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Theoretical atmospheric absorption spectra between 2385 and 2425 kayser are shown to give excellent agreement with high resolution observations. Most of the atmospheric absorption in this region arises from continuum features due to absorption of N2 and the wings of distant CO2 lines. The treatment of each of these factors is discussed.
Calculations of the atmospheric heating rate by absorption of solar radiation by O3, H2O, and CO2 are reported. The method needs only seven parameters for each molecule and is particularly useful for heating calculations in three-dimensional global circulation models below 80 km. Applying the formula to the observed distributions of O3, H2O, and CO2 produces reasonable latitudinal and seasonal variations in the heating rate. The calculated heating rate, however, is sensitive to the global distributions of the absorbing gases, and uncertainties in the O3 distribution above approximately 50 km and the H2O distribution below approximately 20 km may seriously affect the global distributions of the heating rate in these regions.
The first spectral observations of the Venus disk in the 110 to 270 per cm spectral range are reported, made from the Kuiper Airborne Observatory in mid-March 1979, some three months following the start of the Pioneer Venus Orbiter mission. The instrumentation and its differences from earlier flight hardware is discussed. The brightness temperature was 275 K near 110/cm, dropping to 230 K near 270/cm. Radiance calculations, using temperature and cloud structure formation from the Pioneer Venus mission and including gaseous absorption by the collision-induced dipole of CO2, yield results consistently brighter than the observations. The atmospheric environment is reviewed with regard to the FIR opacity and possible particle distribution modifications are discussed. It is concluded that the most likely possibility for supplementing the FIR opacity is a population of large particles in the upper cloud with number densities less than one particle per cu cm which has remained undetected by in situ measurements.
The influence of systematic errors in the parameters of the models describing the geometry and the atmosphere on the profiles of trace gases retrieved from simulated solar occultation spectra, collected at satellite altitudes, is investigated. Because of smearing effects and other uncertainties, it may be preferable to calibrate the spectra internally by measuring absorption lines of an atmospheric gas such as CO2 whose vertical distribution is assumed rather than to relay on externally supplied information.
A flow-through chemical reactor model is developed to describe the mass transfer and chemical processes that atmospheric gases undergo in clouds. The model includes the simultaneous absorption of SO2, NH3, O3, NO(x), HNO3, CO2 and H2O2, the accompanying dissociation and oxidation reactions in cloud water, considers electrical neutrality, and includes qualitative parameterization of cloud microphysics. The model is used to assess the importance of the oxidation reactions H2O2-S(IV), O3-S(IV), and S(IV)-Mn(2+) catalysis, and the effects of cloud parameters such as drop size, rain intensity, liquid water content, and updraft velocity. Both precipitating and nonprecipitating clouds are studied. Model results predict sulfate production rates varying from 3 percent/hr to 230 percent/hr. The actual rate is highly dependent on the chemical composition of the uptake air and the physical conditions of the cloud. Model results also show that both the H2O2 and the O3 oxidation reactions can be significant.
The influence of systematic errors in the parameters of the models describing the geometry and the atmosphere on the profiles of trace gases retrieved from simulated solar occultation spectra, collected at satellite altitudes, is investigated. Because of smearing effects and other uncertainties, it may be preferable to calibrate the spectra internally by measuring absorption lines of an atmospheric gas such as CO2 whose vertical distribution is assumed rather than to rely on externally supplied information.
In 2012, NASA's mission of landing the Mars Science Laboratory (MSL) on Mars was successful. MSL was protected by an ablative heatshield of tiled low density material known as PICA (phenolic impregnated carbon ablator). The heatshield was instrumented with MEDLI (MSL Entry Descent Landing Instrument) a suite of sensors & thermocouples at discrete locations in order to monitor the in-depth ablator temperature response and surface pressure. MEDLI was designed and developed by NASA Langley, in partnership with NASA Ames Research Center for the purposes of probing Mars and evaluating the performance of the spacecraft upon entry into the Martian atmosphere. The flight data reduces the uncertainty in engineer models for predicting the response of a spacecraft towards the extreme heating environment of an entry into the Martian atmosphere. MEDLI2 is a part of the Mars 2020 mission and is the next-generation sensor suite for entry, descent, and landing. This data will again help engineers validate their flight models. Additionally, the atmospheric data, can help us understand atmospheric density and winds. This is a critical study for reducing risks to both robotic and future human missions to Mars. Engineered models for Mars 2020 are dependent upon parameters related to the materials response to heating and radiation. In this work, the thermal properties and other measurements of various ablative materials are analyzed to achieve greater utility of the 2012 MEDLI flight data and more accurately determine the parameters being used in Mars 2020. The purpose of this study was to measure specific heat, thermal conductivity, char yield, reflectance as a function of wavelength, and other thermal parameters and optical properties of various ablative materials. CO2(g) at extreme temperatures emits radiation impacting MEDLI2 flight predictions. Emissivity & absorptivity as a function of temperature were calculated from FTIR and UV-Vis data as a means of investigating whether these materials might absorb CO2 radiation upon entry into the Mars atmosphere.
The albedo of the polar caps on Mars brightens appreciably at high solar zenith angle (Warren et al., J. Geophys. Res., 95, 14717, 1990), an effect not included in prior polar-cap energy-balance models. This decreases absorption of sunlight by the polar cap, hence decreasing sublimation of CO2 ice. Lindner (J. Geophys. Res., 95, 1367, 1990) has shown that the radiative effects of clouds and airborne dust will increase sublimation of CO2 ice over that predicted by prior polar-cap energy-balance models. Furthermore, observations hint that more clouds may exist in the Northern Hemisphere, which Lindner (1990) has shown would sublime CO2 ice more quickly in the north than in the south. I show here that the effects of the solar zenith angle dependence of albedo and the radiative effects of clouds and dust offset each other, but act to extend the lifetime of CO2 ice on the south pole more than on the north pole, possibly explaining the observed hemispherical asymmetry in the residual polar caps without the need of a hemispherical asymmetry in polar-cap albedo required by prior models. Another positive aspect of this solution is that neither the inclusion of the solar zenith angle dependence of albedo nor the radiative effects of clouds and dust should appreciably change prior model agreement with observations of the annual cycle of surface pressure and the recession of the polar caps equatorward of 75 degrees latitude.
As a precursor to and validation of the core technology necessary for NASA's Active Sensing of CO2 Emissions over Nights, Days,and Seasons (ASCENDS) mission, we flew JPL's Carbon Dioxide Laser Absorption Spectrometer (CO2LAS) in a campaign of five flights onboard NASA's DC-8 Airborne Laboratory in July 2010. This is the latest in a series of annual flight campaigns that began in 2006, and our first on the DC-8 aircraft.
A transmittance model was developed for the 200-2000/cm region for interpretation of high spectral resolution measurements of laboratory absorption and of planetary thermal emission. The high spectral resolution requires transmittances to be computed monochromatically by summing the contribution of individual molecular absorption lines. A magnetic tape atlas of H2O,O3, and CO2 molecular line parameters serves as input to the transmittance model with simple empirical representations used for continuum regions wherever suitable laboratory data exist. The theoretical formulation of the transmittance model and the computational procedures used for the evaluation of the transmittances are discussed. Application is demonstrated of the model to several homogenous path laboratory absorption examples.
A transmittance model has been developed for interpretation of high spectral resolution measurements of laboratory absorption and of planetary thermal emission. The high spectral resolution requires transmittances to be computed monochromatically by summing the contribution of individual molecular absorption lines. A magnetic tape atlas of H2O, O3, and CO2 molecular line parameters serves as input to the transmittance model with simple empirical representations used for continuum regions wherever suitable laboratory data exist. The theoretical formulation of the transmittance model and the computational procedures used for the evaluation of the transmittances are discussed, and application of the model to several homogeneous-path laboratory absorption examples is demonstrated.
This paper presents experimental results using an atmospheric backscatter dual CO2 laser DIAL. It is shown that DIAL signals can be averaged to obtain an N exp -1/2 dependence decrease in the standard deviation of the ratio of backscattered returns from two lasers, where N is the number of DIAL signals averaged, and that such a lidar system can make measurements of gas concentrations with a precision of 0.7 percent in absorptance over 75 m in a short measurement time when the signal strength is high. Factors that eventually limit the rate of improvement in the SNR, such as changes in the ratio of the absorption and/or backscatter at the two laser frequencies and background noise, are discussed. In addition, it is noted that DIAL measurements made using hard-target backscatter often show departures from N exp -1/2 dependence improvement in the standard deviation because they are further limited by the combined effects of atmospheric turbulence and speckle (since the relative reproducibility of the speckle pattern on the receiver gives rise to correlations of the lidar signals).
Within the atmosphere of the earth, absorption and emission of thermal radiation by the 15-micron CO2 bands are the largest contributors to infrared cooling rates in the stratosphere. Various techniques for calculating cooling rates due to these bands have been described. These techniques can be classified into one of two categories, including 'exact' or line-by-line calculations and other methods. The latter methods are based on broad band emissivity and band absorptance formulations. The present paper has the objective to present comparisons of the considered computational approaches. It was found that the best agreement with the exact line-by-line calculations of Fels and Schwarzkopf (1981) could be obtained by making use of a new Doppler band model which is described in the appendix of the paper.
This paper presents the findings of the trade study to evaluate carbon dioxide (CO2) sensing technologies for the Constellation (Cx) space suit life support system for surface exploration. The trade study found that nondispersive infrared absorption (NDIR) is the most appropriate high Technology Readiness Level (TRL) technology for the CO2 sensor for the Cx space suit. The maturity of the technology is high, as it is the basis for the CO2 sensor in the Extravehicular Mobility Unit (EMU). The study further determined that while there is a range of commercial sensors available, the Cx CO2 sensor should be a new design. Specifically, there are light sources (e.g., infrared light emitting diodes) and detectors (e.g., cooled detectors) that are not in typical commercial sensors due to cost. These advanced technology components offer significant advantages in performance (weight, volume, power, accuracy) to be implemented in the new sensor. The exact sensor design (light source, transmitting optics, path length, receiving optics and detector) will be specific for the Cx space suit and will be determined by the performance requirements of the Cx space suit. The paper further identifies specifications for some of the critical performance parameters as well as discussing the engineering aspects of implementing the sensor into the Portable Life Support System (PLSS). The paper then presents testing results from three CO2 sensors with respect to issues important to Extravehicular Activity (EVA) applications; stability, humidity dependence and low pressure compatibility. The three sensors include two NDIR sensors, one commercial and one custom-developed by NASA (for a different purpose), and one commercial electrochemical sensor. The results show that both NDIR sensors have excellent stability, no dependence on ambient humidity (when the ambient temperature is above the dew point) and operate in low pressure conditions and after being exposed to a full vacuum. The commercial electrochemical sensor was not suitable for the Cx space suit for surface exploration. Finally, the paper identifies a number of techniques currently under development that offer significant advantages for EVA applications. These include miniaturized, room temperature, solid electrolyte systems and advanced optical detectors.
Part of the NASA plans for future Earth Science missions calls for observations using novel vantage points that can produce science products otherwise unobtainable. Observations of the Earth from the Lagrange-2 point, L-2, (1.5 million km behind the Earth on the Earth-Sun line) affords a unique vantage point for atmospheric science. Spectral observation of the Earth's atmosphere using solar occultation techniques in the near infrared (1 to 4 microns) provides one of the most accurate methods of passively sensing attitude profiles of the major species (CO2, O3, O2, CH4, H2O N2O). While traditional polar orbiting occultation measurements can obtain about 14 measurements per day (2 per orbit), solar occultation observations from the Lagrange-2 point will yield hourly profile measurements at all latitudes. The expected spatial resolution is 2 km in altitude, 0.5 degrees in latitude, and 2 degrees in longitude. The result from 24 hours of observations will be a three-dimensional map of atmospheric composition. To accomplish this task from L-2 requires the development of a large moderate spectral resolution instrument whose entrance aperture is about 10 meters. Use of a standard telescope design with a 10-meter circular mirror or a 10-meter strip mirror would be prohibitively expensive and excessively massive. Instead, we are proposing the development of a 10-meter linear interferometer coupled to a Fourier transform imaging spectrometer. The result will be a highly efficient design with sufficient sensitivity, while having both spatial and spectral resolution to produce the desired results. Preliminary calculations show that seven species (CO2, O3, O2, CH4, H2O N2O) have clearly separated spectral features in the I to 4 microns range with sufficient absorption to produce profile information from near the Earth's surface to the middle stratosphere. For CO2 the estimated sensitivity to change is 0.33% or 1 part in 330. This should be sufficient to detect changes that are significant for the carbon cycle studies. Initial instrument design studies are underway to determine the optimum optical design for the interferometer-spectrometer as well as the necessary highly stable mechanical designs. Separate design studies are being conducted for the spacecraft. shuttle launch facility, low-light solar power design, thermal control, and unique navigation requirements to reach and maintain the tight halo orbit about L-2.
Propellant gases emitted by attitude control systems such as SPARCS (Solar Pointing Aerobee Rocket Control System) and possible interference with experiments aboard the payloads are discussed. The optical properties of seven actual and potential gases emitted by propellant systems (CF4, N2H4, NH3, N2, CO2, Ar, and He) are presented. A compilation of absorption coefficients from 1 Angstrom to 50 microns and a summary of fluorescent spectra and efficiencies are provided. Since Freon-14 (CF4) is of primary importance to SPARCS, an experimental search for the fluorescent spectrum of CF4 was performed by exciting the gas with 920 Angstrom UV photons. The result was compared with an electron impact induced spectrum of CF4, and conclusions drawn about the nature of the radiating species. A detailed study of the CF4 flow fields and plume densities for typical SPARCS controlled payloads was made using gas dynamic codes which included the effects of vehicle shading and condensation. The importance of the optical properties of CF4 plumes was investigated and it is concluded that absorption is negligible but fluoresence may be significant in some cases.
Atmospheric temperature soundings with significantly improved vertical resolution can be obtained from carefully chosen narrow band-pass measurements in the 4.3-micron band of CO2 by taking advantage of the variation of the absorption coefficients, and thereby the weighting functions, with pressure and temperature. A set of channels has been found in the 4.2-micron region that is capable of yielding about 2-km vertical resolution in the troposphere. The concept of a complete system is presented for obtaining high resolution retrievals of temperature and water vapor distribution, as well as surface and cloud top temperatures, even in the presence of broken clouds.
A zonally symmetric primitive equation modelled on a sphere is used to numerically simulate the Martian atmosphere's response to various dust loads, as well as the ability of its meridional circulation to transport dust globally, where the circulation is driven by heating due to the absorption of solar and IR radiation by dust and CO2, in addition to sensible heat exchange with the ground. A preliminary experiment shows the model distribution of winds and temperature to compare favorably with zonally averaged values from a general circulation model. Experiments simulating the evolution of global dust storms show that dust is effectively transported by the zonal mean circulation, which rapidly intensifies as the dust spreads, and that the basic structure of the circulation is relatively insensitive to details, being mostly dependent on the heating of the tropical and subtropical atmosphere.