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All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

The Extragalactic Background Light and the Gamma-ray Opacity of the Universe

The extragalactic background light (EBL) is one of the fundamental observational quantities in cosmology. All energy releases from resolved and unresolved extragalactic sources, and the light from any truly diffuse background, excluding the cosmic microwave background (CMB), contribute to its intensity and spectral energy distribution. It therefore plays a crucial role in cosmological tests for the formation and evolution of stellar objects and galaxies, and for setting limits on exotic energy releases in the universe. The EBL also plays an important role in the propagation of very high energy gamma-rays which are attenuated en route to Earth by pair producing gamma-gamma interactions with the EBL and CMB. The EBL affects the spectrum of the sources, predominantly blazars, in the approx 10 GeV to 10 TeV energy regime. Knowledge of the EBL intensity and spectrum will allow the determination of the intrinsic blazar spectrum in a crucial energy regime that can be used to test particle acceleration mechanisms and VHE gamma-ray production models. Conversely, knowledge of the intrinsic gamma-ray spectrum and the detection of blazars at increasingly higher redshifts will set strong limits on the EBL and its evolution. This paper reviews the latest developments in the determination of the EBL and its impact on the current understanding of the origin and production mechanisms of gamma-rays in blazars, and on energy releases in the universe. The review concludes with a summary and future directions in Cherenkov Telescope Array techniques and in infrared ground-based and space observatories that will greatly improve our knowledge of the EBL and the origin and production of very high energy gamma-rays.

Dwek, Eli↗
NASA NTRS2013

Water in Nominally Anhydrous Minerals from Nakhlites and Shergottites

Estimating the amount of water in the interior of terrestrial planets has tremendous implications on our understanding of solar nebula evolution, planet formation and geological history, and extraterrestrial volcanism. Mars has been a recent focus of such enquiry with complementary datasets from spacecrafts, rovers and martian meteorite studies. In planetary interiors, water can be dissolved in fluids or melts and hydrous phases, but can also be locked as protons attached to structural oxygen in lattice defects in nominally anhydrous minerals (NAM) such as olivine, pyroxene, or feldspar [1-3]. Measuring water in Martian meteorite NAM is challenging because the minerals are fragile and riddled with fractures from impact processes that makes them break apart during sample processing. Moreover, curing the sample in epoxy causes problems for the two main water analysis techniques, Fourier transform infrared spectrometry (FTIR) and secondary ionization mass spectrometry (SIMS). Measurements to date have resulted in a heated debate on how much water the mantle of Mars contains. SIMS studies of NAM [4], amphiboles [5], and apatites [6-8] from Martian meteorites report finding enough water in these phases to infer that the martian mantle is as hydrous as that of the Earth. On the other hand, a SIMS study of glass in olivine melt inclusions from shergottites concludes that the Martian mantle is much drier [9]. The latter interpretation is also supported by the fact that most martian hydrous minerals generally have the relevant sites filled with Cl and F instead of H [10,11]. As for experimental results, martian basalt compositions can be reproduced using water as well as Cl in the parent melts [12,13]. Here FTIR is used to measure water in martian meteorite minerals in order to constrain the origin of the distribution of water in martian meteorite phases.

Peslier, Anne H.↗
NASA NTRS2016

The Role of Extraterrestrial Materials in the Origin of Life

It has been well established for some time now that C-rich organic materials are relatively common in a number of environments in space. This is known through the telescopic detection of these materials using spectroscopy techniques in the infrared and sub-millimeter wavelength ranges and through the identification of organics in extraterrestrial materials. Extraterrestrial materials in which organics have been found include collected meteorites and interplanetary dust particles, and samples returned by NASA spacecraft from comets. These organics are produced by a variety of astrochemical processes. Despite their abiotic origins, these organic materials of are considerable interest to astrobiology for several reasons. First, organic materials of any composition are important as a means of delivering the elements C, H, O, and N to the surfaces of newly formed planets, and these elements are likely critical to the origin and subsequent evolution of life (certainly for life as we know it). In addition, it is clear that at least a portion of the organics found in space are in the form of molecules that play important roles in modern biology - for example, molecules like amino acids, amphiphiles, quinones, etc. Thus, the delivery of extraterrestrial organics to planetary surfaces brings not only bulk C, H, O, and N, but also molecular complexity in forms that are potentially useful for the origin and early evolution of life. This suggests that the production and delivery of cosmic organic compounds may have played key roles in the origin of life on Earth and, by extension, on other planets in the universe.

Astrochemistry↗
NASA NTRSDate not supplied

Transition measurements of upper and lower rotor blade surfaces in forward flight with thermography

Thermography allows for imaging the location of laminar-to-turbulent boundary layer transition on surfaces in air flows. The determination of BL transition of rotor blades was done in 2017 on the lower surface of a rotor blade in forward flight in the NASA Langley 14- by 22-Foot Subsonic Tunnel Subsonic Wind Tunnel. This article reports on the follow-on experiment in the same facility and the same blades where thermography was performed on both upper and lower surface synchronously, with the upper surface mapped throughout the full azimuthal range. Blade-tracking rotating mirrors were used for each thermal camera and were synchronized for simultaneous image acquisition. Furthermore, the Differential Infrared Thermography (DIT) technique depicts the unsteady nature of the BL transition in forward flight. Results are presented and discussed. These data are the first ever recorded of both surfaces of a rotor in forward flight.

Boundary layer transition↗
NASA NTRS2022

Flow Visualization to Complement Modern Wing Tunnel Testing

In recent times, wind tunnel testing at the NASA Ames Unitary Plan Wind Tunnel (UPWT) seeks to validate computational fluid dynamics (CFD) tools. To that end, we find that now more than ever, flow visualization is a powerful capability that provides context to the experimental results bringing real-time insight to the researcher. It enables us to answer questions like: “Why does this drag polar look different?” or “What is the source of this tone in the microphone data?”. Flow visualization can verify that assumptions made in the CFD model are correct, addressing questions like: “Are our trip dots the correct size and location?” or “Does the position of this shock match our prediction?”. Techniques such as infrared flow visualization and schlieren / shadowgraph are powerful capabilities that when taken together can provide results as to the nature of the fluid structure interaction at a test condition in a format that pairs well with computational results. When properly integrated these measurements can be taken with no impact on the productivity of the test program, supplementing traditional measurements and often discovering something unforeseen, helping the researcher to answer those slippery aerodynamic questions and ultimately build confidence in the accuracy of a model.

wind tunnel↗
NASA NTRS2023

Tunable Laser Spectrometers for Planetary Science

Distinguishing planetary formation and evolution pathways and understanding the origins of volatiles on planetary bodies requires determination of relative abundances and isotope ratios in the noble gases, and also of the isotope ratios in C, H, N, O and S at high precisions. Traditional planetary mass spectrometers uniquely provide excellent survey capability including the noble gas relative abundances and their isotope ratios. However, to distinguish planetary evolution models for the outer planets, stable isotope ratios in C and O require precisions of ∼10 or better, readily achievable with a tunable laser spectrometer (TLS). As demonstrated on the Mars Curiosity rover, and as planned for a now-selected NASA Venus mission, tunable laser spectrometers play a unique role synergistic with the capabilities of planetary mass spectrometers. The TLS technique of recording infrared absorption spectra at ultrahigh resolution (resolving power λ/δλ ∼ 5 million) provides unambiguous detection of a wide variety of gases such as H2O, H2O2, H2CO, HOCl, NO, NO2, HNO3, N2O, O3, CO, CO2, NH3, N2H4, PH3, H2S, SO2, OCS, HCl, HF, O2, HCN, and CH4, C2H2, C2H4, C2H6 at parts-per-billion levels. Through line-depth or line-area ratio comparisons of adjacent spectral lines, planetary TLS instruments can achieve isotope ratio measurements in C, H, N, O, and S molecules at precisions of ∼1–2, including for the triple isotope components of O and S. Expected performance of TLS instruments for Venus, Saturn, Enceladus and Uranus will be described as constrained by actual measurements reported at Mars on the Curiosity rover.

Planetary↗
NASA NTRS1992

Atmospheric and spectroscopic research in the far infrared

The University of Oregon (UO) has been a major participant in the development of far infrared spectroscopic research of the stratosphere for the purpose of understanding the ozone layer processes. The UO has had a 15-year collaboration with the Italian group of B. Carli, and have participated in the 1978/79 Sub-millimeter Infrared Balloon Experiment (SIBEX), in the Balloon Intercomparison Campaign, (BIC), in the Infrared Balloon Experiment (IBEX), and in the recently concluded Far Infrared Experiment for UARS Correlative Measurements (FIREX). Both IBEX and FIREX programs were conducted in collaboration with NASA Langley, and were designed as validation flights in support of the Upper Atmosphere Research Satellite (UARS) Program. The technique of atmospheric far infrared spectroscopy offers two important advantages. First, many chemically important species can be measured simultaneously and co-spatially in the atmosphere. Second, far infrared atmospheric spectra can be obtained in thermal emission without reference to the sun's position, enabling full diurnal and global coverage. Recent improvements in instrumentation, field measurements, and molecular concentration retrieval techniques are now making the far infrared a mature measurement technology. This work to date has largely focused on balloon-based studies, but the future efforts will focus also on satellite-based experiments. A program of research in the following general areas was proposed: Laboratory Pressure broadening coefficient studies; specialized detector system assembly and testing; and consultation and assistance with instrument and field support. The proposal was approved and a three-year research grant titled 'Atmospheric and Spectroscopic Research in the Far Infrared' was awarded. A summary of technical accomplishments attained during the grant period are presented.

Park, Kwangjai↗
NASA NTRS1992

The tropospheric emission spectrometer (TES) for the Earth Observing System (EOS)

In recent years, increasing concern has been expressed about Global Change - the natural and anthropogenic alteration of the Earth's environment involving global greenhouse warming and the associated climate change, urban and regional atmospheric pollution, acid deposition, regional increases in tropospheric zone, and the decrease in stratospheric ozone. A common theme among these problems is that they all involve those tropospheric trace gases which are fundamental to the biosphere-troposphere interaction, the chemistry of the free troposphere itself, and troposphere-stratosphere exchange. The chemical species involved all have spectral signatures within the near and mid infrared that can now be measured by advanced techniques of remote-sensing infrared spectroradiometry. Such a system is the Tropospheric Emission Spectrometer (TES), now in Phase B definition for the Earth Observing System (EOS) polar platforms. TES addresses these objectives by obtaining radiometrically calibrated, linewidth-limited spectral resolution, infrared spectra of the lower atmosphere using both natural thermal emission and reflected sunlight (where appropriate) in three different, but fully programmable, modes: a gobal mode, a pointed mode, and a limb-viewing mode. The goals of TES, its instrumentation, operational modes, sensitivity and data handling are discussed.

Beer, R.↗
NASA NTRS1995

A method for combining passive microwave and infrared rainfall observations

Because passive microwave instruments are confined to polar-orbiting satellites, rainfall estimates must interpolate across long time periods, during which no measurements are available. In this paper the authors discuss a technique that allows one to partially overcome the sampling limitations by using frequent infrared observations from geosynchronous platforms. To accomplish this, the technique compares all coincident microwave and infrared observations. From each coincident pair, the infrared temperature threshold is selected that corresponds to an area equal to the raining area observed in the microwave image. The mean conditional rainfall rate as determined from the microwave image is then assigned to pixels in the infrared image that are colder than the selected threshold. The calibration is also applied to a fixed threshold of 235 K for comparison with established infrared techniques. Once a calibration is determined, it is applied to all infrared images. Monthly accumulations for both methods are then obtained by summing rainfall from all available infrared images. Two examples are used to evaluate the performance of the technique. The first consists of a one-month period (February 1988) over Darwin, Australia, where good validation data are available from radar and rain gauges. For this case it was found that the technique approximately doubled the rain inferred by the microwave method alone and produced exceptional agreement with the validation data. The second example involved comparisons with atoll rain gauges in the western Pacific for June 1989. Results here are overshadowed by the fact that the hourly infrared estimates from established techniques, by themselves, produced very good correlations with the rain gauges. The calibration technique was not able to improve upon these results.

Kummerow, Christian↗
NASA NTRS1988

Measurement of HO2 and other trace gases in the stratosphere using a high resolution far-infrared spectrometer at 28 KM

The major events and results to date of the ongoing program of measuring stratospheric composition by the technique of far-infrared Fourier-transform spectroscopy from a balloon-borne platform are reviewed. The highlights of this period were the two balloon flight campaigns which were performed at Palestine, Texas, both of which produced large amounts of scientifically useful data.

Traub, Wesley A.↗
NASA NTRS1990

Monitoring of catalyst performance in CO2 lasers using frequency modulation spectroscopy with diode lasers

Closed-cycle CO2 laser operation with removal of O2 and regeneration of CO2 can be achieved by catalytic CO-O2 recombination. Both parametric studies of the optimum catalyst formulation and long-term performance tests require on line monitoring of CO, O2 and CO2 concentrations. There are several existing methods for molecular oxygen detection. These methods are either intrusive (such as electrochemical method or mass spectrometry) or very expensive (such as CARS, UV laser absorption). Researchers demonstrated a high-sensitivity spectroscopic measurement of O2 using the two-tone frequency modulation spectroscopy (FMS) technique with a near infrared GaAlAs diode laser. Besides its inexpensive cost, fast response time, nonintrusive measurements and high sensitivity, this technique may also be used to differentiate between isotopes due to its high spectroscopic resolution. This frequency modulation spectroscopy technique could also be applied for the on-line monitoring of CO and CO2 using InGaAsP diode lasers operation in the 1.55 microns region and H2O in the 1.3 microns region. The existence of single mode optical fibers at the near infrared region makes it possible to combine FMS with optical fiber technology. Optical fiber FMS is particularly suitable for making point-measurements at one or more locations in the CO2 laser/catalyst system.

Wang, Liang-Guo↗
NASA NTRS1987

Determine precipitation rates from visible and infrared satellite images of clouds by pattern recognition technique

A more advanced cloud pattern analysis algorithm was subsequently developed to take the shape and brightness of the various clouds into account in a manner that is more consistent with the human analyst's perception of GOES cloud imagery. The results of that classification scheme were compared with precipitation probabilities observed from ships of opportunity off the U.S. east coast to derive empirical regressions between cloud types and precipitation probability. The cloud morphology was then quantitatively and objectively used to map precipitation probabilities during two winter months during which severe cold air outbreaks were observed over the northwest Atlantic. Precipitation probabilities associated with various cloud types are summarized. Maps of precipitation probability derived from the cloud morphology analysis program for two months and the precipitation probability derived from thirty years of ship observation were observed.

Weinman, James A.↗
NASA NTRS1989

Improved Method For Making Infrared Imagers

Properties of thin dielectric layer adjusted precisely. Deposition technique found to improve fabrication of infrared imaging devices. Applied to dielectric layer of SiO and SiO2, critical to operation of device. For imager to work properly, thickness of dielectric layer adjusted precisely in coordination with absorption coefficient and wavelength of light imaged. New deposition process enables adjustment of thickness and index of refraction of critical dielectric layer to within plus or minus 1 percent.

Kaganowicz, G.↗
NASA NTRS1984

Far-infrared laser magnetic resonance of vibrationally excited CD2

The detection of 13 rotational transitions in the first excited bending state (010) of CD2 using the technique of far-infrared laser magnetic resonance spectroscopy is reported. Molecular parameters for this state are determined from these new data together with existing infrared observations of the v(2) band. Additional information on the ground vibrational state (000) is also provided by the observation of a new rotational transition, and this is combined with existing data to provide a refined set of molecular parameters for the CD2 ground state. One spectrum has been observed that is assigned as a rotational transition within the first excited symmetric stretching state (100) of CD2. These data will be of use in refining the structure and the potential function of the methylene radical.

Evenson, K. M.↗
NASA NTRS2001

Influence of 3D Radiative Effects on Satellite Retrievals of Cloud Properties

When cloud properties are retrieved from satellite observations, the calculations apply 1D theory to the 3D world: they only consider vertical structures and ignore horizontal cloud variability. This presentation discusses how big the resulting errors can be in the operational retrievals of cloud optical thickness. A new technique was developed to estimate the magnitude of potential errors by analyzing the spatial patterns of visible and infrared images. The proposed technique was used to set error bars for optical depths retrieved from new MODIS measurements. Initial results indicate that the 1 km resolution retrievals are subject to abundant uncertainties. Averaging over 50 by 50 km areas reduces the errors, but does not remove them completely; even in the relatively simple case of high sun (30 degree zenith angle), about a fifth of the examined areas had biases larger than ten percent. As expected, errors increase substantially for more oblique illumination.

Varnai, Tamas↗
NASA NTRS1992

Airborne remote sensing of tropospheric water vapor using a near infrared DIAL system

Summarized here are the results of airborne water vapor measurements in the lower middle and upper troposphere using the Differential Absorption Lidar (DIAL) technique in the near infrared. The measurements were performed in July 1990 in Southern Bavaria between Allersberg and Straubing from 20 to 23 UTC taking advantage of night time conditions. The tropospheric H2O profiles were range investigated both horizontally and vertically. With the DIAL system that was used, water vapor measurements in the upper troposphere have been carried out for the first time. To calibrate the H2O-retrievals, effective absorption cross sections of selected H2O lines in terms of altitude around 724 nm were calculated using line parameter data from the literature (B. E. Grossmann et al). The frequency of the on-line measurements was adjusted by the spectra of a Polyacenic Semiconductor (PAS) cell filled with H2O. We found that the calibration error ranged between 0.005 and 0.015 cm(exp -1). The systematic errors of the H2O as a function of altitude were estimated below 7 km and 12 percent accuracy in the upper troposphere. The vertical H2O profile agrees well with in situ measurements in the investigated range between the top of the planetary boundary layer (PBL) up to near the tropopause. Horizontal and vertical H2O profiles are calculated by means of averaging single lidar returns. Typical horizontal resolutions range from 4 km in the lower to 11 km in the upper troposphere with vertical resolutions varying from 0.3 km up to 1 km, respectively, in order to satisfy a 5 - 10 percent accuracy in the statistical error. The measurement sensibility of the water vapor mixing ration in the upper troposphere is 0.01 g/kg.

Ehret, G.↗