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At least 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

DMTN-197: Streak Masking in DM Image Processing

Streaks caused by satellites are a persistent problem in optical images, and their occurrence will likely increase in the coming years. Many Hyper Suprime-Cam images are already affected by streaks, and the same is expected for Rubin Observatory data. In the LSST Data Release Production (DRP), most streaks and other artifacts are already detected and masked by the algorithm CompareWarpAssembleCoadd. However, some streaks are not caught at this stage and can contaminate the final coadds and detection catalogs. To find and mask these, we adopt a morphologically-based method for detecting streaks, which uses the Kernel-Based Hough Transform to detect straight lines. Once the lines are detected, the streak profile is fit and the affected portion of the image is masked out. This algorithm, maskStreaks, is included in the meas_algorithms package and is used in CompareWarpAssembleCoadd to remove streaks from coadds. Similar implementation in the Alert Production Pipeline is possible but has not been implemented.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1972

A system overview of the Aerospace Safety Research and Data Institute data management programs

The NASA Aerospace Safety Information System, is an interactive, generalized data base management system. The on-line retrieval aspects provide for operating from a variety of terminals (or in batch mode). NASIS retrieval enables the user to expand and display (review) the terms of index (cross reference) files, select desired index terms, combine sets of documents corresponding to selected terms and display the resulting records. It also allows the user to print (record) this information on a high speed printer if desired. NASIS also provides the ability to store the strategy of any given session the user has executed. It has a searching and publication ability through generalized linear search and report generating modules which may be performed interactively or in a batch mode. The user may specify formats for the terminal from which he is operating. The system features an interactive user's guide which explains the various commands available and how to use them as well as explanations for all system messages. This explain capability may be extended, without program changes, to include descriptions of the various files in use. Coupled with the ability of NASIS to run in an MTT (multi-terminal task) mode is its automatic accumulation of statistics on each user of the system as well as each file.

Source record↗
NASA NTRS1972

Calculation of sonic boom signatures by bicharacteristic methods.

An improved method is described for correcting the zeroth order (free stream) characteristics to obtain a uniformly valid first order solution to the exact equations of motion for a compressible fluid. The method is based on constructing first order bicharacteristic lines from the system of ordinary differential equations belonging to the exact equation for the characteristic surface. Calculated sonic boom signatures are compared with experiments conducted at Langley Research Center on a cone-cylinder at Mach numbers 2.96, 3.83, and 4.63. Theory and experiment agree well over the entire Mach number range.

Davis, S. S.↗
NASA NTRS1972

High resolution spectra of Venus.

The existing high resolution spectra of Venus show considerable variations in the abundance of CO2. As this is the major constituent of the atmosphere, these day-to-day variations indicate the effective reflecting cloud layer is undergoing substantial vertical displacements over a relatively short time scale. The published observations indicate that CO is uniformly mixed with the CO2, but that the lines of HF may be formed deeper in the atmosphere and HCl lines considerably deeper. These conclusions are based on extrapolations of laboratory measurements and could be considerably altered by new laboratory measurements made under conditions similar to those near the tropopause in Venus.

Young, L. D. G.↗
NASA NTRS1972

High resolution spectra of Venus - A review.

The existing high-resolution spectra of Venus show considerable variations in the abundance of CO2. As this is the major constituent of the atmosphere, these day-to-day variations indicate that the effective reflecting cloud layer is undergoing substantial vertical displacements over a relatively short time scale. The published observations indicate that CO is uniformly mixed with the CO2, but that the lines of HF may be formed deeper in the atmosphere and HCl lines considerably deeper. These conclusions are based on extrapolations of laboratory measurements and could be considerably altered by new laboratory measurements made under conditions similar to those near the tropopause in Venus.

Young, L. D. G.↗
NASA NTRS1978

Gamma line radiation from supernovae

Recent calculations of core collapse or massive stars result in explosive ejection of the mantle by a reflected shock. These hydrodynamic results are important for predictions of explosive nucleosynthesis and gamma-ray line emission from supernovae. Previous estimates, based on simple parameterized models or the nucleosynthesis in an average supernova, are compared with these latest results.

Arnett, W. D.↗
NASA NTRS1978

Upper limits on the cyclotron lines from Her X-1 as observed with OSO-8

Observations of Her X-1 were obtained during its ON-state in September, 1977, with the high-energy X-ray detector on board OSO-8. Upper limits on the line fluxes at 60 and 135 keV based on these observations are above, and hence consistent with, the positive results reported by Trumper, et al from a balloon flight during the same time interval. A detailed analysis of the time-variable et al background spectrum suggests that the line emission, especially in the time-averaged spectrum of Her X-1 previously reported by other workers at 25, 60, and 135 keV, is due to instrumental effects. The spectrum obtained with OSO-8 in September, 1977, is considerably steeper than that observed in pre-1976 balloon flights. These results are consistent with the results obtained by Trumper showing a decrease in the effective temperature of Her X-1 between May, 1976, and September, 1977.

Dennis, B. R.↗
NASA NTRS1978

The spiral field inhibition of thermal conduction in two-fluid solar wind models

The paper reports on two-field models which include the inhibition of thermal conduction by the spiraling interplanetary field to determine whether any of the major conclusions obtained by Nerney and Barnes (1977) needs to be modified. Comparisons with straight field line models reveal that for most base conditions, the primary effect of the inhibition of thermal conduction is the bottling-up of heat in the electrons as well as the quite different temperature profiles at a large heliocentric radius. The spiral field solutions show that coronal hole boundary conditions do not correspond to states of high-speed streams as observed at 1 AU. The two-fluid models suggest that the spiral field inhibition of thermal conduction in the equatorial plane will generate higher gas pressures in comparison with flows along the solar rotation axis (between 1 and 10 AU). In particular, massive outflows of stellar winds, such as outflow from T Tauri stars, cannot be driven by thermal conduction. The conclusions of Nerney and Barnes remain essentially unchanged.

Nerney, S.↗
NASA NTRS1978

The center-to-limb

Center-to-limb measurements of the Ca I 6573 intercombination line and the Ca II 7324 forbidden line are compared with synthetic profiles based on a simple representation of the non-LTE Ca-Ca(+) ionization equilibrium. The effects of photoionizations from low lying excited states of neutral calcium are found to reduce the sensitivity of the 6573 center-to-limb behavior as a thermal structure diagnostic. The synthetic center-to-limb behavior is also sensitive to uncertainties in the nonthermal broadening. Nevertheless, the measured center-to-limb behavior of 6573 favors a 'cool' photospheric model over hotter models based on the Ca II K wings. The non-LTE calcium abundance obtained from the disk center equivalent widths of 6573 and 7324 using the best fit model is A(Ca) = 2.1 plus or minus 0.2 x 10 to the -6th (by number relative to hydrogen).

Source record↗
NASA NTRS1980

Observations of electron gyroharmonic waves and the structure of the Io torus

Narrow-banded emissions were observed by the Planetary Radio Astronomy experiment on the Voyager 1 spacecraft as it traversed the Io plasma torus. These waves occur between harmonics of the electron gyrofrequency and are the Jovian analogue of electrostatic emissions observed and theoretically studied for the terrestrial magnetosphere. The observed frequencies always include the component near the upper hybrid resonant frequency, (fuhr) but the distribution of the other observed emissions varies in a systematic way with position in the torus. A refined model of the electron density variation, based on identification of the fuhr line, is included. Spectra of the observed waves are analyzed in terms of the linear instability of an electron distribution function consisting of isotropic cold electrons and hot losscone electrons. The positioning of the observed auxiliary harmonics with respect to fuhr is shown to be an indicator of the cold to hot temperature ratio. It is concluded that this ratio increases systematically by an overall factor of perhaps 4 or 5 between the inner and outer portions of the torus.

Birmingham, T. J.↗
NASA NTRS1980

GOES infrared study of tornadic storms

Enhanced convection-initiated gravity waves associated with an isolated tornado in the absence of a squall line are investigated. Ray tracing computations based on data observed on May 29, 1977 indicated that the wave sources were located in north central Oklahoma. Comparison with a radar echo map during the time period when the waves were excited showed that the waves were generated by an isolated cloud with enhanced convection. GOES infrared digital data during the time period from wave excitation to tornado touchdown were analyzed. Results showed that the cloud where the gravity waves were excited was characterized by both a very low temperature at the cloud top and a very high expansion rate of the cold cloud tops area. The lead time between the excitation of the gravity waves and the tornado touchdown is discussed in conjunction with the growth rate of the clouds associated with the tornado.

Hung, R. J.↗
NASA NTRS1982

Charged particle motions in the distended magnetospheres of Jupiter and Saturn

Charged particle motion in the guiding center approximation is analyzed for models of the Jovian and Saturnian magnetospheric magnetic fields based on Voyager magnetometer observations. Field lines are traced and exhibit the distention which arises from azimuthally circulating magnetospheric currents. The spatial dependencies of the guiding center bounce period and azimuthal drift rate are investigated for the model fields. Non-dipolar effects in the gradient-curvature drift rate are most important at the equator and affect particles with all mirror latitudes. The effect is a factor of 10-15 for Jupiter with its strong magnetodisc current and 1-2 for Saturn with its more moderate ring current. Limits of adiabaticity, where particle gyroradii become comparable with magnetic scale lengths, are discussed and are shown to occur at quite modest kinetic energies for protons and heavier ions.

Birmingham, T. J.↗
NASA NTRS1981

Dust-sensitive forbidden line ratios

The paper studies observations of certain pairs of forbidden emission lines in the redshifted spectra of intrinsically bright objects, which may make possible the study of dust at large distances. The forbidden line pairs most likely to be useful in detecting dust in both galactic and extragalactic objects are presented, and forbidden O III 2322, 4364 A, which is the best line pair for the ground-based detection of dust intermediate-redshift quasars is discussed. Spectrophotometric observations at 1-2 microns could permit the study of dust toward highly luminous quasars at redshifts as large as 5, and quasars brighter than visual magnitude 17 are presented as candidates for studying dust with forbidden O III 2322, 4364 A.

Draine, B. T.↗
NASA NTRS1981

Observations of dynamical phenomena in sunspots

A preliminary report of the results of one observing run based on data from one spectral line, the photospheric magnetic line Fe 6303, is presented as part of a series of observations of dynamical phenomena in sunspots using photographic spectra with the SPO vacuum tower telescope and echelle spectrograph. The ejection of a magnetic feature from the outer edge of the penumbra was observed. The initial total field strength of the feature was about 1000 gauss, which appeared to decrease as the feature moved away from the sunspot. The proper motion was about 2 km/s, and the velocity field measured in the V profile showed a downflow of 400 m/s on the spotward side of the moving magnetic feature. Umbral oscillations at the photospheric level with a herringbone structure characteristic of horizontally propagating waves, suggesting some overtone mode of membrane oscillation in the umbra, were seen. The peak amplitude of the oscillation was about 200 m/s, and the mean power spectrum had several clear peaks.

Nye, A. H.↗
NASA NTRS1983

Propagation of flexural and membrane waves with fluid loaded NASTRAN plate and shell elements

Modeling of flexural and membrane type waves existing in various submerged (or in vacuo) plate and/or shell finite element models that are excited with steady state type harmonic loadings proportioned to e(i omega t) is discussed. Only thin walled plates and shells are treated wherein rotary inertia and shear correction factors are not included. More specifically, the issue of determining the shell or plate mesh size needed to represent the spatial distribution of the plate or shell response is of prime importance towards successfully representing the solution to the problem at hand. To this end, a procedure is presented for establishing guide lines for determining the mesh size based on a simple test model that can be used for a variety of plate and shell configurations such as, cylindrical shells with water loading, cylindrical shells in vacuo, plates with water loading, and plates in vacuo. The procedure for doing these four cases is given, with specific numerical examples present only for the cylindrical shell case.

Kalinowski, A. J.↗
NASA NTRS1984

Effect of nonideal square-law detection on static calibration in noise-injection radiometers

The effect of nonideal square-law detection on the static calibration for a class of Dicke radiometers is examined. It is shown that fourth-order curvature in the detection characteristic adds a nonlinear term to the linear calibration relationship normally ascribed to noise-injection, balanced Dicke radiometers. The minimum error, based on an optimum straight-line fit to the calibration curve, is derived in terms of the power series coefficients describing the input-output characteristics of the detector. These coefficients can be determined by simple measurements, and detection nonlinearity is, therefore, quantitatively related to radiometric measurement error.

Hearn, C. P.↗
NASA NTRS1984

Interstellar O2. I - Abundance, excitation, and prospects for detection of O-16O-18 at radio frequencies

Molecular oxygen, O2, is predicted to be an important constituent of the interstellar gas, but it has not yet been detected in interstellar clouds. In this paper, the gas phase production and destruction of O2 are reconsidered, a non-LTE calculation of level populations at cloud temperatures is presented, and O2 column densities in diffuse and dark clouds are predicted. Ground-based detection of the 234 GHz line of O-16O-18 is shown to be feasible; if CO and O2 are comparable in abundance in clouds similar to the Taurus molecular cloud or in giant molecular clouds, the brightness temperature is predicted to be 0.1 K.

Black, J. H.↗