Engineering topics

Smith, J. A.

Publications and source records attributed to Smith, J. A..

At least 19 records

DOE OSTI2023

The Dark Energy Survey Six-Year Calibration Star Catalog

This Technical Note presents a catalog of calibrated reference stars that was generated by the Forward Calibration Method (FGCM) pipeline (arXiv:1706.01542) as part of the FGCM photometric calibration of the full Dark Energy Survey (DES) 6-Year data set (Y6). This catalog provides DES grizY magnitudes for 17 million stars with i-band magnitudes mostly in the range 16 < i < 21 spread over the full DES footprint covering 5000 square degrees over the Southern Galactic Cap at galactic latitudes b < -20 degrees (plus a few outlying fields disconnected from the main survey footprint). These stars are calibrated to a uniformity of better than 1.8 milli-mag (0.18%) RMS over the survey area. The absolute calibration of the catalog is computed with reference to the STISNIC.007 spectrum of the Hubble Space Telescope CalSpec standard star C26202; including systematic errors, the absolute flux system is known at the approximately 1% level. As such, these stars provide a useful reference catalog for calibrating grizY-band or grizY-like band photometry in the Southern Hemisphere, particularly for observations within the DES footprint.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2018

Calibrating the Dark Energy Survey: The Role of DA White Dwarfs [Slides]

We have been searching the southern hemisphere for hot DAs which can be used as part of the Dark Energy Survey (DES) calibration process. This involves photometric and spectroscopic efforts. We will describe the program and results to date; the overall DES calibration effort; and future plans to finalize our project.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

DOE OSTI2017

Discovery of a new quasar: SDSS J022155.26-064916.6

Here, we report the discovery of a new quasar: SDSS J022155.26-064916.6. This object was discovered while reducing the spectra of a sample of stars being considered as spectrophotometric standards for the Dark Energy Survey. The flux- and wavelength-calibrated spectrum is presented with four spectral lines identified. From these lines, the redshift is determined to be z≈0.806. In addition, the rest-frame u- , g- , and r -band luminosity, determined using a k-correction obtained with synthetic photometry of a proxy quasi stellar object (QSO), are reported as 7.496×10 13 L ⊙ , 2.049×10 13 L ⊙ , and 1.896×10 13 L ⊙ , respectively.

79 ASTRONOMY AND ASTROPHYSICS↗

DOE OSTI2017

Characterization of a spectroscopic detector for application in x-ray computed tomography

Recent advances in cadmium telluride (CdTe) energy-discriminating pixelated detectors have enabled the possibility of Multi-Spectral X-ray Computed Tomography (MSXCT) to incorporate spectroscopic information into CT. MultiX ME 100 V2 is a CdTe-based spectroscopic x-ray detector array capable of recording energies from 20 to 160 keV in 1.1 keV energy bin increments. Hardware and software have been designed to perform radiographic and computed tomography tasks with this spectroscopic detector. Energy calibration is examined using the end-point energy of a bremsstrahlung spectrum and radioisotope spectral lines. When measuring the spectrum from Am-241 across 500 detector elements, the standard deviation of the peak-location and FWHM measurements are ±0.4 and ±0.6 keV, respectively. As these values are within the energy bin size (1.1 keV), detector elements are consistent with each other. The count rate is characterized, using a nonparalyzable model with a dead time of 64 ± 5 ns. This is consistent with the manufacturer’s quoted per detector-element linear-deviation at 2 Mpps (million photons per sec) of 8.9% (typical) and 12% (max). When comparing measured and simulated spectra, a low-energy tail is visible in the measured data due to the spectral response of the detector. If no valid photon detections are expected in the low-energy tail, then a background subtraction may be applied to allow for a possible first-order correction. If photons are expected in the low-energy tail, a detailed model must be implemented. A radiograph of an aluminum step wedge with a maximum height of about 20 mm shows an underestimation of attenuation by about 10% at 60 keV. This error is due to partial energy deposition from higher-energy (> 60 keV) photons into a lower-energy (~60 keV) bin, reducing the apparent attenuation. A radiograph of a PTFE cylinder taken using a bremsstrahlung spectrum from an x-ray voltage of 100 kV filtered by 1.3 mm Cu is reconstructed using Abel inversion. As no counts are expected in the low energy tail, a first order background correction is applied to the spectrum. The measured linear attenuation coefficient (LAC) is within 10% of the expected value in the 60 to 100 keV range. Below 60 keV, low counts in the corrected spectrum and partial energy deposition from incident photons of energy greater than 60 keV into energy bins below 60 keV impact the LAC measurements. This report ends with a demonstration of the tomographic capability of the system. The quantitative understanding of the detector developed in this report will enable further study in evaluating the system for characterization of an object’s chemical make-up for industrial and security purposes.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Sub-ice-shelf sediments record history of twentieth-century retreat of Pine Island Glacier [Sub-ice shelf sediments record 20 th century retreat history of Pine Island Glacier]

The West Antarctic Ice Sheet is one of the largest potential sources of rising sea levels. Over the past 40 years, glaciers flowing into the Amundsen Sea sector of the ice sheet have thinned at an accelerating rate, and several numerical models suggest that unstable and irreversible retreat of the grounding line—which marks the boundary between grounded ice and floating ice shelf—is underway. Understanding this recent retreat requires a detailed knowledge of grounding-line history, but the locations of the grounding line before the advent of satellite monitoring in the 1990s are poorly dated. In particular, a history of grounding-line retreat is required to understand the relative roles of contemporaneous ocean-forced change and of ongoing glacier response to an earlier perturbation in driving ice-sheet loss. Here we show that the present thinning and retreat of Pine Island Glacier in West Antarctica is part of a climatically forced trend that was triggered in the 1940s. Our conclusions arise from analysis of sediment cores recovered beneath the floating Pine Island Glacier ice shelf, and constrain the date at which the grounding line retreated from a prominent seafloor ridge. We find that incursion of marine water beyond the crest of this ridge, forming an ocean cavity beneath the ice shelf, occurred in 1945 (±12 years); final ungrounding of the ice shelf from the ridge occurred in 1970 (±4 years). The initial opening of this ocean cavity followed a period of strong warming of West Antarctica, associated with El Niño activity. Furthermore our results suggest that, even when climate forcing weakened, ice-sheet retreat continued.

58 GEOSCIENCES↗

DOE OSTI2016

Progress in developing laser based post irradiation examination infrastructure

To be able to understand the performance of reactor fuels and materials, irradiated materials must be characterized effectively and efficiently in high rad environments. This characterization work is performed remotely and in environments generally hostile to instrumentation. Laser based characterization techniques provide the ability to operate remotely and robustly in a hot-cell environment. Laser based instrumentation also can provide high spatial resolution suitable for scanning and imaging large areas. The INL is currently developing three laser based Post Irradiation Examination (PIE) stations for the Hot Fuel Examination Facility (HFEF) at the INL. These laser based systems will characterize irradiated materials and fuels. The characterization systems are the following: -) laser shock, -) laser based ultrasonic C-scan system and -) gas assay, sample and recharge system (GASR, up-grade to an existing system). The laser shock technique will characterize material properties and failure loads/mechanisms in various materials such as Light Water Reactor (LWR) fuel, plate fuel, and next generation fuel forms in high radiation areas. The laser shock-technique induces large amplitude shock waves to mechanically characterize interfaces such as the fuel-clad bond. As part of the laser shock system, a laser-based ultrasonic C-scan system will be used to detect and characterize de bonding caused by the application of the laser shock as well as performing classical non-destructive evaluation testing and imaging functions such as microstructure characterization, flaw detection and dimensional metrology. A spectroscopy capability can be added later as the salient components to perform Light Induced Breakdown Spectroscopy will be in place. Additional fiber ports in the feed-through will also enable future spectroscopic techniques to be efficiently installed and operated. The purpose of the GASR is to measure the pressure/volume of the plenum of an irradiated fuel element/capsule and obtain fission gas samples for analysis. The study of pressure and volume in the plenum of an irradiated fuel element/capsule and the analysis of fission gases released is important to understanding the performance of reactor fuels and materials. The main function of the laser in this application is to puncture the fuel rod or plate to allow the fission gas to escape and if necessary to weld the hole close. This system may also be used to measure the pressure/volume of other components (such as control blades) and obtain gas samples from these components for analysis. The GASR upgrade will match the functionality of the current system and provide these important functions on fuels made from current and future engineered materials. The GASR station will also have the inherent capability to perform cutting welding and joining functions within a hot-cell. The extra fiber ports built into the hot cell feed-through will also enable the efficient installation of future laser processing work benches. (authors)

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗

DOE OSTI2016

Wireless in-core acoustic telemetry and self-powered sensing

A promising wireless telemetry infrastructure based on acoustic transmission of in-pile measurements (information) is being developed at the Idaho National Laboratory for use in nuclear reactors. In this paper, we will demonstrate an approach to telemetry and sensing that exploits a reactor core's energy-rich environment to generate acoustic telemetry signals from self-powered telemeters that produce sounds. These sounds propagate through the reactor's coolant, whether it is gas, water, or liquid metal, through its mechanical structures (e.g., lattice work, pressure vessel, and piping), and can be detected outside the reactor. A thermo-acoustic (TAC) sensor was designed to be geometrically indistinguishable from the other Training Research Isotopes General Atomics (TRIGA) fuel elements in the Breazeale reactor's core. Heat was produced by fission of two Pathfinder {sup 235}UO{sub 2} fuel pellets contained within a finned heat exchanger. The acoustic signals from the TAC sensor can be picked up by hydro-phones and accelerometers anywhere in the reactor pool and from structures that penetrate the pool. Most of the signals we acquired had sufficient signal-to-noise ratios even with both the {sup 16}N diffusion pump and the pool coolant pump operating. The TAC sensor was tested during eight irradiation runs in the Breazeale Nuclear Reactor over the span of a week. We were able to show that the frequency of the thermo-acoustically generated sound provides an accurate determination of the reactor's coolant temperature. Such a sensor strategy might have provided useful information in a reactor accident like that which destroyed the Fukushima complex in March 2011.

21 SPECIFIC NUCLEAR REACTORS AND ASSOCIATED PLANTS↗

NASA NTRS2008

Formation of Large (Approximately 100 micrometers) Ice Crystals Near the Tropical Tropopause

Recent high-altitude aircraft measurements with in situ imaging instruments indicated the presence of relatively large (approx.100 microns length), thin (aspect ratios of approx.6:1 or larger) hexagonal plate ice crystals near the tropical tropopause in very low concentrations (<0.01/L). These crystals were not produced by deep convection or aggregation. We use simple growth-sedimentation calculations as well as detailed cloud simulations to evaluate the conditions required to grow the large crystals. Uncertainties in crystal aspect ratio leave a range of possibilities, which could be constrained by knowledge of the water vapor concentration in the air where the crystal growth occurred. Unfortunately, water vapor measurements made in the cloud formation region near the tropopause with different instruments ranged from <2 ppmv to approx.3.5 ppmv. The higher water vapor concentrations correspond to very large ice supersaturations (relative humidities with respect to ice of about 200%). If the aspect ratios of the hexagonal plate crystals are as small as the image analysis suggests (6:1, see companion paper (Lawson et al., 2008)) then growth of the large crystals before they sediment out of the supersaturated layer would only be possible if the water vapor concentration were on the high end of the range indicated by the different measurements (>3 ppmv). On the other hand, if the crystal aspect ratios are quite a bit larger (approx.10:1), then H2O concentrations toward the low end of the measurement range (approx.2-2.5 ppmv) would suffice to grow the large crystals. Gravity-wave driven temperature and vertical wind perturbations only slightly modify the H2O concentrations needed to grow the crystals. We find that it would not be possible to grow the large crystals with water concentrations less than 2 ppmv, even with assumptions of a very high aspect ratio of 15 and steady upward motion of 2 cm/s to loft the crystals in the tropopause region. These calculations would seem to imply that the measurements indicating water vapor concentrations less than 2ppmv are implausible, but we cannot rule out the possibility that higher humidity prevailed upstream of the aircraft measurements and the air was dehydrated by the cloud formation. Simulations of the cloud formation with a detailed model indicate that homogeneous freezing should generate ice concentrations larger than the observed concentrations (20/L), and even concentrations as low as 20/L should have depleted the vapor in excess of saturation and prevented growth of large crystals. It seems likely that the large crystals resulted from ice nucleation on effective heterogeneous nuclei at low ice supersaturations. Improvements in our understanding of detailed cloud microphysical processes require resolution of the water vapor measurement discrepancies in these very cold, dry regions of the atmosphere.

Jensen, E. J.↗

NASA NTRS2006

Modeling the Optical Properties of Biomass Burning Aerosols: Young Smoke Aerosols From Savanna Fires and Comparisons to Observations from SAFARI 2000

Annually, farmers in southern Africa manage their land resources and prepare their fields for cultivation by burning crop residual debris, with a peak in the burning season occurring during August and September. The emissions from these fires in southern Africa are among the greatest from fires worldwide, and the gases and aerosol particles produced adversely affect air quality large distances from their source regions, and can even be tracked in satellite imagery as they cross the Atlantic and Pacific Ocean basins. During August and September 2000 an international group of researchers participating in the Southern African Regional Science Initiate field experiment (SAFARI 2000) made extensive ground-based, airborne, and satellite measurements of these gases and aerosols in order to quantify their amounts and effects on Earth's atmosphere. In this study we interpreted the measurements of smoke aerosol particles made during SAFARI 2000 in order to better represent these particles in a numerical model simulating their transport and fate. Typically, smoke aerosols emitted from fires are concentrated by mass in particles about 0.3 micrometers in diameter (1,000,000 micrometers = 1 meter, about 3 feet); for comparison, the thickness of a human hair is about 50 micrometers, almost 200 times as great. Because of the size of these particles, at the surface they can be easily inhaled into the lungs, and in high concentrations have deleterious health effects on humans. Additionally, these particles reflect and absorb sunlight, impacting both visibility and the balance of sunlight reaching -Earth's surface, and ultimately play a role in modulating Earth's climate. Because of these important effects, it is important that numerical models used to estimate Earth's climate response to changes in atmospheric composition accurately represent the quantity and evolution of smoke particles. In our model, called the Community Aerosol and Radiation Model for Atmospheres (CARMA) we used estimates of smoke emissions based on field studies and observations made with the NASA Terra and TRMM satellites. The meteorology used to calculate the transport was based on an assimilation of observed meteorological conditions provided by the National Center for Atmospheric Research.

Matichuk, R. I.↗

NASA NTRS2002

Biological Invasions: A Challenge In Ecological Forecasting

The spread of invasive species is one of the most daunting environmental, economic, and human-health problems facing the United States and the World today. It is one of several grand challenge environmental problems being considered by NASA's Earth Science Vision for 2025. The invasive species problem is complex and presents many challenges. Developing an invasive species predictive capability could significantly advance the science and technology of ecological forecasting.

Schnase, J. L.↗

NASA NTRS2002

A Multi-Wavelength Thermal Infrared and Reflectance Scene Simulation Model

Several theoretical calculations are presented and our approach discussed for simulating overall composite scene thermal infrared exitance and canopy bidirectional reflectance of a forest canopy. Calculations are performed for selected wavelength bands of the DOE Multispectral Thermal Imagery and comparisons with atmospherically corrected MTI imagery are underway. NASA EO-1 Hyperion observations also are available and the favorable comparison of our reflective model results with these data are reported elsewhere.

Ballard, J. R., Jr.↗

NASA NTRS2000

Calculation of TIR Canopy Hot Spot and Implications for Earth Radiation Budget

Using a 3-D model for thermal infrared exitance and the Lowtran 7 atmospheric radiative transfer model, we compute the variation in brightness temperature with view direction and, in particular, the canopy thermal hot spot. We then perform a sensitivity analysis of surface energy balance components for a nominal case using a simple SVAT model given the uncertainty in canopy temperature arising from the thermal hot spot effect. Canopy thermal hot spot variations of two degrees C lead to differences of plus or minus 24% in the midday available energy.

Smith, J. A.↗

NASA NTRS1999

Physics Based Modeling and Rendering of Vegetation in the Thermal Infrared

We outline a procedure for rendering physically-based thermal infrared images of simple vegetation scenes. Our approach incorporates the biophysical processes that affect the temperature distribution of the elements within a scene. Computer graphics plays a key role in two respects. First, in computing the distribution of scene shaded and sunlit facets and, second, in the final image rendering once the temperatures of all the elements in the scene have been computed. We illustrate our approach for a simple corn scene where the three-dimensional geometry is constructed based on measured morphological attributes of the row crop. Statistical methods are used to construct a representation of the scene in agreement with the measured characteristics. Our results are quite good. The rendered images exhibit realistic behavior in directional properties as a function of view and sun angle. The root-mean-square error in measured versus predicted brightness temperatures for the scene was 2.1 deg C.

Smith, J. A.↗

NASA NTRS1994

Application of AI techniques to infer vegetation characteristics from directional reflectance(s)

Traditionally, the remote sensing community has relied totally on spectral knowledge to extract vegetation characteristics. However, there are other knowledge bases (KB's) that can be used to significantly improve the accuracy and robustness of inference techniques. Using AI (artificial intelligence) techniques a KB system (VEG) was developed that integrates input spectral measurements with diverse KB's. These KB's consist of data sets of directional reflectance measurements, knowledge from literature, and knowledge from experts which are combined into an intelligent and efficient system for making vegetation inferences. VEG accepts spectral data of an unknown target as input, determines the best techniques for inferring the desired vegetation characteristic(s), applies the techniques to the target data, and provides a rigorous estimate of the accuracy of the inference. VEG was developed to: infer spectral hemispherical reflectance from any combination of nadir and/or off-nadir view angles; infer percent ground cover from any combination of nadir and/or off-nadir view angles; infer unknown view angle(s) from known view angle(s) (known as view angle extension); and discriminate between user defined vegetation classes using spectral and directional reflectance relationships developed from an automated learning algorithm. The errors for these techniques were generally very good ranging between 2 to 15% (proportional root mean square). The system is designed to aid scientists in developing, testing, and applying new inference techniques using directional reflectance data.

Kimes, D. S.↗

NASA NTRS1991

Inclination distributions and size measurements of hemlock and red spruce needles

Needle inclination angle distributions were plotted for 5 and 10 deg intervals for two hemlock trees and one red spruce. The distributions for the hemlock and spruce were similar, with the peak normal angle occurring between 10 and 20 deg. These distributions are between two theoretical (planophile and spherical) leaf angle distributions. The results can be used as an input to radiative transfer models that require a distribution of the orientation of the scattering elements of the canopy.

Kimes, Daniel S.↗

NASA NTRS1989

Modeling directional thermal radiance from a forest canopy

The thermal vegetation canopy radiance model of Smith et al. (1981) is extended to account for the geometrically rough structure of a forest canopy. Fourier series expansion of a canopy height profile is used to calculate improved view facts which partially account for directional variations in canopy thermal radiance transfers. Predictions from the Smith model and the modified model are compared with experimental data obtained over a deciduous forest site in Tennessee. The results show that thermal radiance from a forest canopy depends on sensor viewing angle, solar position, and the degree of geometric roughness of the canopy surface. The maximum off-nadir angle variation in the original model was 1.6 deg C, compared with 4.4 C for the modified model.

Mcguire, M. J.↗

NASA NTRS1988

Characterizing forest ecosystem dynamics through modelling and remote sensing observations

To gain a better understanding of northern/boreal forest dynamics over a range of spatial and temporal scales, an approach to integrate models of forest growth, soil processes and radiative transfer with remote sensing observations was developed. The integrated model and remote sensing can be used to examine descriptors of ecosystem dynamics. To examine the scaling of vegetation pattern from the local to the regional domain, distributions of area and perimeters of vegetation community associations were determined from satellite and aircraft images. Relationships between computed fractal dimensions (1.5 to 1.8) and succession history for managed and unmanaged areas are being explored.

Ranson, K. J.↗

NASA NTRS1987

Directional thermal infrared exitance distributions of a deciduous forest in summer

Directional measurements of effective radiant temperatures (ERT) were made from a rotating mount suspended above an Oak-Hickory canopy. A directional ERT distribution is presented showing fairly weak trends with view angle. Additional data are presented to illustrate the character of spatial variations of ERT as a function of view and sun angle.

Balick, Lee K.↗