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Absorption features of several trace gases have been detected in 0.017-cm-resolution infrared spectra recorded over surface-level paths of 0.5 and 1.5 km at the National Solar Observatory on Kitt Peak, near Tucson, Arizona. Measurements of O3, HCOOH, NH3, and H2CO are briefly discussed.
The paper discusses the correlated k(absorption coefficient)-distribution (CKD) method for radiative transfer in nonhomogeneous atmospheres, in terms of the physical and mathematical conditions under which this method is valid. The CKD approach is theoretically formulated, and the mathematical and physical conditions under which this method is valid are identified. The parameterization for incorporating pressure and temperature effects in the k distribution is presented. The errors of CKD for absorption bands in the solar and thermal infrared spectra are examined, and the errors due to both the CKD method and the use of the optimum number of quadrature points are identified. Finally, an overall treatment for various absorption bands is developed, which will provide high efficiency and accuracy.
The VIMS instrument (Visible and Infrared Mapping Spectrometer) will be flown in the late 1990s on the CASSINI mission to Saturn and its moons. VIMS is designed to generate two-dimensional multispectral images of planetary surfaces and their features in the visible and infrared spectra. Compared to earth-based instruments, the stellar occultation experiment will provide unprecedented thickness resolution and chemical composition of planetary atmospheres. It will also gather high SNR optical depth profiles and particle size distribution of the Saturnian rings. The stellar occultation mode ideally requires continuous data acquisition for periods of up to several hours as the instrument stares at a star. This presents a sizeable challenge to the instrument's operational mode: processes that normally occur during mirror retrace must be shifted to data acquisition cycles, thereby creating timing difficulties in the sequencing of these cycles. The presentation focuses on the analysis of the stellar occultation mode and presents solutions to the challenge of an uninterrupted data stream. Several options will be presented that minimize any possible degradation of the experiment's science content.
Infrared spectra of thin films of pure CH4 have been measured for a range of temperatures from 22 to 68 K. The bandwidth for the fundamental nu3 near 3000/cm varies from 12.7 to 33.2/cm, while that for nu4 near 1300/cm varies from 6.2 to 16.0/cm. The real and imaginary parts of the index of refraction also exhibit significant dependence on temperature. These broadband measurements at low temperatures are useful for an understanding of clouds and hazes in the atmosphere of Uranus, clouds and ices in the atmosphere of Titan, and ices on the surfaces of Pluto and Triton.
The chemical characterization of a thermoplastic resin exposed to the low Earth orbit (LEO) environment for 10 months and for 5.8 years is reported. The resin, processed as a thick film and as a matrix for a graphite fiber reinforced composite, few exposed in the RAM direction on the NASA Long Duration Exposure Facility (LDEF). Differences attributable to environmental exposure were detected in infrared spectra and in various molecular weight parameters of film after 10 months in LEO. Those effects were not as apparent in composites after 5.8 years in LEO. Increased exposure to atomic oxygen toward the end of the LDEF mission probably scrubbed these effects from specimens exposed for 5.8 years. The intent of this study is to increase our fundamental understanding of space environmental effects on polymeric materials and to develop a benchmark for enhancing our methodology for and understanding of the ground-based simulation of space environmental effects.
Accurate frequencies for the lowest rotational transitions of five transition metal hydrides (CrH, FeH, CoH, NiH, and CuH) in their ground electronic states are reported to help the identification of these species in astrophysical sources from their far-infrared spectra. Accurate frequencies are determined in two ways: for CuH, by calculation from rotational constants determined from higher J transitions with an accuracy of 190 kHz; for the other species, by extrapolation to zero magnetic field from laser magnetic resonance spectra with an accuracy of 0.7 MHz.
The surfaces of atmosphereless bodies are subjected to a variety of chemical, thermal, accretionary, and shock processes related to their regolith environment. These processes are responsible for a number of alterations that occur in regoliths. Alterations include particle size commutation, implantation of solar wind gases, formation of agglutinates, spectral darkening, and, in the lunar case, the development of the very strong red continuum slope in the visible and near infrared spectra. A great deal of work has pointed to the role of agglutinates as the principal agent for darkening and reddening the lunar soil. The measures of regolith maturity are strongly linked to the accumulation of agglutinates. Recent work has suggested that the finest fractions of agglutinitic glass are major source of the spectral red slope. In particular, the red slope is most strongly associated with the agglutinitic glasses that are rich in blebs of sub-micron sized metal particles. It is thought that these metal particles, because of their size and scattering efficiently relative to the wavelength of light, are responsible for the red continuum slope. This fine fraction of metal particles is produced primarily by reduction of Fe(+2) from silicates. One mechanism for the reduction process is the reaction of solar implanted wind protons with the regolith soil during impact events. In this case the presence of hydrogen creates a reducing environment and the thermal pulse from the impact greatly speeds the reaction kinetics. To explore other reducing and thermal environments a series of experiments were done using samples in evacuated capsules buffered by Tantalum and heated to subsolidus temperatures.
Spatial variations in infrared spectra of the seasonal south polar cap of Mars were noted by the original Mariner 7 IRS instrument team as well as in subsequent examinations of the Mariner 7 data set. Up to now, however, there has been little effort to synthesize this information to understand variations in the south seasonal cap as a function of position or latitude. An attempt to quantify the spectra is made by providing estimates of CO2 grain sizes as well as upper limits on the amount of water frost contained in the polar collar. The variation in brightness at two wavelengths as well as the band depth of a weak CO2-ice feature at 2.28 microns as a function of spectrum number or subsequent location on the cap is presented. The full spectra, corrected only for the solar incidence angle, of three of the most significant areas are compared.
During the Galileo spacecraft encounter with the Earth-Moon system in December, 1992, a variety of spectral data and imagery were obtained for the eastern limb region as well as much of the lunar nearside. In order to support this encounter, we have been collecting near-infrared spectra and other remote sensing data for that portion of the northeastern nearside (NEM region) for which the highest resolution Galileo data were obtained. Analysis of spectra obtained for highlands units in the NEN region indicates that most surface units are dominated by anorthositic norite. To date, no pure anorthosites have been identified in the region. Several dark-haloed impact craters have exposed mare material from beneath highlands-rich surface units. Hence, ancient mare volcanism occurred in at least a portion of the NEN region. Endogenic dark-haloed craters in the region are the source of localized dark mantle deposits (LDMD) of pyroclastic origin and at least two compositional groups are present. The Galileo spacecraft obtained very high-resolution remote sensing data for the northeastern part of the nearside of the Moon. In order to prepare for and support this encounter, we have collected and analyzed a variety of spectral data for the NEN region. Numerous unanswered questions exist for this region. These include: (1) the composition and stratigraphy of the local highlands crust, (2) the nature and mode of formation of regional light plains, (3) the composition of localized pyroclastic deposits, and (4) the distribution of possible cryptomare in the region. The purpose of this paper is to present the preliminary results of our analyzes of remote sensing data of remote sensing data obtained for the NEN region.
The crater Bullialdus is a 61 km, Eratosthenian-age impact crater located on the western edge of Mare Nubium. Previous analysis of the spatial distribution of materials in the area using nine telescopic near-infrared spectra suggested a possible three-layer structure prior to the impact event: two shallow gabbroic layers and one deeper noritic layer (from a potential depth of 5.5 km). The initial interpretation of this stratigraphy was that Bullialdus may have tapped a layered mafic pluton, such as have been invoked to explain the existence of Mg-suite rocks. High-spatial resolution CCD images of Bullialdus were analyzed to better map the spatial distribution of the observed lithologies, and to assess the plausibility of the pluton interpretation.
Supernova 1993J in the nearby galaxy M81 is one of the closest - and hence brightest - supernovae to be witnessed this century. The early spectrum of SN1993J showed the characteristic hydrogen signature of type II supernovae, but its subsequent evolution is atypical for this class of supernova. Here we present optical and infrared spectra of SN1993J up to 43 days after outburst, which reveal the onset of the helium absorption and emission features more commonly associated with hydrogen-free type Ib supernovae. Corresponding model spectra show that the progenitor star must have possessed an unusually thin (for type II supernovae) hydrogen-rich envelope overlying a helium-rich mantle. Moreover, the supernova ejecta must have remained compositionally stratified, with little transport of the hydrogen-rich material down into the underlying helium layer or mixing of heavier elements outwards. SN1993J therefore represents a transition object between hydrogen-dominated type II supernovae, and hydrogen-free, helium-dominated type Ib supernovae.
The remote sensing of objects in the solar system using infrared radiation is discussed. Theories of radiative transfer, molecular spectroscopy, and atmospheric physics are used to show how infrared spectra of model planetary atmospheres are calculated. Instrumental techniques are described and the effect of instruments on the measurement of the emerging radiation field is addressed. Techniques that allow the retrieval of atmospheric and surface parameters from observations are examined. All the planets except Pluto are studied, and many of the planetary satellites.
The problems that now confront Mars Pathfinder are much the same as those that confronted Viking, but more and better information exists today. Like Viking, Mars Pathfinder must select a landing site compatible with lander and rover designs as evidenced by available data (Viking images, radar and thermal observations, albedo and color observations, visible-infrared spectra, etc.). Most regions at low elevations probably contain favorable sites, but some sites at low elevations with weak quasispecular echoes and low thermal inertias may be unfavorable.
This volume consists of Appendices A and B to the report on the Weightless Environment Training Facility Materials Coating Evaluation project. The project selected 10 coating systems to be evaluated in six separate exposure environments, and subject to three tests for physical properties. Appendix A holds the coating system, surface preparation, and application data. Appendix B holds the coating material infrared spectra.
Interstellar C2 F-X (1342 A) and D-X (2313 A) bands in the spectrum of zeta Oph were detected using the Goddard High-Resolution Spectrograph (GHRS) on the Hubble Space Telescope (HST). The total C2 column density is (1.79 +/- 0.06) 10(exp 13)/sq cm for an adopted f-value of 0.0545 for the 2313 A band of the Mulliken (D-X) system. Relative f-values for the 0-0 F-X, 0-0 D-X, and 2-0 A-X (Phillips) bands are derived by combining ultraviolet and near-infrared spectra: f(sub 00 sup FX)/f(sub 00 sup DX) = 1.83 +/- 0.18 and f(sub 20 sup AX)/f(sub 00 sup DX) = 0.0226 +/- 0.0029. For the Mulliken system, lines are detected up to a rotational level J double prime = 24. The relative populations along the rotational ladder are shown to be consistent with the physical and environmental conditions suggested by other diagnostics. Interstellar C2 molecules were detected towards zeta Per (N(C2) = (0.80 +/- 0.23) 10(exp 13)) but not towards Beta(sup 1), pi, and omega(sup 1) Sco(N(C2) less than or equal to 0.17 x 10(exp 13)/sq cm.
We present 1-5 micrometer moderate- and high-resolution infrared spectra of the ONeMg nova V1974 (Nova Cygni 1992) obtained at multiple epochs during an approximately 500 day period after outburst. During the first 80 days, the spectra exhibited continuum emission from thermal bremsstrahlung (free-free radiation) with prominent recombination line emission from hydrogen, helium, nitrogen, and oxygen. The measurement Full Width at Half Maximum (FWHM) of these recombination lines suggests that the initial velocity of the ejecta was approximately equals 2400-3400 km/s. We estimate from the hydrogen recombination line ratios that the density of the ionized shell at this epoch was approximately equals 10(exp 9), with an effective electron temperature of approximately equals 5 x 10(exp 3) K. As the temporal evolution of the ejecta progressed, the hydrogen and helium lines diminished in intensity, and coronal lines of aluminum, calcium, magnesium, neon, and sulfur appeared by approximately day 80. The coronal line emission phase persisted for over 400 days. During this epoch, no significant dust formation occurred. We find that the ejecta of V1974 Cyg were overabundant in aluminum with respect to silicon by a factor of approximately equals 5 and in magnesium with respect to silicon by a factor of greater than or equal to 3 relative to the solar photosphere. Comparison of our observed overabundances with recent model predictions of elemental synthesis in ONeMg outbursts suggests that the accreted envelope on V1974 Cyg was close to solar composition and that the precursor ONeMg white dwarf had a mass of approximately equals 1 solar mass.
Theoretical O I density-sensitive emission-line ratios R = I(2s(sup 2))(2p(sup 4))((sup 3)P(sub 0))-((2s(sup 2))(2p(sup 4))((sup 3)P(sub 1)))/I((2s(sup 2))(2p(sup 4))((sup 3)P(sub 1))-(2s(sup 2))(2p(sup 4))((sup 3)P(sub 2))) = I(146 micrometers)/I(63 micrometers) are presented for a range of temperatures (T = 100-10,000 K), neutral hydrogen densities (N(sub H) = 10(exp -2) to 10(exp 7)/cu cm) and radiation fields (G(sub 0) = 1-10(exp 6)) applicable to both photodissociation regions (PDRs) and H II regions and the diffuse ionized medium (DIM). The observed values of R for several PDRs, measured from far-infrared spectra obtained with the Kuiper Airborne Observatory (KAO), imply hydrogen densities which are in good agreement with those determined using other methods. This provides observational support for the validity of the theoretical O I line ratios, and hence the atomic data used in their derivation.
The infrared spectra of nitric-acid/ice films representative of polar stratospheric clouds (PSCs) were collected with simultaneous optical interference measurements to determine the real refractive indices at lambda = 632 nm. Ice and amphorous nitric-acid/ice films were prepared by condensation of water and nitric acid vapors onto a wedged Al2O3 substrate. The real refractive indices of these films were determined from the optical interference of a reflected helium-neon laser during film growth. The indices of the amphorous films varied smoothly from n = 1.30 for ice to n = 1.49 for nitric acid, similar to observations in previous work. We were unable to obtain the refractive index of crystlline films during adsorption because of optical scattering caused by surface roughness. Therefore crystlline nitric acid hydrate films were prepared by annealing amphorous nitric-acid/ice films. Further heating caused desorption of the crystalline hydrate films. During desorption, the refractive indices for ice, NAM (nitric acid monohydrate), alpha- and beta-NAT (nitric acid trihydrate) films were measured using the optical interference technique. In agreement with earlier data, the real refractive indices for ice and NAM determined in desorption were n = 1.30 +/- 0.01 and n = 1.53 +/- 0.03, respectively. The real refractive indices for alpha- and beta-NAT were found to be n = 1.51 +/- 0.01 and n greater than or equal to 1.46, respectively. Our measurements also suggest that the shape of crystalline nitric acid particles may depend on whether they nucleate from the liquid or by vapor deposition. If confirmed by future studies, this observation may provide a means of distinguishing the nucleation mechanism of crystalline PSCs.