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NASA NTRSDate not supplied

Bimodal SLD Ice Accretion on a CRM Midspan Wing Section Model

An ice shape database has been created to document ice accretions on a 65 per cent scale version of the mid-span section of the Common Research Model resulting from an exposure to a Supercooled Large Drop (SLD) icing cloud with a bimodal drop size distribution. The ice shapes created were documented with photographs, laser scanned surface measurements over a section of the model span, and measurement of the ice mass over the same section of each accretion. Drop distribution effects were evaluated by using the same IRT icing conditions except with either monomodal or bimodal drop distributions. Ice shapes resulting from the bimodal distribution as well as from equivalent monomodal drop size distributions were obtained and compared. Results indicate that the ice shapes resulting from the monomodal and bimodal drop size distributions had equivalent mass and volume, as expected with this approach. Note: No audio portion for this record, additionally slide 9 has a playable video but must be downed in order to view.

Icing↗

NASA NTRS1993

An Optical Study of the Faint End of the Stellar Luminosity Function

Herbst, W.↗

NASA NTRS1994

An optical study of the faint end of the stellar luminosity function

We implement a new method by which to study the faint end of the field star luminosity function. The method relies on deep, multicolor photometry of fields projected against highly obscured, nearby molecular clouds. The clouds act as nearby opaque screens and delimit a well-defined survey volume which is in principle free of the problem of distinguishing nearby, intrinsically faint dwarf stars from more distant red giants. This study is based upon deep photographic and CCD photometry at optical (V, R, I) bandpasses toward the most highly obscured portions of the Taurus and Ophiuchus molecular clouds. The total volume delimited by the clouds is approximately 200 cu pc. Within this region our survey is complete for all stars brighter than M(sub V) = 16-17 mag; at R and I, the survey is complete down to the lowest mass stars capable of sustaining core hydrogen burning. We estimate the faint end of the field star luminosity function for the composite Taurus and Ophiuchus foreground sample and find that it resembles the local luminosity function down to M(sub V) approx. 16. At still fainter magnitudes we find more stars than do photometric parallex studies of the polar regions. This difference widens dramatically if even the simplest correction for incompleteness is applied to our data. We therefore tentatively conclude that the luminosity function rises beyond M(sub V) approx. 16; even if we discard our attempts to correct for incompleteness in the faintest magnitude bins, the luminosity function at least remains flat for the lowest mass stars. Our provisional finding that the luminosity function rises beyond its well-known peak at M(sub V) approx. 12-13, implies that the initial mass function (IMF) probably rises beyond the turnover point associated with this peak. Even if our most conservative estimate for the faint end of the luminosity function is used-in which no corrections are made for incompleteness-the IMF must at least remain flat down to the edge of the hydrogen-burning main sequence.

Jarrett, T. H.↗

NASA NTRS2004

Convective Generation of Cirrus Near the Tropopause

The July 2004 CRYSTAL-FACE field program, based from Key West, Florida, showed that long-lived thin tropopause cirrus (TTC) layers were common above thunderstorm anvils. This paper investigates the origins of these cloud using airborne measurements. The horizontal dimensions of the TTC were nearly identical to the convectively formed anvil beneath. However, the TTC did not appear to have originated from convective detrainment. Rather it appears to have formed in stably stratified air derived from high altitudes near the tropopause. The TTC was separated from the anvil by approx. 1 km, it lacked precipitation particles, and it was strongly depleted in HDO. Nonetheless, compared to surrounding clear air near the tropopause, the TTC was enriched in moisture and trace gases in a manner consistent with it having mixed with the same convective airmass that produced the anvil. Unlike surrounding air, the TTC had embedded a monochromatic gravity wave with a wavelength of 2 km and an amplitude of several hundred meters. Combined, this evidence, supported by a photograph from CRYSTAL-FACE, leads to the conjecture that the TTC originated as a pileus cloud layer, which formed near the tropopause ahead of vigorous convective uplift. We hypothesize that the pileus was penetrated by the convection, moistened through mixing, and once the convection subsided, it was sustained by radiative cooling due to the presence of the anvil layer beneath.

Garrett, T. J.↗

NASA NTRS1989

Feasibility of reduced gravity experiments involving quiescent, uniform particle cloud combustion

The study of combustible particle clouds is of fundamental scientific interest as well as a practical concern. The principal scientific interests are the characteristic combustion properties, especially flame structure, propagation rates, stability limits, and the effects of stoichiometry, particle type, transport phenomena, and nonadiabatic processes on these properties. The feasibility tests for the particle cloud combustion experiment (PCCE) were performed in reduced gravity in the following stages: (1) fuel particles were mixed into cloud form inside a flammability tube; (2) when the concentration of particles in the cloud was sufficiently uniform, the particle motion was allowed to decay toward quiescence; (3) an igniter was energized which both opened one end of the tube and ignited the suspended particle cloud; and (4) the flame proceeded down the tube length, with its position and characteristic features being photographed by high-speed cameras. Gravitational settling and buoyancy effects were minimized because of the reduced gravity enviroment in the NASA Lewis drop towers and aircraft. Feasibility was shown as quasi-steady flame propagation which was observed for fuel-rich mixtures. Of greatest scientific interest is the finding that for near-stoichiometric mixtures, a new mode of flame propagation was observed, now called a chattering flame. These flames did not propagate steadily through the tube. Chattering modes of flame propagation are not expected to display extinction limits that are the same as those for acoustically undisturbed, uniform, quiescent clouds. A low concentration of fuel particles, uniformly distributed in a volume, may not be flammable but may be made flammable, as was observed, through induced segregation processes. A theory was developed which showed that chattering flame propagation was controlled by radiation from combustion products which heated the successive discrete laminae sufficiently to cause autoignition.

Ross, Howard D.↗

NASA NTRS1968

Techniques and precisions associated with chemical trail measurements.

Cloud position, motion and expansion measured by chemical release techniques, noting rocket-borne equipment, photographic recording and data reduction for precise histories

Bedinger, J. F.↗

NASA NTRS1974

Multispectral signatures in relation to ground control signature using nested sampling approach

The author has identified the following significant results. Principal effort has been on the development of a PDP-10 software package to read the CCT tapes more cheaply and rapidly. This is 90% completed and debugged. A shade print example of Treasure Island is provided. Stanford area was overflown with the U-2 as an add-on photographic mission to help fill in record-gaps in ERTS-1 overpass which was clouded out.

Lyon, R. J. P.↗

NASA NTRS1976

General pattern of the turbid water in the Seto-inland sea extracted from multispectral imageries by the LANDSAT-1 and 2

The author has identified the following significant results. Each distribution pattern of turbid water changes with the time in accordance with daily tides, seasonal variation of tides, and occasional rainfall. Two cases of successfully repeated LANDSAT observations for the same sea regions suggested a general pattern of turbid water could be extracted for each region. Photographic and digital processes were used to extract patterns of turbid water separately from the cloud and smog-layer in MSS 4, 5, and 7 imageries. A mosaic of image-masked imageries displays a general pattern of turbid water for almost the entire Seto Inland Sea. No such pattern was extracted for the Aki-Nada south of Hiroshima City where the water is fairly polluted, nor for the Iyo-Nada where the water is generally clearer than in other regions of the Seto Inland Sea.

Maruyasu, T.↗

NASA NTRS1969

Venus photographs. III - UV photographs of Venus taken with the 61-inch NASA telescope, 1967

Venus photography in UV by 61-inch telescope, discussing low contrast clouds recognition technique

Fountain, J.↗

NASA NTRS1987

Martian north polar cap and circumpolar clouds - 1975-1980 telescopic observations

Observational data on the late-winter/spring sublimation and recession of the north polar cap of Mars are analyzed statistically. Ground-based photographic data obtained by the International Planetary Patrol during the oppositions of 1975, 1978, and 1980 are compiled in tables and graphs, and Viking data from the 1977-1978 and 1980 recessions are included for comparison. The results indicate that the recession of the cap from its maximum extent (near 55 deg N) reaches a plateau during midspring. The end of this plateau is associated with (1) a sharp increase in circumpolar cloud cover (suggesting that the cap is the water source) and (2) a probable reversal of the northern-hemisphere meridional wind (as observed by Kahn, 1983).

James, Philip B.↗

NASA NTRS1973

A feasibility study of using remotely sensed data for water resource models

Remotely sensed data were collected to demonstrate the feasibility of applying the results to water resource problems. Photographs of the Wolf Creek watershed in southwestern Colorado were collected over a one year period. Cloud top temperatures were measured using a radiometer. Thermal imagery of the Wolf Creek Pass area was obtained during one pre-dawn flight. Remote sensing studies of water resource problems for user agencies were also conducted. The results indicated that: (1) remote sensing techniques could be used to assist in the solution of water resource problems; (2) photogrammetric determination of snow depths is feasible; (3) changes in turbidity or suspended material concentration can be observed; and (4) surface turbulence can be related to bed scour; and (5) thermal effluents into rivers can be monitored.

Ruff, J. F.↗

NASA NTRS1990

Lidar and aircraft studies of deep Cirrus systems from the 1986 FIRE IFO

Several NCAR King Air flight missions were conducted during the Wisconsin FIRE IFO experiment in support of the University of Utah polarization lidar observations of deep cirrus cloud systems at the Wausau ground site. Data collected from four cirrus systems are included in this analysis, including those of 22 and 28 October, and 1 and 2 November. Lidar data were generally obtained at 2 min intervals in the zenith direction over observation periods that ranged from approximately 4 to 10 h, bracketing the aircraft missions. The data were processed to yield height-time (HTI) displays of lidar linear depolarization ratio sigma and relative range-normalized return power P. King Air operations consisted of a combination of rapid profiling and Lagrangian spiral descents and stacked racetrack patterns in the vicinity of the field site. From the spiral descents are constructed vertical profiles of ice particle concentration N(sub i) and ice mass content IWC derived from PMS 2-D probe imagery and, when detected, FSSP cloud droplet concentration N(sub W) and liquid water content, LWC. Aircraft flight leg data are presented for the vertical velocity W and the same ice and water cloud content parameters. In addition, aerosol particle concentrations obtained with the ASAS probe are examined, and photographs of ice particles collected in-situ on oil-coated slides are presented to illustrate ice particle habit.

Sassen, Kenneth↗

NASA NTRS2006

Latest Developments in SLD Scaling

Scaling methods have been shown previously to work well for super cooled large droplet (SLD) main ice shapes. However, feather sizes for some conditions have not been well represented by scale tests. To determine if there are fundamental differences between the development of feathers for appendix C and SLD conditions, this study used time-sequenced photographs, viewing along the span of the model during icing sprays. An airspeed of 100 kt, cloud water drop MVDs of 30 and 140 microns, and stagnation freezing fractions of 0.30 and 0.50 were tested in the NASA Glenn Icing Research Tunnel using an unswept 91-cm-chord NACA0012 airfoil model mounted at 0deg AOA. The photos indicated that the feathers that developed in a distinct region downstream of the leading-edge ice determined the horn location and angle. The angle at which feathers grew from the surface were also measured; results are shown for an airspeed of 150 kt, an MVD of 30 microns, and stagnation freezing fractions of 0.30 to 0.60. Feather angles were found to depend strongly on the stagnation freezing fraction, and were independent of either chordwise position on the model or time into the spray. Feather angles also correlated well with horn angles. For these tests, there did not appear to be fundamental differences between the physics of SLD and appendix C icing; therefore, for these conditions similarity parameters used for appendix C scaling appear to be valid for SLD scaling as well. Further investigation into the cause for the large feather structures observed for some SLD conditions will continue.

Tsao, Jen-Ching↗

NASA NTRS2018

Overview of the Digitization Workflow Post Image Acquisition of Apollo Lunar and Antarctic Meteorite Samples Using Agisoft Photoscan for the NASA 3D Astromaterials Virtual Samples Collection

The 3D Virtual Astromaterials Samples (3DVAS) collection is a multi-year funded project to create a digital database of sixty Apollo Lunar and Antarctic Meteorite samples following non-destructive documentation conservation protocols. After initial image processing, the photos are evaluated and processed using unique structure-from-motion photogrammetric techniques in a high performance modelling software designed to create a 3D model from 2D images: Agisoft Photoscan Pro. Agisoft Photoscan Pro uses image processing algorithms and techniques originating in computer vision to resolve 3D models for accurate and detailed visualization of a subject. The software provides a stepwise process that is tailored per model based on spatial and specular reflectance properties, for example. The process includes: photo alignment, creation of a dense point cloud, mesh, and finally texture. Photo alignment is dependent on model properties. The 3DVAS process requires a special rotation platform with calibrated photogrammetric targets, specific distance rotation protocols, and a contrasting background for alignment and scale accuracy. As a result of the photographic process, alignment will complete with two mirrored hemispheres that, in a sense, represent the 2D images overlapping to create a 3D model. Each dense point cloud is analyzed with provided statistical measures in a gradual selection process to eliminate outliers. The point cloud is reduced to include only data valuable to the final model. When a precise dense point cloud is achieved, a mesh and texture are applied. Each model is scaled with scale bar accuracies within 100 microns. Each sample has its own intimate process for modelling; there is no standard for the parameters required in the final creation of a high resolution model. By processing multiple samples, a skill is gained in practice to allow a close definition of the original sample and will result in the most detailed version of the sample shell. This process completes one-fifth of the 3DVAS protocol for providing accurate digital documentation. Each model shell is merged with X-ray Computed Tomography data to create a full volumetric sample. All 3DVAS data will be served on NASA's Astromaterials Acquisition and Curation website with an early subset of data available in 2019 and the 3D Virtual Astromaterials Samples Collection launch in 2020.

Thomas, Andi B.↗

NASA NTRS1993

Gas-rich dwarf galaxies in dense and sparse environments

Dwarf irregular galaxies (generically labelled Im for the present purposes) pose an enigma to students of galaxy evolution. In nearby groups and the Virgo cluster, Im galaxies are at least as abundant as spiral galaxies, and their low surface brightnesses and high gas-to-stars ratios suggest that (at least in the stochastic self-propagating star formation scenario) there should be significant numbers of HI clouds with masses approaching 10(exp 8) solar mass which have undergone very little or no star formation. To date, however, no clouds with so little star formation that they would not be recognized as Im galaxies on high-quality photographic plates have been identified. There have been suggestions that such dwarfs may be tidally disrupted in regions of high galactic density, but may be prevalent in low density regions. We offer data from three parallel programs relevant to this issue. (1) A large number of Im galaxies throughout the Local Supercluster have been mapped in the HI spectral line using the Arecibo Radiotelescope, and we can establish the frequency with which HI disks much more extended than their optically visible portions are found. (2) Our extensive mapping of spiral and dwarf galaxies in the Virgo cluster allows us to set stringent limits on the density of star-free Hi clouds in that cluster. (3) We have conducted a sampling of the void in the distribution of galaxies toward the super galactic pole, optimized for finding low-mass HI clouds at redshifts out to approximately 2000 km/s.

Hoffman, G. Lyle↗

DOE OSTI2024

Principles of stereo reconstruction of aerial objects using stationary cameras

An overview is given here of the principles and mathematics of stereo reconstruction of objects in the sky using stationary cameras with an emphasis on meteorological applications. Through its Atmospheric Radiation Measurement program, the Department of Energy has operated stereo-photogrammetric cameras since 2017 as part of an effort to measure the life-cycle properties of clouds. At the core of that technology is stereo reconstruction, which calculates the real-world position of an object from the location of the object’s image in two cameras’ photographs. Here, stereo reconstruction is stripped down to its basic elements and presented using conventions tailored to applications in atmospheric science. In addition, the resulting equations are used to illustrate the high sensitivity of reconstructed cloud positions to errors in the cameras’ Euler angles. The interested reader will find here a self-contained guide to performing stereo reconstructions using distortion-corrected images from a pair of calibrated, stationary cameras, as well as a demonstration of the need for high accuracy in the measurement of camera properties and orientations.

47 OTHER INSTRUMENTATION↗

NASA NTRS1985

Dust devils on Mars

Viking Orbiter photographic imagery has confirmed the occurrence of dust devils on Mars. The images were of small bright clouds with long, tapered shadows viewed from a nearly-nadir angle. Spectra of the features were consistent with dust and not condensates. A maximum height of 6.8 km and width of 1 km were measured. The dust devils appeared on smooth planes, and had average dimensions of 2 km height and 200 m diam, carrying 3000 kg of dust. The data may be of use in interpreting convective processes on earth.

Thomas, P.↗

NASA NTRS1988

The Atlas-Centaur 67 incident

The conditions leading to the breakup of the Atlas-Centaur 67 (AC-67) vehicle launched on March 26, 1987 during a typical winter-time storm are analyzed, and a most probable lightning strike scenario was developed based on inspection of the AC-67 debris, the AC-68 vehicle, and appropriate drawings, electrical diagrams, and photographs. It is shown that, during ascent, the vehicle encountered increasingly larger electric fields and flew through clouds that produced precipitation static on the vehicle, eventually triggering a cloud-to-ground lightning, comprised of at least four return strokes. The resulting lightning current coupled a signal into the wiring which goes to the AC-67 digital computer unit (DCU), effecting a single-word memory alteration and causing the DCU to issue a hardover engine gimbal command. This led to an excessive angle of attack, large dynamic loads, and the breakup of the AC-67.

Christian, H. J.↗