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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS1985

Lidar observations of the El Chichon cloud in the stratosphere over Fukuoka

A volcanic cloud in the stratosphere, originating from the March to April 1982 eruptions of El Chichon, has been observed for about 2.5 years at Fukuoka (33.5 degrees N, 130.4 degrees E) with two wavelengths of Nd-YAG lidar, 1.06 and 0.53 microns. Time and height variabilities of the cloud are described, using the 1.06 microns data, and some results of the two-wavelength measurements are presented. A sudden enormous increase in the total aerosol backscattering from the stratosphere (backscattering coefficient for 1.06 microns integrated over 13.5 to 28.5 km range) was followed by a decrease from late spring to summer with large fluctuations. The cloud initially appeared stratified into two layers: the upper one with fine structure and sharp edges in the easterly wind region and the lower dumpy one in the westerly wind region. Most of the aerosols were contained in the upper layer. The two layers merged into a broad, single-peaked layer as the easterly prevailed in the whole region in fall, when the total aerosol backscattering began to increase. The layer then decreased its peak height as it broadened. The difference in shape of both layers and the increase of total backscattering from fall can be interpreted by the difference in velocity of material transport in the easterly and the westerly wind region.

Fujiwara, M.↗
NASA NTRS1985

Numerical simulation of El Chichon volcanic cloud

The stratospheric volcanic cloud from the eruption of El Chichon, Mexico, on April 4, 1982 was observed routinely by a Nd:YAG lidar system from April 18, 1982 at Kyushu University. There were two phenomena detected by lidar observation of the El Chichon volcanic cloud: (1) The main enhanced layer was formed in the summer easterly wind region over Fukuoka (33.5 deg N, 130.4 deg E). The layer had two high gradient top and bottom boundaries. The layer width slowly broadened until September 1982, when the easterly wind changed to the westerly wind. A similar phenomenon was observed after the eruption of Mt. St. Helens in May 1980. (2) The stratospheric integrated backscattering coefficient (IBC) reached a peak value on May 3, 1982. It then gradually decreased until August, but reincreased significantly from September to December 1982. After January 1983, IBC decreased slowly. This remarkable reincrease had not been seen in past increases which had been observed by lidar at Kyushu University. These phenomena are briefly discussed.

Shibata, T.↗
NASA NTRS1985

UV lidar measurements of the stratospheric aerosol layer and comparison with other optical data

After the violent volcanic eruptions of El Chichon in Mexico (17.33 deg. N, 93.20 deg. W) in late March and early April 1982, enhanced stratospheric aerosols have been monitored by ruby (lasing wavelength lambda=694.3 nm) or Nd:YAG lidars (lambda=1064 or 532 nm). By these lidars, visible or near-infrared optical informations of stratospheric aerosols and their space-time variations can be obtained. It is usually difficult to measure the background level of stratospheric aerosols by an ultraviolet (UV) lidar, since Rayleigh scattering prevails over Mie scattering in the stratosphere. However, after the large volcanic eruptions, UV lidar measurements of stratospheric aerosols are possible. In order to obtain UV optical properties of stratospheric aerosols, measurements have been made at Fukuoka (33.65 deg. N, 130.35 deg. E) by a p-terphenyl dye laser at a wavelength of 340.5 nm. Observational results during October 1982, through May 1983, are shown and are compared with the results obtained by a ruby lidar at Tsukuba (36.05 deg. N, 140.13 deg. E).

Uchino, O.↗
NASA NTRS1986

Quantitative determination of engine water ingestion

This paper describes a novel non-intrusive optical technique for determination of liquid mass flux in a droplet laden airstream. The technique was developed for quantitative determination of engine water ingestion resulting from heavy rain or wheel spray. Independent measurements of the liquid water content (LWC) of the droplet laden aircraft and of the droplet velocities were made at the simulated nacelle inlet plane for the liquid mass flux determination. The liquid water content was measured by illuminating and photographing the droplets contained within a thin slice of the flow field by means of a sheet of light from a pulsed YAG laser. A fluorescent dye introduced in the water greatly improved the droplet image definition. The droplet velocities were determined from double exposed photographs of the moving droplet field. The technique was initially applied to a steady spray generated in a wind tunnel. It was found that although the spray was initially steady, the aerodynamic breakup process was inherently unsteady. This resulted in a wide variation of the instantaneous liquid water content of the droplet laden airstream. The standard deviation of ten separate LWC measurements was 31 percent of the average. However, the liquid mass flux calculated from the average LWC and droplet velocities came within 10 percent of the known water ingestion rate.

Parikh, P.↗
NASA NTRS1986

Spectroscopic and laser characteristics of Ti:Al2O3

Spectroscopic measurements and laser performance of T:Al2O3 are discussed in detail. Data on absorption and fluorescence spectra and fluorescence lifetime as a function of temperature are presented. Laser characteristics observed with pulsed-dye-laser, frequency-doubled Nd:YAG-laser, and argon-ion-laser pumping are covered and show that nearly quantum-limited conversion of pump radiation cna be achieved, along with tuning over the wavelength range 660-986 nm.

Moulton, P. F.↗
NASA NTRS1985

Lidar observations of the planetary boundary layer

The application of an airborne downward-looking lidar to the study of organized cellular convection in the planetary boundary layer (PBL) over the ocean is described. The lidar consisted of a frequency doubled Nd-YAG 530 mm-wavelength laser whose axis was aligned colinearly with the optical axis of an all-reflecting 40 mm-diameter Newtonian telescope. The airborne lidar provided a unique observation of both microscale and mesoscale variations of the PBL top. The lidar data, presented as constant backscatter isopleth soundings, provide a visual indication of the presence of vertically organized convection cells. Comparisons of the lidar-derived PBL structure with both a conceptual model of the PBL and laboratory simulations of Deardorf et al. (1980) of a developing convective PBL showed that the observations are consistent with a model of mixing in the PBL, which involves a field of organized updrafts separated by downdrafts.

Melfi, S. H.↗
NASA NTRS1985

Tunable solid state lasers for remote sensing; Proceedings of the Conference, Stanford University, CA, October 1-3, 1984

Papers are presented on solid-state lasers for remote sensing, diode-pumped Nd:YAG lasers, and tunable solid-state-laser systems. Topics discussed include titanium-sapphire tunable laser systems, the performance of slab geometry, and the development of slab lasers. Consideration is given to garnet host solid-state lasers, the growth of lasers and nonlinear materials, and nonlinear frequency conversion and tunable sources.

Byer, R. L.↗
NASA NTRS1985

Solid state laser technology - A NASA perspective

NASA's program for developing solid-state laser technology and applying it to the Space Shuttle and Space Platform is discussed. Solid-state lasers are required to fulfill the Earth Observation System's requirements. The role of the Office of Aeronautics and Space Technology in developing a NASA tunable solid-state laser program is described. The major goals of the program involve developing a solid-state pump laser in the green, using AlGaAs array technology, pumping a Nd:YAG/SLAB crystal or glass, and fabricating a lidar system, with either a CO2 laser at 10.6 microns or a Nd:YAG laser at 1.06 microns, to measure tropospheric winds to an accuracy of + or - 1 m/s and a vertical resolution of 1 km. The procedures to be followed in order to visualize this technology plan include: (1) material development and characterization, (2) laser development, and (3) implementation of the lasers.

Allario, F.↗
NASA NTRS1985

Efficient frequency conversion of laser sources in nonlinear crystals

The use of nonlinear crystals to extend the frequency range of solid-state laser sources is proposed. The harmonic generation of high-average-power laser sources and CW-laser-sources nonlinear crystals is considered. The development of Nd:YAG pumped parametric oscillators and optical parametric amplifiers using LiNbO3 or AgGaS2 is studied. The LiNbO3 oscillator has tunable output over the 1.4-4.0 micron range and is applicable for remote sensing measurements of molecules and of humidity and temperature; AgGaS2 oscillators provide the potential for 3-15 micron infrared generation. Advances in material synthesis techniques related to the design and synthesis of nonlinear media are discussed. Various procedures for the synthesis of nonlinear crystals are described.

Byer, R. L.↗
NASA NTRS1986

Linewidth characteristics of Raman-shifted dye laser output at 720 and 940 nm

Raman conversion efficiency and line broadening are reported for Stokes operation at 720 and 940 nm, with hydrogen and deuterium as the Raman source, and using an Nd:YAG pumped Quanta-Ray PDL-2 dye laser. The dye laser linewidth is 0.2/cm (FWHM) with the grating alone as an intracavity element, and the conversion efficiency at 400 psi was found to be 40 and 20 percent for outputs of 720 and 940 nm, respectively. Pressure broadening coefficients of (9.2 + or - 0.9) x 10 to the -5th per cm/psi for hydrogen, and 7.7 x 10 to the -5th per cm/psi for deuterium, were obtained in good agreement with previous results. The linewidth at the first Stokes wavelength was shown to be determined by pressure broadening in the Raman medium.

Grossmann, B. E.↗
NASA NTRS1986

The Lidar In-Space Technology Experiment (LITE)

A spaceborne lidar system is presently being constructed for flight aboard the U. S. Space Shuttle in early 1991. The experiment, Lidar In Space Technology Experiment (LITE), utilizes a neodymium:YAG laser and 0.85 meter effective diameter Cassegranian-configured telescope receiver for making elastic backscatter measurements. The laser will be frequency doubled and tripled simulataneously producing a 10 Hz rate of 200 mJ at 1064 nm, 400 mJ at 532 nm, and 150 mJ at 355 nm. The technological objectives of LITE are to evaluate lidar system operations in space, lidar techniques in space, and to provide a test bed for new lidar technologies in later flights. The measurement objectives include the determination of cloud top and planetary boundary layer heights, the measurement of tropospheric and stratospheric aerosols, and the measurement of temperature and density between 10 to 40 km altitude. Detailed simulations will be presented showing the errors associated with each of these measurement objectives. In addition, the experiment scenario will be described including measurement times, data flow, processing and archival, and initial plans for validation of the LITE data set with correlative measurements.

Mccormick, M. P.↗
NASA NTRS1986

Rotationally resolved collisional transfer rates in OH

Fluorescence lidar measurements of the hydroxyl radical require detailed information concerning collision induced processes in order to deduce the radical number density from a lidar return. The Goddard SFC OH lidar currently utilizes a broadband detector which precludes the necessity of fully understanding collisional redistribution of rotational energy within the excited state. Numerous advantages result however from the inclusion of a detector with a bandpass only slightly larger that the Doppler width of a rotational line. This however places more stringent requirements on the spectroscopy. Measurements were accordingly made of rotationally resolved quenching rates for collisions with O2, N2, and H2O. Rotational transfer rates were also measured for the same colliders. Quenching rates were measured using a Nd-YAG pumped Rh6G dye laser doubled into the UV. The OH lifetimes were measured as a function of pressure of quenching gas at total pressures of between 50 and 250 microns. Rotational transfer rates were measured by recording the emission spectrum on an intensified diode array and integrating over 10.000 laser shots.

Mcgee, T. J.↗
NASA NTRS1986

Progress in coherent laser radar

Considerable progress with coherent laser radar has been made over the last few years, most notably perhaps in the available range of high performance devices and components and the confidence with which systems may now be taken into the field for prolonged periods of operation. Some of this increasing maturity was evident at the 3rd Topical Meeting on Coherent Laser Radar: Technology and Applications. Topics included in discussions were: mesoscale wind fields, nocturnal valley drainage and clear air down bursts; airborne Doppler lidar studies and comparison of ground and airborne wind measurement; wind measurement over the sea for comparison with satellite borne microwave sensors; transport of wake vortices at airfield; coherent DIAL methods; a newly assembled Nd-YAG coherent lidar system; backscatter profiles in the atmosphere and wavelength dependence over the 9 to 11 micrometer region; beam propagation; rock and soil classification with an airborne 4-laser system; technology of a global wind profiling system; target calibration; ranging and imaging with coherent pulsed and CW system; signal fluctuations and speckle. Some of these activities are briefly reviewed.

Vaughan, J. M.↗
NASA NTRS1986

Lower atmospheric temperature profile measurements using a Raman lidar

A Raman lidar system was used to measure the temperature profile of the upper troposphere and lower stratosphere. The system consists of a tripled Nd-YAG laser and a 1.5 meter diameter telescope. Two photomultipliers are used at the output of the telescope to allow for measurements at both the laser wavelength and at the Raman shifted wavelength due to atmospheric nitrogen. The signal from the photomultipliers is recorded as photon counts in 1 microsec bins. The results of a number of laser shots are summed together to provide atmospheric returns which have acceptable signal to noise characteristics. Measurements of the Raman nitrogen return were acquired up to an altitude in excess of 20 km. Temperature profiles were retrieved from the attenuation corrected Raman nitrogen return assuming the atmosphere to be in hydrostatic equilibrium and using the ideal gas law. Retrieved temperature profiles are shown compared with independent temperature measurements.

Melfi, S. H.↗
NASA NTRS1986

XeF lidar measurements of density and temperature in the middle atmosphere

In recent years, it has been widely recognized that vertically propagating internal gravity waves in the middle atmosphere play an important role in determining the large scale wind field by their momentum transport and deposition. However, very little is known about them in the upper stratosphere and lower mesosphere because of the lack of adequate techinques to observe small scale motions. A XeF excimer laser was used for the Rayleigh lidar observation. The characteristics of the XeF lidar system are given. The wavelength of the XeF laser is in the region that is ozone absorption free, and the Rayleigh scattering cross section is 5 times larger than in 532 nm. The advantages of using the XeF laser as against the YAG laser have been discussed in detail. The density and temperature profiles between the altitude range of 30 and 70 km measured with this lidar system are illustrated. The accuracy is less than + or - 3% and 10k at 60 km for an observation time of 15 min. The results on the gravity waves by the observation through about one year since Apr. 1985 is presented.

Shibata, T.↗
NASA NTRS1986

Lidar stratospheric ozone measurements at the observatoire de Haute Provence (France)

Strastospheric ozone monitoring is of particular importance to confirm present day theories predicting a maximal ozone depletion, due to chlorofluorocarbon emission, in the 35 to 45 km altitude range. Measurements presently rely on both ground based and satellite-borne passive experiments. Such systems have been recently shown to have intrinsic limitations mainly due to atmospheric aerosol presence and calibration problems. During the last few years, active lidar profiling of the ozone vertical distribution by the Differential Absorption Laser technique (DIAL) in the UV wavelength range has been developed using two different laser sources: a Nd-YAG pumped dye laser which enables a large tuning range of the UV emitted wavelengths; and exciplex laser sources using xenon chloride as an active medium and emitting at 308 nm, the off wavelength being usually generated by Raman shifting techniques. Advantages and limitations of using both of these systems are briefly discussed.

Godin, S.↗
NASA NTRS1986

Gas correlation lidar for methane detection

A new type of DIAL system for the detection of methane in the atmosphere is being developed. The main feature of this lidar is the use of a gas correlation technique to obtain the reference signal by means of a single laser pulse, instead of two shots at different wavelengths. This fact is useful to make measurements on fast moving platforms. To meet the infrared absorption band of methane an optical parametric oscillator (OPO) was used with a LiNbO3 crystal as active element, and a tuning range between 1.5 divided by 4 microns. As known, the major problem to overcome in parametric oscillators are the pump beam quality and the difficulty in reducing the linewidth. The first requirement is met by using, as a pump, a Nd-YAG laser based on a new type of resonator cavity, named SFUR (Self Filtering Unstable Resonator). The laser emits, with high efficiency, near diffraction limited pulsed beams of about 250 mJ of energy, 20 ns of duration at 10 pps of frequency repetition rate. On the other hand, the gas correlation technique allows the operation with a bandwidth as large as 1/cm, which is obtainable using only a diffraction grating as a dispersive element in the OPO cavity.

Galletti, E.↗
NASA NTRS1986

Linewidth characteristics of Raman-shifted dye laser output at 720 and 940 nm

Existing DIAL systems for water vapor measurements in the troposphere operate at wavelengths near 720 nm. The use of stronger water vapor absorption lines in the range 930 to 960 nm will significantly improve DIAL measurements in the upper troposphere and lower stratosphere where water vapor concentrations are low. The generation of light at 940 nm using a frequency doubled Nd:YAG pumped dye laser is inefficient due to the small absorption if infrared dyes at the pump wavelength. However, 940 nm generation utilizing stimulated Raman scattering of dye lasers is attractive because of a potentially high conversion efficiency plus the possibility of retaining the narrow linewidth available from some dye lasers. The Raman conversion efficiency and line broadening are presented for first Stokes operation at 720 and 940 nm using hydrogen and deuterium as the Raman media.

Grossmann, B. E.↗