Stephen J. Young

Nonisothermal band model theory

Abstract Theoretical formulations of radiation band models for general nonuniform optical paths are presented. The models are framed within the statistical band model for an array of Lorentz lines and an inverse line strength distribution. Radiative transfer for an isolated line in a general nonuniform medium and the statistical model for a uniform optical path are reviewed in order to provide the foundation required for the band model formulations. Two approaches to the development of these models are taken. The first is based on making approximations to such radiative transfer functions as transmittance or equivalent width and yields models equivalent or similar to the traditional Curtis-Godson approximation. The second treats approximations to the spatial derivatives of these functions. From the standpoint of computing line or band radiance, the spatial derivatives are more fundamental quantities than the transfer functions themselves; consequently, these latter “derivative approximations” are instrinsically more accurate than the Curtis-Godson type approximations. All of the models are formulated to give the spatial derivative of the mean equivalent width function W (s) δ in the form 1 δ d W (s) ds =c(s)p(s) k (s)y(s) , where c(s), p(s) and k(s) are the concentration, total pressure and absorption band model parameter, respectively, at the local path position s. The functional form of the derivative function y(s) is derived for each of the models. In general, y(s) is a function of both local and path-averaged (subscript e) band model parameters. These local and averaged parameters are used to define a dimensionless optical depth parameter x e = u k e β e and three nonuniformity indexes ρ= γ γ e , r= β β e and θ = δ e δ (γ is line width, ḡd is the mean line spacing band model parameter, and β = 2μ γ γ ). The explicit manner in which these parameters enter into the various functional forms for y(s) is derived and discussed. The introduction of the parameter q is an important aspect of the new models and is an explicit measure of nonisothermality along the optical path. In addition to the traditional Curtis-Godson definitions for the effective parameters ke and βe, new definitions for the path averages γe and δe are derived. These new definitions are obtained from the fundamental properties of the assumed inverse line strength distribution. A summary of all the models is given as a table of relevant equations for use in practical calculations.

Evaluation of nonisothermal band models for H2O

Abstract Comparisons of predicted and measured radiance spectra for nonuniform hot H 2 O gas samples are reported. The predicted spectra are generated with band models formulated in a companion paper, and band model parameters constructed to handle optical path temperature variations from 200 to 3000°K. The model identified in the companion paper as the intuitive derivative approximation is shown to be superior to the traditional Curtis-Godson approximation in treating general optical paths along which high degrees of nonuniformity occur.

Band model formulation for inhomogeneous optical paths

Abstract The band-model formulation developed by Lindquist and Simmons to handle radiance calculations for highly inhomogeneous and nonisothermal optical paths is discussed and extended. The original formulation was based on the statistical band model for a random array of equal-intensity pressure-broadened Lorentz lines. Here, the formulation is extended to include bands of constant-intensity Doppler lines and bands of Lorentz or Doppler lines with an exponential distribution of line strenghts. Results are presented for the equivalent width derivative functions y(x,ϱ) for the constant-intensity Lorentz, constant-intensity Doppler, and exponential-intensity Doppler cases. Various approximations to these functions for extreme x and ϱ conditions are also presented. A closed-form solution for y(x,ϱ ) is given for the exponentially distributed Lorentz line case.

Measurements of Temperatures of Vibrationally Excited N2

A comparison of the vibrational and rotational temperatures of microwave discharged N2 as measured by the CO tracer and the Penning ionization with He(23S) techniques has been performed in a flow tube apparatus. A vibrational temperature range of 1000–3000°K was covered at a kinetic temperature of ∼350°K. A detailed analysis of each technique is presented. The effect of pressure quenching of the N2+(1−) radiation occurring in the Penning ionization technique and the effect of vibrational temperature gradient across the flow tube in the CO tracer technique are discussed. Because of the good agreement of vibrational temperatures deduced from the two techniques, it is concluded that the Treanor‐Teare relationship between the vibrational temperatures of diatomic gases in binary mixture in the V–V quasiequilibrium regime is valid. This work represents the first experimental confirmation of this relationship. The agreement of rotational temperatures implied by the N2+ and CO spectra indicates that the rotationa...

Space-based mineral and gas identification using a high-performance thermal infrared imaging spectrometer

A novel thermal-band imager is proposed for space-based Earth science measurement applications such as rock identification and volcano monitoring. The instrument, MAGI-L (Mineral and Gas Identifier - LEO), would also enable detection of gases from natural and anthropogenic sources. Its higher spectral resolution, compared to ASTER-type sensors, will improve discrimination of rock types, greatly expand the gas-detection capability, and result in more accurate land-surface temperatures. The optical design for MAGI-L will incorporate a novel compact Dyson spectrometer. Data from SEBASS have been used to examine the trade-offs between spectral resolution, spectral range, and instrument sensitivity for the proposed sensor.

Model for Radiation Contamination by Outgassing from Space Platforms

Abstract : Infrared sensors mounted on space platforms (e.g., Space Shuttle and satellites) may be subject to infrared radiation contamination from molecular gases released from the platform itself. Models for order-of-magnitude estimates of the contamination level caused by this effect are formulated. The mechanisms for vibrational excitation of the ejected species include: (1) thermal excitation at the platform surface, (2) absorption of solar and earthshine radiation, and (3) collisions with ambient atmospheric species. Application of the model to estimate the effects that the outgassing of H20 from the Shuttle environment would have on the CIRRIS 1A earth-limb radiance mission indicates that detection in the 2.7-micro spectral region would by only slightly degraded, but that detection around 6.3 micro may be seriously impaired by the mechanism of absorption and reemission of earthshine radiation by the H20 contamination molecules. Keywords: Radiation contamination, Shuttle environment, Infrared radiation, Spacecraft outgassing.

Iterative Abel Inversion of Optically Thick, Cylindrically Symmetric Radiation Sources.

Abstract An inversion algorithm for obtaining the radial emission and absorption coefficients of a cylindrically symmetric radiation source from transverse profiles of monochromatic radiance and absorptance is described and compared with the algorithm of Elder et al. It is shown that the present method converges to the correct solution, whereas that of Elder et al. does not.

Measurement of vibrational temperature of CO and N2 using the He(23S) Penning ionization technique

The vibrational temperatures of N2 and CO in binary gas mixture and in the VV quasiequilibrium regime of high vibrational temperature and low kinetic temperature were measured in a flow tube apparatus. The Penning ionization with He (23S) technique was used to determine the vibrational temperatures of both gases. The Treanor‐Teare expression relating vibrational temperatures for such conditions was verified. The formulation of the Penning ionization technique for CO allowed the CO rotational energy and the kinetic energy of relative motion between CO and He to play a role in the normally nonenergetically allowed CO(X, 0)→CO+(B, 1) excitation reaction. The unexpected result of a collisional quenching rate that is smaller for CO+(B, 1) than for CO+(B, 0) was also observed.

Addendum to: Band model formulation for inhomogeneous optical paths☆

Abstract The statistical band-model formulation for highly inhomogeneous optical paths presented in a previous paper is extended to the case where the strengths of lines in Δ ν are distributed according to a modified inverse probability function.

MAGI: A New High-Performance Airborne Thermal-Infrared Imaging Spectrometer for Earth Science Applications

A new airborne facility instrument for Earth science applications is introduced. The Mineral and Gas Identifier (MAGI) is a wide-swath (programmable up to ±42° off nadir) moderate spectral resolution thermal-infrared (TIR) imaging spectrometer that spans the 7.1- to 12.7-μm spectral window in 32 uniform and contiguous channels. Its spectral resolution enables improved discrimination of rock and mineral types, greatly expanded gas-detection capability, and generally more accurate land-surface temperature retrievals. The instrument design arose from trade studies between spectral resolution, spectral range, and instrument sensitivity and has now been validated by flight data acquired with the completed sensor. It offers a potential prototype for future space-based TIR instruments, which will require much higher spectral resolution than is currently available in order to address more detailed climate, anthropogenic, and solid Earth science questions.