Showing papers by "Spectral Sciences Incorporated published in 1994"

Classical dynamics of the N(4S) + O2 (X³ Σg−) → NO(X²II) + O(³P) reaction

Abstract: Classical trajectory calculations have been performed to determine the reaction rate constants and NO final vibrational-rotational distributions of the N(4S) + O2 reaction at hyperthermal translational energies. The reaction occurs on two electronic potential energy surfaces, both of which must be considered for a realistic description of the N(4S) + O2 dynamics. The calculations, which are in good agreement with the available experimental data, show that the reaction has a very strong translational energy dependence and produces NO with extensive vibrational and rotational excitation. The present study provides the N(4S) + O2 reaction attributes necessary to predict NO formation and emission from translationally hot N(4S) in the thermosphere.

Multi-pass optical cell species concentration measurement system

Abstract: A multi-pass optical cell for measuring the concentration of one or more species in a fluid to be monitored includes a sample region; a source of collimated radiation; a detector device for sensing the intensity of the radiation; at least two reflective surfaces for reflecting in a first direction in the sample region a number of times the radiation from the source and delivering it to the detector device.

Off-line-locked laser diode species monitor system

Abstract: An off-line-locked laser diode species monitor system includes: reference means for including at least one known species having a first absorption wavelength; a laser source for irradiating the reference means and at least one sample species having a second absorption wavelength differing from the first absorption wavelength by a predetermined amount; means for locking the wavelength of the laser source to the first wavelength of the at least one known species in the reference means; a controller for defeating the means for locking and for displacing the laser source wavelength from said first absorption wavelength by said predetermined amount to the second absorption wavelength; and a sample detector device for determining laser radiation absorption at the second wavelength transmitted through the sample to detect the presence of the at least one sample species.

MODTRAN2: Evolution and applications

Abstract: MODTRAN2' is the most recent version of MODTRAJP, the Moderate Resolution Atmospheric Radiance and Transmittance Model, officially released by the Geophysics Directorate, Phillips Laboratory, in early 1993. It encompasses all the capabilities of LOWTRAN 73, the historic 20 cni' resolution (full width at half maximum, FWHM) radiance code, but incorporates a much more sensitive molecular band model with 2 ciii' resolution. The band model is based directly upon the HITRAN4 spectral parameters, including both temperature and pressure (line shape) dependencies. Because the band model parameters and their applications to transmittance calculations have been independently developed using equivalent width "binning" procedures, validation against full Voigtline-by-line calculations (eg. FASCODEb) is important. Extensive spectral comparisons have shown excellent agreement. In addition, simple timing runs of MODTRAN vs. FASCOD3P (released in 1992) show an improvement of more than a factor of 100 for a typical 500 cm spectral interval and comparable vertical layering. It has been previously established that not only is MODTRAN an excellent band model for "full path" calculations (that is, radiance and/or transmittance from point A to point B), but it replicates layer-specific quantities to a very high degree of accuracy6. Such layer quantities, derived from ratios and differences of longer path MODTRAN calculations from point A to adjacent layer boundaries, can be used to provide inversion algorithm weighting functions or similarly formulated quantities. One of the most exciting new applications is the rapid calculation of reliable IR cooling rates7, including species, altitude, and spectral distinctions, as well as the standard integrated quantities. Comparisons with prior line-by-line cooling rate calculations'9 are excellent, and the techniques can be extended to incorporate global climatoIogies°.

Infrared radiance fluctuations in the upper atmosphere

Abstract: Simulation of infrared radiance fluctuations in the atmosphere depends on detailed descriptions of fluctuations in atmospheric species number densities, vibrational state populations, and the kinetic temperatures along the sensor line-of-sight. The relationship between kinetic and vibrational temperature fluctuations depends on the subtle interplay between changes in the total number densities, changes in the temperature-dependent kinetic rates, and the relative contribution of the radiative relaxation. The model developed in this paper predicts the two- dimensional radiance covariance function for nonequilibrium effect conditions. The radiance statistics are non-stationary and are explicitly bandpass and sensor FOV dependent. The SHARC model is used to calculate mean LOS radiance values and radiance derivatives which are necessary to determine the radiance statistics. Inputs to the model include the statistical parameters of a non-stationary atmospheric temperature fluctuation model and an atmospheric profile. The radiance statistics are used in a simple model for synthesizing images. The model has been applied to calculate the radiance structure for the OH((Delta) v equals 1) SWIR band and the CO 2 ((nu) 3 ) MWIR band under nighttime conditions.

Automated remote monitoring of toxic gases with diode-laser-based sensor systems

Abstract: Spectral Sciences has developed a family of automated remote gas sensors including a long-path absorption system, and a fiber- optic-based system utilizing multiple remote-sensing heads. Results are presented from initial field tests of the long-path sensor.

SHARC-3: a model for infrared atmospheric radiance at high altitudes

Abstract: 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.