Search NASA⌕ Search

SEARCH · Search NASA

Results for “ATMOSPHERIC ABSORPTION”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1991

A description of the correlated k distributed method for modeling nongray gaseous absorption, thermal emission, and multiple scattering in vertically inhomogeneous atmospheres

A radiative transfer method for treating nongray gaseous absorption and thermal emission in vertically inhomogeneous multiple scattering atmospheres is described. Probability density distributions of absorption coefficient strength are derived from line-by-line calculations to construct line-by-line and band model based k distributions. The monotonic ordering of absorption coefficient strengths in these k distributions implicitly preserves the monochromatic structure of the atmosphere at different pressure levels, thus simulating monochromatic spectral integration at a fraction of the line-by-line computing cost. The k distribution approach also permits accurate modeling of overlapping absorption by different atmospheric gases and accurate treatment of nongray absorption in multiple scattering media. It is shown that the correlated k distribution method is capable of achieving numerical accuracy to within 1 percent of cooling rates obtained with line-by-line calculations throughout the troposphere and most of the stratosphere.

Lacis, Andrew A.↗
NASA NTRS1982

High resolution atmospheric spectroscopy using a diode laser heterodyne spectrometer

Ultrahigh resolution (0.007 per cm) atmospheric solar absorption spectra that have been obtained from a tunable infrared heterodyne radiometer are discussed. The radiometer was developed for ground based observations in the 8-12 micron region, and tunability is achieved through the use of Pb-salt semiconductor laser local oscillators. Spectra have been obtained in a piecewise fashion from 9.1 to 11.1 microns using laser emission modes that exhibit characteristics suitable for local-oscillator operation. Spectra showing absorption features of HNO3, O3, CO2, and H2O are presented along with comparisons of experimental and synthetic spectra calculated using a line-by-line atmospheric transmission model.

Hoell, J. M., Jr.↗
NASA NTRS1974

The nu sub 9 fundamental of ethane - Integrated intensity and band absorption measurements with application to the atmospheres of the major planets

Measurements of the absolute intensity and integrated band absorption have been performed for the nu sub 9 fundamental band of ethane. The intensity is found to be about 34 per sq cm per atm at STP, and this is significantly higher than previous estimates. It is shown that a Gaussian profile provides an empirical representation of the apparent spectral absorption coefficient. Employing this empirical profile, a simple expression is derived for the integrated band absorption, which is in excellent agreement with experimental values. The band model is then employed to investigate the possible role of ethane as a source of thermal infrared opacity within the atmospheres of Jupiter and Saturn, and to interpret qualitatively observed brightness temperatures for Saturn.

Varanasi, P.↗
NASA NTRS1973

Introduction to stellar atmospheres and interiors

Stellar atmospheres are examined, giving attention to the transfer of radiation, the physical properties of gases, model atmospheres, and questions of line absorption in stellar atmospheres. Observational data are considered together with the equations for the stellar interior and aspects of stellar evolution. The calculation of model atmospheres and interiors is also discussed, taking into account numerical integration, a model solar atmosphere, and model stellar interiors.

Novotny, E.↗
NASA NTRS1976

Laser absorption spectroscopy - Method for monitoring complex trace gas mixtures

A frequency stabilized CO2 laser was used for accurate determinations of the absorption coefficients of various gases in the wavelength region from 9 to 11 microns. The gases investigated were representative of the types of contaminants expected to build up in recycled atmospheres. These absorption coefficients were then used in determining the presence and amount of the gases in prepared mixtures. The effect of interferences on the minimum detectable concentration of the gases was measured. The accuracies of various methods of solution were also evaluated.

Green, B. D.↗
NASA NTRS2010

Utilizing the MODIS 1.38 micrometer Channel for Cirrus Cloud Optical Thickness Retrievals: Algorithm and Retrieval Uncertainties

The cloud products from the Moderate Resolution Imaging Spectroradiometers (MODIS) on Terra and Aqua have been widely used within the atmospheric research community. The retrieval algorithms, however, oftentimes have difficulty detecting and retrieving thin cirrus, due to sensitivities to surface reflectance. Conversely, the 1.38 micron channel, located within a strong water vapor absorption band, is quite useful for detecting thin cirrus clouds since the signal from the surface can be blocked or substantially attenuated by the absorption of atmospheric water vapor below cirrus. This channel, however, suffers from nonnegligible attenuation due to the water vapor located above and within the cloud layer. Here we provide details of a new technique pairing the 1.38 micron and 1.24 micron channels to estimate the above/in-cloud water vapor attenuation and to subsequently retrieve thin cirrus optical thickness (tau) from attenuation-corrected 1.38 p.m reflectance measurements. In selected oceanic cases, this approach is found to increase cirrus retrievals by up to 38% over MOD06. For these cases, baseline 1.38 micron retrieval uncertainties are estimated to be between 15 and 20% for moderately thick cirrus (tau > 1), with the largest error source being the unknown cloud effective particle radius, which is not retrieved with the described technique. Uncertainties increase to around 90% for the thinnest clouds (tau < 0.5) where instrument and surface uncertainties dominate.

Meyer, Kerry↗
NASA NTRS1994

Absolute calibration and atmospheric versus mineralogic origin of absorption features in 2.0 to 2.5 micron Mars spectra obtained during 1993

We obtained new high resolution reflectance spectra of Mars during the 1993 opposition from Mauna Kea Observatory using the UKIRT CGS4 spectrometer. Fifty spectra of 1600-2000 km surface regions and a number of standard star spectra were obtained in the 2.04 to 2.44 micron wavelength region on 4 February 1993 UT. Near-simultaneous observations of bright standard stars were used to perform terrestrial atmospheric corrections and an absolute flux calibration. Using the known magnitude of the stars and assuming blackbody continuum behavior, the flux from Mars could be derived. A radiative transfer model and the HITRAN spectral line data base were used to compute atmospheric transmission spectra for Mars and the Earth in order to simulate the contributions of these atmospheres to our observed data. Also, we examined the ATMOS solar spectrum in the near-IR to try to identify absorption features in the spectrum of the Sun that could be misinterpreted as Mars features. Eleven absorption features were detected in our Mars spectra. Our data provide no conclusive identification of the mineralogy responsible for the absorption features we detected. However, examination of terrestrial spectral libraries and previous high spectral resolution mineral studies indicates that the most likely origin of these features is either CO3(sup 2-), HCO3(-), or HSO4(-) anions in framework silicates or possibly (Fe, Mg)-OH bonds in sheet silicates.

Bell, James F., III↗
NASA NTRS2000

Difference-frequency-based tunable absorption spectrometer for detection of atmospheric formaldehyde

High-sensitivity detection of formaldehyde (CH2O) at 3.5315 micrometers (2831.64 cm-1) is reported with a diode-laser-pumped, fiber-coupled, periodically poled LiNbO3 spectroscopic source. This source replaced the Pb-salt diode laser Dewar assembly of an existing tunable diode-laser absorption spectrometer designed for ultrasensitive detection of CH2O. Spectra are recorded with 2f-modulation spectroscopy and zero-air rapid background subtraction. Initial measurements reported here, determined from multiple measurements of a flowing 7.7 parts per billion by volume (ppbv, parts in 10(9)) CH2O in air mixture, indicate replicate precisions as low as 0.24 ppbv.

Non-NASA Center↗
NASA NTRS1985

Spectroscopic measurements of atmospheric HCN at northern and southern latitudes

A number of lines belonging to the nu(3) fundamental vibration-rotation band of hydrogen cyanide (HCN) have been identified in atmospheric infrared absorption spectra obtained on high-altitude balloon flights at 32 deg N in 1976 and at 30 deg S in 1977. Quantitative analysis of these spectral features has resulted in the first determination of atmospheric HCN concentrations in the Southern Hemisphere, as well as an independent estimate of stratospheric HCN abundance in the Northern Hemisphere. Within the uncertainties of the present and previous measurements, the Northern Hemisphere result is consistent with those of other investigators, and Southern Hemisphere HCN concentrations appear to be similar to those in the Northern Hemisphere.

Smith, M. A. H.↗
NASA NTRS1983

Infrared limb-darkening effects for the earth-atmosphere system

An infrared radiative transfer model has been developed for evaluating anisotropic functions in the longwave region (5-50 microns) due to limb-darkening effects in the earth's atmosphere. An accurate narrow-band model of absorption has been used for computing transmission functions of the atmosphere. Absorption due to all major and minor atmospheric constituents has been taken into account including the continuum absorption due to water vapor. Anisotropic functions have been calculated for several latitudinal and seasonal climatological-average model atmospheres. The effects of the variability of various meteorological parameters, e.g. surface temperature, surface relative humidity, and cloud-top height have been examined. It has been found that the variability of cloud parameters has the largest effect on the infrared anisotropic functions.

Gupta, S. K.↗
NASA NTRS2000

Influence of the Surface and Cloud Nonuniformities in the Solar Energy Fluxes in the Arctic

Solar energy fluxes reaching the surface and absorbed by it are basic components of the energy balance of the Arctic. They depend mainly on the solar zenith angle, a state of the atmosphere, especially the cloudiness, and the surface albedo. However, they can also be modified by variabilities in the surface albedo and cloud optical thickness. The surface of the Arctic can be highly nonuniform. The surface of the Arctic Ocean, which covers the huge part of the Arctic can be view as a mosaic of sea water, sea ice, snow and, in the melting period, melting ponds. In our paper, results are presented of Monte Carlo simulations of the expected influence of nonuniform cloud structure and nonuniform surface albedo on radiative fluxes at the Arctic surface. In particular, the plane parallel biases in the surface absorptance and atmospheric transmittance are studied. The bias is defined as the difference between the real absorptance or transmittance (i.e. nonuniform conditions) averaged over a given area, and the uniform or plane parallel case with the same mean cloud optical thickness and the same mean surface albedo. The dependence of the biases is analysed with respect to the following: domain averaged values of the cloud optical thickness and surface albedo, scales of their spatial variabilities, correlation between cloud optical thickness and cloud albedo variabilities, cloud height, and the solar zenith angle. Ranges of means and standard deviations of the input parameters typical of Arctic conditions are obtained from the SHEBA experiment.

Rozwadowska, A.↗
NASA NTRS2012

Greenhouse Gas Concentration Data Recovery Algorithm for a Low Cost, Laser Heterodyne Radiometer

The goal of a coordinated effort between groups at GWU and NASA GSFC is the development of a low-cost, global, surface instrument network that continuously monitors three key carbon cycle gases in the atmospheric column: carbon dioxide (CO2), methane (CH4), carbon monoxide (CO), as well as oxygen (O2) for atmospheric pressure profiles. The network will implement a low-cost, miniaturized, laser heterodyne radiometer (mini-LHR) that has recently been developed at NASA Goddard Space Flight Center. This mini-LHR is designed to operate in tandem with the passive aerosol sensor currently used in AERONET (a well established network of more than 450 ground aerosol monitoring instruments worldwide), and could be rapidly deployed into this established global network. Laser heterodyne radiometry is a well-established technique for detecting weak signals that was adapted from radio receiver technology. Here, a weak light signal, that has undergone absorption by atmospheric components, is mixed with light from a distributed feedback (DFB) telecommunications laser on a single-mode optical fiber. The RF component of the signal is detected on a fast photoreceiver. Scanning the laser through an absorption feature in the infrared, results in a scanned heterodyne signal io the RF. Deconvolution of this signal through the retrieval algorithm allows for the extraction of altitude contributions to the column signal. The retrieval algorithm is based on a spectral simulation program, SpecSyn, developed at GWU for high-resolution infrared spectroscopies. Variations io pressure, temperature, composition, and refractive index through the atmosphere; that are all functions of latitude, longitude, time of day, altitude, etc.; are modeled using algorithms developed in the MODTRAN program developed in part by the US Air Force Research Laboratory. In these calculations the atmosphere is modeled as a series of spherically symmetric shells with boundaries specified at defined altitudes. Temperature, pressure, and species mixing ratios are defined at these boundaries. Between the boundaries, temperature is assumed to vary linearly with altitude while pressure (and thus gas density) vary exponentially. The observed spectrum at the LHR instrument will be the integration of the contributions along this light path. For any absorption measurement the signal at a particular spectral frequency is a linear combination of spectral line contributions from several species. For each species that might absorb in a spectral region, we have pre-calculated its contribution as a function of temperature and pressure. The integrated path absorption spectrum can then by calculated using the initial sun angle (from location, date, and time) and assumptions about pressure and temperature profiles from an atmospheric model. The modeled spectrum is iterated to match the experimental observation using standard multilinear regression techniques. In addition to the layer concentrations, the numerical technique also provides uncertainty estimates for these quantities as well as dependencies on assumptions inherent in the atmospheric models.

Miller, J. Houston↗
NASA NTRS1993

Near-infrared spectra of the Martian surface: Reading between the lines

Moderate-resolution near-infrared (NIR) spectra of Mars have been widely used in studies of the Martian surface because many candidate surface materials have distinctive absorption features at these wavelengths. Recent advances in NIR detector technology and instrumentation have also encouraged studies in this spectral region. The use of moderate spectral resolution has often been justified for NIR surface observations because the spectral features produced by most surface materials are relatively broad, and easily discriminated at this resolution. In spite of this, NIR spectra of Mars are usually very difficult to interpret quantitatively. One problem is that NIR surface absorption features are often only a few percent deep, requiring observations with great signal-to-noise ratios. A more significant problem is that gases in the Martian atmosphere contribute numerous absorption features at these wavelengths. Ground-based observers must also contend with variable absorption by several gases in the Earth's atmosphere (H2O, CO2, O3, N2O, CH4, O2). The strong CO2 bands near 1.4, 1.6, 2.0, 2.7, 4.3, and 4.8 micrometers largely preclude the analysis of surface spectral features at these wavelengths. Martian atmospheric water vapor also contributes significant absorption near 1.33, 1.88, and 2.7 micrometers, but water vapor in the Earth's atmosphere poses a much larger problem to ground-based studies of these spectral regions. The third most important NIR absorber in the Martian atmosphere is CO. This gas absorbs most strongly in the relatively-transparent spectral windows near 4.6 and 2.3 micrometers. It also produces 1-10 percent absorption in the solar spectrum at these NIR wavelengths. This solar CO absorption cannot be adequately removed by dividing the Martian spectrum by that of a star, as is commonly done to calibrate ground-based spectroscopic observations, because most stars do not have identical amounts of CO absorption in their spectra. Here, we describe tow effective methods for eliminating contamination of Martian surface spectra by absorption in the solar, terrestrial, and Martian atmospheres. Both methods involve the use of very-high-resolution spectra that completely resolve the narrow atmospheric absorption lines.

Crisp, D.↗
NASA NTRS1982

Stratospheric measurements of collision-induced absorption by molecular oxygen

High-resolution stratospheric solar absorption spectra recorded at sunset with a balloon-borne interferometer, from an altitude of 33 km, are used in a study of collision-induced absorption by the fundamental vibration-rotation band of O2, whose continuum has been identified in the 1400-1700/cm region in spectra obtained at tangent altitudes below 22 km. It is found that transmittance measurements in intervals free of atmospheric line absorption agree with values calculated with the O2 absorption coefficients of Timofeyev and Tonkov (1978), and that the measurements indicate a 20% upper limit for the uncertainty of the available O2 absorption coefficients at lower stratospheric temperatures, on the order of 220 K.

Rinsland, C. P.↗