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NASA NTRS2018

The Kepler Light Curves of AGN: A Detailed Analysis

We present a comprehensive analysis of 21 light curves of Type 1 active galactic nuclei (AGN) from the Kepler spacecraft. First, we describe the necessity and development of a customized pipeline for treating Kepler data of stochastically variable sources like AGN. We then present the light curves, power spectral density functions (PSDs), and flux histograms. The light curves display an astonishing variety of behaviors, many of which would not be detected in ground-based studies, including switching between distinct flux levels. Six objects exhibit PSD flattening at characteristic timescales that roughly correlate with black hole mass. These timescales are consistent with orbital timescales or free-fall accretion timescales. We check for correlations of variability and high-frequency PSD slope with accretion rate, black hole mass, redshift, and luminosity. We find that bolometric luminosity is anticorrelated with both variability and steepness of the PSD slope. We do not find evidence of the linear rms-flux relationships or lognormal flux distributions found in X-ray AGN light curves, indicating that reprocessing is not a significant contributor to optical variability at the 0.1%-10% level.

power spectral density functions(PSDs)↗
NASA NTRS2016

Regime-Based Evaluation of Cloudiness in CMIP5 Models

The concept of Cloud Regimes (CRs) is used to develop a framework for evaluating the cloudiness of 12 fifth Coupled Model Intercomparison Project (CMIP5) models. Reference CRs come from existing global International Satellite Cloud Climatology Project (ISCCP) weather states. The evaluation is made possible by the implementation in several CMIP5 models of the ISCCP simulator generating for each gridcell daily joint histograms of cloud optical thickness and cloud top pressure. Model performance is assessed with several metrics such as CR global cloud fraction (CF), CR relative frequency of occurrence (RFO), their product (long-term average total cloud amount [TCA]), cross-correlations of CR RFO maps, and a metric of resemblance between model and ISCCP CRs. In terms of CR global RFO, arguably the most fundamental metric, the models perform unsatisfactorily overall, except for CRs representing thick storm clouds. Because model CR CF is internally constrained by our method, RFO discrepancies yield also substantial TCA errors. Our findings support previous studies showing that CMIP5 models underestimate cloudiness. The multi-model mean performs well in matching observed RFO maps for many CRs, but is not the best for this or other metrics. When overall performance across all CRs is assessed, some models, despite their shortcomings, apparently outperform Moderate Resolution Imaging Spectroradiometer (MODIS) cloud observations evaluated against ISCCP as if they were another model output. Lastly, cloud simulation performance is contrasted with each model's equilibrium climate sensitivity (ECS) in order to gain insight on whether good cloud simulation pairs with particular values of this parameter.

cloud climatology↗
NASA NTRS1981

The surface albedo of the earth in the near ultraviolet /330-340 nm/

Satellite-borne measurements of solar radiation backscattered by the earth and atmosphere allow a determination of the surface albedo in the near ultraviolet. The data yielded albedos at tropical latitudes during a 15-month period in 1979-1980. The wavelengths studied are 331.2 and 339.8 nm. Sixty-nine percent of the measurements imply albedos less than 0.3. Higher values include a contribution due to reflection from clouds and are consistent with previous estimates of the fractional cloudover in the tropics. An albedo histogram based on a bin width of 0.1 shows results in the range 0.1-0.2 to be the most frequent, appearing in 29% of the cases, although values which span the entire range 0.0-1.0 are present. The derived albedos show no correlation with solar zenith angle. This result is consistent with the fact that, at the wavelengths considered, the diffuse integrated intensity is larger than the attenuated direct solar beam near the ground.

Frederick, J. E.↗
NASA NTRS1991

Effects of satellite data resolution on measuring the space/time variations of surfaces and clouds

The correlated distributions of satellite-measured visible and infrared radiances, caused by spatial and temporal variations in clouds and surfaces, have been found to be characteristic of the major climate regimes and can be described by the attributes of bidimensional and monodimensional histograms and time-composite images. Most of the variability of both the surfaces and clouds is found to occur at scales larger than the minimum resolved by satellite imagery. Since satellite imaging data sets are difficult to analyze because of their large volumes, many studies reduce the volume by various sampling or averaging schemes. The effects of data resolution and sampling on the radiance histogram statistics and on the time-composite image characteristics are examined. In particular, the sampling strategy used by the International Satellite Cloud Climatology Project is tested. This sampling strategy is found to preserve the statistics of smaller cloud variations for most regions, with the exception of very rare events, if they are accumulated over large enough areas (at least 500 km in dimension) and long enough time periods (at least one month).

Seze, Genevieve↗
NASA NTRS1992

Calculation of area-averaged vertical profiles of the horizontal wind velocity from volume-imaging lidar data

Area-averaged horizontal wind measurements are derived from the motion of spatial inhomogeneities in aerosol backscattering observed with a volume-imaging lidar. Spatial averaging provides high precision, reducing sample variations of wind measurements well below the level of turbulent fluctuations, even under conditions of very light mean winds and strong convection or under the difficult conditions represented by roll convection. Wind velocities are measured using the two-dimensional spatial cross correlation computed between successive horizontal plane maps of aerosol backscattering, assembled from three-dimensional lidar scans. Prior to calculation of the correlation function, three crucial steps are performed: (1) the scans are corrected for image distortion by the wind during a finite scan time; (2) a temporal high pass median filtering is applied to eliminate structures that do not move with the wind; and (3) a histogram equalization is employed to reduce biases to the brightest features.

Schols, J. L.↗
NASA NTRS2002

Carbon Nanostructure Examined by Lattice Fringe Analysis of High Resolution Transmission Electron Microscopy Images

The dimensions of graphitic layer planes directly affect the reactivity of soot towards oxidation and growth. Quantification of graphitic structure could be used to develop and test correlations between the soot nanostructure and its reactivity. Based upon transmission electron microscopy images, this paper provides a demonstration of the robustness of a fringe image analysis code for determining the level of graphitic structure within nanoscale carbon, i.e. soot. Results, in the form of histograms of graphitic layer plane lengths, are compared to their determination through Raman analysis.

VanderWal, Randy L.↗
NASA NTRS2003

Carbon Nanostructure Examined by Lattice Fringe Analysis of High Resolution Transmission Electron Microscopy Images

The dimensions of graphitic layer planes directly affect the reactivity of soot towards oxidation and growth. Quantification of graphitic structure could be used to develop and test correlations between the soot nanostructure and its reactivity. Based upon transmission electron microscopy images, this paper provides a demonstration of the robustness of a fringe image analysis code for determining the level of graphitic structure within nanoscale carbon, i.e., soot. Results, in the form of histograms of graphitic layer plane lengths, are compared to their determination through Raman analysis.

VanderWal, Randy L.↗
NASA NTRS2003

Macromolecular Topography Leaps into the Digital Age

A low-cost, real-time digital topography system is under development which will replace x-ray film and nuclear emulsion plates. The imaging system is based on an inexpensive surveillance camera that offers a 1000x1000 array of 8 im square pixels, anti-blooming circuitry, and very quick read out. Currently, the system directly converts x-rays to an image with no phosphor. The system is small and light and can be easily adapted to work with other crystallographic equipment. Preliminary images have been acquired of cubic insulin at the NSLS x26c beam line. NSLS x26c was configured for unfocused monochromatic radiation. Six reflections were collected with stills spaced from 0.002 to 0.001 degrees apart across the entire oscillation range that the reflections were in diffracting condition. All of the reflections were rotated to the vertical to reduce Lorentz and beam related effects. This particular CCD is designed for short exposure applications (much less than 1 sec) and so has a relatively high dark current leading to noisy raw images. The images are processed to remove background and other system noise with a multi-step approach including the use of wavelets, histogram, and mean window filtering. After processing, animations were constructed with the corresponding reflection profile to show the diffraction of the crystal volume vs. the oscillation angle as well as composite images showing the parts of the crystal with the strongest diffraction for each reflection. The final goal is to correlate features seen in reflection profiles captured with fine phi slicing to those seen in the topography images. With this development macromolecular topography finally comes into the digital age.

Lovelace, J.↗
NASA NTRS2016

Prospects of the ICESat-2 Laser Altimetry Mission for Savanna Ecosystem Structural Studies Based on Airborne Simulation Data

The next planned spaceborne lidar mission is the Ice, Cloud and land Elevation Satellite 2 (ICESat-2), which will use the Advanced Topographic Laser Altimeter System (ATLAS) sensor, a photon counting technique. To pre-validate the capability of this mission for studying three dimensional vegetation structure in savannas, we assessed the potential of the measurement approach to estimate canopy height in an oak savanna landscape. We used data from the Multiple Altimeter Beam Experimental Lidar (MABEL), an airborne photon counting lidar sensor developed by NASA's Goddard Space Flight Center. ATLAS-like data was generated using the MATLAS simulator, which adjusts MABEL data's detected number of signal and noise photons to that expected from the ATLAS instrument. Transects flown over the Tejon ranch conservancy in Kern County, California, USA were used for this work. For each transect we chose to use data from the near infrared channel that had the highest number of photons. We segmented each transect into 50 m, 25 m and 14 m long blocks and aggregated the photons in each block into a histogram based on their elevation values. We then used an automated algorithm to identify cut off points where the cumulative density of photons from the highest elevation indicates the presence of the canopy top and likewise where such cumulative density from the lowest elevation indicates the mean terrain elevation. MABEL derived height metrics were moderately correlated to discrete return lidar (DRL) derived height metrics r(sub 2) and RMSE values ranging from 0.60 to 0.73 and 2.9 m to 4.4 m respectively) but MATLAS simulation resulted in more modest correlations with DRL indices r(sub 2) ranging from 0.5 to 0.64 and RMSE from 3.6 m to 4.6 m). Simulations also indicated that the expected number of signal photons from ATLAS will be substantially lower, a situation that reduces canopy height estimation precision especially in areas of low density vegetation cover. On the basis of the simulated data, there is reason to believe that the ability of ICESat-2 to estimate height in savannas will be comparable to the original ICESat mission although the respective sensors have different measurement principles.

Gwenzi, David↗
NASA NTRS1995

Preliminary results of the analysis of CaII K spectroheliograms

The preliminary results of the photometry of CaII K spectroheliograms are presented. From the spectrograms for 1992, plages, the magnetic network, intranetwork elements and the chromospheric background were separated using the histogram method. The intensity and area of these separated features, as well as the full disk intensity, were derived. The spatial K index was compared to the spectral CaII K index derived from line profiles. It was found that the spatial K index and intensity of plages, the network elements and the intranetwork and background regions were highly correlated with the MgII h and k c/w ratio.

Kariyappa, R.↗
NASA NTRS2017

Experimental Visualizations of a Generic Launch Vehicle Flow Field: Time-Resolved Shadowgraph and Infrared Imaging

Time-Resolved shadowgraph and infrared (IR) imaging were performed to investigate off-body and on-body flow features of a generic, 'hammer-head' launch vehicle geometry previously tested by Coe and Nute (1962). The measurements discussed here were one part of a large range of wind tunnel test techniques that included steady-state pressure sensitive paint (PSP), dynamic PSP, unsteady surface pressures, and unsteady force measurements. Image data was captured over a Mach number range of 0.6 less than or equal to M less than or equal to 1.2 at a Reynolds number of 3 million per foot. Both shadowgraph and IR imagery were captured in conjunction with unsteady pressures and forces and correlated with IRIG-B timing. High-speed shadowgraph imagery was used to identify wake structure and reattachment behind the payload fairing of the vehicle. Various data processing strategies were employed and ultimately these results correlated well with the location and magnitude of unsteady surface pressure measurements. Two research grade IR cameras were positioned to image boundary layer transition at the vehicle nose and flow reattachment behind the payload fairing. The poor emissivity of the model surface treatment (fast PSP) proved to be challenging for the infrared measurement. Reference image subtraction and contrast limited adaptive histogram equalization (CLAHE) were used to analyze this dataset. Ultimately turbulent boundary layer transition was observed and located forward of the trip dot line at the model sphere-cone junction. Flow reattachment location was identified behind the payload fairing in both steady and unsteady thermal data. As demonstrated in this effort, recent advances in high-speed and thermal imaging technology have modernized classical techniques providing a new viewpoint for the modern researcher

Shadowgraph↗
NASA NTRS1985

Search for solar neutrons using NM-64 equipment

Two years (1980 to 1982) neutron monitor data from the Chacaltaya (geographic coordinates: N16.32 deg W68. 15 deg; cutoff rigidity: 13.1 GV; altitude: 5,300 m a.s.l.) station has been scanned; the sampling time of the 12NM-64 neutron monitor is 5 min. The nucleonic component increases have been correlated with 66 hard X-, gamma rays satellite data from solar origin, as reported by several groups. Typical neutron monitor time profiles of the events are presented. Chree-analysis was performed discriminating the events according to its solar coordinates. Ground data from solar limb locii are more enhanced at the time of the onset than other geometrically visible flares. Chree histograms of neutron monitor output profiles are also presented from geometrically invisible events from the Chacaltaya station.

Martinic, N. J.↗
NASA NTRS1994

Charge-induced secondary atomization in diffusion flames of electrostatic sprays

The combustion of electrostatic sprays of heptane in laminar counterflow diffusion flames was experimentally studied by measuring droplet size and velocity distributions, as well as the gas-phase temperature. A detailed examination of the evolution of droplet size distribution as droplets approach the flame shows that, if substantial evaporation occurs before droplets interact with the flame, an initially monodisperse size distribution becomes bimodal. A secondary sharp peak in the size histogram develops in correspondence of diameters about one order of magnitude smaller than the mean. No evaporation mechanism can account for the development of such bimodality, that can be explained only in terms of a disintegration of droplets into finer fragments of size much smaller than that of the parent. Other evidence in support of this interpretation is offered by the measurements of droplet size-velocity correlation and velocity component distributions, showing that, as a consequence of the ejection process, the droplets responsible for the secondary peak have velocities uncorrelated with the mean flow. The fission is induced by the electric charge. When a droplet evaporates, in fact, the electric charge density on the droplet surface increases while the droplet shrinks, until the so-called Rayleigh limit is reached at which point the repulsion of electric charges overcomes the surface tension cohesive force, ultimately leading to a disintegraton into finer fragments. We report on the first observation of such fissions in combustion environments. If, on the other hand, insufficient evaporation has occurred before droplets enter the high temperature region, there appears to be no significant evidence of bimodality in their size distribution. In this case, in fact, the concentration of flame chemi-ions or, in the case of positively charged droplets, electrons may be sufficient for them to neutralize the charge on the droplets and to prevent disruption.

Gomez, Alessandro↗
NASA NTRS1973

Elemental composition of individual chondrules from ordinary chondrites.

Sequential nondestructive neutron activation analysis was used to determine the bulk abundance of Fe, Al, Na, Mn, Cr, Sc, Co, and Ir in approximately 300 individual chondrules from 16 chondrites representing the H(3-5), L4, and LL(3-6) compositional and petrologic classes. The histograms indicate that the most probable abundances for lithophilic elements, except Cr, are enriched in the chondrules, while the siderophilic elements are depleted in the chondrules compared to the whole chondrite. Some of the abundance populations, such as Al and Fe, appear to be multimodal. Systematic variations in the composition of the chondrules with increasing petrologic type were observed; most consistent are an increasing Na-Al and Cr-Al correlation, a decreasing Na-Mn correlation, increasing Na abundance, and decreasing Na and Mn dispersions among chondrules.

Osborn, T. W.↗
NASA NTRS1981

A comparative statistical study of long-term agroclimatic conditions affecting the growth of US winter wheat: Distributions of regional monthly average precipitation on the Great Plains and the state of Maryland and the effect of agroclimatic conditions on yield in the state of Kansas

A histogram analysis of average monthly precipitation over 30 and 84 year periods for both Maryland and Kansas was made and the results compared. A second analysis, a statistical assessment of the effect of average monthly precipitation on Kansas winter wheat yield was made. The data sets covered the three periods of 1941-1970, 1887-1970, and 1887-1921. Analyses of the limited data sets used (only the average monthly precipitation and temperature were correlated against yield) indicated that fall precipitation values, especially those of September and October, were more important to winter wheat yield than were spring values, particularly for the period 1941-1970.

Welker, J.↗
NASA NTRS1998

Generic Signatures of the Time Profiles of BATSE Cosmic Gamma-Ray Bursts

A new method is proposed, which allows the study of generic signatures of cosmic gamma-ray burst time histories. We average the 64 ms resolution time profiles of 275 bright bursts detected by BATSE. The profile of each burst is normalized by the maximum number of counts at the peak of the primary pulse, and individual pulses and interpulse valleys are selected from the normalized profiles by identical selection criteria. New generic temporal parameters are introduced, which characterize the duration and equivalent width of each pulse and the duration of each valley. The histograms of the total equivalent pulse width and summed pulse duration are bimodal. Bimodality is also seen in the histogram of the mean duration of individual pulses. Bursts from the short and long peaks of these distributions correspond to the two modes of the Third BATSE Burst Catalog T(sub 50) and T(sub 90) distributions. Therefore, these new burst parameters demonstrate that the observed bimodal temporal behavior results from properties of the pulsed emission of gamma-ray bursts. The long mode of the T(sub 90) histogram includes bursts with from one to approximately 20 pulses; the logarithmic mean pulse duration is 1.17 +/- 0.09 S; for the long events with more than one pulse, the logarithmic mean valley duration is 1.28 +/- 0.15 S. Bursts of the short mode of T(sub 90) are mainly single-pulse events, and the logarithmic mean pulse duration is much smaller, 0.20 +/- 0.01 s. For multipulse bursts of the T(sub 90) long mode, marginal correlations were found between the parameters of the pulses and valleys and the number of pulses. The basic signatures of the evolution of pulses and valleys along the time course of bursts are examined. Conclusions are drawn concerning the physics of gamma-ray emission by taking into account these signatures.

Mitrofanov, Igor G.↗
NASA NTRS2021

SHARPEN: A Scheme to Restore the Distribution of Averaged Precipitation Fields

A key strategy in obtaining complete global coverage of high-resolution precipitation is to combine observations from multiple fields, such as the intermittent passive microwave observations, precipitation propagated in time using motion vectors, and geosynchronous infrared observations. These separate precipitation fields can be combined through weighted averaging, which produces estimates that are generally superior to the individual parent fields. However, the process of averaging changes the distribution of the precipitation values, leading to an increase in precipitating area and a decrease in the values of high precipitation rates, a phenomenon observed in IMERG. To mitigate this issue, we introduce a new scheme called SHARPEN (Scheme for Histogram Adjustment with Ranked Precipitation Estimates in the Neighborhood), which recovers the distribution of the averaged precipitation field based on the idea of quantile mapping applied to the local environment. When implemented in IMERG, precipitation estimates from SHARPEN exhibit a distribution that resembles that of the original instantaneous observations, with matching precipitating area and peak precipitation rates. Case studies demonstrate its improved ability in bridging between the parent precipitation fields. Evaluation against ground observations reveals a distinct improvement in precipitation detection skill, but also a slightly reduced correlation likely because of a sharper precipitation field. The increased computational demand of SHARPEN can be mitigated by striding over multiple grid boxes, which has only marginal impacts on the accuracy of the estimates. SHARPEN can be applied to any precipitation algorithm that produces an average from multiple input precipitation fields and is being considered for implementation in IMERG V07.

Jackson Tan↗
NASA NTRS1992

Crab pulsar giant pulses: Simultaneous radio and GRO observations

Observations are reported of the Crab pulsar made at radio frequencies concurrent with Oriented Scintillation Spectrometer Experiment (OSSE) observations from 15 to 27 May 1991. Using the 43 m telescope at Green Bank at 0.8 and 1.4 GHz, samples were made continuously for 10 hrs/day at intervals of 100 to 300 microsecs. The analysis of the radio data includes calculation of histograms of pulse intensities, absolute timing to about 20 microsec precision, and characterization of intensity variations on time scales from the 33 ms spin period to days. The most detailed analysis is presented made of giant pulses. The ultimate goal is to bin the radio data into giant and nongiant pulses and to form average waveforms of OSSE data for the corresponding pulse periods. A test is done to see whether the violet radio fluctuations (which are not seen in other radio pulsars to the same degree) are correlated with low energy gamma rays, yielding constraints on the radio coherence mechanism and the steadiness of the electron-positron outflow in the magnetosphere. Timing analysis of the radio data provides a well defined ephemeris over the specified range of epochs. The gamma ray pulse phase was predicted with an error of less than 70 microsecs.

Lundgren, Scott C.↗