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NASA NTRS2004

Heterodyne Spectroscopy in the Thermal Infrared Region: A Window on Physics and Chemistry

The thermal infrared region contains molecular bands of many of the most important species in gaseous astronomical sources. True shapes and frequencies of emission and absorption spectral lines from these constituents of planetary and stellar atmospheres contain unique information on local temperature and abundance distribution, non-thermal effects, composition, local dynamics and winds. Heterodyne spectroscopy in the thermal infrared can remotely measure true line shapes in relatively cool and thin regions and enable the retrieval of detailed information about local physics and chemistry. The concept and techniques for heterodyne detection will be discussed including examples of thermal infrared photomixers and instrumentation used in studies of several astronomical sources. Use of heterodyne detection to study non-LTE phenomena, planetary aurora, minor planetary species and gas velocities (winds) will be discussed. A discussion of future technological developments and relation to space flight missions will be addressed.

Kostiuk, Theodor↗
NASA NTRS2004

Non-Thermal Hard X-Ray Emission in Galaxy Clusters Observed with the BeppoSAX PDS

We study the X-ray emission in a sample of galaxy clusters using the BeppoSAX PDS instrument in the 20-80 keV energy band. We estimate the nonthermal hard X-ray (HXR) cluster emission by modeling the thermal contribution from the cluster gas and the nonthermal contamination from the unobscured active galactic nuclei (AGNs) in the clusters. We also evaluate the systematic uncertainties due to the background fluctuations. Assuming negligible contamination from the obscured AGNs, the resulting nonthermal component is detected at a 2 sigma level in approx. 50% of the nonsignificantly AGN-contaminated clusters: A2142, A2199, A2256, A3376, Coma, Ophiuchus, and Virgo. The data are consistent with a scenario whereby relaxed clusters have no hard X-ray component of nonthermal origin, whereas merger clusters do, with a 20-80 keV luminosity of approx. 10(exp 43)-10(exp 44) h(sup -2 sub 50) ergs/s. The co-added spectrum of the above clusters indicates a power-law spectrum for the HXR emission with a photon index of 2.8(sup +0.3 sub -0.4) in the 12-115 keV band, and we find indication that it has extended distribution. These indications argue against significant contamination from obscured AGNs, which have harder spectra and a centrally concentrated distribution. These results are supportive of the assumption of the merger shock acceleration of electrons in clusters, which has been proposed as a possible origin of the nonthermal hard X-ray emission models. Assuming that the cosmic microwave background photons experience inverse Compton scattering from the merger-accelerated relativistic electrons and thus produce the observed HXR, the measured hard X-ray slope corresponds to a differential momentum spectra of the relativistic electrons with a slope of mu = 3.8-5.0. In presence of cluster magnetic fields this relativistic electron population produces synchrotron emission with a spectral index of 1.4-2.1, consistent with radio halo observations of merger clusters. Thus both hard X-ray and radio observations of merger clusters are consistent with the inverse Compton model.

Nevalainen, J.↗
NASA NTRS2006

The SWIFT Gamma-Ray Burst X-Ray Telescope

The Swift Gamma-Ray Burst Explorer is designed to make prompt multi-wavelength observations of Gamma-Ray Bursts and GRB afterglows. The X-ray Telescope enables Swift to determine GRB positions with a few arcseconds accuracy within 100 seconds of the burst onset. The XRT utilizes a mirror set built for JET-X and an XMM-Newton/ EPIC MOS CCD detector to provide a sensitive broad-band (0.2-10 keV) X-ray imager with an effective area of more than 120 sq cm at 1.5 keV, a field of view of 23.6 x 23.6 arcminutes, and an angular resolution of 18 arcseconds (HPD). The detection sensitivity is 2x10(exp 14) erg/sq cm/s in 10(exp 4) seconds. The instrument provides automated source detection and position reporting within 5 seconds of target acquisition. It can also measure the redshifts of GRBs with Iron line emission or other spectral features. The XRT operates in an auto-exposure mode, adjusting the CCD readout mode automatically to optimize the science return as the source intensity fades. The XRT measures spectra and lightcurves of the GRB afterglow beginning about a minute after the burst and follows each burst for days or weeks. We provide an overview of the X-ray Telescope scientific background from which the systems engineering requirements were derived, with specific emphasis on the design and qualification aspects from conception through to launch. We describe the impact on cleanliness and vacuum requirements for the instrument low energy response and to maintain the high sensitivity to the fading signal of the Gamma-ray Bursts.

Hill, J. E.↗
NASA NTRS2013

What Do Millimeter Continuum and Spectral Line Observations Tell Us about Solar System Bodies?

Solar system objects are generally cold and radiate at low frequencies and tend to have strong molecular rotational transitions. Millimeter continuum and spectral line observations provide detailed information for nearly all solar system bodies. At these wavelengths, details of the bulk physical composition of icy surfaces, the size and albedo of small objects, the composition of planetary atmospheres can be measured as well as monitoring of time variable phenomena for extended periods (not restricted to nighttime observations), etc. Major issues in solar system science can be addressed by observations in the millimeter/sub-millimeter regime such as the origin of the solar system (isotope ratios, composition) and the evolution of solar system objects (dynamics, atmospheric constituents, etc). ALMA s exceptional sensitivity, large spectral bandwidth, high spectral resolution, and angular resolution (down to 10 milliarcsec) will enable researchers for the first time to better resolve the smallest bodies in the solar system and provide detailed maps of the larger objects. Additionally, measurements with nearly 8 GHz of instantaneous bandwidth to fully characterize solar system object s spectrum and detect trace species. The spatial information and line profiles can be obtained over 800 GHz of bandwidth in 8 receiver bands to not only assist in the identification of spectral lines and emission components for a given species but also to help elucidate the chemistry of the extraterrestrial bodies closest to us.

Milam, Stefanie N.↗
NASA NTRS2014

Surface Spectroscopy Center Of Excellence Project

We propose to develop a national center of excellence in Regolith Radiative Transfer (RRT), i.e., in modeling spectral reflectivity and emissivity of grainy or structured surfaces. The focus is the regime where the structural elements of grainy surfaces have grain sizes and separations of tens of microns, comparable to the wavelengths carrying diagnostic compositional information. This regime is of fundamental interest to remote sensing of planetary and terrestrial surfaces.

Regolith Radiative Transfer (RRT)↗
NASA NTRS2015

Marshall Space Flight Center Faculty Fellowship Program

The Faculty Fellowship program was revived in the summer of 2015 at NASA Marshall Space Flight Center, following a period of diminished faculty research activity here since 2006 when budget cuts in the Headquarters' Education Office required realignment. Several senior Marshall managers recognized the need to involve the Nation's academic research talent in NASA's missions and projects to the benefit of both entities. These managers invested their funds required to establish the renewed Faculty Fellowship program in 2015, a 10-week residential research involvement of 16 faculty in the laboratories and offices at Marshall. These faculty engineers and scientists worked with NASA collaborators on NASA projects, bringing new perspectives and solutions to bear. This Technical Memorandum is a compilation of the research reports of the 2015 Marshall Faculty Fellowship program, along with the Program Announcement (appendix A) and the Program Description (appendix B). The research touched on seven areas-propulsion, materials, instrumentation, fluid dynamics, human factors, control systems, and astrophysics. The propulsion studies included green propellants, gas bubble dynamics, and simulations of fluid and thermal transients. The materials investigations involved sandwich structures in composites, plug and friction stir welding, and additive manufacturing, including both strength characterization and thermosets curing in space. The instrumentation projects involved spectral interfero- metry, emissivity, and strain sensing in structures. The fluid dynamics project studied the water hammer effect. The human factors project investigated the requirements for close proximity operations in confined spaces. Another team proposed a controls system for small launch vehicles, while in astrophysics, one faculty researcher estimated the practicality of weather modification by blocking the Sun's insolation, and another found evidence in satellite data of the detection of a warm-hot intergalactic medium filament. Our goal is to continue the Faculty Fellowship effort with Center funds in succeeding summers.

Six, N. F.↗
NASA NTRS2019

High-Resolution Mid-Infrared Molecular Line Survey of the Orion Hot Core

The basic building blocks of life are synthesized in space as part of the natural stellar evolutionary cycle, whereby elements ejected into the interstellar medium by dying stars are incorporated back into the dense clouds, which form the next generation of stars and planets. The formation of stars and planets are fundamental to the evolution of matter in the Universe as complex molecules are created and destroyed during this step. Understanding these processes will allow us to answer “What is the relation between the molecules we see in the ISM and the molecular inventory of Earth and the terrestrial planets in the Solar System?” Measuring and cataloging the inventory of organic molecules and understanding their evolution requires observations over a broad wavelength range (IR, MIR, FIR, (sub)mm, and radio) to cover all stages of this evolutionary cycle needed to link interstellar material to that delivered to planets. High-resolution molecular line surveys provide chemical inventories for star forming regions and are essential for studying their chemistry, kinematics and physical conditions. Previous high spectral resolution surveys have been limited to radio, sub-mm and FIR wavelengths; however, Mid-infrared observations are the only way to study symmetric molecules that have no dipole moment and thus cannot be detected in the (sub)mm line surveys from ALMA. Past midinfrared missions such as ISO and Spitzer had low to moderate resolving power that were only able to link broad features with particular molecular bands and could not resolve the individual rovibrational transitions. JWST will provide exceptional sensitivity in the MIR, but will also not have sufficient spectral resolution, which can lead to confusion in identifying the contribution from strong to moderate strength molecular species. We present new results from an on-going high resolution (R ~ 60,000) line survey of the Orion hot core between 12.5 - 28.3 μm and 7 - 8 μm, using the EXES instrument on the SOFIA airborne observatory. SOFIA's higher-resolution and smaller beam compared to ISO allows us to spatially and spectrally isolate the emission towards the hot core. This survey will provide the best infrared measurements (to date) of molecular column densities and physical conditions, providing strong constraints on the current chemical network models for star forming regions. This survey will greatly enhance the inventory of resolved line features in the MIR, making it an invaluable reference to be used by the JWST and ALMA scientific communities.

Rangwala, Naseem↗
NASA NTRSDate not supplied

Understanding the Uncertainty and Variability of Earth’s Radiation Budget Components Over the Past 3 Decades from the NASA’s GEWEX Surface Radiation Budget Release 4 Integrated Product

The NASA/GEWEX Surface Radiation Budget (SRB) project produced a 30+ year time series of 3-hourly Top-of-Atmosphere (TOA) and surface radiative flux components at a 1x1 degree resolution. This SRB Release 4 Integrated Productare derived using imager data products from the cross-calibrated from ISCCP (International Satellite Cloud Climatology Project) “HSeries” radiance, cloud and surface property data products. The ISCCP HXS product replaces ISCCP DX with a ninefold increase in pixel count (10km instead of 30km). ISCCP also provides an atmospheric temperature and moisture dataset known as nnHIRS which we use and discuss radiative flux sensitivities to in this presentation. Total solar irradiance is now variable consistent with SORCE measurements. Sea surface (SeaFlux v2.0) and land surface products (LandFlux) are utilized to achieve an radiative flux estimatesintegrated with global data sets from these GEWEX projects. The variable aerosol composition are specified using a detailed aerosol history from the Max Planck Institute Aerosol Climatology (MAC) also used for background aerosol in the ISCCP HX. Numerous other improvements were made to the SW and LW algorithms including improved cloud optical property treatments and specification of surface spectral albedo and emissivity for various surface conditions. Here we analyze the new SWand LWSRB datasets, comparing them to the previous Release 3, BSRN, GEBA and PMEL surface measurements, and ERBE and CERES satellite datasets. For surface flux validation besides ensemble comparisons, we show the variability of SRB vs surface measurements from BSRN beginning in 1992 and GEBA SW from 1983. We assess the variability of the surface flux anomalies, particularly the net fluxes and the cloud radiative effects, over the entire time period including the period containing CERES overlap. For the TOA fluxes, the anomalies of the fluxes in the early period are compared to the MEaSURES ERBE and the latter period to CERES EBAF/SYN1Deg datasets for a benchmark. Long-term changes in the surface radiation budget components and cloud radiative effects are shown and discussed relative to CERES and surface measurements. This includes a change point analysis that helps associate various changes in the ISCCP GEO/LEO configurations and other inputs to variations in the radiative budget components.

Earth Radiation Budget↗
NASA NTRSDate not supplied

Jpss-4 VIIRS Polarization Sensitivity Performance Comparison With Heritage VIIRS Sensors

The Joint Polar Satellite System 4 (JPSS-4) is the follow-on for the Suomi-National Polar-orbiting Partnership (S-NPP) and Joint Polar Satellite Systems 1-3 (JPSS-1, -2 and -3) missions. A primary sensor on both JPSS and S-NPP spacecrafts is the Visible-Infrared Imaging Radiometer Suite (VIIRS) that provides valuable weather and climate products to the user community. VIIRS covers the Reflective Solar Band (RSB) and Thermal Emissive Band (TEB) spectral regions and contains a Day Night Band (DNB) that uses Lunar illumination at night. VIIRS provides top-of-atmosphere radiance, reflectance, and brightness temperature within the Sensor Data Records (SDRs) that are used in sea surface temperature, cloud characterization, land surface properties and ocean color/chlorophyll Environmental Data Record (EDR) products. The SDR calibration is performed using unpolarized sources such as a Solar Diffuser (SD) for the RSBs or an On-Board Calibrator BlackBody (OBCBB) for the TEBs. Earth scenes with polarizing properties will create radiometric bias errors within the SDRs based on how sensitive VIIRS is to polarized illumination and must be corrected in some EDR algorithms. This paper will discuss the JPSS-4 VIIRS polarization characterization methodology, polarization sensitivity results and compare its performance to its predecessors S-NPP and JPSS-1 through -3 VIIRS.

David Moyer↗
NASA NTRS2007

Physical Retrieval of Surface Emissivity Spectrum from Hyperspectral Infrared Radiances

Retrieval of temperature, moisture profiles and surface skin temperature from hyperspectral infrared (IR) radiances requires spectral information about the surface emissivity. Using constant or inaccurate surface emissivities typically results in large retrieval errors, particularly over semi-arid or arid areas where the variation in emissivity spectrum is large both spectrally and spatially. In this study, a physically based algorithm has been developed to retrieve a hyperspectral IR emissivity spectrum simultaneously with the temperature and moisture profiles, as well as the surface skin temperature. To make the solution stable and efficient, the hyperspectral emissivity spectrum is represented by eigenvectors, derived from the laboratory measured hyperspectral emissivity database, in the retrieval process. Experience with AIRS (Atmospheric InfraRed Sounder) radiances shows that a simultaneous retrieval of the emissivity spectrum and the sounding improves the surface skin temperature as well as temperature and moisture profiles, particularly in the near surface layer.

Li, Jun↗
DOE OSTI2026

Hyperspectral radiance mapping and chromatic correction for temperature measurement in laser-heated diamond anvil cells

In laser-heated diamond anvil cell (DAC) experiments, the effective heated region typically decreases in size with increasing pressure, leading to steeper thermal gradients. Under these conditions, chromatic aberration in the optical path from sample to detector can significantly create bias in spectro-radiometric temperature measurement. We present a radiance-mapping approach using a hyperspectral camera that records 25 spectral channels spanning 605–875 nm at each pixel in a single exposure, providing spatially and spectrally resolved radiance in each frame. This enables chromatic effects to be recorded and corrected in data processing. We developed a procedure for hyperspectral mapping, involving per-camera calibration, crosstalk removal, measured spectral throughput functions, and optional sub-pixel co-registration to minimize chromatic distortion. The calibrated radiance maps are then used to derive temperature maps of the laser-heated hotspots. For smaller heating spots, the radiance mapping approach reveals chromatic shifts that conventional spectro-radiometric methods cannot quantify. Ambient-pressure heating experiments confirm accurate temperature retrieval. At high pressure, application of the hyperspectral system to a platinum-heating experiment at 12 GPa demonstrates stable temperature reconstruction under steep thermal gradients. Beyond mitigating chromatic aberrations, the ability to diagnose optical artifacts separately from emissivity variations during controlled test experiments or in situ suggests a path toward more rigorous spectral emissivity analysis and improved modeling of thermal transport in laser-heated DAC experiments.

47 OTHER INSTRUMENTATION↗
NASA NTRS1994

Rare Earth Garnet Selective Emitter

Thin film Ho-YAG and Er-YAG emitters with a platinum substrate exhibit high spectral emittance in the emission band (epsilon(sub lambda) approx. = 0.75, sup 4)|(sub 15/2) - (sup 4)|(sub 13/2),for Er-YAG and epsilon(sub lambda) approx. = 0.65, (sup 5)|(sub 7) - (sup 5)|(sub 8) for Ho-YAG) at 1500 K. In addition, low out-of-band spectral emittance, epsilon(sub lambda) less than 0.2, suggest these materials would be excellent candidates for high efficiency selective emitters in thermophotovoltaic (TPV) systems operating at moderate temperatures (1200-1500 K). Spectral emittance measurements of the thin films were made (1.2 less than lambda less than 3.0 microns) and compared to the theoretical emittances calculated using measured values of the spectral extinction coefficient. In this paper we present the results for a new class of rare earth ion selective emitters. These emitters are thin sections (less than 1 mm) of yttrium aluminum garnet (YAG) single crystal with a rare earth substitutional impurity. Selective emitters in the near IR are of special interest for thermophotovoltaic (TPV) energy conversion. The most promising solid selective emitters for use in a TPV system are rare earth oxides. Early spectral emittance work on rare earth oxides showed strong emission bands in the infrared (0.9 - 3 microns). However, the emittance outside the emission band was also significant and the efficiency of these emitters was low. Recent improvements in efficiency have been made with emitters fabricated from fine (5 - 10 microns) rare earth oxide fibers similar to the Welsbach mantle used in gas lanterns. However, the rare earth garnet emitters are more rugged than the mantle type emitters. A thin film selective emitter on a low emissivity substrate such as gold, platinum etc., is rugged and easily adapted to a wide variety of thermal sources. The garnet structure and its many subgroups have been successfully used as hosts for rare earth ions, introduced as substitutional impurities, in the development of solid state laser crystals. Doping, dependent on the particular ion and crystal structure, may be as high as 100 at. % (complete substitution of yttrium ion with the rare earth ion). These materials have high melting points, 1940 C for YAG (Yttrium Aluminum Garnet), and low emissivity in the near infrared making them excellent candidates for a thin film selective emitter. As previously stated, the spectral emittance of a rare earth emitter is characterized by one or more well defined emission bands. Outside the emission band the emittance(absorptance) is much lower. Therefore, it is expected that emission outside the band for a thin film selective emitter will be dominated by the emitter substrate. For an efficient emitter (power in the emission band/total emitted power) the substrate must have low emittance, epsilon(sub S). This paper presents normal spectral emittance, epsilon(sub lambda), measurements of holmium(Ho) and erbium (Er) doped YAG thin film selective emitters at (1500 K), and compares those results with the theoretical spectral emittance.

Lowe, Roland A.↗
NASA NTRS1985

High spectral resolution observations of the coronal X-ray emission from the RS CVn binary Sigma Corona Borealis

The results of high-resolution observations of the RS CVn binary star Rho Cr B are reported. The observations were carried out using the Focal Plane Crystal Spectrometer (FPCS) onboard the Einstein Observatory satellite. A spectral scan in the interval 800-840 eV shows clear evidence of an X-ray emission line at 826 eV identified with 1S(0)-1P(1) transition of Fe XVII. A prominent peak at 1007 eV in the scan band 986-1014 eV was attributed to a blend of lines produced by highly ionized iron. On the basis of the observed fluxes of the lines and the theoretical calculations of Raymond and Smith (1977), best-fit values of corona temperature and volume emission measures of 6.92 (+0.84 or -0.75) x 10 to the 6th K, and 1.74 (+0.55 or -0.69) x 10 to the 35th are derived, respectively. Some implications of the results are briefly discussed.

Agrawal, P. C.↗
DOE OSTI2026

Titanium alloy response sensitivity to variations in spectral reconstructions of National Ignition Facility xenon line-emission x-ray sources

Thermomechanical shock experiments on the National Ignition Facility (NIF) aim to study high strain rate dynamic material response. In such experiments, the NIF laser is used to generate high fluence x-ray emission sources, which irradiate material samples of interest. Under sufficiently high x-ray energy deposition, thermomechanical impulses are generated in the materials. While it is known that the characteristics of x-ray generated impulses vary as a function of incident x-ray spectra, it remains unclear how spectral assumptions and uncertainties in NIF spectral reconstructions affect our interpretation of impulsive loading. Here, in this paper, we simulate the response of a standard titanium alloy baseline sample to synthetic analytically derived and measured NIF xenon line-emission x-ray sources with a radiation hydrodynamics code. We vary the source spectral characteristics based on different source reconstruction techniques to understand the resulting variation in baseline sample response and compare the simulated response with experimental results. We find that the response is highly sensitive to assumptions made about the spectral contents and that knowledge of spectral uncertainties bounds our understanding of the resulting material response. The results of this effort help to extend our ability to use baseline material samples to extract quantitative properties from x-ray experiments on the NIF.

Alloys↗
DOE OSTI2020

A framework for quantitative analysis of spectral data in two channels

Simultaneous acquisition of emission intensity from two channels in dual-color fluorescence measurements can be used to determine the spectral properties of an emitter. We detail a method to extract quantitative information from dual-color measurements by considering two models: a single spectral component model for peak wavelength determination and a dual spectral component model for relative strength determination. The former model is useful for spectral characterization and establishing heterogeneity within an emitter species, while the latter model is useful for analyzing energy transfer efficiency. Both models are formalized to yield probability distributions that reflect uncertainties due to shot noise. We applied these analysis tools to single-particle measurements of CdSe/CdS quantum dots. Isolated emitters had narrow spectral-intensity distributions that reflected their static emission profiles and fluorescence stability. Small assemblies of mixed donor/acceptor particles exhibited dynamic behavior where emission configuration changes reveal different spectral characteristics due to energy transfer.

36 MATERIALS SCIENCE↗
NASA NTRS1987

Measurements of OH(X2pi) in the stratosphere by high resolution UV spectroscopy

This paper reports the first results obtained using high spectral resolution imaging ultraviolet spectroscopy to observe multiple rotational lines of OH A2 Sigma-X2pi (0-0) band. A 9.2 A spectral segment from 3075.8 A to 3085.0 A is imaged at 0.08 A FWHM spectral resolution, allowing the simultaneous acquisition of six of the brightest OH resonance fluorescence emission lines. The high spectral resolution and low scattered light design of the instrument allows these lines to be detected above the Rayleigh scattered sunlight background. The technique permits remote sensing of stratospheric OH from a high altitude instrument. The instrument was flown to an altitude of 40 km on Aug. 25, 1983, and again on June 12, 1986, on scientific balloons from Palestine, TX. The OH profiles inverted from the limb scans made during these flights are reported here. These profiles represent the first measurements of the temporal variation of OH over an extended height range. The results demonstrate that the technique can be used to monitor OH from orbit.

Torr, D. G.↗
NASA NTRS1991

Ground-based observations of comets, the Jupiter plasma Torus, and Io

Aspects of cometary and magnetospheric physics were investigated by means of ground-based astronomical spectroscopy. High-throughput, dual-etalon Fabry-Perot spectrometers were used to obtain very high resolution spectra of atomic, molecular, and ionic emission lines from the diffuse gases and plasmas associated with comets and the Jupiter plasma torus. The Fabry-Perot spectrometers were also used with a charge coupled device (CCD) camera to obtain images of these extended emission sources in individual spectral lines at high spectral resolution. A new program using the McMath solar-stellar spectrograph to observe emission lines from Io was recently initiated. The McMath spectrograph has a high resolution mode which allows the detection of narrow, relatively faint emission lines superimposed on Io's reflected solar spectrum.

Scherb, Frank↗
NASA NTRS1980

Solar limb emission lines near Ca II H & K and their spatial intensity variations

The paper employs solar observations of high spatial and spectral resolution to identify emission lines seen in the extended wings of Ca II H & K near the solar limb. Emission lines in the wings of H & K represent valuable diagnostics of the atmospheres of cool stars, with a varying information content which depends on their particular formation mechanism. In solar spectrograms different emission line formation mechanisms can be distinguished by the character of the spatial intensity variation (SIV) apparent in the lines. Various classes of H & K emission features, their spatial intensity variations and their formation mechanisms (of which some pose further problems) are discussed. A new extended list of line identifications is compiled based on their formation class and compared with other line lists. Evidence is found that stellar luminosity-sensitive lines tend to show large spatial intensity variation on the sun.

Rutten, R. J.↗