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The Interferometric Monitor for Greenhouse Gases (IMG) operated aboard the polar-orbiting Advanced Earth Observing Satellite from October 1996 through June 1997. The IMG measured upwelling infrared radiance at fine spectral resolution. This paper identifies previously undocumented issues with IMG interferograms and describes procedures for correcting the majority of the affected data. In particular, single-sided interferograms should be used to avoid large noise bursts, and phase ambiguities must be resolved in uncalibrated spectra before radiometric calibration. The corrections are essential for studies that require accurately calibrated radiance spectra, including those that track atmospheric changes globally on decadal time scales.

The National Polar-Orbiting Operational Environmental Satellite System (NPOESS) Airborne Sounder Testbed (NAST) consists of two passive collocated cross-track scanning instruments, an infrared interferometer (NAST-I) and a microwave radiometer (NAST-M), that fly onboard high-altitude aircraft such as the NASA ER-2 at an altitude near 20 km. NAST-I provides relatively high spectral resolution (0.25-cm(-1)) measurements in the 645-2700-cm(-1) spectral region with moderate spatial resolution (a linear resolution equal to 13% of the aircraft altitude at nadir) cross-track scanning. We report the methodology for retrieval of atmospheric temperature and composition profiles from NAST-I radiance spectra. The profiles were determined by use of a statistical eigenvector regression algorithm and improved, as needed, by use of a nonlinear physical retrieval algorithm. Several field campaigns conducted under varied meteorological conditions have provided the data needed to verify the accuracy of the spectral radiance, the retrieval algorithm, and the scanning capabilities of this instrumentation. Retrieval examples are presented to demonstrate the ability to reveal fine-scale horizontal features with relatively high vertical resolution.

The validation of fascod3 and modtran3 against ground-based and airborne high-resolution Michelson interferometer measurements under clear-sky conditions is presented. Important considerations including water vapor continuum, frequency-dependent sea surface emissivity in the IR window region, and spectral resolution of modtran3 in the comparison of model calculations with high-resolution interferometer measurements are discussed. Our results indicate that it is not adequate to assume sea surface emissivity of 1.0 [?(ν) = 1.0] or a constant in the simulation of upwelling radiance observed by the airborne Michelson interferometer. The use of spectral emissivity (frequency-dependent emissivity) leads to much better agreement between model calculations and interferometer measurements in the IR window region from 750.0 to 1050.0 cm(-1). This could have important implications for the retrieval of sea surface temperature, thin cirrus properties, and aerosol parameters because of the sea surface emissivity of 1.0 assumption commonly used by many researchers. Comparisons of modtran3 calculations with interferometer measurements show that the agreement might not be adequate at the nominal resolution of 2.0 cm(-1), and further spectral degradation might be necessary to improve the agreement between measurements and modtran3 calculations. modtran should be used with caution for relatively high spectral resolution remote-sensing applications.

The Galileo probe net flux radiometer measured radiation within Jupiter's atmosphere over the 125-kilometer altitude range between pressures of 0.44 bar and 14 bars. Evidence for the expected ammonia cloud was seen in solar and thermal channels down to 0.5 to 0.6 bar. Between 0.6 and 10 bars large thermal fluxes imply very low gaseous opacities and provide no evidence for a deep water cloud. Near 8 bars the water vapor abundance appears to be about 10 percent of what would be expected for a solar abundance of oxygen. Below 8 bars, measurements suggest an increasing water abundance with depth or a deep cloud layer. Ammonia appears to follow a significantly subsaturated profile above 3 bars. Unexpectedly high absorption of sunlight was found at wavelengths greater than 600 nanometers.

An experimental study performed to evaluate the atmospheric transmission model FASCODE and its water vapor continuum [Clough, Kneizys, and Davies (CKD) model, Atmos. Res. 23, 229-241 (1989)] in the 850-2250-cm-(1) spectral region is presented. The analysis is based on a comparison between model calculations and transmission measurements carried out at the Defence Research Establishment Valcartier over a 5.7-km horizontal path for a wide range of ambient temperature (from -8.6 to 29.4°C) and humidity (from 1.16 to 14.2 g/m(3)) conditions. The agreement between measurements and calculations is good on the average. However, there are three specific spectral intervals where the differences cannot be explained by experimental errors. For summer conditions, it is shown that FASCODE overestimates the transmittance by approximately 3-6% (absolute terms) in the 850-950-cm(-1) region. For winter conditions, measurements are higher than calculations by as much as a factor of 2 at the edges of the 6.3µm absorption band of water vapor, namely near 1250-1380 cm(-1) and 1800-2000 cm(-1). The continuous nature of these differences is interpreted as anomalies that are due to the broadening coefficients of the water vapor continuum (CKD model). A set of coefficients is derived from experimental spectra and compared with coefficients from the CKD model. The results suggest that first the self-broadening coefficients at high temperature, C¯(s)(ν, 296), need to be increased by 10-16% near 850-950 cm(-1) and second the foreign broadening coefficients, C¯(ν), need to be decreased by approximately a factor of 2 near 1250-1380 cm-(1) and 1800-2000 cm(-1) to recover a good model-measurement agreement in these three spectral intervals. A modified continuum (based on coefficients derived from transmittances) has been implemented in FASCODE and used to analyze emission spectra from the High-Resolution Interferometer Sounder instrument. The modified continuum reduces the discrepancy by almost a factor of 5 near 1350 cm(-1).

A linear form of the radiative transfer equation (RTE) is formulated for the direct and simultaneous estimation of temperature and absorbing constituent profiles (e.g., water vapor, ozone, methane) from observations of spectral radiances. This unique linear form of the RTE results from a definition for the deviation of the true gas concentration profiles from an initial specification in terms of the deviation of their effective temperature profiles from the true atmospheric temperature profile. The effective temperature profile for any absorbing constituent is that temperature profile which satisfies the observed radiance spectra under the assumption that the initial absorber concentration profile is correct. Differences between the effective temperature, derived for each absorbing constituent, and the true atmospheric temperature are proportional to the error of the initial specification of the gas concentration profiles. The gas concentration profiles are thus specified after inversion of the linearized RTE from the retrieved effective temperature profiles assuming that one of the assumed concentration profiles is known (e.g., CO(2)). Because the solution is linear and simultaneous, the solution is computationally efficient. This efficiency is important for dealing with radiance spectra containing several thousand radiance observations as obtained from current airborne and planned future spaceborne interferometer spectrometer sounders. Here the solution is applied to spectral radiance observations simulated for current filter radiometers and planned spectrometers to demonstrate the anticipated improvement in future satellite sounding performance as a result of improved instrumentation and associated sounding retrieval methodology.

Net radiation measurements in the atmosphere of Venus indicate that the bulk of the atmosphere is radiatively cooling at high latitudes and heating at low latitudes. Similarity of features observed by all three probes indicate planetwide stratification. Flux variations within the clouds provide evidence of significant differences in cloud structure. A feature of unusually large opacity found near 60 kilometers at the north probe site is probably related to the unique circulation regime revealed by ultraviolet and infrared imagery. A stable layer between the cloud bottoms and about 35 kilometers contains several features in the flux profiles probably resulting from large-scale compositional stratifications rather than clouds. In the layer below 35 kilometers unexpectedly large fluxes were observed.

A calibrated Fourier transform spectrometer, known as the High-Resolution Interferometer Sounder (HIS), has been flown on the NASA U-2 research aircraft to measure the infrared emission spectrum of the earth. The primary use-atmospheric temperature and humidity sounding-requires high radiometric precision and accuracy (of the order of 0.1 and 1 degrees C, respectively). To meet these requirements, the HIS instrument performs inflight radiometric calibration, using observations of hot and cold blackbody reference sources as the basis for two-point calibrations at each wavenumber. Initially, laboratory tests revealed a calibration problem with brightness temperature errors as large as 15 degrees C between 600 and 900 cm(-1). The symptom of the problem, which occurred in one of the three spectral bands of HIS, was a source-dependent phase response. Minor changes to the calibration equations completely eliminated the anomalous errors. The new analysis properly accounts for the situation in which the phase response for radiance from the instrument itself differs from that for radiance from an external source. The mechanism responsible for the dual phase response of the HIS instrument is identified as emission from the interferometer beam splitter.

The first general multicomponent equations for transport through semipermeable membranes are derived from basic statistical-mechanical principles. The procedure follows that used earlier for open membranes, but semipermeability is modelled mathematically by the introduction of external forces on the impermeant species. Gases are treated first in order to clarify the problems involved, but the final results apply to general nonideal solutions of any concentration. The mixed-solvent effect is treated rigorously, and a mixed-solvent osmotic pressure is defined. A useful specific identification of so-called osmotic flow is given, along with a demonstration that such an identification cannot be unique. Results are obtained both for discontinuous membrane models, and for a continuous model.