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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 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

The Global Backscatter Experiment Airborne Pulsed Lidar Measurements

The Global Backscatter Experiment (GLOBE) was intended to provide data on prevailing values of atmospheric backscatter cross section. The primary intent was predicting the performance of space-borne lidar systems. A second and related goal was to understand the source and characteristics of atmospheric aerosol particles. In this paper the authors give a summary of measurement results with emphasis on the magnitude, structure, characteristics and variability of the observed atmospheric aerosol and cloud scattering. The GLOBE pulsed lidar measurements provide an extensive data set on the magnitude and variability of aerosol and cloud backscatter of the atmosphere. The data defines atmospheric aerosol scattering characteristics and should prove to be an important resource for determination of the performance and design of laser remote sensing instruments.

Spinhirne, James D.↗
NASA NTRS2020

Position-Sensitive Magnetic Calorimeters for Lynx

We describe the performance of position-sensitive metallic magnetic calorimeter X-ray detectors for potential future astrophysics missions, such as Lynx. The motivation behind this is to achieve a large focal plane area by increasing the number of pixels compared to the number of readout channels (called hydra). The detector consists of a 5×5 array of gold absorbers thermally coupled to a paramagnetic sensor. Since each absorber has a different thermal link to the sensor, it generates a different pulse shape and enables discrimination of pixel position. Recently, we have been successfully able to discriminate 25 averaged pulse shapes by means of rise-time and pulse height. The measured pulse shapes and distribution agree well with the modeling results. The estimated energy resolutions based on the pulse height and noise data we measured are 2.8–3.7 eV for MnKα X-ray photons at 50 mK.

Magnetic calorimeters↗
NASA NTRS2012

Pulsed Lidar Measurements of Atmospheric CO2 Column Absorption in the ASCENDS 2011 Airborne Campaign

We have previously demonstrated an efficient pulsed, wavelength-resolved IPDA lidar technique for measuring the tropospheric CO2 concentrations as a candidate for NASA's ASCENDS mission. Our team participated in the 2010 ASCENDS airborne campaigns we flew airborne version of the CO2 and O2 lidar on the NASA DC-8. The CO2 lidar measures the atmospheric backscatter profiles and shape of the 1572.33 nm absorption line using 250 mW average laser power, 30 wavelength samples per scan and 300 scans per second. Most flights had 5-6 altitude steps to greater than 12 km, and clear CO2 line shapes were observed at all altitudes. Our post-flight analysis estimated the Iidar range and pulse energies at each wavelength every second. We then solved for the best-fit CO2 absorption line shape, and calculated the Differential Optical Depth (DOD) at the line peak. We compared these to CO2 DODs calculated from spectroscopy based on HITRAN 2008 and the conditions from airborne in-situ readings. Analysis of the 2010 measurements over the Pacific Ocean and Lamont OK shows the expected -linear change of the peak DOD with altitude. For measurements at altitudes greater than 6 km the random errors were approximately 0.3 ppm for 80 sec averaging times. After the 2010 flights we improved the airborne lidar's scan uniformity, calibration and receiver sensitivity. Our team participated in the seven ASCENDS science flights during late July and August 2011. These flights were made over a wide variety of surface and cloud conditions near the US, including over the central valley of California, over several mountain ranges, over both broken and solid stratus cloud deck over the Pacific Ocean, snow patches on mountain tops, over thin and broken clouds above the US Southwest and Iowa, and over forests near the WLEF tower in Wisconsin. Analyses show the retrievals of lidar range and CO2 column absorption, as wen as estimates of CO2 mixing ratio worked well when measuring over topography with rapidly changing height and reflectivity, through thin clouds and to stratus cloud tops. For regions where the CO2 concentration was relatively constant, the measured CO2 absorption profile (averaged for 50 sec) matched the predicted profile to better than 1% RMS error for all flight altitudes. For 1 & 10 second averaging, the scatter in the retrievals was limited by signal shot noise (i.e. the sigual photon count). Analysis to date shows the decrease in CO2 due to vegetation when flying easterward over the Great Plains as well as the increase in CO2 concentration in the vicinity ofthe coal-fired power plant in New Mexico. Examples of these and other results will be presented.

Abshire, James B.↗
NASA NTRS2019

Implementation of a Pulsed-Laser Measurement System in the National Transonic Facility

A remotely-adjustable laser transmission and imaging system has been developed for use in a high-pressure, cryogenic wind tunnel. Implementation in the National Transonic Facility has proven the system suitable for velocity and signal lifetime measurements over a range of operating conditions. The measurement system allows for the delivery of high-powered laser pulses through the outer pressure shell and into the test section interior from a mezzanine where the laser is free from environmental disturbances (such as vibrations and excessive condensation) associated with operation of the wind tunnel. Femtosecond laser electronic excitation tagging (FLEET) was utilized to provide freestream velocity measurements, and first results show typical data that may be obtained using the system herein described.

Reese, Daniel T.↗
NASA NTRS2000

Vertical Roughness of the Polar Regions of Mars from Mars Orbiter Laser Altimeter Pulse-Width Measurements

The sub-kilometer scale vertical roughness of the martian surface in the polar regions can be investigated using calibrated, optical pulse width data provided by the Mars Orbiter Laser Altimeter (MOLA). Garvin and others have previously discussed initial observations of what we have called "total vertical roughness" or TVR, as derived from MOLA optical pulse width observations acquired during the pre-mapping phases of the Mars Global Surveyor (MGS) mission. Here we present the first assessment of the Mars polar region properties of the TVR parameter from more than nine months of continuous mapping by MOLA as part of the MGS mapping mission. Other than meter-scale surface properties directly inferred from Mars Orbiter Camera (MOC) images, MOLA measurements of footprint-scale TVR represent the only direct measurements of the local vertical structure of the martian surface at approx. 150 m length scales. These types of data have previously been shown to correlate with geologic process histories for terrestrial desert surfaces on the basis of Shuttle Laser Altimeter (SLA) observations. Additional information is obtained in the original extended abstract.

Garvin, J. B.↗
NASA NTRS1984

Fizeau wavemeter for pulsed laser wavelength measurement

A Fizeau wavelength meter optimized for use with pulsed laser sources has been developed and characterized which demonstrates a CW resolution better than 2 parts in 10 to the 7th and a pulsed resolution better than 1 part in 10 to the 6th. The static optical design is based on a Fizeau wedge interferometer, which together with spatial filtering and collimating optics is used to produce a pattern of parallel fringes which is imaged on a linear photodiode array and analyzed by a minicomputer. A series of CW and pulsed measurements of various narrowband laser sources are described, and particular difficulties involved in pulsed laser measurements with the wavemeter are examined.

Morris, M. B.↗
NASA NTRS1981

Temporal correlation measurements of pulsed dual CO2 lidar returns

A pulsed dual-laser direct-detection differential-absorption lidar DIAL system, operating near 10.6 microns, is used to measure the temporal correlation and statistical properties of backscattered returns from specular and diffuse topographic targets. Results show that atmospheric-turbulence fluctuations can effectively be frozen for pulse separation times on the order of 1-3 msec or less. The diffuse target returns, however, yielded a much lower correlation than that obtained with the specular targets; this being due to uncorrelated system noise effects and different statistics for the two types of target returns.

Menyuk, N.↗
NASA NTRS1990

Single pulse vibrational Raman scattering by a broadband KrF excimer laser in a hydrogen-air flame

Spontaneous vibrational Raman scattering (VRS) is produced by a broadband excimer laser at 248 nm (KrF) in a H2-air flame, and VRS spectra are recorded for lean, stoichiometric, and rich flames. Except at very lean flame conditions, laser-induced fluorescence (LIF) processes interfere with VRS Stokes lines from H2, H2O, and O2. No interference is found for the N2 Stokes and N2 anti-Stokes lines. In a stoichiometric H2/air flame, single-pulse measurements of N2 concentration and temperature (by the VRS Stokes to anti-Stokes ratio) have a relative standard deviation of 7.7 and 10 percent, respectively. These single pulse measurement errors compare well with photon statistics calculations using measured Raman cross sections.

Pitz, Robert W.↗
NASA NTRS1972

Short pulse radar measurements of layered ice and snow

Using a radar system with high range resolution, it was shown that measurements of snow and ice thickness are feasible with an accuracy of better than 3 inches. In addition, the water equivalent of the snowpack can be estimated, given a single surface measurement of the snow depth. Discontinuities in density were also detected and their location determined by inspection of the radar returns. The remote measurement of layer thickness is described. The system was designed for eventual incorporation into a light aircraft.

Vickers, R. S.↗
NASA NTRS1977

Field ionization device used for measuring the pulse height defect of He/+/ in silicon

A neutral particle detector using field ionization and liquid-nitrogen-cooled solid state detectors has been developed to investigate the pulse height defect of low energy He(+) ions in silicon. The field ionization tip is fabricated from a short length of tungsten wire; a typical detector is of the surface-barrier Si type with a thin Au window and low capacitance (about 15 pF); the assembly is mounted in a cylindrical vacuum chamber which is pumped to about 10 to the -6th torr. As an example, pulse height distributions for He(+) and H(+) taken at tip bias of 25.7 kV are presented. The detected energy of the H and He ions are studied as a function of the actual energies of accelerated ions, for a detector having a gold front conducting surface layer of 32 micrograms/sq cm.

Curtis, C. C.↗