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At least 1,567 records · Page 87
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Imaging antiferromagnetic antiphase domain boundaries using magnetic Bragg diffraction phase contrast

Manipulating magnetic domains is essential for many technological applications. Recent breakthroughs in Antiferromagnetic Spintronics brought up novel concepts for electronic device development. Imaging antiferromagnetic domains is of key importance to this field. Unfortunately, some of the basic domain types, such as antiphase domains, cannot be imaged by conventional techniques. Herein, we present a new domain projection imaging technique based on the localization of domain boundaries by resonant magnetic diffraction of coherent X rays. Contrast arises from reduction of the scattered intensity at the domain boundaries due to destructive interference effects. We demonstrate this approach by imaging antiphase domains in a collinear antiferromagnet Fe 2 Mo 3 O 8 , and observe evidence of domain wall interaction with a structural defect. Here, this technique does not involve any numerical algorithms. It is fast, sensitive, produces large-scale images in a single-exposure measurement, and is applicable to a variety of magnetic domain types.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
NASA NTRS1999

Evaluation of the Compressive Response of Notched Composite Panels using a Full-Field Displacement Measurement System

An experimental and analytical evaluation of the compressive response of two composite, notched stiffened panels representative of primary composite wing structure is presented. A three-dimensional full-field image correlation technique is used to measure all three displacement components over global and local areas of the test panels. Point-wise and full-field results obtained using the image correlation technique are presented and compared to experimental results and analytical results obtained using nonlinear finite element analysis. Both global and global-local image correlation results are presented and discussed. Results of a simple calibration test of this image correlation technique are also presented.

McGowan, David M.↗
NASA NTRS2016

The Maturing of High Contrast Imaging and Starlight Suppression Techniques for Future NASA Exoplanet Characterization Missions

Over 3000 exoplanets and hundreds of exoplanetary systems have been detected to date and we are now rapidly moving toward an era where the focus is shifting from detection to direct imaging and spectroscopic characterization of these new worlds and their atmospheres. NASA is currently studying several exoplanet characterization mission concepts for the 2020 Decadal Survey ranging from probe class to flagships. Detailed and comprehensive exoplanet characterization, particularly of exo-Earths, leading to assessment of habitability, or indeed detection of life, will require significant advances beyond the current state-of-the-art in high contrast imaging and starlight suppression techniques which utilize specially shaped precision optical elements to block the light from the parent star while controlling scattering and diffraction thus revealing and enabling spectroscopic study of the orbiting exoplanets in reflected light. In this paper we describe the two primary high contrast starlight suppression techniques currently being pursued by NASA: 1) coronagraphs (including several design variations) and 2) free-flying starshades. These techniques are rapidly moving from the technology development phase to the design and engineering phase and we discuss the prospects and projected performance for future exoplanet characterization missions utilizing these techniques coupled with large aperture telescopes in space.

high contrast↗
DOE OSTI2019

Laser-wakefield accelerators for high-resolution X-ray imaging of complex microstructures

Laser-wakefeld accelerators (LWFAs) are high acceleration-gradient plasma-based particle accelerators capable of producing ultra-relativistic electron beams. Within the strong focusing felds of the wakefeld, accelerated electrons undergo betatron oscillations, emitting a bright pulse of X-rays with a micrometer-scale source size that may be used for imaging applications. Non-destructive X-ray phase contrast imaging and tomography of heterogeneous materials can provide insight into their processing, structure, and performance. To demonstrate the imaging capability of X-rays from an LWFA we have examined an irregular eutectic in the aluminum-silicon (Al-Si) system. The lamellar spacing of the Al-Si eutectic microstructure is on the order of a few micrometers, thus requiring high spatial resolution. We present comparisons between the sharpness and spatial resolution in phase contrast images of this eutectic alloy obtained via X-ray phase contrast imaging at the Swiss Light Source (SLS) synchrotron and X-ray projection microscopy via an LWFA source. An upper bound on the resolving power of 2.7±0.3μm of the LWFA source in this experiment was measured. These results indicate that betatron X-rays from laser wakefeld acceleration can provide an alternative to conventional synchrotron sources for high resolution imaging of eutectics and, more broadly, complex microstructures.

43 PARTICLE ACCELERATORS↗
NASA NTRS1985

Image processing of aerodynamic data

The use of digital image processing techniques in analyzing and evaluating aerodynamic data is discussed. An image processing system that converts images derived from digital data or from transparent film into black and white, full color, or false color pictures is described. Applications to black and white images of a model wing with a NACA 64-210 section in simulated rain and to computed low properties for transonic flow past a NACA 0012 airfoil are presented. Image processing techniques are used to visualize the variations of water film thicknesses on the wing model and to illustrate the contours of computed Mach numbers for the flow past the NACA 0012 airfoil. Since the computed data for the NACA 0012 airfoil are available only at discrete spatial locations, an interpolation method is used to provide values of the Mach number over the entire field.

Faulcon, N. D.↗
NASA NTRS2007

A Software Platform for Post-Processing Waveform-Based NDE

Ultrasonic, microwave, and terahertz nondestructive evaluation imaging systems generally require the acquisition of waveforms at each scan point to form an image. For such systems, signal and image processing methods are commonly needed to extract information from the waves and improve resolution of, and highlight, defects in the image. Since some similarity exists for all waveform-based NDE methods, it would seem a common software platform containing multiple signal and image processing techniques to process the waveforms and images makes sense where multiple techniques, scientists, engineers, and organizations are involved. This presentation describes NASA Glenn Research Center's approach in developing a common software platform for processing waveform-based NDE signals and images. This platform is currently in use at NASA Glenn and at Lockheed Martin Michoud Assembly Facility for processing of pulsed terahertz and ultrasonic data. Highlights of the software operation will be given. A case study will be shown for use with terahertz data. The authors also request scientists and engineers who are interested in sharing customized signal and image processing algorithms to contribute to this effort by letting the authors code up and include these algorithms in future releases.

Roth, Donald J.↗
NASA NTRS1990

An expert system for geologic mapping with imaging spectrometers

Techniques have been developed for the extraction and characterization of absorption features from visible and infrared reflectance spectra and an expert system has been designed, implemented, and successfully tested that allows automated identification of minerals based on their spectral characteristics. A suite of laboratory spectra of common minerals was analyzed and the absorption band characteristics tabulated and used to develop a generalized knowledge base for analysis of the reflectance spectra. A tree hierarchy was designed to emulate the decision process followed by an experienced analyst for analysis of laboratory and field reflectance spectra and aircraft imaging spectrometer spectra. Good results were obtained with the expert system for all three types of spectra, with the critical factor in the analysis being the signal-to-noise ratio of the spectral data.

Kruse, F. A.↗
DOE OSTI2014

Mass-ablation-rate measurements in direct-drive cryogenic implosions using x-ray self-emission images

A technique to measure the mass ablation rate in direct-drive inertial confinement fusion implosions using a pinhole x-ray framing camera is presented. In target designs consisting of two layers of different materials, two x-ray self-emission peaks from the coronal plasma were measured once the laser burned through the higher-Z outer layer. The location of the inner peak is related to the position of the ablation front and the location of the outer peak corresponds to the position of the interface of the two layers in the plasma. The emergence of the second peak was used to measure the burnthrough time of the outer layer, giving the average mass ablation rate of the material and instantaneous mass remaining. By varying the thickness of the outer layer, the mass ablation rate can be obtained as a function of time. Simulations were used to validate the methods and verify that the measurement techniques are not sensitive to perturbation growth at the ablation surface.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2019

Effective Cloud Detection and Segmentation Using a Gradient-Based Algorithm for Satellite Imagery: Application to Improve PERSIANN-CCS

The effective identification of clouds and monitoring of their evolution are important toward more accurate quantitative precipitation estimation and forecast. In this study, a new gradient-based cloud-image segmentation algorithm is developed using image processing techniques. This method integrates morphological image gradient magnitudes to separate cloud systems and patches boundaries. A varying scale kernel is implemented to reduce the sensitivity of image segmentation to noise and to capture objects with various finenesses of the edges in remote sensing images. The proposed method is flexible and extendable from single to multispectral imagery. Case studies were carried out to validate the algorithm by applying the proposed segmentation algorithm to synthetic radiances for channels of the Geostationary Operational Environmental Satellite ( GOES-16) simulated by a high-resolution weather prediction model. The proposed method compares favorably with the existing cloud-patch-based segmentation technique implemented in the Precipitation Estimation from Remotely Sensed Information Using Artificial Neural Networks–Cloud Classification System (PERSIANN-CCS) rainfall retrieval algorithm. Evaluation of event-based images indicates that the proposed algorithm has potentials comparing to the conventional segmentation technique used in PERSIANN-CCS to improve rain detection and estimation skills with an accuracy rate of up to 98% in identifying cloud regions.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2015

Two-dimensional wave-number spectral analysis techniques for phase contrast imaging turbulence imaging data on large helical device

An analysis method for unfolding the spatially resolved wave-number spectrum and phase velocity from the 2D CO{sub 2} laser phase contrast imaging system on the large helical device is described. This is based on the magnetic shear technique which identifies propagation direction from 2D spatial Fourier analysis of images detected by a 6 × 8 detector array. Because the strongest modes have wave-number at the lower end of the instrumental k range, high resolution spectral techniques are necessary to clearly resolve the propagation direction and hence the spatial distribution of fluctuations along the probing laser beam. Multiple-spatial point cross-correlation averaging is applied before calculating the spatial power spectrum. Different methods are compared, and it is found that the maximum entropy method (MEM) gives best results. The possible generation of artifacts from the over-narrowing of spectra are investigated and found not to be a significant problem. The spatial resolution Δρ (normalized radius) around the peak wave-number, for conventional Fourier analysis, is ∼0.5, making physical interpretation difficult, while for MEM, Δρ ∼ 0.1.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
NASA NTRS1997

Image registration by parts

In spite of the large number of different image registration techniques, most of these techniques use the correlation operation to match spatial image characteristics. Correlation is known to be one of the most computationally intensive operations and its computational needs grow rapidly with the increase in the image sizes. In this article, we show that, in many cases, it might be sufficient to determine image transformations by considering only one or several parts of the image rather than the entire image, which could result in substantial computational savings. This paper introduces the concept of registration by parts and investigates its viability. It describes alternative techniques for such image registration by parts and presents early empirical results that address the underlying trade-offs.

Chalermwat, Prachya↗
NASA NTRS1972

Some new techniques for processing remotely obtained images by self-generated spectral masks.

An extension of a new technique that makes possible parallel, simultaneous processing of remotely obtained images is presented. The technique holds out promise for automatic onboard classification of data. The central feature involves the generation of binary masks, directly from the image, based on object reflectance data, that group objects into equivalence classes. These masks, called equivalence class masks, can be used in various logical combinations to isolate classes of objects with a priori known reflectance or radiance signatures. Experimental verification of the technique is furnished for simple scenes. A computational scheme, based on a sequence of integrated irradiance measurements on the image, that makes it possible to identify objects within an equivalence class is suggested.

Stark, H.↗
DOE OSTI2015

Education and Training Needs in Radiation Oncology in India: Opportunities for Indo–US Collaborations

Purpose: To conduct a survey of radiation oncologists in India, to better understand specific educational needs of radiation oncology in India and define areas of collaboration with US institutions. Methods and Materials: A 20-question survey was distributed to members of the Association of Indian Radiation Oncologists and the Indian Brachytherapy Society between November 2013 and May 2014. Results: We received a total of 132 responses. Over 50% of the physicians treat more than 200 patients per day, use 2-dimensional or 3-dimensional treatment planning techniques, and approximately 50% use image guided techniques. For education needs, most respondents agreed that further education in intensity modulated radiation therapy, image guided radiation therapy, stereotactic radiation therapy, biostatistics, and research methods for medical residents would be useful areas of collaboration with institutions in the United States. Other areas of collaboration include developing a structured training module for nursing, physics training, and developing a second-opinion clinic for difficult cases with faculty in the United States. Conclusion: Various areas of potential collaboration in radiation oncology education were identified through this survey. These include the following: establishing education programs focused on current technology, facilitating exchange programs for trainees in India to the United States, promoting training in research methods, establishing training modules for physicists and oncology nurses, and creating an Indo–US. Tumor Board. It would require collaboration between the Association of Indian Radiation Oncologists and the American Society for Radiation Oncology to develop these educational initiatives.

29 ENERGY PLANNING, POLICY, AND ECONOMY↗
NASA NTRS1975

Design constraints of the LST fine guidance sensor

The LST Fine Guidance Sensor design is shaped by the rate of occurrence of suitable guide stars, the competition for telescope focal plane space with the Science Instruments, and the sensitivity of candidate image motion sensors. The relationship between these parameters is presented, and sensitivity to faint stars is shown to be of prime importance. An interferometric technique of image motion sensing is shown to have improved sensitivity and, therefore, a reduced focal plane area requirement in comparison with other candidate techniques (image-splitting prism and image dissector tube techniques). Another design requirement is speed in acquiring the guide star in order to maximize the time available for science observations. The design constraints are shown parametrically, and modelling results are presented.

Wissinger, A. B.↗
DOE OSTI2014

Modality comparison for small animal radiotherapy: A simulation study

Purpose: Small animal radiation therapy has advanced significantly in recent years. Whereas in the past dose was delivered using a single beam and a lead shield for sparing of healthy tissue, conformal doses can be now delivered using more complex dedicated small animal radiotherapy systems with image guidance. The goal of this paper is to investigate dose distributions for three small animal radiation treatment modalities. Methods: This paper presents a comparison of dose distributions generated by the three approaches—a single-field irradiator with a 200 kV beam and no image guidance, a small animal image-guided conformal system based on a modified microCT scanner with a 120 kV beam developed at Stanford University, and a dedicated conformal system, SARRP, using a 220 kV beam developed at Johns Hopkins University. The authors present a comparison of treatment plans for the three modalities using two cases: a mouse with a subcutaneous tumor and a mouse with a spontaneous lung tumor. A 5 Gy target dose was calculated using the EGSnrc Monte Carlo codes. Results: All treatment modalities generated similar dose distributions for the subcutaneous tumor case, with the highest mean dose to the ipsilateral lung and bones in the single-field plan (0.4 and 0.4 Gy) compared to the microCT (0.1 and 0.2 Gy) and SARRP (0.1 and 0.3 Gy) plans. The lung case demonstrated that due to the nine-beam arrangements in the conformal plans, the mean doses to the ipsilateral lung, spinal cord, and bones were significantly lower in the microCT plan (2.0, 0.4, and 1.9 Gy) and the SARRP plan (1.5, 0.5, and 1.8 Gy) than in single-field irradiator plan (4.5, 3.8, and 3.3 Gy). Similarly, the mean doses to the contralateral lung and the heart were lowest in the microCT plan (1.5 and 2.0 Gy), followed by the SARRP plan (1.7 and 2.2 Gy), and they were highest in the single-field plan (2.5 and 2.4 Gy). For both cases, dose uniformity was greatest in the single-field irradiator plan followed by the SARRP plan due to the sensitivity of the lower energy microCT beam to target heterogeneities and image noise. Conclusions: The two treatment planning examples demonstrate that modern small animal radiotherapy techniques employing image guidance, variable collimation, and multiple beam angles deliver superior dose distributions to small animal tumors as compared to conventional treatments using a single-field irradiator. For deep-seated mouse tumors, however, higher-energy conformal radiotherapy could result in higher doses to critical organs compared to lower-energy conformal radiotherapy. Treatment planning optimization for small animal radiotherapy should therefore be developed to take full advantage of the novel conformal systems.

62 RADIOLOGY AND NUCLEAR MEDICINE↗
NASA NTRS1985

Retrieval of cloud cover parameters from multispectral satellite images

A technique is described for extracting cloud cover parameters from multispectral satellite radiometric measurements. Utilizing three channels from the AVHRR (Advanced Very High Resolution Radiometer) on NOAA polar orbiting satellites, it is shown that one can retrieve four parameters for each pixel: cloud fraction within the FOV, optical thickness, cloud-top temperature and a microphysical model parameter. The last parameter is an index representing the properties of the cloud particle and is determined primarily by the radiance at 3.7 microns. The other three parameters are extracted from the visible and 11 micron infrared radiances, utilizing the information contained in the two-dimensional scatter plot of the measured radiances. The solution is essentially one in which the distributions of optical thickness and cloud-top temperature are maximally clustered for each region, with cloud fraction for each pixel adjusted to achieve maximal clustering.

Arking, A.↗
NASA NTRS1986

Destriping AIS data using Fourier filtering techniques

Airborne Imaging Spectrometers (AIS) data collected in 1984 and 1985 showed pronounced striping in the vertical and horizontal directions. This striping reduced the signal to noise ratio so that features of the spectra of forest canopies were obscured or altered by noise. This noise was removed by application of a notch filter to the Fourier transform of the imagery in each waveband.

Hlavka, C.↗