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NASA's CLARREO Pathfinder Mission: The Reflected Solar’s First SITSat

The Climate Absolute Radiance and Refractivity Observatory (CLARREO) Pathfinder mission will take reflected solar (RS) highly accurate measurements needed to monitor Earth’s climate and will be the first RS SI-traceable Satellite Sensor (SITSat). The mission includes a RS spectrometer that will be installed on the International Space Station (ISS) and take measurements for at least one year. CLARREO Pathfinder (CPF) will use on-orbit calibration to achieve an unprecedented high accuracy with SI-traceability and the inter-calibration of other on-orbit instruments. The spectrometer is based on the HyperSpectral Imager for Climate Science (HySICS) instrument developed by the University of Colorado/Laboratory for Atmospheric and Space Physics of Boulder, CO, USA. HySICS is being designed to have a radiometric uncertainty of 0.3% (1-sigma), a five to ten times improvement over existing spaceflight RS instruments. High accuracy SI-traceable measurements such as these are critical to develop long-term climate-quality data sets. Additionally, by measuring spectral reflectance with high accuracy the CPF instrument will serve as an on-orbit intercalibration radiometric reference for operational Earth-viewing sensors, such as the Clouds and Earth’s Radiant Energy System (CERES) broadband shortwave instrument and the Visible/Infrared Imaging Radiometer Suite (VIIRS). Two-axis pointing, a spectral range from 350 nm to 2300 nm, and a spectral resolution ≤6 nm enable CPF to provide nearly coincident temporal, spatial, angular, and spectral matching of intercalibration targets, with sampling sufficient to reduce random errors. The intercalibration method will refine knowledge of target sensors’ effective offsets, gain, non-linearity, spectral response, and polarization sensitivity (as is relevant). Calibrated reflectance and reflected radiance spectra will be distributed to the scientific community through a NASA Distributed Active Archive Center (DAAC). We will present an overview of the CLARREO Pathfinder mission, its anticipated impact on monitoring climate variability, and the novel CPF direct intercalibration approach.

climate↗
DOE OSTI2016

Titanium and Aluminum Rod-Replacement Experiments in Fully-Reflected 6.90% Enriched UO{sub 2} Fuel Rod Lattices

The Seven Percent Critical Experiment (7uPCX) was designed to provide benchmark criticality and reactor physics data for water-moderated pin-fueled nuclear reactor cores. The enrichment of the fuel was chosen to explore the enrichment range above the current 5% ceiling for US commercial pressurized water reactors. The experiment was part of the US Department of Energy (DOE) Nuclear Energy Research Initiative Project 01-124 titled 'Reactor Physics and Criticality Benchmark Evaluations for Advanced Nuclear Fuel'. Three sets of benchmark experiments have been completed using the 7uPCX and documented as LEUCOMP-THERM-080, LEU-COMP-THERM-078, and LEUCOMP-THERM-096. The experiments for LEUCOMP-THERM-080 and LEU-COMP-THERM-078 were done in fully-reflected arrays with the number of fuel rods in the array as the approach parameter. The experiments for LEU-COMP-THERM-096 are similar to those in LEUCOMP-THERM-080 except that the arrays are partially-reflected - the arrays were larger than would be possible with full reflection and the approach-to-critical experiments were done with the depth of the water in the critical assembly as the approach parameter. The experiments described here are similar to the fully-reflected experiments in LEU-COMP-THERM-080 with some of the central fuel rods in the array replaced by titanium rods, aluminum rods, and/or water. The experiments are designed to provide criticality safety benchmarks with significant reactivity from titanium and equivalent configurations with aluminum experiment rods. These experiments are documented as LEU-COMP-THERM-097. (authors)

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2026

Imaging surface topography with coherent x-ray reflectivity: Theory, kinematics, and simulations

A theoretical formalism is described for understanding coherent x-ray reflectivity (CXR) from the surface of a semi-infinite crystal having a variable surface topography, described by the height profile ℎ(𝑥,𝑦). The surface topography is imaged as a complex “effective density,” obtained from the phasing and inversion of the coherent x-ray reflectivity data, measured through a rocking scan centered at a vertical momentum transfer 𝑄$^{0}_{𝑧}$ and a vertical range Δ⁢𝑄 𝑧 . The formalism predicts that the effective density has an amplitude with a maximum located at the surface height for each position within the surface plane. The phase of the effective density has a lateral variation that is controlled by the surface height and a vertical variation that reflects a combination of the interfacial structure and specific choice of measurement conditions. This understanding enables direct observation of nanometer-scale interfacial topography, i.e., ℎ⁡(𝑥,𝑦)⁢𝑐 𝑠 (where 𝑐 𝑠 is the vertical substrate lattice parameter) with Å-scale sensitivity to surface height. Numerical simulations illustrate and confirm the theoretical results. These results show how the interpretation of the interfacial density phase obtained by CXR data inversion (i.e., surface topography with respect to a flat surface) is conceptually similar to that previously known for Bragg coherent diffraction imaging (BCDI) measurements of isolated nanoparticles (i.e., lattice displacements with respect to an ideal crystal lattice). This suggests that CXR can be thought of as a form of dark field imaging with respect to the bright field BCDI approach. An implication of these results is that interfacial imaging may bypass some of the significant challenges associated with BCDI imaging of multiple particles having different orientations.

X-ray imaging↗
DOE OSTI2018

Resonant Optical Reflection from AsSb–AlGaAs Metamaterials and Structures

The optical reflection in periodic structures based on a semiconductor AlGaAs matrix containing two-dimensional arrays of plasmonic AsSb nanoinclusions was studied. The number of periods was 12 or 24. The spatial period was near 110 nm in both cases. In the experimental optical reflection spectra at normal incidence we observed resonant Bragg diffraction with the main peaks at wavelengths of 757 or 775 nm, depending on the spatial period of the nanostructure. The magnitudes of the resonance peaks reached 19 and 31% for the systems of 12 and 24 AsSb–AlGaAs layers, while the volume fraction of the nanoinclusions was much less than 1%. In the case of light incident at inclined angles, the Bragg-diffraction pattern shifted according to Wulff-Bragg’s law. Numerical calculations of the optical reflection spectra were performed using the transfer-matrix method by taking into account the spatial geometry of the structures and the resonance characteristics of the plasmonic AsSb layers.

36 MATERIALS SCIENCE↗
NASA NTRS2019

Evaluation of NOAA-20 VIIRS reflective solar bands calibration performance using vicarious approaches

The newly launched polar-orbiting NOAA-20 satellite is the follow-on mission to the SNPP (Suomi National Polar-orbiting Partnership) satellite. Both satellites are in an afternoon orbit with a close equatorial cross time. The Visible Infrared Imaging Radiometer Suite (VIIRS) is a key sensor onboard NOAA-20 and SNPP. The two VIIRS sensors are within the same engineering design with nearly identical spectral ranges. Its on-board calibration components include a solar diffuser and a solar diffuser stability monitor for the reflective solar bands (RSB), a V-groove blackbody for the thermal emissive bands (TEB), and a space view as background reference. This study evaluates calibration performance of the NOAA-20 VIIRS RSB using the first internally released L1B data product by NASA Land SIPS, which has consistent calibration coefficient look up tables (LUT) throughout the entire mission. Several independent vicarious approaches are used to examine the stability and consistence of reflectance. The first approach is based on a double difference method by comparison with SNPP VIIRS using observations from simultaneous nadir overpasses (SNO) with Aqua MODIS. The second is based on the reflectance trends from 16-day repeatable orbits obtained over the widely used Liby-4 desert site so each data point has the nearly same viewing angles relative to the site. The third approach is to use the frequent overpasses over the Dome C snow site. Results of this study provide NOAA-20 VIIRS post-launch calibration stability performance and radiometric agreement with SNPP for the first 18 months of mission.

VIIRS↗
DOE OSTI2017

Characterization of the Surface of Silver Ion-Implanted Silicon by Optical Reflectance

The optical reflection of the surface of silicon implanted with Ag{sup +} ions at low energy of 30 keV in a wide dosage range of 5.0·10{sup 14}–1.5·10{sup 17} ion/cm{sup 2} was studied in parallel with electron microscopy observation of the samples. It was found that with increasing ion dose of irradiation, the reflection intensity in the UV range of the Si spectrum decreases monotonically due to amorphization and macrostructuring of Si near-surface layer. In the long-wavelength region of the reflection spectra, a selective band with a maximum near 830 nm is recorded due to the plasmon resonance of ion-synthesized Ag nanoparticles.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2017

Social relations: A critical reflection on the notion of social impacts as change

This article seeks to reflect upon the dominant conception of social impacts as the change produced by development projects and programs, and the ways in which those affected perceive and experience them. Identifying change may be a necessary but not sufficient step in acknowledging the complexity of social life. Engaging with critical scholarship produced in the fields of both social impact assessment (SIA) and of the social studies of technical/planned interventions, I discuss how the understanding of social impacts as change responds ultimately to a causal–instrumental logic that, in order to make sense of the complexity of social life, tends to reduce it to a series of variables and matrices. I suggest a complementary dialectical approach focusing on social relations. This approach, allows an alternative means of analysing social impacts concerning the way policies and projects reconfigure conditions and possibilities on a societal level. To accomplish this, and in order to go beyond the sequence of potential impacts (or changes) and their generic indicators, I propose a set of analytical questions that highlight how social relations are structured. Besides, on the assumption that development is both a form of governance and a space of contestation, negotiation, and activism, this approach may contribute to further the potential for reflection and mobilisation that the practice of SIA presents. - Highlights: •Change, which is inherent to social life, is insufficient to determine social impacts. •The critique of causal-instrumental logic provides insights to reflect on social impacts. •Social impacts should rather refer to how interventions reconfigure social relations. •The complex, mutually constitutive nature of social phenomena may thus be recognized. •SIA should go beyond change to the understanding of its socio-political significance.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Bidirectional reflection of semitransparent polytetrafluoroethylene (PTFE) sheets on a silver film

In our recent work, record-high solar reflectance (exceeding 99%) has been demonstrated by placing a layer of highly scattering, semitransparent polytetrafluoroethylene (PTFE) sheet on top of a silver film. This can significantly improve the performance of daytime radiative cooling system. Although a PTFE slab of 10-mm thick acts as an excellent diffuse reflector, it is unclear how this dual-layer structure made of a thin PTFE on a mirror-like reflector will alter the bidirectional reflection. Here, we report measurements of the bidirectional reflectance distribution function (BRDF) of the dual-layer structure using a laser scatterometer at the wavelength of 635 nm. Measurements of the BRDF and the bidirectional transmittance distribution function (BTDF) of free-standing PTFE sheets are also performed. The measured BRDF for a PTFE sheet as thin as 236 μm on Ag is essentially diffuse except at large incidence angles. A Monte Carlo ray-tracing method incorporating both surface scattering and volumetric scattering is developed to theoretically model the BRDF in order to elucidate the underlying mechanisms. Finally, the numerical model captures the main features and can be used to study the bidirectional properties for PTFE sheets thinner than what is experimentally available.

42 ENGINEERING↗
DOE OSTI2019

Experimental study of vibration isolation in thin-walled structural assemblies with embedded total-internal-reflection metasurfaces

The concept of total-internal-reflection elastic metasurface (TIR-MS) was recently proposed [1] and employed within flexible planar waveguides in order to create highly subwavelength sound-hard barriers impenetrable to low frequency elastic waves. The underlying physical mechanism relies on the design of engineered interfaces exhibiting extreme phase gradients such that any incoming wave at, approximately, any incidence will experience total-internal-reflection conditions. At the design frequency, the metasurface exhibits a large phase gradient such that, in accordance with the generalized Snell's law, the first critical angle is virtually always exceeded. It is worth noting that in practical realizations, the actual total reflection performance might vary depending on the angle of incidence. This dependence is due to the discrete implementation of the metasurface which results in diffraction effects. This paper presents the results of an experimental study that explores the vibration isolation performance of TIR-MS when applied to structures made of complex combinations of different elastic waveguides (e.g. bolted assemblies of beams, plates, and shells). Such system can be seen as a prototypical structure emulating mechanical assemblies of practical interest for many engineering applications. Experimental results confirm that, when the TIR-MS is embedded in the host waveguide, significant vibration isolation capabilities are achieved under quasi-omnidirectional incidence and highly subwavelength excitation conditions (i.e. the ratio of the operating wavelength to the width of the TIR-MS is approximately 5.25). Furthermore, these experimental results suggest new interesting directions to achieve vibration isolation and mechanical energy filtering for practical engineering systems.

42 ENGINEERING↗
DOE OSTI2022

Using soil library hyperspectral reflectance and machine learning to predict soil organic carbon: Assessing potential of airborne and spaceborne optical soil sensing

Soil organic carbon (SOC) is a key variable to determine soil functioning, ecosystem services, and global carbon cycles. Spectroscopy, particularly optical hyperspectral reflectance coupled with machine learning, can provide rapid, efficient, and cost-effective quantification of SOC. However, how to exploit soil hyperspectral reflectance to predict SOC concentration, and the potential performance of airborne and satellite data for predicting surface SOC at large scales remain relatively underknown. Here, this study utilized a continental-scale soil laboratory spectral library (37,540 full-pedon 350–2500 nm reflectance spectra with SOC concentration of 0–780 g·kg –1 across the US) to thoroughly evaluate seven machine learning algorithms including Partial-Least Squares Regression (PLSR), Random Forest (RF), K-Nearest Neighbors (KNN), Ridge, Artificial Neural Networks (ANN), Convolutional Neural Networks (CNN), and Long Short-Term Memory (LSTM) along with four preprocessed spectra, i.e. original, vector normalization, continuum removal, and first-order derivative, to quantify SOC concentration. Furthermore, by using the coupled soil-vegetation-atmosphere radiative transfer model, we simulated twelve airborne and spaceborne hyper/multi-spectral remote sensing data from surface bare soil laboratory spectra to evaluate their potential for estimating SOC concentration of surface bare soils. Results show that LSTM achieved best predictive performance of quantifying SOC concentration for the whole data sets (R 2 = 0.96, RMSE = 30.81 g·kg –1 ), mineral soils (SOC ≤ 120 g·kg –1 , R 2 = 0.71, RMSE = 10.60 g·kg –1 ), and organic soils (SOC > 120 g·kg –1 , R 2 = 0.78, RMSE = 62.31 g·kg –1 ). Spectral data preprocessing, particularly the first-order derivative, improved the performance of PLSR, RF, Ridge, KNN, and ANN, but not LSTM or CNN. We found that the SOC models of mineral and organic soils should be distinguished given their distinct spectral signatures. Finally, we identified that the shortwave infrared is vital for airborne and spaceborne hyperspectral sensors to monitor surface SOC. This study highlights the high accuracy of LSTM with hyperspectral/multispectral data to mitigate a certain level of noise (soil moisture <0.4 m 3 ·m –3 , green leaf area < 0.3 m 2 ·m –2 , plant residue <0.4 m 2 ·m –2 ) for quantifying surface SOC concentration. Forthcoming satellite hyperspectral missions like Surface Biology and Geology (SBG) have a high potential for future global soil carbon monitoring, while high-resolution satellite multispectral fusion data can be an alternative.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2019

Surface albedo and reflectance: Review of definitions, angular and spectral effects, and intercomparison of major data sources in support of advanced solar irradiance modeling over the Americas

This study defines albedo and reflectance in the context of solar applications. It examines the main sources of surface albedo data that can be used to help solar irradiance modeling efforts, such as undertaken by the National Renewable Energy Laboratory (NREL) over the Americas, for instance, per the National Solar Radiation Database (NSRDB). The MODIS-based albedo database, as used as input to derive historical time series of solar irradiance in the current version of the NSRDB, is compared to other sources of global gridded data over the Americas in general and some specific areas in particular. The particular role of snow cover is analyzed. It is found that, in the current MODIS-based NSRDB implementation, snow-impacted areas have been assigned a too high albedo in general because of the lack of consideration for the antagonistic effect of surface roughness, among other factors. Other albedo databases, such as CMSAF, MINES-ParisTech or the ERA5 reanalysis, do not display such high albedos at latitudes above ~40 degrees N. The gap-free and snow-free MODIS MCD43GF product is found affected by a long-term downward trend over some areas and out-of-phase seasonal effects over other areas, in comparison with MERRA-2 reanalysis data in particular. Comparisons with actual albedo measurements at the arid Desert Rock site in Nevada also show that albedo data derived from land surface models are affected by systematic bias. Five albedo databases are intercompared for the area around Ivanpah Playa, California, which has great importance in both remote sensing and solar applications. Various aspects of the proper usage of albedo data in solar radiation modeling are discussed, regarding calculations of both the backscattering process and reflections on a tilted surface: spatial resolution, temporal resolution, angular effects, and spectral effects. An important distinction is made between the use of albedo data at ~4 km resolution for backscattering calculations and at ~10 m resolution for transposition calculations to tilted planes, which might additionally require spectral information for monofacial or bifacial PV applications. It is shown that the tilted calculations usually performed in solar resource assessments are far from realistic in the case of most large-scale PV applications, for which a more suitable methodological approach is described. For such needs, the limitations of the current sources of high-resolution reflectance data are discussed. The impact of surface albedo estimation errors on the estimation of backscattered irradiance over snowy areas is evaluated. It is found non-negligible, and even large under cloudy conditions.

14 SOLAR ENERGY↗
DOE OSTI2021

Thermal model to quantify the impact of sub-bandgap reflectance on operating temperature of fielded PV modules

Minimizing module heating is an effective way to increase the lifetime energy output of photovoltaic systems. Maximizing the reflection of light that is unusable for energy conversion is one of the most promising ways to reduce the operating temperature of fielded modules. We derive a model based on a steady-state energy balance to quantify the temperature benefit of cell or module optical modifications aimed at improving reflection of light with photon energies below the photovoltaic cell bandgap energy. This more detailed model is then simplified so that, from outdoor measured data, temperature differences arising from reflectance can be isolated from those arising from irradiance, wind speed, and module standard-test-condition efficiency.

14 SOLAR ENERGY↗
DOE OSTI2022

Noncontact Andreev Reflection as a Direct Probe of Superconductivity on the Atomic Scale

Direct detection of superconductivity has long been a key strength of point-contact Andreev reflection. However, its applicability to atomic-scale imaging is limited by the mechanical contact of the Andreev probe. To this end, we present a new method to probe Andreev reflection in a tunnel junction, leveraging tunneling spectroscopy and junction tunability to achieve quantitative detection of Andreev scattering. This method enables unambiguous assignment of superconducting origins of current-carrying excitations, as well as detection of higher order Andreev processes in atomic-scale junctions. Herein, we furthermore revealed distinct sensitivity of Andreev reflection to natural defects, such as step edges, even in classical superconductors. The methodology opens a new path to nano- and atomic-scale imaging of superconducting properties, including disordered superconductors and proximity to phase transitions.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Probing carrier dynamics of individual layers in a heterostructure using transient reflectivity

We report the wavelength dependent transient reflectivity measurements in AlGaAs-GaAs heterostructures having two-dimensional electron (or hole) gas near the interface. Using a multilayer model for transient reflectivity, we show that the magnitude and sign of contributions from the carriers in two-dimensional electron (or hole) gas and GaAs to the total signal depends on the wavelength. Further, it has been shown that it is possible to study the carrier dynamics in a given layer of a heterostructure by performing transient reflectivity at specific wavelengths.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Measurements of low-energy electron reflection at a plasma boundary

It is demonstrated that low-energy (<3 eV) electron reflection from a solid surface in contact with a low-temperature plasma can have significant variation with time. An uncontaminated, i.e., “clean,” metallic surface (just after heating up to glow) in a plasma environment may have practically no reflection of low-energy incident electrons. However, a contaminated, i.e., “dirty,” surface (in some time after cleaning by heating) that has a few monolayers of absorbent can reflect low-energy incident electrons and therefore significantly affect the net electron current collected by the surface. This effect may significantly change plasma properties and should be taken into account in plasma experiments and models. A diagnostic method is demonstrated for measurements of low-energy electron absorption coefficient in plasmas with a mono-energetic electron group.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

A simplified method for generating periodic nanostructures by interference lithography without the use of an anti-reflection coating

Interference lithography has proven to be a useful technique for generating periodic sub-diffraction limited nanostructures. Interference lithography can be implemented by exposing a photoresist polymer to laser light using a two-beam arrangement or more simply a one beam configuration based on a Lloyd's Mirror Interferometer. For typical photoresist layers, an anti-reflection coating must be deposited on the substrate to prevent adverse reflections from cancelling the holographic pattern of the interfering beams. For silicon substrates, such coatings are typically multilayered and complex in composition. By thinning the photoresist layer to a thickness well below the quarter wavelength of the exposing beam, we demonstrate that interference gratings can be generated without an anti-reflection coating on the substrate. We used ammonium dichromate doped polyvinyl alcohol as the positive photoresist because it provides excellent pinhole free layers down to thicknesses of 40 nm, and can be cross-linked by a low-cost single mode 457 nm laser, and can be etched in water. Gratings with a period of 320 nm and depth of 4 nm were realized, as well as a variety of morphologies depending on the photoresist thickness. This simplified interference lithography technique promises to be useful for generating periodic nanostructures with high fidelity and minimal substrate treatments.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Dynamics of spallation during femtosecond laser ablation studied by time-resolved reflectivity with double pump pulses

The dynamics of photomechanical spallation during femtosecond laser ablation of fused silica was studied by time-resolved reflectivity with double pump pulses. Oscillation of reflectivity was caused by interference between the probe pulses reflected at the sample surface and the spallation layer, and was enhanced when the surface was irradiated with the second pump pulse within a time interval, Δτ, of several picoseconds after the first pump pulse. However, as Δτ was increased, the oscillation amplitude decreased with an exponential decay time of 10 ps. The oscillation disappeared when Δτ exceeded 20 ps. This result suggests that the formation time of the spallation layer is approximately 10 ps. A second pump pulse with Δτ shorter than 10 ps excites the bulk sample. The spallation layer that is photo-excited by the first and second pump pulses is separated afterward. In contrast, a pulse with Δτ longer than the formation time excites and breaks up the spallation layer that has already been separated from the bulk. The formation time of the spallation layer, as determined in this experiment, is attributed to the characteristic time of the mechanical equilibration corresponding to the thickness divided by the sound velocity of the photo-excited layer.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Comparison of sub-Doppler-width resonances in transmission and reflection spectra of micrometer-thick Cs vapor layers

We report experimental study of resonance sign reversal at the hyperfine F{sub g} = 4 → F{sub e} = 5 transition on D{sub 2} line of {sup 133}Cs. Alkali vapors are confined in an optical cell with micrometric thickness. For circular polarization of the irradiating light, transmission and reflection spectra, recorded at different laser intensities and different temperature of alkali vapor, are studied and compared. At low laser intensity, in the transmission spectra we observe a narrow resonance of increased absorption (bright resonance) at the F{sub g} = 4 → F{sub e} = 5 transition, however in reflection spectra, recorded at the same experimental conditions, this bright resonance transforms into a dark resonance of reduced absorption. A simple explanation is proposed in order to explain the observed difference between the transmission and reflection spectra.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗