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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

A simple method to incorporate water vapor absorption in the 15 microns remote temperature sounding

The water vapor absorption in the 15 micron CO2 band, which can affect the remotely sensed temperatures near the surface, are estimated with the help of an empirical method. This method is based on the differential absorption properties of the water vapor in the 11-13 micron window region and does not require a detailed knowledge of the water vapor profile. With this approach Nimbus 4 IRIS radiance measurements are inverted to obtain temperature profiles. These calculated profiles agree with radiosonde data within about 2 C.

Dallu, G.↗
NASA NTRS1976

Water vapor absorption of carbon dioxide laser radiation

An optoacoustic detector or spectrophone has been used to perform detailed measurements of the absorptivity of mixtures of water vapor in air. A (C-12) (O-16)2 laser was used as the source, and measurements were made at forty-nine different wavelengths from 9.2 to 10.7 microns. The details of the optoacoustic detector and its calibration are presented, along with a discussion of its performance characteristics. The results of the measurements of water vapor absorption show that the continuum absorption in the wavelength range covered is 5-10% lower than previous measurements.

Shumate, M. S.↗
NASA NTRS1976

Optoacoustic measurements of water vapor absorption at selected CO laser wavelengths in the 5-micron region

Measurements of water vapor absorption were taken with a resonant optoacoustical detector (cylindrical pyrex detector, two BaF2 windows fitted into end plates at slight tilt to suppress Fabry-Perot resonances), for lack of confidence in existing spectral tabular data for the 5-7 micron region, as line shapes in the wing regions of water vapor lines are difficult to characterize. The measurements are required for air pollution studies using a CO laser, to find the differential absorption at the wavelengths in question due to atmospheric constituents other than water vapor. The design and performance of the optoacoustical detector are presented. Effects of absorption by ambient NO are considered, and the fixed-frequency discretely tunable CO laser is found suitable for monitoring urban NO concentrations in a fairly dry climate, using the water vapor absorption data obtained in the study.

Menzies, R. T.↗
NASA NTRS1990

Water vapor absorption coefficients in the 8-13-micron spectral region - A critical review

Measurements of water vapor absorption coefficients in the thermal IR atmospheric window (8-13 microns) during the past 20 years obtained by a variety of techniques are reviewed for consistency and compared with computed values based on the AFGL spectral data tapes. The methods of data collection considered were atmospheric long path absorption with a CO2 laser or a broadband source and filters, a White cell and a CO2 laser or a broadband source and a spectrometer, and a spectrophone with a CO2 laser. Advantages and disadvantages of each measurement approach are given as a guide to further research. Continuum absorption has apparently been measured accurately to about the 5-10 percent level in five of the measurements reported.

Grant, William B.↗
NASA NTRS1993

Water-vapor absorption line measurements in the 940-nm band by using a Raman-shifted dye laser

We report water-vapor absorption line measurements that are made by using the first Stokes radiation (930-982 nm) with HWHM 0.015/cm generated by a narrow-linewidth, tunable dye laser. Forty-five absorption line strengths are measured with an uncertainty of 6 percent and among them are fourteen strong lines that are compared with previous measurements for the assessment of spectral purity of the light source. Thirty air-broadened linewidths are measured with 8 percent uncertainty at ambient atmospheric pressure with an average of 0.101/cm. The lines are selected for the purpose of temperature-sensitive or temperature-insensitive lidar measurements. Results for these line strengths and linewidths are corrected for broadband radiation and finite laser linewidth broadening effects and compared with the high-resolution transmission molecular absorption.

Chu, Zhiping↗
NASA NTRS1995

Water vapor absorption in the atmospheric window at 239 GHz

Absolute absorption rates of pure water vapor and mixtures of water vapor and nitrogen have been measured in the atmospheric window at 239 GHz. The dependence on pressure as well as temperature has been obtained. The experimental data are compared with several theoretical or empirical models, and satisfactory agreement is obtained with the models involving a continuum; in the case of pure water vapor, the continuum contribution based upon recent theoretical developments gives good results. The temperature dependence is stronger than that proposed in a commonly used atmospheric transmission model.

Bauer, A.↗
NASA NTRS1987

A critical review of measurements of water vapor absorption in the 840 to 1100 cm(-1) spectral region

A set of eleven measurements of the water vapor continuum absorption in the 840 to 1100 sq cm spectral region is reviewed and compared with spectral models maintained by the Air Force Geophysics Laboratory. The measurements were made in four different ways: spectrometer with a White cell, CO2 laser with a White cell, CO2 laser with a spectrophone, and broadband radiation source over a long atmospheric path. Where possible, the data were selected at a water vapor partial pressure of ten torr buffered to 760 torr with N2 or synthetic air and a temperature of between 296 and 300 K. The intercomparison of the data leads to several observations and conclusions. First, there are four sets of laboratory data taken with nitrogen as the buffer gas which generally agree well mutually and with AFGL's HITRAN code. Second, there is one set of laboratory data that shows that using air as the buffer gas gives a few percent decrease in the water vapor continuum compared with using nitrogen as the buffer gas. Third, the atmospheric long-path measurements for water vapor partial pressure below about 12 torr are roughly grouped within 20 percent of the HITRAN values. Fourth, there are three sets of spectrophone data for water vapor in synthetic air which are significantly higher than any of the other measurements. This discrepancy is attributed to the effects of impurity gases in the cell.

Grant, William B.↗
NASA NTRS1979

Determination of the Telluric Water Vapor Absorption Correction for Astronomical Data Obtained from the Kuiper Airborne Observatory

The amount of telluric water vapor along the line of sight of the Kuiper Airborne Observatory telescope as obtained concommitantly on 23 flights is compared with the NASA-Ames Michelson interferometer and with the NOAA-Boulder radiometer. A strong correlation between the two determinations exists, and a method for computing the atmospheric transmission for a given radiometer reading is established.

Erickson, E. F.↗
NASA NTRS1985

High temperature measurement of water vapor absorption

An investigation was undertaken to measure the absorption coefficient, at a wavelength of 10.6 microns, for mixtures of water vapor and a diluent gas at high temperature and pressure. The experimental concept was to create the desired conditions of temperature and pressure in a laser absorption wave, similar to that which would be created in a laser propulsion system. A simplified numerical model was developed to predict the characteristics of the absorption wave and to estimate the laser intensity threshold for initiation. A non-intrusive method for temperature measurement utilizing optical laser-beam deflection (OLD) and optical spark breakdown produced by an excimer laser, was thoroughly investigated and found suitable for the non-equilibrium conditions expected in the wave. Experiments were performed to verify the temperature measurement technique, to screen possible materials for surface initiation of the laser absorption wave and to attempt to initiate an absorption wave using the 1.5 kW carbon dioxide laser. The OLD technique was proven for air and for argon, but spark breakdown could not be produced in helium. It was not possible to initiate a laser absorption wave in mixtures of water and helium or water and argon using the 1.5 kW laser, a result which was consistent with the model prediction.

Keefer, Dennis↗
NASA NTRS1991

Line-shape asymmetry of water vapor absorption lines in the 720-nm wavelength region

Spectral line-shape analyses were performed for water vapor lines broadened by argon, oxygen, and xenon in the 720-nm wavelength region. A line-shape asymmetry was observed, which is attributed to statistical dependence or correlation between velocity- and state-changing collisions. The generalized (asymmetric) Galatry profile, which results from the soft-collision profile and includes correlation between velocity- and state-changing collisions, was fitted to the observed line shapes and was found to compare favorably with the observed data. The most prominent asymmetries were observed with xenon as the buffer gas.

Grossmann, Benoist E.↗
NASA NTRS1996

Enhanced Water Vapor Absorption within Tropospheric Clouds: A Partial Explanation for Anomalous Absorption

Comparisons between solar flux measurements and predictions obtained from theoretical radiative transfer models indicate that most of these models underestimate the globally averaged solar energy absorbed by cloudy atmospheres by up to 25Wm&sup-2;.The origin of this anomalous absorption has not yet been established, but it has been attributed to a variety of sources including oversimplified or missing physical processes in the existing models, uncertainties in the input data, and even measurement errors. We used a sophisticated atmospheric radiative transfer model to provide improved constraints on the physical processes that contribute to the absorption of solar radiation by Earth's atmosphere. The results are described herein.

solar flux measurement water vapor absorption atmo↗
NASA NTRS2019

Homogenized Water Vapor Absorption Band Radiances From International Geostationary Satellites

In the past 20+ years, GEO Imagers with infrared 6.5‐μm bands have been observing the Earth's atmosphere, providing useful information of upper tropospheric moisture. Due to the instrumental differences and local viewing angles in GEO satellites, these observations are not consistent for generating climate data records (CDRs). In this study, a methodology has been developed to homogenize the 6.5‐μm radiances from the international GEO satellites, to generate a consistent CDR. Validations with Infrared Atmospheric Sounding Interferometer radiances from Metops for 2015–2017for seven GEO Imager sensors show that the GEO radiances are homogenized well with small standard deviation and biases of the differences (smaller for newer sensors), temporally stable radiometric accuracy, and weak angle dependency (even weaker for sensors with two water vapor bands). The homogenized 20+ years of consistent 6.5‐μm radiance CDR can be used to evaluate reanalysis and climate models, especially the diurnal variation of the model simulation.

Water Vapor↗
NASA NTRS2001

Laboratory Measurements of the 940, 1130, and 1370 nm Water Vapor Absorption Band Profiles

We have used the solar spectral flux radiometer (SSFR) flight instrument with the Ames 25 meter base-path White cell to obtain about 20 moderate resolution (8 nm) pure water vapor spectra from 650 to 1650 nm, with absorbing paths from 806 to 1506 meters and pressures up to 14 torr. We also obtained a set at 806 meters with several different air-broadening pressures. Model simulations were made for the 940, 1130, and 1370 nm absorption bands for some of these laboratory conditions using the Rothman, et al HITRAN-2000 linelist. This new compilation of HITRAN includes new intensity measurements for the 940 nm region. We compared simulations for our spectra of this band using HITRAN-2000 with simulations using the prior HITRAN-1996. The simulations of the 1130 nm band show about 10% less absorption than we measured. There is some evidence that the total intensity of this band is about 38% stronger than the sum of the HITRAN line intensities in this region. In our laboratory conditions the absorption depends approximately on the square root of the intensity. Thus, our measurements agree that the band is stronger than tabulated in HITRAN, but by about 20%, substantially less than the published value. Significant differences have been shown between Doppler-limited resolution spectra of the 1370 nm band obtained at the Pacific Northwest National Laboratory and HITRAN simulations. Additional new intensity measurements in this region are continuing to be made. We expect the simulations of our SSFR lab data of this band will show the relative importance of improving the HITRAN line intensities of this band for atmospheric measurements.

Giver, Lawrence P.↗
NASA NTRS1998

Removal of Thin Cirrus Path Radiances in the 0.4-1.0 micron Spectral Region Using the 1.375-micron Strong Water Vapor Absorption Channel

Through analysis of spectral imaging data acquired with the Airborne Visible Infrared Imaging Spectrometer (AVIRIS) from an ER-2 aircraft at 20 km altitude during several field programs, it was found that narrow channels near the center of the strong 1.38-micron water vapor band are very sensitive in detecting thin cirrus clouds. Based on this observation from AVIRIS data, a channel centered at 1.375 microns with a width of 30 nm was selected for the Moderate Resolution Imaging Spectrometer (MODIS) for remote sensing of cirrus clouds from space. The sensitivity of the 1.375-micron MODIS channel to detect thin cirrus clouds during the day time is expected to be one to two orders of magnitude better than the current infrared emission techniques. As a result, a larger fraction of the satellite data will likely be identified as containing cirrus clouds. In order to make better studies of surface reflectance properties, thin cirrus effects must be removed from satellite images. We have developed an empirical approach for removing/correcting thin cirrus effects in the 0.4 - 1.0 micron region using channels near 1.375 microns. This algorithm will be incorporated into the present MODIS atmospheric correction algorithms for ocean color and land applications and will yield improved MODIS atmospheric aerosol, land surface, and ocean color products.

Gao, Bo-Cai↗
NASA NTRS2009

Multilayer Cloud Detection with the MODIS Near-Infrared Water Vapor Absorption Band

Data Collection 5 processing for the Moderate Resolution Imaging Spectroradiometer (MODIS) onboard the NASA Earth Observing System EOS Terra and Aqua spacecraft includes an algorithm for detecting multilayered clouds in daytime. The main objective of this algorithm is to detect multilayered cloud scenes, specifically optically thin ice cloud overlying a lower-level water cloud, that presents difficulties for retrieving cloud effective radius using single layer plane-parallel cloud models. The algorithm uses the MODIS 0.94 micron water vapor band along with CO2 bands to obtain two above-cloud precipitable water retrievals, the difference of which, in conjunction with additional tests, provides a map of where multilayered clouds might potentially exist. The presence of a multilayered cloud results in a large difference in retrievals of above-cloud properties between the CO2 and the 0.94 micron methods. In this paper the MODIS multilayered cloud algorithm is described, results of using the algorithm over example scenes are shown, and global statistics for multilayered clouds as observed by MODIS are discussed. A theoretical study of the algorithm behavior for simulated multilayered clouds is also given. Results are compared to two other comparable passive imager methods. A set of standard cloudy atmospheric profiles developed during the course of this investigation is also presented. The results lead to the conclusion that the MODIS multilayer cloud detection algorithm has some skill in identifying multilayered clouds with different thermodynamic phases

Wind, Galina↗