Assuming large signal-to-noise ratio and using the rotationally resolved fundamental vibration-rotation band emission from NO near 5.3 μm we propose a scheme for remotely sensing temperature above the altitudes where the 15 μm emission from CO2 becomes very weak. We also find that the rotationally resolved 5.3 μm emission can be used to remotely sense N(4S) atom, O2, and O densities in the terrestrial thermosphere -- this being the only method for remotely sensing the first two species.
This paper proposes to remotely sense the translational temperature and the densities of important nocturnal radiators, viz., nitric oxide, carbon dioxide, and atomic oxygen, as functions of altitude in the quiescent nighttime terrestrial thermosphere. The densities of the excited states as functions of altitude are obtained by inverting the measured infrared limb emissions from nitric oxide near 5.3 micrometers , from carbon dioxide near 15 micrometers , and the fine structure lines of atomic oxygen at 63.2 micrometers and 145.5 micrometers . A knowledge of the excitation mechanisms then permits the calculation of the ground states densities.
Classical trajectory calculations have been performed to determine the rotational distribution of vibrationally excited nitric oxide from collisions with atomic oxygen. The reaction occurs on two electronic potential energy surfaces which must be considered for a realistic description of the O+NO collision dynamics. The results, which have been statistically averaged over both electronic potential energy surfaces, are in good agreement with the available experimental data for vibrational relaxation of NO(v less than or equal to 9), as well as the temperature dependence of NO(v equals 1). The state-to-state relaxation rate coefficients involve the formation of long-lived collision complexes and indicate statistical behavior in O+NO collisions. The present study confirms earlier analysis that the NO(v equals 1) rotational distributions can indeed by described by a Maxwell-Boltzmann distribution, albeit with a rotational temperature of approximately 75% of the initial translational temperature. Thus, it appears possible to establish a lower bound to, and an estimate of, the nighttime quiescent terrestrial thermosphere by measuring the rotational envelope of the 5.3 micrometer emission from NO.
Atmospheric infrared radiance fluctuations result from fluctuations in the density of atmospheric species, individual molecular state populations, and kinetic temperatures and pressures along the sensor line of sight (LOS). The SHARC-4 program models the atmospheric background radiance fluctuations. It predicts a two dimensional radiance spatial covariance function from the underlying 3D atmospheric structures. The radiance statistics are non-stationary and are dependent on bandpass, sensor location and field of view (FOV). In the upper atmosphere non-equilibrium effects are important. Fluctuations in kinetic temperature can result in correlated or anti-correlated fluctuations in vibrational state temperatures. The model accounts for these effects and predicts spatial covariance functions for molecular state number densities and vibrational temperatures. SHARC predicts the non-equilibrium dependence of molecular state number density fluctuations on kinetic temperature and density fluctuations, and calculates mean LOS radiances and radiance derivatives. The modeling capabilities are illustrated with sample predictions of MSX like experiments with MSX sensor bandpasses, sensor locations and FOV. The model can be applied for all altitudes and arbitrary sensor FOV including nadir and limb viewing.
This paper describes the development of a new version of the SHARC code, SHARC-3, which includes the ability to simulate changing atmospheric conditions along the line-of-sight (LOS) paths being calculated. SHARC has been developed by the U.S. Air Force for the rapid and accurate calculation of upper atmospheric IR radiance and transmittance spectra with a resolution of better than 1 cm-1 in the 2 to 40 micrometers (250 to 5,000 cm-1) wavelength region for arbitrary LOSs in the 50 - 300 km altitude regime. SHARC accounts for the production, loss, and energy transfer processes among the molecular vibrational states important to this spectral region. Auroral production and excitation of CO2, NO, and NO+ are included in addition to quiescent atmospheric processes. Calculated vibrational temperatures are found to be similar to results from other non-LTE codes, and SHARC's equivalent-width spectral algorithm provides very good agreement with much more time-consuming `exact' line-by-line methods. Calculations and data comparisons illustrating the features of SHARC-3 are presented.
The analysis of CIRRIS 1A (Cryogenic InfraRed Radiance Instrumentation for Shuttle) interferometric and radiometric data obtained during the flight of STS-39 (28 Apr - 6 May 1991) reveals the presence of IR emission in the 400-900/cm (11-25 micron) region not attributable to atmospheric emission. In this paper, data are shown which identify the signal as nearfield water vapor present during all CIRRIS IA observations. Variability of the near-field water vapor emissions is characterized and compared to mass spectrometer data also obtained on STS-39 (QINMS). Further investigation indicates that the water is excited to extremely high effective temperatures, possibly in excess of 9000 K. The data presented support the theory that water outgassed from the shuttle tiles is highly excited by collisions with atmospheric O, classifying it as a type of shuttle-induced glow never before measured in the LWIR.
Progress made in the last ten years in understanding the daytime earthlimb emission around 2.7 microns is reviewed. It is pointed that the solar pumped emission from the earth's atmosphere consists of radiation primarily from carbon dioxide and from water vapor. Radiation from CO2 was the subject of a thorough investigation (Sharma and Wintersteiner, 1985). The radiation from water vapor is studied using the newly developed Strategic High-Altitude Radiance Code, and the results are compared with the SPectral Infrared Rocket Experiment. The next few years should see dramatic progress in the backgrounds models because of the global measurement made by the CIRRIS 1A.
The present version of the PRUV code (Plume Radiation of Ultra-Violet) utilizes flowfield input from the JANNAF SPF2 code and computes plume ultra-violet spectral signatures resulting from the emissions of CO-0 chemiluminescence, aluminum oxide, zirconium oxide or carbon particulates, and the individual lines of four molecular band systems. Collision and Doppler effects are computed for each molecular line for use in absorption calculations. Spectral signatures were computed for two missiles, herein named Missile A and Missile B. The Missile A plume contains aluminum oxide particulates while those of Missile B are composed of zirconium oxide. Temperature dependent imaginary refractive index (n ) values of zirconium oxide were estimated through use of the phenomenological Urbach Tail Model. Agreement with measured results for both missiles was generally within a factor of two. Such agreement is considered good for this stage of development of the code. A brief description of the present stage of development of the PRUV code is given.
An IRAMMP field measurement exercise was conducted during July 1990 in the Florida Keys. The purpose of the exercise was to investigate horizon radiance phenomenology and associated clutter structure. In the exercise both the IRAMMP sensor and a PtSi imager were used. The sensors were located 31 m above the surface of the water in a ocean side apartment building. The IRAMMP sensor is a dual band 120 element radiometric scanner with an IFOV of 250 microradians. The PtSi sensor was a commercial staring instrument with a 85 microradian IFOV. High quality digital data were obtained on a number of days and nights over a three week time span. In most of the data sequences a bright IR point source on a small boat was observed as it transited over the horizon. The precise range to the point source was recorded at all times. An excellent set of meteorological "ground truth" data was collected in conjunction with a parallel NRL/NOSC field exercise called KEY90. This paper is a partial report on results obtained from the analysis of data from the Florida field measurements. Emphasis in this paper will be on three aspects of the low horizon phenomenology. These are: 1) the form of the radiance profile singularity in the vicinity of the horizon line, 2) the appearance of a point source as it traverses the horizon, and 3) the solar glitter pattern seen on the water under a favorable illumination geometry.
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