Jack S. Margolis

Water vapor column abundance retrievals during FIFE

A variation of the modified Langley plot algorithm is reported here and applied to the retrieval of atmospheric water column abundance from a filtered sunphotometer. In this new methodology an absorption data base (LOWTRAN 7) is used to compute a water abundance versus transmittance curve of growth, rather than the square-root dependence previously assumed. Validation of the technique is provided from an uncertainty analysis, and plans to further validate using Fourier transform spectrometers are detailed. The new sunphotometer technique is used to report total column water vapor during the First ISLSCP Field Experiment (FIFE), and comparisons are made with abundances retrieved via FIFE radiosonde observations. The sunphotometer data can best be utilized, however, to in turn validate data from airborne or in-orbit measurements of water vapor. With these flight sensors, horizontal and topographic variability within the scene can be viewed. An example of the airborne data set is given using an image from the airborne visible infrared imaging spectrometer (AVIRIS), as acquired on August 31, 1990.

Spaceborne measurements of atmospheric CO2 by high-resolution NIR spectrometry of reflected sunlight: An introductory study

We introduce a strategy for measuring the column-averaged CO_2 dry air volume mixing ratio X_(CO_2) from space. It employs high resolution spectra of reflected sunlight taken simultaneously in near-infrared (NIR) CO_2 (1.58-mm and 2.06-mm) and O_2 (0.76-mm) bands. Simulation experiments, show that precisions of ~0.3–2.5 ppmv for X_(CO_2) can be achieved from individual clear sky soundings for a range of atmospheric/surface conditions when the scattering optical depth t_s is less than ~0.3. When averaged over many clear sky soundings, random errors become negligible. This high precision facilitates the identification and correction of systematic errors, which are recognized as the most serious impediment for the satellite X_(CO_2) measurements. We briefly discuss potential sources of systematic errors, and show that some of them may result in geographically varying biases in the measured X_(CO_2). This highlights the importance of careful calibration and validation measurements, designed to identify and eliminate sources of these biases. We conclude that the 3-band, spectrometric approach using NIR reflected sunlight has the potential for highly accurate X_(CO_2) measurements.

Computer Measurement of Line Strengths with Application to the Methane Spectrum

Computer-aided measurement of absorption line strengths from high resolution spectra greatly improves the accuracies to which relative line strengths can be determined. This article describes a computer program written for interactive use on a Prime minicomputer to fit simultaneously absorption line positions, strengths, linewidths, and continuum parameters. Application to the methane spectrum indicates that relative line strengths have been measured with accuracies of 2% or better for single isolated absorptions. Line strengths from the Q branches of the ν4 and ν1 + ν4 bands of methane are reported and compared to calculated values given in the 1980 Air Force Geophysical Laboratory (AFGL) Compilation of Molecular Parameters.

Atmospheric CO2 retrieved from ground‐based near IR solar spectra

The column-averaged volume mixing ratio (VMR) of CO_2 over Kitt Peak, Arizona, has been retrieved from high-resolution solar absorption spectra obtained with the Fourier transform spectrometer on the McMath telescope. Simultaneous column measurements of CO_2 at ∼6300 cm^−1 and O_2 at ∼7900 cm^−1 were ratioed to minimize systematic errors. These column ratios were then scaled by the mean O_2 VMR (0.2095) to yield column-averaged vmrs of CO_2. These display similar behavior to the Mauna Loa in situ surface measurements. During the period 1977–1995, the column-averaged mixing ratio of CO_2 increased at an average rate of 1.49 ± 0.04 ppmv/yr with seasonal variations of ∼7 ppmv peak-to-peak. Our retrievals demonstrate that this remote technique is capable of precisions better than 0.5%.

The infrared and microwave spectra of ozone for the (0, 0, 0), (1, 0, 0), and (0, 0, 1) states

Abstract New measurements of the ozone spectrum in the microwave and 10-μm infrared regions have been made. These new lines have been fit to a three-state Hamiltonian model which includes Coriolis interactions beteen (0, 0, 1) and (1, 0, 0). The model requires additional Coriolis parameters, as well as an appreciation for the parameters which are indeterminate. Transition dipole moments have been derived from the intensities of selected infrared lines.

The temperature dependence of the half widths of some self-and foreign-gas-broadened lines of methane☆

The temperature dependence of the half width of four lines of the 2v3 band of methane has been measured. The broadeners used were H2, He, N2, and CH4. The temperature coefficients, defined by the relation γ = γ0(TT0)n, have been determined for all of the broadeners and, in some cases, depart significantly from a kinetic theory value of -0.5. Where possible, the half-widths were determined by two independent methods. All measurements were made at pressures below 2 atm absolute to reduce interfering effects from the wings of neighboring lines.

Measurements of pressure-broadening coefficients of NO and O3 using a computerized tunable diode laser spectrometer.

Foreign-gas broadening coefficients have been measured for selected lines of ozone in the 9.2-microm region and for several R -branch lines of nitric oxide in the 5.4-microm region using a computerized tunable diode laser spectrometer. The data analysis showed the importance of fitting a Lorentzian line shape out to several times the halfwidth to obtain a correct value of the broadening coefficient. The measured broadening coefficients of nitric oxide were in good agreement with those obtained by Abels and Shaw. The results of the analysis of eleven lines in the nu(1) band and five lines in the nu(3) band of ozone show a transition-dependent broadening coefficient. The average value of the foreign-gas broadening coefficients for the measured nu(1) and nu(3) lines are 0.075 and 0.073 cm(-1) atm(-1), respectively.

Measurement of the fundamental vibration–rotation spectrum of CIO

The ClO fundamental absorption band near 850/cm is observed, with a tunable PbSnTe diode laser used as a source of monochromatic radiation. The chlorine monoxide concentration in the absorption tube was measured indirectly via a UV transmission technique. Frequencies and assignments for the ClO lines, and band centers and rotational constants for the ClO fundamental vibration, are tabulated. Diatomic vibration-rotation transitions within and between electronic substates are discussed. The tunable diode laser is valuable for studying the hyperfine structure. The IR spectroscopic technique is developed in order to monitor chlorine monoxide concentration in the stratosphere, since the short-lived ClO is a crucial intermediate participant in reactions involving destruction of stratospheric ozone.

Empirical line parameters of NH3 from 4791 to 5294 cm−1

To support remote sensing of planetary atmospheres at 2 μm, laboratory spectra of NH3 and enriched 14NH3 and 15NH3 were recorded at 0.011 cm−1 resolution with the McMath Fourier transform spectrometer (FTS) located at Kitt Peak National Observatory/National Solar Observatory. Multiple optical paths and pressures were used with sample temperatures between 297 and 185K. Some 2000 line positions and intensities at room temperature were measured with precisions of 0.0003 cm−1 and 3%, respectively, for unblended transitions. Low and room temperature intensities were then combined to determine empirical lower state energies for 1815 lines. These data permitted the assignments for v1 + v4 of 14NH3 to be extended to J′ = 10. Transitions of v3 + v4 of 15NH3 were also cataloged for the first time. Nearly 45% of the 2000 measured features were identified, and empirical upper state levels were obtained. The experimental results for lines with measured intensities greater than 3 × 10−24 cm−1/(molecule·cm−2) at 296 K were included in the 1996 HITRAN database. To obtain consistent NH3 line positions, the positions of 28 H2O transitions between 5206 and 5396 cm−1 were also calibrated using the 2-0 band of CO at 4260 cm−1.

Microwave and Fourier-transform infrared spectroscopy of the v4 = 1 and v2 = 2 s states of NH3

Seventy-nine microwave transitions of the v4 = 1 and v2 = 2 s states of 14NH3, including two forbidden rotational transitions with the selection rules Δk = ±1, Δl = ⊣2, have been measured up to 400 GHz. The ν4 and 2ν2 s band spectra of the molecule have also been recorded by a Fourier-transform infrared spectrometer with a resolution of 0.005 cm−1 and an accuracy of 0.0002 cm−1. More than 700 infrared transitions have been assigned up to the J = 14 rotational levels. The obtained microwave and infrared data were fitted to a 91-parameter Hamiltonian in which several Δ(k − l) = ±3 interaction terms were explicitly considered together with existing microwave results. The determined molecular constants for the v4 = 1 and v2 = 2s states reproduce the observed data with a root mean square deviation of 0.00038 cm−1.