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At least 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
NASA NTRSDate not supplied

The NASA Space Radiation Laboratory

The Space Radiation Element (SRE) of the Human Research Program (HRP) aims to establish a robust biospecimen and tissue sharing collection (BTSC) to improve sample collection, tracking, access, distribution, and usability to maximize scientific return with intention. Future missions to the Moon, Mars, and beyond will require the appropriate characterization and mitigation of the many of the health risks associated with cosmic radiation exposure. An ongoing partnership between the National Aeronautics and Space Agency (NASA) and the Office of Science for the U.S. Department of Energy (DOE) has established the NASA Space Radiation Laboratory (NSRL) at the DOE Brookhaven National Laboratory (BNL) to create a space radiation ground-analog. NSRL provides the capability to use simulated space radiation with high energy ion beams for assessment of biological outcomes relevant space radiation risks as well as electronics testing for avionics safety. Current NSRL irradiation capabilities include a variety of exposure variables available for experimental needs: - Up to approximately 10 Gy/min dose-rates with a 20 × 20 cm 2 beam area. - Down to several hundred particles within a 60 × 60 cm 2 beam area. - Dose fractionation across multiple days is also possible. - For most radiobiology experiments the exposure structure, referred to as “spills”, has a 4 second repetition time where ions are extracted uniformly during a 0.3-0.4 second spill, followed by a ~3.6 second recovery time when the beam is off. - Both single or mixed-beam field irradiations are possible including a full 33-beam GCRSim and 6-beam SimGCRSim. Biological experiment capabilities: Two labs for Cell/tissue culture procedures can be conducted in two lab spaces with a separate lab available for sample processing that contains two chemical fume hoods. Sixteen fully equipped cell culture laboratories are available in the NSRL’s Long Term Support area in the Medical Building. The current vivarium configuration can support approximately 8,000 rodents/year for animal-based experiments. The NSRL area animal husbandry system includes five caging racks with 48 spaces in each coupled to a ventilation/filtration system in largest room, and two smaller rooms with conventional caging systems. Schedule: The NSRL is nominally open for experiment scheduling during three runs per year; Spring (March – May), Summer (May - June), and Fall (Sept – Nov). NASA funding is not required for biological and electronic testing experiments at the NSRL.

Jason M Weeks↗
NASA NTRS2002

Karyotypes of Human Lymphocytes Exposed to High-Energy Iron Ions

Chromosomal aberrations were analyzed using multicolor fluorescence in situ hybridization (mFISH) in human peripheral blood lymphocytes after in vitro exposure to gamma rays or accelerated (56)Fe ions (1 GeV/nucleon, 145 keV/microm) at Brookhaven National Laboratory (Upton, NY). Doses of 0.3 and 3 Gy were used for both radiation types. Chromosomes were prematurely condensed by a phosphatase inhibitor (calyculin A) to avoid the population selection bias observed at metaphase as a result of the severe cell cycle delays induced by heavy ions. A total of 1053 karyotypes (G(2) and M phases) were analyzed in irradiated lymphocytes. Results revealed different distribution patterns for chromosomal aberrations after low- and high-LET radiation exposures: Heavy ions induced a much higher fraction of cells with multiple aberrations, while the majority of the aberrant cells induced by low doses of gamma rays contained a single aberration. The high fraction of complex-type exchanges after heavy ions leads to an overestimation of simple-type asymmetrical interchanges (dicentrics) from analysis of Giemsa-stained samples. However, even after a dose of 3 Gy iron ions, about 30% of the cells presented no complex-type exchanges. The involvement of individual chromosomes in exchanges was similar for densely and sparsely ionizing radiation, and no statistically significant evidence of a nonrandom involvement of specific chromosomes was detected.

NASA Center JSC↗
NASA NTRS1991

Supernova remnants in dense clouds. I - Blast-wave dynamics and X-ray irradiation

Simplified models of cooling SNRs in uniform media together with an idealized emission spectrum are used to investigate the X-ray irradiation of the surrounding gas. The radiative transfer of the emitted X-rays through both the dense cooling shell and the unshocked cloud is calculated, with a simplified treatment to allow for an ionized zone surrounding the SNR. Numerical results are presented for SN energy of 10 exp 51 ergs and ambient densities ranging from 100 to 1,000,000 cu cm. It is found that an appreciable fraction of the X-ray energy is absorbed in regions where the X-ray energy deposited per H nucleon is between 1 and 30 eV; if the gas is initially molecular, the X-ray irradiation will result in warm molecular gas in which endothermic chemical reactions may proceed, and from which there may be strong emission in rotation-vibration transitions of H2 and other molecular species.

Draine, B. T.↗
NASA NTRS1992

Trapping of noble gases in proton-irradiated silicate smokes

We have measured Ne, Ar, Kr, and Xe in Si2O3 'smokes' that were condensed on Al substrates, vapor-deposited with various mixtures of CH4, NH3, H2O3 and noble gases at 10 K and subsequently irradiated with 1 MeV protons to simulate conditions during grain mantle formation in interstellar clouds. Neither Ne nor Ar is retained by the samples upon warming to room temperature, but Xe is very efficiently trapped and retained. Kr is somewhat less effectively retained, typically depleted by factors of about 10-20 relative to Xe. Isotopic fractionation favoring the heavy isotopes of Xe and Kr of about 5-10-percent/amu is observed. Correlations between the specific chemistry of the vapor deposition and heavy noble gas retention are most likely the result of competition by the various species for irradiation-produced trapping sites. The concentration of Xe retained by some of these smokes exceeds that observed in phase Q of meteorites and, like phase Q, they do not seem to be carriers of the light noble gases.

Nichols, R. H., Jr.↗
NASA NTRS2007

Chromosome Aberrations in Human Epithelial Cells Exposed Los Alamos High-Energy Secondary Neutrons: M-BAND Analysis

High-energy secondary neutrons, produced by the interaction of galactic cosmic rays (GCR) with the atmosphere, spacecraft structure and planetary surfaces, contribute a significant fraction to the dose equivalent radiation measurement in crew members and passengers of commercial aviation travel as well as astronauts in space missions. The Los Alamos Nuclear Science Center (LANSCE) neutron facility's 30L beam line (4FP30L-A/ICE House) is known to generate neutrons that simulate the secondary neutron spectrum of the Earth's atmosphere at high altitude. The neutron spectrum is also similar to that measured onboard spacecrafts like the MIR and the International Space Station (ISS). To evaluate the biological damage, we exposed human epithelial cells in vitro to the LANSCE neutron beams with an entrance dose rate of 2.5 cGy/hr, and studied the induction of chromosome aberrations that were identified with multicolor-banding in situ hybridization (mBAND) technique. With this technique, individually painted chromosomal bands on one chromosome allowed the identification of inter-chromosomal aberrations (translocation to unpainted chromosomes) and intra-chromosomal aberrations (inversions and deletions within a single painted chromosome). Compared to our previous results with gamma-rays and 600 MeV/nucleon Fe ions of high dose rate at NSRL (NASA Space Radiation Laboratory at Brookhaven National Laboratory), the neutron data from the LANSCE experiments showed significantly higher frequency of chromosome aberrations. However, detailed analysis of the inversion type revealed that all of the three radiation types in the study induced a low incidence of simple inversions. Most of the inversions in gamma-ray irradiated samples were accompanied by other types of intrachromosomal aberrations but few inversions were accompanied by interchromosomal aberrations. In contrast, neutrons and Fe ions induced a significant fraction of inversions that involved complex rearrangements of both inter- and intrachromosome exchanges. The distribution of damage sites on chromosome 3 was also compared for different radiation types. The breakpoints were randomly localized on chromosome 3 with neutrons and Fe ions exposure, whereas non-random distribution with clustering breakpoints was observed with gamma-rays exposure. The specific fingerprint of neutron radiations on chromosomal aberrations will be discussed.

Hada, M.↗
DOE OSTI2024

Thermal and dynamic partition of dumbbell interstitials in complex concentrated alloys

Complex concentrated alloys (CCAs) are promising candidates for applications in extreme conditions, such as irradiation where interstitial mediated diffusion is important. In CCAs with N principal elements, $\frac{N(N+1)}{2}$ types of dumbbell interstitials exist. Currently, there is no way to predict the thermal partition (fractional concentration at equilibrium) and the dynamic partition (fractional time an interstitial spends during diffusion) of each type of dumbbell interstitial. To mitigate this issue, this work proposes a theoretical model for computing the equilibrium concentrations and thermal partition of dumbbell interstitials in CCAs and validates the model using grand canonical Monte Carlo simulations. Lattice kinetic Monte Carlo simulations show that the thermal partition is equivalent to the dynamic partition, and both are governed by composition and formation energies of dumbbells. As a result, the model proposed provides a foundation for understanding radiation enhanced diffusion and induced segregation in CCAs under irradiation.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Influences of Cloud Microphysics on the Components of Solar Irradiance in the WRF-Solar Model

An accurate forecast of Global Horizontal solar Irradiance (GHI) and Direct Normal Irradiance (DNI) in cloudy conditions remains a major challenge in the solar energy industry. This study focuses on the impact of cloud microphysics on GHI and its partition into DNI and Diffuse Horizontal Irradiance (DHI) using the Weather Research and Forecasting model specifically designed for solar radiation applications (WRF-Solar) and seven microphysical schemes. Three stratocumulus (Sc) and five shallow cumulus (Cu) cases are simulated and evaluated against measurements at the US Department of Energy’s Atmospheric Radiation Measurement (ARM) user facility, Southern Great Plains (SGP) site. Results show that different microphysical schemes lead to spreads in simulated solar irradiance components up to 75% and 350% from their ensemble means in the Cu and Sc cases, respectively. The Cu cases have smaller microphysical sensitivity due to a limited cloud fraction and smaller domain-averaged cloud water mixing ratio compared to Sc cases. Cloud properties also influence the partition of GHI into DNI and DHI, and the model simulates better GHI than DNI and DHI due to a non-physical error compensation between DNI and DHI. The microphysical schemes that produce more accurate liquid water paths and effective radii of cloud droplets have a better overall performance.

54 ENVIRONMENTAL SCIENCES↗
DOE OSTI2024

Hourly dynamic line ratings for existing transmission across the contiguous United States (preliminary results) [Slides]

The thermal rating of a transmission line depends on the rate at which heat generated by current flow through the line can be dissipated into the environment by convective and radiative cooling, keeping the conductor below a maximum operating temperature. Static or seasonal line ratings assume nearly-worst-case weather conditions (high ambient air temperature, high solar irradiance, and low wind speed), resulting in a low risk of "overrating" a line (i.e., allowing more current to flow than the line is designed for) but a high fraction of time when the line is "underrated" (i.e., able to flow more current while staying below the maximum temperature). Dynamic transmission line ratings (DLR) use real-time measurements of weather conditions, line sag, or line temperature to determine the thermal rating of transmission lines at hourly or higher time resolution, allowing for increased ratings during some (cold, windy, and/or dark) periods and correcting for overrating during other (hot, calm, and/or sunny) periods. Many studies have explored the benefits of DLR, but typically for small collections of transmission lines under a limited sample of weather conditions, leaving open the question of how widely applicable the benefits of DLR might be over diverse geographies and weather conditions. Here, we combine geospatial data on tens of thousands of transmission line routes across the contiguous United States with high-resolution hourly historical weather data for 2007-2013 to estimate the impact of DLR and other weather-adjusted rating systems. We compare static and dynamic line ratings to intermediate ratings adjusted by ambient temperature, day/night irradiance, clear-sky irradiance, and/or measured irradiance, illustrating the benefits of incorporating progressively more detailed weather data into the calculated line ratings. Moving from nighttime-adjusted ratings to clear-sky-adjusted ratings provides more benefit than moving from clear-sky-adjusted ratings to measured-irradiance-adjusted ratings. Depending on the assumed static windspeed for irradiance-adjusted-ratings, DLR either corrects for overrated hours or provides substantially increased ratings in the majority of hours on the majority of lines.

14 SOLAR ENERGY↗
NASA NTRS1996

Microstructure, Chemistry, and Origin of Grain Rims on ilmenite from the Lunar Soil Finest Fraction

Analytical transmission electron microscope (TEM) observations reveal that ilmenite grains sampled from the sub-10 micron size fraction of Apollo 11 (10084) and Apollo 16 (61221, 67701) soils have rims 10-300 nm thick that are chemically and microstructurally distinct from the host ilmenite. The rims have a thin outer sublayer 10-50 nm thick that contains the ilmenite-incompatible elements Si, Al, Ca and S. This overlies a relatively thicker (50-250 nm) inner sublayer of nanocrystalline Ti-oxide precipitates in a matrix of single-crystal ilmenite that is structurally continuous with the underlying host grain. Microstructural information, as well as data from x-ray spectrometry (EDS) and electron energy loss spectrometry (EELS) analysis of the inner sublayer, suggest that both the inner and outer sublayer assemblages are reduced and that the inner layer is depleted in Fe relative to the underlying ilmenite. The chemistry of the outer sublayer suggests that it is a surface deposit of sputtered or impact-vaporized components from the bulk lunar soil. The inner sublayer is part of the original host grain that has been physically and chemically processed, but not amorphized, by solar ion irradiation and possibly some subsolidus heating. The fact that the deposited outer sublayer is consistently much thinner than the radiation-altered inner sublayer indicates that only a minor fraction of the total rim volume is a product of vapor or sputter deposition. This finding is in contrast to recent descriptions of thick deposited layers on one-third of regolith silicate grains and indicates that ilmenite and silicate rims as a group are different in the fraction of deposited material that they contain.

Christoffersen, Roy↗
DOE OSTI2025

Structural properties and recrystallization effects in ion beam modified B20-type FeGe films

Disordered iron germanium (FeGe) has recently garnered interest as a testbed for a variety of magnetic phenomena as well as for use in magnetic memory and logic applications. This is partially owing to its ability to host skyrmions and antiskyrmions—nanoscale whirlpools of magnetic moments that could serve as information carriers in spintronic devices. In particular, a tunable skyrmion–antiskyrmion system may be created through precise control of the defect landscape in B20-phase FeGe, motivating the development of methods to systematically tune disorder in this material and understand the ensuing structural properties. To this end, we investigate a route for modifying magnetic properties in FeGe. In particular, we irradiate epitaxial B20-phase FeGe films with 2.8 MeV Au 4+ ions, which creates a dispersion of amorphized regions that may preferentially host antiskyrmions at densities controlled by the irradiation fluence. To further tune the disorder landscape, we conduct a systematic electron diffraction study with in situ annealing, demonstrating the ability to recrystallize controllable fractions of the material at temperatures ranging from ~150 to 250°C. Finally, we describe the crystallization kinetics using the Johnson–Mehl–Avrami–Kolmogorov model, finding that the growth of crystalline grains is consistent with diffusion-controlled one-to-two dimensional growth with a decreasing nucleation rate.

36 MATERIALS SCIENCE↗
NASA NTRS1976

Noble gases in 60009-60010 drive tube samples - Trapped gases and irradiation history

Concentrations and isotopic composition of noble gases are reported for grain size separates: nine soils from the 60010-60009 double drive tube, two soils from the 60007 drill core section, and surface soil 65501. Data are reported on concentrations of solar wind gases, surface-correlated gases (involving solar wind and lunar atmosphere), surface maturity indices, cosmogenic gases, possible soil mixing, and irradiation by cosmic rays. Good correlation is found between solar wind gases in 60009 soils and such surface maturity indices as petrographic agglutinates, magnetic soil fraction, and fine-grained iron. Cosmogenic He-3, Ne-21, Ar-38, Kr-80, and Xe-126 all display close correlations in the drive tube soils.

Bogard, D. D.↗
NASA NTRS1977

Effects of soil maturation on grain size-dependence of trapped solar gases

A description is presented of a simple two-part model which relates the retention of solar-wind-implanted noble gases and N in different grain sizes of lunar soils to the maturation level of that soil. It is assumed that concentrations of solar-wind gases are implanted into surfaces of soil grains in inverse proportion to grain diameter and that differences in irradiation probability and surface saturation as a function of grain diameter generally are not a major factor. The model demonstrates that incorporation of a major fraction of this surface-correlated gas into constructional particles such as agglutinates causes much of the gas to become volume-correlated in mature soils. This volume-correlated gas produces a relative enrichment in gas concentrations in coarser grains and a selective enrichment of more retentive gases (e.g., N) over less retentive gases (e.g., He). It is shown that the maturity model plays a major role in determining the complexities of the distribution of solar-wind gases in soils.

Bogard, D. D.↗
NASA NTRS2007

M-Band Analysis of Chromosome Aberrations in Human Epithelial Cells Induced By Low- and High-Let Radiations

Energetic primary and secondary particles pose a health risk to astronauts in extended ISS and future Lunar and Mars missions. High-LET radiation is much more effective than low-LET radiation in the induction of various biological effects, including cell inactivation, genetic mutations, cataracts and cancer. Most of these biological endpoints are closely correlated to chromosomal damage, which can be utilized as a biomarker for radiation insult. In this study, human epithelial cells were exposed in vitro to gamma rays, 1 GeV/nucleon Fe ions and secondary neutrons whose spectrum is similar to that measured inside the Space Station. Chromosomes were condensed using a premature chromosome condensation technique and chromosome aberrations were analyzed with the multi-color banding (mBAND) technique. With this technique, individually painted chromosomal bands on one chromosome allowed the identification of both interchromosomal (translocation to unpainted chromosomes) and intrachromosomal aberrations (inversions and deletions within a single painted chromosome). Results of the study confirmed the observation of higher incidence of inversions for high-LET irradiation. However, detailed analysis of the inversion type revealed that all of the three radiation types in the study induced a low incidence of simple inversions. Half of the inversions observed in the low-LET irradiated samples were accompanied by other types of intrachromosome aberrations, but few inversions were accompanied by interchromosome aberrations. In contrast, Fe ions induced a significant fraction of inversions that involved complex rearrangements of both the inter- and intrachromosome exchanges.

Hada, M.↗
NASA NTRS1978

Petrology, chemistry, age and irradiation history of Luna 24 samples

The results of petrological, chemical, isotopic age determination and irradiation studies of sample 24170 from the 170 cm depth of the regolith core returned from Mare Crisium by Luna 24 are presented. The sample is found to be comprised of fragments from a single igneous rock, with mineralogical evidence indicating it to be a mare basalt. The crystallization age is determined by Sm-Nd and Ar(40)-Ar(39) ages to be 3.30 AE, establishing the presence of relatively young flows. All soil samples show low trace element compositions with minimum contamination by KREEPUTh-rich materials. Rb-Sr and Sm-Nd relations reflect the absence of significant fractionation at ages younger than 4.5 AE. One soil sample shows extremely large neutron capture effects, imposing a new lower limit to the neutron production rate in the regolith and requiring the addition of irradiated materials from depth.

Wasserburg, G. J.↗
DOE OSTI2021

BISON As-run AGR-3/4 Irradiation Test Predictions

BISON, a nuclear fuel performance application built using the Multiphysics Object-Oriented Simulation Environment (MOOSE) finite element library, was used to model the Advanced Gas Reactor (AGR)-3/4 irradiation test using as-run physics and thermal hydraulics data. The AGR-3/4 test consists of the combined third and fourth planned irradiations of the AGR Fuel Development and Qualification Program. The AGR-3/4 test train consists of twelve separate and independently controlled and monitored capsules. Each capsule contains four compacts filled with both uranium oxycarbide (UCO) unaltered “driver” fuel particles and UCO designed-to-fail (DTF) fuel particles. The DTF fraction was specified to be 1×10-2. This report documents the calculations performed to predict the failure probability of tristructural isotropic (TRISO) coated driver fuel particles during the AGR-3/4 experiment on a single compact. This report will demonstrate the capabilities of BISON to model the complex AGR-3/4 irradiation test and identify further development needed to capture the fuel particle failure probability and source term on every compact for further comparison from post-irradiation examination (PIE) data. The calculations include the modeling of the AGR-3/4 irradiation that occurred from December 2011 to April 2014 in the Advanced Test Reactor (ATR) over a total of 10 ATR cycles including seven normal cycles, one low power cycle, one unplanned outage cycle, and one Power Axial Locator Mechanism (PALM) cycle.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
NASA NTRS2001

Advection from the North Atlantic as the Forcing of Winter Greenhouse Effect Over Europe

In winter, large interannual fluctuations in the surface skin temperature are observed over central Europe: we observe a difference of 9.8 K comparing warm February 1990 with cold February 1996 for the region 50-60 degrees N; 5-35 degrees E. Previous studies show that advection from the North Atlantic constitutes the forcing to such fluctuations. The advection is quantified by Index I(sub na), the average of the ocean-surface wind speed over the eastern North Atlantic when the direction is from the southwest (when the wind is from another direction, it counts as a zero speed to the average). Average Ina for February 1990 was 10.6 in s(exp -1), but for February 1996 I(sub na) was only 2.4 m s(exp -1). A large value of I(sub na) means a strong southwesterly flow which brings warm and moist air into Europe at low level, producing a steeper tropospheric lapse rate. Strong ascending motions result, which we observe in February 1990 at 700 mb. The near-surface moisture rises to higher (and cooler) levels, producing clouds and precipitation. Total preciptable water and cloud-cover fraction have larger values in February 1990 than in 1996. The difference in the greenhouse effect between these two scenarios can be translated into a virtual irradiating source of 2.6 W m(exp -2) above the February 1990 atmosphere, which, as an order of magnitude estimate, contributes to the warming of the surface by 2.6 K. If we accept this estimate as numerically pertinent, the direct effect stands as 7.2 K (9.8 K - 2.6 K), and therefore its greenhouse-effect reinforcement is by 36%. This constitutes a substantial positive feedback to the direct effect, which is the inflow of warm air to the low troposphere over Europe.

Otterman, Jay↗
NASA NTRS1992

A field measure of the shade fraction

'Shade' has a technical definition peculiar to linear spectral mixture analysis of imaging spectrometer data: it is the reduction in radiance from a surface due to lighting conditions and geometry, and includes topographic shading described by photometric functions as well as shadowing at all scales. 'Shade' is an important constituent of nearly all remotely sensed images, and is one endmember resolved in spectral mixture analysis, where it is represented as a fraction of the measured radiance and a characteristic spectrum. This spectrum is typically the null vector, provided the data have been corrected for atmospheric and instrument effects: i.e., 'shade' is the radiance from an ideal black surface. In topographic shading, irradiance is reduced - typically in proportion to cos(i), where i (incidence angle) is the angle between the sun and the local surface normal vectors. Therefore, the radiance is lowered by a multiplicative factor. Shadowing occurs when i is greater than 90 deg, or when sunlight is blocked by adjacent high terrain; the only irradiance is down-welling skylight and bounce light from adjacent terrain. In spectral mixture analysis, 'shade' is regarded as an additive term. In this regard, it is an accurate description of the proportion of a scene that consists of ideal shadows ('checkerboard mixing'); however, 'shade' represents the multiplicative cos(i) factor as well, as here it should be interpreted as the proportion of shadow that would darken the scene an equivalent amount. In either case, the 'shade' fraction is lessened by adjacency effects, because the scene has a non-zero reflectivity instead of the ideal black surface generally assumed.

Gillespie, Alan R.↗
NASA NTRS2004

Top-of-Atmosphere Shortwave Broadband Observed Radiance and Estimated Irradiance over Polar Regions from Clouds and the Earth's Radiant Energy System (CERES) Instruments on Terra

Empirical angular distribution models for estimating top-of-atmosphere shortwave irradiances from radiance measurements over permanent snow, fresh snow and sea ice are developed using CERES measurements on Terra. Permanent snow angular distribution models depend on cloud fraction, cloud optical thickness, and snow brightness. Fresh snow and sea ice angular distribution models depend on snow and sea ice fraction, cloud fraction, cloud optical thickness, and snow and ice brightness. These classifications lead to 10 scene types for permanent snow and 25 scene types for fresh snow and sea ice. The average radiance over clear-sky permanent snow is more isotropic with satellite viewing geometry than that over overcast permanent snow. On average, the albedo of clear-sky permanent snow varies from 0.65 to 0.68 for solar zenith angles between 60$logical and\circ$ and 80 deg, while the corresponding albedo of overcast scenes varies from 0.70 to 0.73. Clear-sky permanent snow albedos over Antarctica estimated from two independent angular distribution models are consistent to within 0.6%, on average. Despite significant variability in sea ice optical properties with season, the estimated mean relative albedo error is -1 % for very dark sea ice and 0.1% for very bright sea ice when albedos derived from different viewing angles are averaged. The estimated regional root-mean-square (RMS) relative albedo error is 5.6% and 2.6% when the sea ice angular distribution models are applied to a region that contains very dark and very bright sea ice, respectively. Similarly, the estimated relative albedo bias error for fresh snow is -0.1% for very dark snow.

Kato, S.↗