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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS1983

Ultraviolet interstellar absorption toward HD 5980 in the Small Magellanic Cloud

Individual high-dispersion International Ultraviolet Explorer (IUE) spectra of extragalactic stars are noisy because of the long exposure times required and the inherent limitations of the IUE detectors. A program has, therefore, been undertaken to obtain multiple ultraviolet spectra of the brightest Magellanic Cloud stars in order to produce composite spectra with higher signal-to-noise ratios than in individual spectra. The present investigation is concerned with results for HD 5980. The target star, HD 5980, is one of the brightest extragalactic far-ultraviolet sources in the sky. HD 5980 is located in the northeast quadrant of NGC 346, the largest H II region and OB star cluster in the SMC. The analysis of the interstellar line spectrum of HD 5980 provides a number of conclusions about the complex absorption characteristics of the interstellar gas toward the SMC.

Fitzpatrick, E. L.↗
NASA NTRSDate not supplied

Autoencoders for Denoising Atmospheric Profiles from ICESat-2

Abstract: The 2nd generation Ice, Cloud, and land Elevation Satellite (ICESat-2) is an altimetry mission designed primarily for measuring ice sheet elevation and sea ice thickness, provides atmospheric profiles of clouds and aerosols at 532 nm using a photo counting detection approach. While highly sensitive for the detection of tenuous aerosol and cloud features, during the day signal-to-noise-ratio (SNR) photon counting detectors are adversely impacted by solar contributions to the total signal. Averaging the data to coarser horizontal resolutions has been the standard way to increase SNR and thus allow clouds and aerosols to be more easily detectable. Recent work has demonstrated success in boosting SNR without decreasing resolution using advanced filtering techniques [Yorks et al., 2021], however, rapid advancements in Deep Learning based image denoising algorithms can further improve the SNR. Here, we present results using a state-of-the-art Deep Learning autoencoder applied to noisy ICESat-2 data to improve daytime SNR and discuss implications for atmospheric feature detection, classification, and optical property retrievals.

denoising↗
NASA NTRS1985

Spacelab 2 - A preview

The Spacelab 2 mission, which is scheduled for Space Shuttle Challenger launch in July of 1985, will carry four telescopes for solar study, a dual X-ray telescope for observation of galaxy clusters, and a helium-cooled IR telescope for studies of interstellar clouds and other extended sources. The largest cosmic ray detector carried to space thus far will also be part of the payload. Life science experiment packages will examine the vitamin D chemistry of human blood under zero-G conditions, and the manner in which pine tree seedlings sense gravity and respond to it. Spacelab 2 will carry a crew of seven, including three mission specialists and two payload specialists.

Henize, K. G.↗
NASA NTRS1986

The dynamics of charged dust in the tail of Comet Giacobini-Zinner

A numerical simulation has been performed to calculate the distributions of dust particles of various sizes down the tail of comet P/Giacobini-Zinner. When the electrostatic charging of the grains in the plasma and radiative environment of the comet is taken into account, it is found that the distribution of the grains (particularly at the lowest end of the mass spectrum) in a plane normal to the orbital plane is entirely different from what is expected had the grains been uncharged. Although the NASA-ICE spacecraft, which will fly through the tail of this comet almost normal to its orbital plane on September 11, 1985, has no dedicated dust experiments, it is expected that the plasma wave instrument will serve as an indirect detector, even of the smallest grains, via the plasma clouds created by the high-velocity dust impacts. Knowledge of the spatial variation of the grain sizes encountered along the flight path of the spacecraft will provide us with the information necessary to calculate the electrostatic potential of the grains, which in turn will lead to an estimation of the role of the electromagnetic forces on the dynamics of such grains.

Horanyi, M.↗
DOE OSTI2023

EPiC-GAN: Equivariant point cloud generation for particle jets

With the vast data-collecting capabilities of current and future high-energy collider experiments, there is an increasing demand for computationally efficient simulations. Generative machine learning models enable fast event generation, yet so far these approaches are largely constrained to fixed data structures and rigid detector geometries. In this paper, we introduce EPiC-GAN - equivariant point cloud generative adversarial network - which can produce point clouds of variable multiplicity. This flexible framework is based on deep sets and is well suited for simulating sprays of particles called jets. The generator and discriminator utilize multiple EPiC layers with an interpretable global latent vector. Crucially, the EPiC layers do not rely on pairwise information sharing between particles, which leads to a significant speed-up over graph- and transformer-based approaches with more complex relation diagrams. We demonstrate that EPiC-GAN scales well to large particle multiplicities and achieves high generation fidelity on benchmark jet generation tasks.

Buhmann, Erik↗
NASA NTRS1990

Cloud field reflectance variations traceable to finite cloud effects

Variations in cloud field reflectances resulting from the organization of clouds within a cloud field are examined using a cloud field optical simulator. The problem of changing spot size is studied as a function of view angle for a fixed field of view detector. Also, problems associated with the assumption of isotropy are discussed and the effect of cloud interactions within cloud fields is investigated. The results show that radiance variation increases when the photodiodes measure radiances from portions of cloud fields which move in and out of the fields of view as the position of the photodiode changes. In addition, the experiments reveal several factors that are important in the determination of accurate reflectances.

Alberta, Timothy L.↗
NASA NTRS2004

Combined Infrared Stereo and Laser Ranging Cloud Measurements from Shuttle Mission STS-85

Multiangle remote sensing provides a wealth of information for earth and climate monitoring, such as the ability to measure the height of cloud tops through stereoscopic imaging. As technology advances so do the options for developing spacecraft instrumentation versatile enough to meet the demands associated with multiangle measurements. One such instrument is the infrared spectral imaging radiometer, which flew as part of mission STS-85 of the space shuttle in 1997 and was the first earth- observing radiometer to incorporate an uncooled microbolometer array detector as its image sensor. Specifically, a method for computing cloud-top height with a precision of +/- 620 m from the multispectral stereo measurements acquired during this flight has been developed, and the results are compared with coincident direct laser ranging measurements from the shuttle laser altimeter. Mission STS-85 was the first space flight to combine laser ranging and thermal IR camera systems for cloud remote sensing.

Lancaster, R. S.↗
NASA NTRS2001

Combined Infrared Stereo and Laser Ranging Cloud Measurements from Shuttle Mission STS-85

Multi-angle remote sensing provides a wealth of information for earth and climate monitoring. And, as technology advances so do the options for developing instrumentation versatile enough to meet the demands associated with these types of measurements. In the current work, the multiangle measurement capability of the Infrared Spectral Imaging Radiometer is demonstrated. This instrument flew as part of mission STS-85 of the space shuttle Columbia in 1997 and was the first earth-observing radiometer to incorporate an uncooled microbolometer array detector as its image sensor. Specifically, a method for computing cloud-top height from the multi-spectral stereo measurements acquired during this flight has been developed and the results demonstrate that a vertical precision of 10.6 km was achieved. Further, the accuracy of these measurements is confirmed by comparison with coincident direct laser ranging measurements from the Shuttle Laser Altimeter. Mission STS-85 was the first space flight to combine laser ranging and thermal IR camera systems for cloud remote sensing.

Lancaster, Redgie S.↗
NASA NTRS2021

Compact Thermal Imager (CTI) for Atmospheric Remote Sensing

The demonstration of a newly developed compact thermal imager (CTI) on the International Space Station (ISS) has provided not only a technology advancement but a rich high-resolution dataset on global clouds, atmospheric and land emissions. This study showed that the free-running CTI instrument could be calibrated to produce scientifically useful radiance imagery of the atmosphere, clouds, and surfaces with a vertical resolution of ~460 m at limb and a horizontal resolution of ~80 m at nadir. The new detector demonstrated an excellent sensitivity to detect the weak limb radiance perturbations modulated by small-scale atmospheric gravity waves. The CTI’s high-resolution imaging was used to infer vertical cloud temperature profiles from a side-viewing geometry. For nadir imaging, the combined high-resolution and high-sensitivity capabilities allowed the CTI to better separate cloud and surface emissions, including those in the planetary boundary layer (PBL) that had small contrast against the background surface. Finally, based on the ISS’s orbit, the stable detector performance and robust calibration algorithm produced valuable diurnal observations of cloud and surface emissions with respect to solar local time during May–October 2019, when the CTI had nearly continuous operation.

thermal imager↗
NASA NTRS1985

Calcium depletion toward moderately reddened stars

Calcium depletions toward five moderately reddened (E/B - V/ greater than 0.35 and less than 0.45) stars and toward HD 147889, a heavily reddened (E/B - V/ = 1.08) member of the Rho Ophiuchi cloud complex is reported. A developmental Multi-Anode Microchannel Array Detector was used to collect the data; its performance is characterized. Comparing the results for calcium from one line of sight to another and to those for other species, it is found that calcium exhibits a depletion pattern remarkably similar to that of silicon. The depletion of iron, on the other hand, has smaller variations and therefore does not correlate as well. Also, the depletion results for manganese and sulfur, both normally undepleted in diffuse clouds, have been included for comparison.

Joseph, C. L.↗
NASA NTRS1974

Binary-selectable detector holdoff circuit

High-speed switching circuit protects detectors from sudden, extremely-intense backscattered radiation that results from short-range atmospheric dust layers, or low-level clouds, entering laser/radar field of view. Function of circuit is to provide computer-controlled switching of photodiode detector, preamplifier power-supply voltages, in approximately 10 nanoseconds.

Kadrmas, K. A.↗
DOE OSTI2022

FORTE Measurements of Global Optical Lightning Waveforms and Implications for Optical Lightning Detection

Lightning processes generate a diverse collection of optical pulses from current traversing the lightning channels. These signals are then broadened spatially and temporally via scattering in the clouds. The resulting waveforms measured from space with instruments like the photodiode detector (PDD) on the Fast On-orbit Recording of Transient Events (FORTE) satellite have a variety of shapes. In this study, we use coincident optical and Radio-Frequency measurements to document the properties of optical PDD waveforms associated with different types of lightning, estimate delays from scattering in the clouds, and comment on how pulse shape impacts optical lightning detection. We find that the attributes of optical pulses recorded by the PDD are consistent with prior studies, but vary globally and with event amplitude. The most powerful lightning tends to be single-peaked with faster rise times (median: ~100 µs) and shorter effective widths (median: ~400 µs) than normal lightning. Particularly dim events, meanwhile, include cases of broad optical waveforms with sustained optical emission throughout the PDD record, which the pixelated FORTE Lightning Location System (LLS) instrument has difficulty detecting. We propose that this is due to the optical signal being divided between individual LLS pixels that are each, individually, not bright enough to trigger. We use PDD waveforms and Monte Carlo radiative transfer modeling to demonstrate that increasing the temporal and spatial resolution of a pixelated lightning imager will make it more difficult to detect these broad/dim pulses as their energy becomes divided between additional pixels/integration frames.

54 ENVIRONMENTAL SCIENCES↗
NASA NTRS1987

An X-ray survey for pre-main-sequence stars in the Taurus-Auriga and Perseus molecular cloud complexes

Seventy-five fields from the Einstein X-Ray Observatory IPC detector between 3h and 5h right ascension and 15 deg and 35 deg declination are examined to search for X-ray-emitting low-mass pre-main-sequence (PMS) stars. Six such stars were previously found; they appear to be similar to T Tauri stars but without dense circumstellar envelopes or winds. Finding charts are presented for 59 X-ray sources that may be PMS stars. While some are likely to be spurious X-ray sources, chance coincidences with unrelated stars, or non-PMS stellar sources such as RS CVn type binaries, approximately half are probably X-ray-selected PMS stars.

Feigelson, E. D.↗
NASA NTRS2007

Performance of the Lidar Design and Data Algorithms for the GLAS Global Cloud and Aerosol Measurements

The Geoscience Laser Altimeter System (GLAS) launched in early 2003 is the first polar orbiting satellite lidar. The instrument design includes high performance observations of the distribution and optical scattering cross sections of atmospheric clouds and aerosol. The backscatter lidar operates at two wavelengths, 532 and 1064 nm. For the atmospheric cloud and aerosol measurements, the 532 nm channel was designed for ultra high efficiency with solid state photon counting detectors and etalon filtering. Data processing algorithms were developed to calibrate and normalize the signals and produce global scale data products of the height distribution of cloud and aerosol layers and their optical depths and particulate scattering cross sections up to the limit of optical attenuation. The paper will concentrate on the effectiveness and limitations of the lidar channel design and data product algorithms. Both atmospheric receiver channels meet and exceed their design goals. Geiger Mode Avalanche Photodiode modules are used for the 532 nm signal. The operational experience is that some signal artifacts and non-linearity require correction in data processing. As with all photon counting detectors, a pulse-pile-up calibration is an important aspect of the measurement. Additional signal corrections were found to be necessary relating to correction of a saturation signal-run-on effect and also for daytime data, a small range dependent variation in the responsivity. It was possible to correct for these signal errors in data processing and achieve the requirement to accurately profile aerosol and cloud cross section down to 10-7 llm-sr. The analysis procedure employs a precise calibration against molecular scattering in the mid-stratosphere. The 1064 nm channel detection employs a high-speed analog APD for surface and atmospheric measurements where the detection sensitivity is limited by detector noise and is over an order of magnitude less than at 532 nm. A unique feature of the GLAS is a full acquisition of the surface return pulse, which has important application to the atmospheric transmission retrieval.

Spinhirne, James D.↗
NASA NTRS1982

Compact X-ray sources in the Large Magellanic Cloud

Sixteen Einstein X-ray sources in the field of the Large Magellanic Cloud (LMC) that appear non-extended in the IPC detector have recently been accurately positioned with the HRI to make optical follow-up studies feasible. At least twelve of these are not associated with the LMC, including one Seyfert galaxy at a redshift of 0.076 and eleven late type galactic foreground stars, some showing photometric behavior typical for RS CVn and BY Dra variables. Two sources are identified with faint blue variable objects, one of them has been observed to exhibit He II 4686 and variable Balmer emission lines being reminiscent of the low mass X-ray binary LMC X-2. The IPC source 1E0501438-7037.6 is probably associated with the LMC OB star Sk-70 36 which has been found to show ellipsoidal light variations with a period of 6.94 d. The results strongly suggest that a gap in the X-ray binary luminosity function of the LMC exists between 10 to the 36th and 10 to the 38th ergls.

Pakull, M. W.↗