant features of underwater target radiated noise, the transmission technology of underwater voice/image data and its anti-interference technique. Some frontier technologies in sonar design are also discussed, including large aperture towed line array sonar, high resolution synthetic aperture sonar, deep sea siren and deep sea manned subsea vehicle, diver detection sonar and demonstration projector of national ocean monitoring system in China, etc. [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]

To improve the results of the Delay-And-Sum (DAS) beamformer a weighting factor based on a measurement of the phase dispersion of the signals in the image point under consideration has been proposed. With this objective, the spectral analysis of the phase dispersion is used here to obtain a new descriptor that can be easily computed and introduced as a ponderation factor in the beamforming process. Theoretical results show that, for a linear array of 32 elements operating in synthetic aperture technique with dynamic focussing in emission and reception (Total Focussing Method) the improvement can reach up to 24dB. In order to validate the theoretical hypothesis, experimental results obtained using a linear array of 64 elements (2,4MHz) and a CIRS 040GSE phantom also are presented. [ABSTRACT FROM AUTHOR]

The synthetic aperture focusing technique is a method for focusing ultrasonic scans used in nondestructive testing. Traditionally, the technique has mainly been used for contact testing, where the speed of sound is constant throughout the whole medium, but a number of recently proposed algorithms have extended the technique to multilayered media. One important application for such multilayer methods is immersion testing, where an object is immersed in water and the transducer is scanned within the water layer. Similarly, a multilayer technique is useful for inline ultrasound inspection of pipelines filled with liquid, for example water or oil. The multilayer methods have so far only been applied to the 2-dimensional line scan case, but in this paper we extend the the focusing procedure to the 3-dimensional surface scan case. The proposed method is based on the frequency-domain Phase Shift Migration algorithm, which is both conceptually simpler and more computationally efficient than similar time-domain methods. The performance of the focusing algorithm is tested on a three-layer structure, consisting of acrylic glass and aluminum blocks immersed in water. Several small flat-bottom holes in each block are used to simulate point scatterers, and the scatterer responses are studied using both B- and C-scan presentation. The lateral resolution of the focused image is shown to be approximately equal to half the transducer diameter, independent of both depth and layer. [ABSTRACT FROM AUTHOR]

Ultrasonic testing (UT) has been used for nondestructive evaluation (NDE) of materials for more than half a century. A number of NDE techniques have been developed and specific standards have been created for the UT applications in different areas of engineering. UT has two main goals related to inspection of solid objects, firstly, detection and characterization of material discontinuities (flaws), and secondly, material characterization. This paper is focused on the selected techniques for flaw detection and imaging using bulk waves as well as guided waves. The main part of the paper contains presentation of array techniques used for the inspection of solid structures with focus on ultrasonic imaging of discontinuities. An overview of the high resolution imaging methods based on synthetic aperture concept (SAFT) is given and illustrated with experimental results. The UT review is concluded with a short presentation of recently developed methods using Lamb waves for monitoring planar structures in structural health monitoring (SHM) applications. Damage detection methods based on application of multiple transducers (2D arrays) for generating and detecting Lamb waves in metallic and composite plates are presented. [ABSTRACT FROM AUTHOR]

In the field of ultrasonic imaging, the synthetic aperture techniques are well known due to their ability for obtain images using fewer resources. Initially, these techniques were developed to reduce the cost and complexity of phased array instrumentation. Although these drawbacks have already been overcome, the interest on the synthetic aperture systems has not decayed. The reasons of that are the high image quality achieved with these techniques (images dynamically focused both in emission and reception), and the fact that they are an excellent solution for the design of new high performance instrumentation with a low volume and power consumption, easily integrable in autonomous and embedded systems. Using the coarray as a model of the pulse-echo systems, the present work analyzes experimentally the main synthetic aperture strategies appeared until now, introducing two new proposals (2R-SAFT and nR-SAFT) that allow to improve the quality of the images without increase the hardware complexity of the system. [ABSTRACT FROM AUTHOR]

The two main preconditions for the application of the Synthetic Aperture Focusing Technique (SAFT) are: (i) a large divergence of the sound beam of the transducer and (ii) an exact knowledge about the sound propagation path. These requirements are easily fulfilled for point sources directly mounted on the surface of the specimen. In many cases, however, the transducer is wedge mounted and/or coupled using a water delay line, e.g. in immersion technique. These delay lines change the beam index and the propagation path has to be evaluated for each pixel separately considering Fermat's principle. Using phased array transducers, a sector scan can improve the divergence of the sound beam. The introduced method combines the advantages of using a phased array transducer in immersion technique to improve SAFT reconstruction. An algorithm is presented accounting the influence of the delay line on the reconstruction method. The applicability of the algorithm is shown by validation with simulated echo responses and with experimental results collected from a specimen with artificial flaws. [ABSTRACT FROM AUTHOR]

Creep damage in heat affected zone of welded high-chromium pipes is a crucial problem in ultra super critical power plants. The phased array ultrasonic testing is a powerful tool for detection of creep damage. When a weld crown exists, ultrasonic waves are transmitted through the flat surface over the base metal and at a high refraction angle to detect the damage near the outer surface. However, detection sensitivity becomes low with increase in the refraction angle. Therefore, it is expected to detect creep damage over the weld metal with appropriate refraction angle. In such a case, in order to control ultrasonic beam orientation transmitted through complicated interfaces, it is necessary to measure their surface profile. In this paper, a method to reconstruct surface profiles of specimen is proposed by the means of the synthetic aperture focusing technique (SAFT). Surface profiles of simulating crown of butt welding specimen and fillet of nozzle welding specimen with side-drilled holes (SDHs) determined by the proposed method agrees well with real shapes. Moreover, positions of indications for SDHs displayed in side views were in excellent agreement with their actual positions. [ABSTRACT FROM AUTHOR]

This contribution addresses ultrasonic inspection and evaluation of welds in large components. An approach has been developed in order to enhance the reliability of welded ship propellers. The Synthetic Aperture Focusing Technique (SAFT) has been modified with regard to the curved surfaces and the sound attenuation of cast Ni-Al bronzes. For weld inspection in steels the Time-of-Flight Diffraction technique (TOFD) can provide additional information for specific defect orientations. Both techniques have been combined in view of the determination of defect sizes and shapes in longitudinal welds of pipes with diameters of up to 48 inches. Details on the inspection and evaluation concepts as well as experimental results are presented. [ABSTRACT FROM AUTHOR]

Acoustic as well as electromagnetic methods can provide a valuable tool for the quality assessment of concrete bridges. For the efficient application in the field, the capabilities of the different methods in solving a specific testing problem have to be known. In a research project funded by the Florida Department of Transportation (FDOT) a first stage facility for the calibration and validation of NDT methods has been established. A test frame with two automated scanners has been designed and built, in which concrete blocks with artificial defects or testing problems can be tested by NDT methods such as ultrasonic-echo, impact-echo, covermeter or Ground Penetrating Radar. The most relevant testing problems dealt with in this project are the location of reinforcement steel, tendon duct inspections and thickness measurements. Furthermore, the capabilities and limitations of NDT methods in determining elastic parameters have also been investigated. 2D and 3D imaging techniques as well as signal processing such as the Synthetic Aperture Focusing Technique (SAFT) applied to the data provide a vivid representation of the results and make the interpretation easier and more intuitive. The capabilities and limitations of the different methods regarding the different testing problems are discussed. [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]

In this work, the multi-element synthetic aperture method (n-SAF) is presented in combination with a data reduction algorithm that reduces the number of signals intervening in the image processing. The proposed method, called nR-SAF, simplifies the beamforming process by directly adding in phase all the signals that contribute to each element of the coarray (signals with same spatial frequency). By this method, a reduction of approximately 2/n of the data intervening in the beamforming process is attained. [ABSTRACT FROM AUTHOR]

Time reversal can focus in both time and space. The temporal focusing properties have been used in underwater acoustics communications. Typical passive time reversal communication experiments use a vertical array of receivers and a sound source. The property of a horizontal time reversal array that it focuses well in the temporal domain indicates the utilization of synthetic aperture time reversal. Passive synthetic aperture processing repeats emitting same signals during the cruising and records the received signal using one or more receivers. Passive synthetic aperture time reversal communication techniques are presented and applied to results from a sea trail. The experiment consisted of a towed hydrophone and a vertical array. During the experiment, a probe signal is emitted to sample the transmit function then be used by time reversal processing. Due to the moving of the hydrophone, Doppler shift compensation and receive wave forms synchronization must be performed before the time reversal processing. The signal-to-noise ratio is increased and the temporal side lobes are decreased in the time reversal process. Additional communication algorithms can be appended after the time reversal process to increase performance. The result from the at-sea experiment confirms the ability of passive synthetic time reversal communications. [ABSTRACT FROM AUTHOR]

Elliptical, parabolic and Wolter type glass monocapillaries were fabricated for use as x-ray condensers in the energy range of 250 eV to 20 keV. On a routine basis a diameter error of +/-0.4 μm and straightness error of 0.8 μm (peak to valley) can be reached. The final test of condensers was performed at-wavelength by imaging the far field x-ray reflection intensity distribution using a laboratory microfocus x-ray source. For medium length condensers with a total length <80 mm, a total slope error of 40 μrad rms was obtained. The applications in full-field x-ray microscopes and the future effort in developing capillary Wolter mirrors based on this technology are reported. [ABSTRACT FROM AUTHOR]

In order to meet the demand for X-ray lenses with large apertures and, hence, photon flux, a new type of X-ray lenses has been developed: Rolled prismatic X-ray lenses feature a vast number of refracting surfaces to increase transparency and aperture, respectively. Prototypes of such lenses have been fabricated by molding and rolling of a structured polyimide film. In this work, rolled prismatic X-ray lenses are pictured, and results of first tests performed at the ANKA storage ring in Karlsruhe are presented. [ABSTRACT FROM AUTHOR]

We propose and discuss three methods for increasing the resolution of an aperture limited optical system by illuminating the input with structured light. The kind of illumination can be varied, ranging from tilted plane waves, coherence shaped light or speckle patterns. In any case the high resolution of the projected pattern demodulates the high frequencies of the sample and permits its passage through the system aperture. A decoding process provides the superresolved image after some digital post processing stage. © 2006 American Institute of Physics [ABSTRACT FROM AUTHOR]