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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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NASA NTRS1993

Airborne tunable diode laser spectrometer for trace-gas measurement in the lower stratosphere

This paper describes the airborne tunable laser absorption spectrometer, a tunable diode laser instrument designed for in situ trace-gas measurement in the lower stratosphere from an ER-2 high-altitude research aircraft. Laser-wavelength modulation and second-harmonic detection are employed to achieve the required constituent detection sensitivity. The airborne tunable laser absorption spectrometer was used in two polar ozone campaigns, the Airborne Antarctic Ozone Experiment and the Airborne Arctic Stratospheric Expedition, and measured nitrous oxide with a response time of 1 s and an accuracy not greater than 10 percent.

Podolske, James↗
NASA NTRS1994

Ground based NO2 and O3 measurements by visible spectrometer at Syowa Base (69 deg S), Antarctica

The column amounts of NO2 and ozone have been measured using visible spectroscopy at Syowa Base (69 deg S) since March 1990. Ozone was also measured at the same location with a Dobson spectrometer as well as ozonesondes being flown regularly. The characteristic features of the seasonal and diurnal variations of NO2 are presented. The column ozone values from the visible spectrometers are compared with the Dobson data. The very low values of NO2 in midwinter and early spring are consistent with the conditions predicted to be needed for heterogeneous ozone destruction in early spring. In late spring and summer of 1991, NO2 amounts were considerably smaller than in 1990, presumably due to the effect of Mt. Pinatubo eruption.

Kondo, Y.↗
NASA NTRS1994

Measurements of stratospheric composition using a star pointing spectrometer

Measurements of stratospheric composition have been made with a novel star-pointing spectrometer. The instrument consists of a telescope that focuses light from stars, planets, or the moon onto a spectrometer and two dimensional CCD array detector. Atmospheric absorptions can be measured, from which atmospheric columns of several gases can be determined. The instrument was deployed in Abisko, 69 deg N, during the European Arctic Stratospheric Ozone Experiment (EASOE). The instrument has the potential for measuring O3, OClO, NO2, and NO3. In this paper, a method for the retrieval of vertical columns is described, and some examples of ozone measurements given.

Fish, Deb J.↗
NASA NTRS1994

Radiative transfer code based estimation of atmospheric parameters for inversion of imaging spectrometer measured radiance to apparent surface reflectance

Surface reflectance is required to quantitatively investigate molecular absorption and particle scattering properties of materials on the Earth's surface. Atmospheric aerosol optical depth, surface pressure and water vapor are required to constrain a radiative transfer code for the inversion of measured spectral radiance to apparent surface reflectance. A suite of algorithms using nonlinear least squares fitting techniques are described that directly estimate these atmospheric parameters from spectral radiance measured by the Airborne Visible/Infrared Imaging Spectrometer (AVIRIS). The derived atmospheric parameters are used to constrain a radiative transfer code for the inversion of the imaging spectrometer radiance to apparent reflectance. The derived apparent reflectance is validated with respect to in situ measurement on the same target.

Green, Robert O.↗
NASA NTRS1991

Recovery of reflectance from imaging spectrometer measured radiance using a radiative transfer code

Radiance data were acquired over part of the Clark Mountain Range, California in 1990 by the Airborne Visible Infrared Imaging Spectrometer (AVIRIS). From these calibrated radiance data, the lateral distribution of water vapor in precipitable mm was recovered through analysis of the 940 nm water absorption. Surface pressure height was calculated from the 760 nm oxygen absorption band in the AVIRIS data. Surface slopes are estimated from relative elevations derived from the equivalent water vapor elevation for a standard atmosphere. Atmospheric optical depths measured at the Mountain Pass site in these data are extended to the entire region and varied based on the calculated surface pressure elevation. These parameters, derived from every AVIRIS spatial element, are used to constrain the LOWTRAN 7 radiative transfer code for the recovery of surface reflectance. Once transformed to reflectance, the imaging spectrometer data may be analyzed quantitatively for determination of surface composition, and compared with reflectance measurements acquired from different locations, times, and instruments.

Green, Robert O.↗
NASA NTRS1993

Field observations using an AOTF polarimetric imaging spectrometer

This paper reports preliminary results of recent field observations using a prototype acousto-optic tunable filter (AOTF) polarimetric imaging spectrometer. The data illustrate application potentials for geoscience. The operation principle of this instrument is different from that of current airborne multispectral imaging instruments, such as AVIRIS. The AOTF instrument takes two orthogonally polarized images at a desired wavelength at one time, whereas AVIRIS takes a spectrum over a predetermined wavelength range at one pixel at a time and the image is constructed later. AVIRIS does not have any polarization measuring capability. The AOTF instrument could be a complement tool to AVIRIS. Polarization measurement is a desired capability for many applications in remote sensing. It is well know that natural light is often polarized due to various scattering phenomena in the atmosphere. Also, scattered light from canopies is reported to have a polarized component. To characterize objects of interest correctly requires a remote sensing imaging spectrometer capable of measuring object signal and background radiation in both intensity and polarization so that the characteristics of the object can be determined. The AORF instrument has the capability to do so. The AOTF instrument has other unique properties. For example, it can provide spectral images immediately after the observation. The instrument can also allow observations to be tailored in real time to perform the desired experiments and to collect only required data. Consequently, the performance in each mission can be increased with minimal resources. The prototype instrument was completed in the beginning of this year. A number of outdoor field experiments were performed with the objective to evaluate the capability of this new technology for remote sensing applications and to determine issues for further improvements.

Cheng, Li-Jen↗
NASA NTRS1993

Airborne Visible/Infrared Imaging Spectrometer (AVIRIS): Recent improvements to the sensor

AVIRIS is a NASA-sponsored Earth-looking imaging spectrometer designed, built and operated by the Jet Propulsion Laboratory. Spectral, radiometric and geometric characteristics of the data acquired by AVIRIS are given in Table 1. AVIRIS has been operational since 1989, however in each year since 1989 major improvements have been completed in most of the subsystems of the sensor. As a consequence of these efforts, the capabilities of AVIRIS to acquire and deliver calibrated imaging spectrometer data of high quality have improved significantly over those in 1989. Improvements to AVIRIS prior to 1992 have been described previously (Porter et al., 1990, Chrien et al., 1991, & Chrien et al., 1992). In the following sections of this paper we describe recent and planned improvements to AVIRIS in the sensor task.

Chrien, Thomas G.↗
NASA NTRS1995

ASCA solid state imaging spectrometer observations of O stars

We report ASCA Solid State Imaging Spectrometer (SIS) x-ray observations of the O stars delta Ori and lambda Ori. The energy resolution of the SIS allows us to resolve features in the O star x-ray spectra which are not apparent in spectra obtained by x-ray spectrometers with lower energy resolution. SIS spectra from both stars show evidence of line emission, suggesting the thermal nature of the x-ray source. However, the observed line strengths are different for the two stars. The observed stellar x-ray spectra are not well described by isothermal models although absorbed thermal emission models with two or more temperatures can provide an adequate fit to the data. For both stars we present evidence of absorbing columns significantly larger than the known ISM columns, indicative of absorption by a circumstellar medium, presumably the stellar winds. In addition, the lambda Ori spectrum shows the presence of emission at energies greater than 3 keV which is not seen in the delta Ori spectrum.

Corcoran, M. F.↗
NASA NTRS1995

STS-46 plasma composition measurements using the EOIM-3 mass spectrometer

One of the active instruments incorporated into the Evaluation of Oxygen Interactions with Materials - 3 experiment was a quadrupole mass spectrometer. The primary objectives for this instrument, which was built by the Air Force Phillips Laboratory and was a veteran of the STS-4 flight in 1982, were to quantify the flux of atomic oxygen striking the test surfaces in the EOIM-3 payload and to detect surface reaction products from the materials in the carousel. Other speakers in this session have covered the results of these experiments. Prior to the 40-hour-long dedicated EOIM-3 mission segment at the end of the STS-46 flight, the authors used the mass spectrometer to make measurements of ion and neutral gas composition in the shuttle environment. About 25 hours of data were collected during a variety of mission events, including Eureca deployment at high altitude and many tethered satellite system operations.

Hunton, Donald E.↗
NASA NTRS1995

Determination of Benzene, Toluene, and Xylene by means of an ion mobility spectrometer device using photoionization

The continuous monitoring of changes on the quality of ambient air is a field of advantage of ion mobility spectrometry. Benzene, Toluene, and Xylene are substances of special interest because of their toxicity. We present an optimized drift tube for ion mobility spectrometers, which uses photo-ionization tubes to produce the ions to be analyzed. The actual version of this drift tube has a length of 45 mm, an electric field strength established within the drift tube of about 180 V/cm and a shutter-opening-time of 400 mus. With the hydrogen tube used for ionisation a mean flux of 10(exp 12) photons/sq cm s was established for the experiments described. We discuss the results of investigations on Benzene, Toluene, and Xylene in normal used gasoline SUPER. The detection limits obtained with the ion mobility spectrometer developed in co-operation are in the range of 10 ppbv in this case. Normally, charge transfer from Benzene ions to Toluene takes place. Nevertheless the simultaneous determination in mixtures is possible by a data evaluation procedure developed for this case. The interferences found between Xylene and others are rather weak. The ion mobility spectra of different concentrations of gasoline SUPER are attached as an example for the resolution and the detection limit of the instrument developed. Resolution and sensitivity of the system are well demonstrated. A hand-held portable device produced just now is to be tested for special environmental analytical problems in some industrial and scientific laboratories in Germany.

Leonhardt, J. W.↗
NASA NTRS1995

Combined hyperspatial and hyperspectral imaging spectrometer concept

There is a user need for increasing spatial and spectral resolution in Earth Observation (EO) optical instrumentation. Higher spectral resolution will be achieved by the introduction of spaceborne imaging spectrometers. Higher spatial resolutions of 1 - 3m will be achieved also, but at the expense of sensor redesign, higher communications bandwidth, high data processing volumes, and therefore, at the risk of time delays due to large volume data-handling bottlenecks. This paper discusses a design concept whereby the hyperspectral properties of a spaceborne imaging spectrometer can be used to increase the image spatial resolution, without such adverse cost impact.

Burke, Ian↗
NASA NTRS1995

Airborne Visible/Infrared Imaging Spectrometer (AVIRIS): Sensor improvements for 1994 and 1995

AVIRIS is a NASA-sponsored Earth-remote-sensing imaging spectrometer designed, built and operated by the Jet Propulsion Laboratory (JPL). While AVIRIS has been operational since 1989, major improvements have been completed in most of the sensor subsystems during the winter maintenance cycles. As a consequence of these efforts, the capabilities of AVIRIS to reliably acquire and deliver consistently high quality, calibrated imaging spectrometer data continue to improve annually, significantly over those in 1989. Improvements to AVIRIS prior to 1994 have been described previously. This paper details recent and planned improvements to AVIRIS in the sensor task.

Sarture, C. M.↗
NASA NTRS1994

ASCA solid state imaging spectrometer observations of O stars

We report ASCA Solid State Imaging Spectrometer (SIS) X-ray observations of the O stars delta Ori and lambda Ori. The energy resolution of the SIS allows us to resolve features in the O star X-ray spectra which are not apparent in spectra obtained by X-ray spectrometers with lower energy resolution. SIS spectra from both stars show evidence of line emission, suggesting the thermal nature of the X-ray source. However, the observed line strengths are different for the two stars. The observed stellar X-ray spectra are not well described by isothermal models although absorbed thermal emission models with two or more temperatures can provide an adequate fit to the data. For both stars we present evidence of absorbing columns significantly larger than the known Interstellar Medium (ISM) columns, indicative of absorption by a circumstellar medium, presumably the stellar winds. In addition, the lambda Ori spectrum shows the presence of emission at energies greater than 3 keV which is not seen in the delta Ori spectrum.

Corcoran, M. F.↗
NASA NTRS1995

Performance of a focused cavity aerosol spectrometer for measurements in the stratosphere of particle size in the 0.06-2.0-micrometer-diameter range

A focused cavity aerosol spectrometer aboard a NASA ER-2 high-altitude aircraft provided high-resolution measurements of the size of the stratospheric particles in the 0.06-2.0-micrometer-diameter range in flights following the eruption of Mount Pinatubo in 1991. Effects of anisokinetic sampling and evaporation in the sampling system were accounted for by means adapted and specifically developed for this instrument. Calibrations with monodisperse aerosol particles provided the instrument's response matrix, which upon inversion during data reduction yielded the particle size distributions. The resultant dataset is internally consistent and generally shows agreement to within a factor of 2 with comparable measurements simultaneously obtained by a condensation nuclei counter, a forward-scattering spectrometer probe, and aerosol particle impactors, as well as with nearby extinction profiles obtained by satellite measurements and with lidar measurements of backscatter.

Jonsson, H. H.↗
NASA NTRS1994

Giotto ion mass spectrometer measurements at comet P/Grigg-Skjellerup

The Giotto ion mass spectrometer high-intensity spectrometer (IMS-HIS) measured fluxes of ions from about 260,000 km before (1008:37 UT spacecraft time) to about 86,000 km after (1701:33 UT spacecraft time) closest approach to comet P/Grigg-Skjellerup during the encounter on July 10, 1992. Although the HIS sensor was not designed to measure protons, these ions were measured far from the comet. Close in to the comet, the ions observed were probably also protons, although heavier ions cannot be completely ruled out. Considerable temporal structure appears in the data, well-correlated with the data of other instruments onboard, especially those of the magnetometer. In particular, the ion count rate correlates with the direction of the magnetic field. This strong modulation at the water group ion cyclotron period (approx. 90 s) inside the inbound bow wave indicates a very narrow ion pitch angle distribution. Hence at Grigg-Skjellerup the ions appear to experience very little pitch angle scattering. This may result from strong compression in the rapidly increasing magnetic field.

Goldstein, R.↗
NASA NTRS1993

Primary results from the Berkeley EUV airglow rocket spectrometer: O I and N2 FUV/EUV dayglow in the thermosphere and lower exosphere

The Berkeley extreme-ultraviolet airglow rocket spectrometer (BEARS) made spectroscopic measurements of far and extreme UV, atomic oxygen emissions from a Black Brandt XII (12.041 WT) sounding rocket launched from Wallops Island, Virginia, on September 30, 1988. BEARS' primary instrument, a near-normal Rowland mount spectrometer, measured several atomix oxygen and molecular nitrogen dayglow features at high spectral resolution (1.5 A): O I (989, 1027, 1304, and 1356 A); and N2 Lyman-Birge-Hopfield (4, 0) and (3, 0) bands at 1325 and 1354 A. The instrument collected over 800 s of data spanning altitudes of 150 - 963 km with look directions between 95 deg and 125 deg from zenith. We have analyzed the data using electrons and radiative transport models in a forward modeling approach. The model and data are generally in good agreement. However, there are some discrepancies, which are discussed in terms of remote sensing capabilities and improvements to the models.

Cotton, Daniel M.↗
NASA NTRS1995

Two-Diffraction-Order, Beam-Splitting, Imaging Spectrometer

Two-octave imaging spectrometer utilizes light of two harmonically related wavelengths diffracted to harmonically related orders at same angles, followed by separation via dichroic beam splitter before final imaging. Conceptual design of spectrometer calls for minimum number of optical elements to achieve coverage of required visible and near-infrared wavelengths in instrument of reduced size, weight, and cost.

Labaw, Clayton C.↗
NASA NTRS1995

Mass spectrometer measurements of test gas composition in a shock tunnel

Shock tunnels afford a means of generating hypersonic flow at high stagnation enthalpies, but they have the disadvantage that thermochemical effects make the composition of the test flow different to that of ambient air. The composition can be predicted by numerical calculations of the nozzle flow expansion, using simplified thermochemical models and, in the absence of experimental measurements, it has been necessary to accept the results given by these calculations. This note reports measurements of test gas composition, at stagnation enthalpies up to 12.5 MJ.kg(exp -1), taken with a time-of-flight mass spectrometer. Limited results have been obtained in previous measurements. These were taken at higher stagnation enthalpies, and used a quadruple mass spectrometer. The time-of-flight method was preferred here because it enabled a number of complete mass spectra to be obtained in each test, and because it gives good mass resolution over the range of interest with air (up to 50 a.m.a.).

Skinner, K. A.↗