Consideration Of Radiative Transfer Research Articles

Martian CO2 Ice Observation at High Spectral Resolution With ExoMars/TGO NOMAD.

The Nadir and Occultation for MArs Discovery (NOMAD) instrument suite aboard ExoMars/Trace Gas Orbiter spacecraft is mainly conceived for the study of minor atmospheric species, but it also offers the opportunity to investigate surface composition and aerosols properties. We investigate the information content of the Limb, Nadir, and Occultation (LNO) infrared channel of NOMAD and demonstrate how spectral orders 169, 189, and 190 can be exploited to detect surface CO2 ice. We study the strong CO2 ice absorption band at 2.7 μm and the shallower band at 2.35 μm taking advantage of observations across Martian Years 34 and 35 (March 2018 to February 2020), straddling a global dust storm. We obtain latitudinal‐seasonal maps for CO2 ice in both polar regions, in overall agreement with predictions by a general climate model and with the Mars Express/OMEGA spectrometer Martian Years 27 and 28 observations. We find that the narrow 2.35 μm absorption band, spectrally well covered by LNO order 189, offers the most promising potential for the retrieval of CO2 ice microphysical properties. Occurrences of CO2 ice spectra are also detected at low latitudes and we discuss about their interpretation as daytime high altitude CO2 ice clouds as opposed to surface frost. We find that the clouds hypothesis is preferable on the basis of surface temperature, local time and grain size considerations, resulting in the first detection of CO2 ice clouds through the study of this spectral range. Through radiative transfer considerations on these detections we find that the 2.35 μm absorption feature of CO2 ice clouds is possibly sensitive to nm‐sized ice grains.

A new Differential Optical Absorption Spectroscopy instrument to study atmospheric chemistry from a high-altitude unmanned aircraft

Abstract. Observations of atmospheric trace gases in the tropical upper troposphere (UT), tropical tropopause layer (TTL), and lower stratosphere (LS) require dedicated measurement platforms and instrumentation. Here we present a new limb-scanning Differential Optical Absorption Spectroscopy (DOAS) instrument developed for NASA's Global Hawk (GH) unmanned aerial system and deployed during the Airborne Tropical TRopopause EXperiment (ATTREX). The mini-DOAS system is designed for automatic operation under unpressurized and unheated conditions at 14–18 km altitude, collecting scattered sunlight in three wavelength windows: UV (301–387 nm), visible (410–525 nm), and near infrared (900–1700 nm). A telescope scanning unit allows selection of a viewing angle around the limb, as well as real-time correction of the aircraft pitch. Due to the high altitude, solar reference spectra are measured using diffusors and direct sunlight. The DOAS approach allows retrieval of slant column densities (SCDs) of O3, O4, NO2, and BrO with relative errors similar to other aircraft DOAS systems. Radiative transfer considerations show that the retrieval of trace gas mixing ratios from the observed SCD based on O4 observations, the most common approach for DOAS measurements, is inadequate for high-altitude observations. This is due to the frequent presence of low-altitude clouds, which shift the sensitivity of the O4 SCD into the lower atmosphere and make it highly dependent on cloud coverage. A newly developed technique that constrains the radiative transfer by comparing in situ and DOAS O3 observations overcomes this issue. Extensive sensitivity calculations show that the novel O3-scaling technique allows the retrieval of BrO and NO2 mixing ratios at high accuracies of 0.5 and 15 ppt, respectively. The BrO and NO2 mixing ratios and vertical profiles observed during ATTREX thus provide new insights into ozone and halogen chemistry in the UT, TTL, and LS.

Observational Possibility of the “Snow Line” on the Surface of Circumstellar Disks with the Scattered Light

Abstract We discuss how we obtain the spatial distribution of ice on the surface of the circumstellar disk around young stars. Ice in the disks plays a very important role in various issues, for instance, on the disk structure, on planet formation, on an isotopic anomaly in meteorites, and on the origin of the oceans on Earth. Therefore, spatially resolved observations of the condensation/sublimation front of ice, the so-called snow line is strongly required. Here, we propose a new method for obtaining a spatially resolved snow line on circumstellar disks by observing a 3µ H $_2$ O ice feature in the scattered light. Based on radiative transfer considerations, we show that the feature is clearly imprinted in the spectrum of the scattered light from both optically thick and thin circumstellar disks. We also show that the scattered light and the H $_2$ O ice feature from protoplanetary disks are detectable and spatially resolvable with current instruments through an $H_{\mathit{2}}O$ narrowband filter around 3µ. Finally, we present a diagnostics of disk dust properties on $K-H_{\mathit{2}}O$ and $K-L’$ two-color diagram.

The dynamics of stellar outflows dominated by interaction of dust and radiation

Wind outflow around a late-type star driven by radiation pressure on dust grains is investigated in detail. The equation of motion for the outflow coupled with the equation of radiative transfer is solved treating the circumstellar envelope, which consists of gas and dust, as a two-component fluid. Because of the drift of the dust particles through the gas, the dust-to-gas ratio varies with distance even if grain formation is a prompt process. The coupling between dust and gas weakens as the mass-loss rate decreases until finally the rate of momentum transfer to the gas is insufficient to overcome gravity when the mass-loss rate is too low. This results in a lower limit, on the order of 10 exp -7 solar mass/yr, to the possible mass-loss rates that can be driven by radiation pressure on dust. Radiative transfer considerations pose a bound on the capability of the radiation field to overcome gravity also in the opposite limit of large mass-loss rates. Due to the difference in optical properties between carbon stars and oxygen stars, these considerations produce a meaningful upper limit on the mass-loss rate, of several times 10 exp -4 solar mass/yr, only for carbon stars.

Particle radiative feedback in ammonium perchlorate deflagration

The deflagration behavior of ammonium perchlorate (AP) with carbon black and copper chromite catalyst additives was studied over a pressure range of 4.3-171 MPa (50-2500 psig) using light transmission and emission measurements in a window bomb and burn rate measurements in a conventional strand burner. It was found that a maximum value of the lower pressure limit PDL exists at intermediate values of carbon black concentration similar to that already reported for copper chromite catalyst. It was also found that sufficiently high concentrations of carbon black augment the steady deflagration rate of AP. Since carbon black is not a catalyst of AP decomposition , it is postulated that particle radiative feedback is more likely to be the cause of the observed behavior than previously suggested catalyst effects. To quantify the amount of radiative heat feedback, flame temperature and emissivity values were calculated from light emission/transmission measurements. These calculations yielded flame temperatures between 1406 and 1449 K and a value for the effective particle absorption efficiency over diameter Qa/d of 4.1 jun1 in good agreement with expected values. A simple analysis shows that the observed trends (increasing PDL at low particle concentrations and decreasing PDL at higher concentrations) can be predicted from simple radiative transfer considerations together with particle and matrix continuity equations.

Formation of the Giant Planets

The structure of a gaseous envelope surrounding a icy/rocky core is studied in consideration of radiative transfer. It is found that when the core grows beyond a critical core mass, the envelope cannot be in equilibrium and collapses onto the core to form a proto-giant planet. The results are as follows (for details, see Mizuno 1980).1) The critical core mass is smaller than that estimated by Perri and Cameron (1974) and Mizuno, Nakazawa and Hayashi (1978). 2) When the grain opacity in the envelope varies from 0 to 1 cm2/g, the critical core mass changes from ~2 to ~12 Earth's masses. 3) The critical core mass is independent of the region in the solar nebula.These are due to the existence of the radiative region in the envelope.

Long-slit spectroscopy in the rocket ultraviolet of the Orion Nebula

The study deals with the extensive nebulosity in the Trapezium region of Orion. An entrance slit was placed at the focal plane of rocketborne telescope, creating a long-slit spectrograph with a wavelength resolution of 22 A FWHM and a spatial resolution of 14 in. along the slit. Data reduction is outlined, the structure of the Orion Nebula is discussed, and radiative transfer considerations are presented.

Radio observations of interstellar CH. I

view Abstract Citations (108) References (296) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Radio observations of interstellar CH. I. Rydbeck, O. E. H. ; Kollberg, E. ; Hjalmarson, A. ; Sume, A. ; Ellder, J. ; Irvine, W. M. Abstract Results are presented for some eight months of almost continuous high-sensitivity observations of the three hyperfine transitions of the CH ground state in the directions to or in extended areas around more than 30 H I and H II regions, dark dust clouds, OH/IR stars, and other sources. The observations were made with a traveling-wave maser preamplifier on a 25.6-m telescope, giving a zenith-system noise temperature of about 34 K. Detailed discussions of the CH spectra are given in source descriptions and tables; radiative-transfer considerations and possible CH excitation mechanisms are included. Some major findings are that: (1) CH is widespread in the Galaxy; (2) the three CH transitions are observed in emission almost everywhere and exhibit weak maser characteristics; (3) satellite transitions are generally more inverted than the main line; (4) CH, OH, and H2CO seem to be well mixed in Orion-arm and Perseus-arm cloud configurations; (5) the average main-line excitation temperature is about -15 K; (6) the lower satellite transition seems to be a very sensitive far-IR indicator; (7) significant departures from equilibrium line-intensity ratios appear toward H I and H II regions; and (8) the relative abundance of CH with respect to other molecular species seems to diminish systematically from dilute H I clouds to the densest molecular clouds. Publication: The Astrophysical Journal Supplement Series Pub Date: July 1976 DOI: 10.1086/190385 Bibcode: 1976ApJS...31..333R Keywords: Hydrocarbons; Interstellar Matter; Microwave Spectra; Radio Sources (Astronomy); H Ii Regions; Hyperfine Structure; Interstellar Masers; Milky Way Galaxy; Astrophysics full text sources ADS |