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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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At least 1,657 records · Page 92
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NASA NTRS1989

Common source cascode amplifiers for integrating IR-FPA applications

Space based astronomical infrared measurements present stringent performance requirements on the infrared detector arrays and their associated readout circuitry. To evaluate the usefulness of commercial CMOS technology for astronomical readout applications a theoretical and experimental evaluation was performed on source follower and common-source cascode integrating amplifiers. Theoretical analysis indicates that for conditions where the input amplifier integration capacitance is limited by the detectors capacitance the input referred rms noise electrons of each amplifier should be equivalent. For conditions of input gate limited capacitance the source follower should provide lower noise. Measurements of test circuits containing both source follower and common source cascode circuits showed substantially lower input referred noise for the common-source cascode input circuits. Noise measurements yielded 4.8 input referred rms noise electrons for an 8.5 minute integration. The signal and noise gain of the common-source cascode amplifier appears to offer substantial advantages in acheiving predicted noise levels.

Woolaway, James T.↗
NASA NTRS1990

IR spectral characteristics of cirrus clouds

The recent focus of parameterization of the radiative properties of clouds has been to include the microphysical properties of the cloud. A variety of parameterization have been developed for both the shortwave and the longwave. In parameterizing the longwave properties of clouds, it is useful to consider the two stream solution of the radiative transfer equation appropriate for a thermal source. These radiative transfer equations are considered.

Ackerman, Steven A.↗
NASA NTRS1990

On the use of IR lidar and K(sub a)-band radar for observing cirrus clouds

Advances in lidar and radar technology have potential for providing new and better information on climate significant parameters of cirrus. Consequently, the NOAA Wave Propagation Lab. is commencing CLARET (Cloud Lidar And Radar Exploratory Test) to evaluate the promise of these new capabilities. Parameters under study include cloud particle size distribution, height of cloud bases, tops, and multiple layers, and cloud dynamics revealed through measurement of vertical motions. The first phase of CLARET is planned for Sept. 1989. The CO2 coherent Doppler lidar and the sensitive K sub a band radar hold promise for providing valuable information on cirrus that is beyond the grasp of current visible lidars.

Eberhard, Wynn L.↗
NASA NTRS1989

Near-IR imaging and imaging polarimetry of OMC 2

NIR and 2.2-micron imaging polarimetry of the molecular cloud region OMC 2, reveals a cluster of low- to intermediate-mass premain-sequence stars embedded in circumstellar disks. The 2.2-micron imaging polarimetry indicates that the compact NIR sources OMC 2 IRS1, IRS2, IRS3 and IRS4 N, are illumination centers for the surrounding extended emission. By application of Hubble's relation to the nebulae illuminated by IRS1, IRS2 and IRS4 N, the illuminating geometry is explained and the intrinsic NIR colors of these objects are estimated.

Rayner, John↗
NASA NTRS1990

NGC 1614 - An IR-luminous merger but not (yet?) an active galaxy

New observations of the merging galaxy NGC 1614 are described. The system has a nuclear region of QSO-like luminosity, but shows no direct evidence for an active nucleus. It is heavily and unevenly reddened across its nucleus, while infrared imaging also shows a 'ridge' of dust. The inner spiral structure of the galaxy has normal rotation for an inclined disk, as indicated by the H-alpha emission. A linear 'tail' to the S and extended arms to the E have more positive velocities, and probably are the remains of an interacting companion and the tidal plume(s) caused by the collision. The only H I seen in emission appears to coincide with bright knots of H-alpha and forbidden O III emission of the base of the tail. The lack of direct evidence for an active nucleus indicates that if NGC 1614 is a precursor to a Seyfert-like system the AGN has not yet turned on.

Neff, S. G.↗
NASA NTRS1989

On the far-IR and sub-mm spectra of spiral galaxies

Photometric measurements of three Virgo cluster spirals (NGC4254, NGC4501, and NGC4654) at 160-microns (far-infrared) and 360-microns (submillimeter) wavelengths are compared with theoretical models and observations at other wavelengths. It is shown that the data at the observed wavelengths do not fit any of interstellar dust grain models very well; four possibilities are given in order to explain discrepancies: the observed wavelength points are incorrect; previously observed data is incorrect; both data are incorrect; and the premise of the analysis is incorrect - a composite far-infrared spectrum of normal spiral galaxies is meaningless because they vary considerably in their far-infrared properties. It is also noted that the observed data are inconsistent with models having large cold grains.

Stark, A. A.↗
NASA NTRS1990

Ground-based thermal IR images of Comet Tempel 2

The 10.8-micron images of Comet Tempel 2 obtained on the four days from September 21 to 24, 1988, indicate that the dust coma contributed about half of the nuclear pixel brightness. The nuclear condensation brightness exhibited a temporal variability slightly larger than observational uncertainty. The structure of the observed extended dust emission is interpretable as (1) a large grain tail primarily generated by cm-scaled particles, (2) the result of an outburst near 2.5-3.0 AU perihelion, and (3) a sunward emission of dust in a fanlike pattern.

Campins, Humberto↗
NASA NTRS1990

Tunable far-IR laser spectroscopy of jet-cooled carbon clusters - The nu-2 bending vibration of C3

Seven rovibrational transitions of the (01/1/0)-(00/0/0) fundamental bending band of C3 have been measured with high precision with the use of a tunable far-infrared laser spectrometer. The C3 molecules were produced by laser vaporization of a graphite rod and cooled in a supersonic expansion. The astrophysically important nu-2 fundamental frequency is determined to be 63.416529(40)/cm. These measurements provide the basis for studies of C3 in the interstellar medium with far-infrared astronomy.

Schmuttenmaer, C. A.↗
NASA NTRS1990

NOAA-11 AVHRR visible and near-IR inflight calibration

An inflight calibration method for NOAA-11 AVHRR visible and near-infrared bands using desert reflectance is discussed. The results show a decrease in sensor systems response of 22 percent and 32 percent for the visible and near-infrared bands, respectively, relative to the published preflight calibration. The relative accuracy of the present calibration to the calibration of NOAA-9, published elsewhere, is + or - 3 percent. The absolute accuracy is around + or - 6 percent. An approximate correction to the Normalized Difference Vegetation Index ratio suggests that an increase of 0.06 is required.

Holben, B. N.↗
NASA NTRS1990

High spatial resolution studies of galaxies in the far IR: Observations with the KAO, and the promise of SOFIA

NASA, in collaboration with the West German Science Ministry (BMFT), plans a larger airborne telescope as a successor to the Kuipper Airborne Observatory (KAO) that will achieve these goals. The Stratospheric Observatory for Infrared Astronomy (SOFIA) is entering the final stages of Phase B review with targeted new start early in the next decade. SOFIA is a 2.7 m diameter telescope that is carried in a Boeing 747SP. In addition to having 3 times the spatial resolution of the KAO, and 10 times the light gathering power, it will incorporate improvements over the KAO in lower optical emissivity and better telescope tracking stability. The thin primary mirror will equilibrate quickly to ambient temperature at an altitude which, accompanied by airflow improvements across the telescope cavity, will result in better image quality. The sensitivity of SOFIA will allow us to see a large number of typical bright galactic HII regions in local group galaxies. The spatial resolution of 8 seconds (full width half maximum Airy disk) at 100 microns will allow these regions to be measured independently, if they are distributed similarly to those in our own galaxy. At this spatial resolution, the disks of normal galaxies will be easily resolved out to distances of several hundred Mpc. This portion of space includes many of the superluminous galaxies discovered by the Infrared Astronomy Satellite (IRAS), and this spatial scale is relevant for studies of the morphology of regions of interaction among the majority of these galaxies that are members of colliding pairs.

Lester, Dan F.↗
NASA NTRS1990

Resonant tunneling IR detectors

Researchers propose a novel semiconductor heterojunction photodetector which would have a very low dark current and would be voltage tunable. A schematic diagram of the device and its band structure are shown. The two crucial components of the device are a cathode (InGaAs) whose condition band edge is below the conduction band edge of the quantum wells and a resonant tunneling filter (GaAs-AlGaAs). In a standard resonant tunneling device the electrodes are made of the same material as the quantum wells, and this device becomes highly conducting when the quantum levels in the wells are aligned with the Fermi level in the negatively biased electrode. In contrast, the researchers device is essentially non-conducting under the same bias conditions. This is because the Fermi Level of the cathode (InGaAs) is still well below the quantum levels so that no resonant transport occurs and the barriers (AlGaAs) effectively block current flow through the device. However, if light with the same photon energy as the conduction-band discontinuity between the cathode and the quantum wells, E sub c3-E sub c1, is shone on the sample, free carriers will be excited to an energy corresponding to the lowest quantum level in the well closest to the cathode (hv plue E sub c1 = E sub o). These electrons will resonantly tunnel through the quantum wells and be collected as a photocurrent in the anode (GaAs). To improve the quantum efficiency, the cathode (InGaAs) should be very heavily doped and capped with a highly reflective metal ohmic contact. The thickness of the device should be tailored to optimize thin film interference effects and afford the maximum absorption of light. Because the device relies on resonant tunneling, its response should be very fast, and the small voltages needed to change the responsivity should allow for very high frequency modulation of the photocurrent. In addition, the device is tuned to a specific photon energy so that it can be designed to detect a fairly narrow range of wavelengths. This selectivity is important for reducing the photocurrent due to spurious light sources.

Woodall, Jerry M.↗
NASA NTRS1989

IR emission from circumstellar envelopes of C-rich stars

The reliability of a theoretical model that solves the radiative transfer equation in dust clouds surrounding a central star is checked. In particular, it is found that both classical scattering by dust and the back-heating effects are negligible in the radiative transfer when envelopes similar to IRC+10216 are taken into consideration. In addition, new fits of IRC+10216 spectra are presented which were obtained, when the source is in different luminosity phases, under the assumption that amorphous carbon grains are in the circumstellar envelope. The same model is currently used to simulate the emission from carbon-rich sources showing the silicon carbide feature at 11.3 microns.

Blanco, A.↗
NASA NTRS1990

Statistics of associations among IR galaxies

In the course of expanding the search of Kleinmann et. al. (1988) for distant, infrared-luminous objects, the authors noticed (as is often remarked) that a large number of infrared-selected galaxies have close neighbors or show merger characteristics (e.g., tidal tails, distorted disks). Because the sample size is large (567 infrared galaxies and 2182 field galaxies), this sample is ideal for statistically examining the importance of interactions among infrared galaxies. In particular, the authors compare the nearest-neighbor distribution and the two-point correlation function of their sample with that of a control sample of field galaxies.

Gallimore, Jack F.↗
NASA NTRS1991

Twenty-five years of aerodynamic research with IR imaging: A survey

Infrared imaging used in aerodynamic research evolved during the last 25 years into a rewarding experimental technique for investigation of body-flow viscous interactions, such as heat flux determination and boundary layer transition. The technique of infrared imaging matched well its capability to produce useful results, with the expansion of testing conditions in the entire spectrum of wind tunnels, from hypersonic high-enthalpy facilities to cryogenic transonic wind tunnels. With unique achievements credited to its past, the current trend suggests a change in attitude towards this technique: from the perception as an exotic, project-oriented tool, to the status of a routine experimental procedure.

Gartenberg, Ehud↗
NASA NTRS1991

Status of NASA's IR wind shear detection research

The status of NASA's wind shear detection research is reported in viewgraph form. Information is given on early experience, FLIR detectors, quantities measured by Airborne Warning and Avoidance System 1 (AWAS 1), the time series model for Flight 551, conclusions from NASA 737 flights, conclusions on Orlando 7-7-90, and AWAS 3 mnemonics.

Mckissick, Burnell↗
NASA NTRS1991

Phobos - Spectrophotometry between 0.3 and 0.6 micron and IR-radiometry

A 0.3 - 0.6 micron UV-visible spectrophotometer and a 5 - 50 micron radiometer in the KRFM experiment on Phobos 2 measured two groundtracks in the equatorial region of Phobos. Preliminary results indicate that three surface units can be recognized on the basis of differing UV-visible spectral reflectance properties. One of the units is most comparable spectrally to optically darkened mafic material, and a second is comparable either to anhydrous carbonaceous chondrite or to blackened mafic material. Spectral properties of the third unit do not resemble those of known meteorite types. Brightness temperatures measured by the radiometer are consistent with a typical surface thermal inertia of 1 - 3 x 10 to the -3 cal/(sq cm deg s exp 1/2), as suggested by previous investigations, implying a lunar-like regolith texture. At least one area of possibly higher thermal inertia has been tentatively identified, where a large degraded crater is crossed by several grooves. These results indicate significant lateral heterogeneity in the optical and textural properties of Phobos' surface.

Ksanfomality, L.↗
NASA NTRS1991

Use of aerosol microphysical measurements to model IR backscatter in support of GLOBE

Data on the concentration and composition of free tropospheric aerosol over the Pacific Ocean, collected during the GAMETAG program in 1977-1978 (Davis, 1980 and Patterson et al., 1980) are used to model values of aerosol optical extinction coefficients (sigma) at two wavelengths (0.55 and 1 micron) and values of volume backscatter coefficients (beta) at four wavelengths (1 micron, 9.11 microns, 9.25 microns, and 10.6 microns) and to investigate the relationship between these parameters. The mass concentrations inferred from the GAMETAG measurements with optical particle spectrometers agreed with the results of simultaneous chemical measurements. The study of the relationships among the optical parameters indicates that visible and near-visible values of beta and sigma may be useful in predicting 9.11- and 10.6-micron backscatter.

Patterson, Edward M.↗
NASA NTRS1991

Ultrafast IR detector response in high Tc superconducting thin films

The response from a high Tc superconducting multielement optical detector made of a laser deposited Y-Ba-Cu-O thin film has been evaluated. Several microscopic and spectroscopic techniques were used to establish the presence of the correct phase of the thin film. Optical pulses from a laser diode at 830 nm and from a Q-switched CO2-laser at 10.6 microns were used. The detector responded to 50 ps (FWHM) pulses. A comparison between dR/dT of the film and the response amplitude as a function of temperature indicated a bolometric response.

Lindgren, Mikael↗