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Pericynthion altitude of selenocentric orbits determined from angular rate of line of sight with respect to prominant lunar surface features along ballistic trajectories
Amplitude variations over a 12.9 km terrestrial line-of-sight path were measured simultaneously on a 1400 lambda and a 29 lambda antenna at 86.16 GHz. Clear atmosphere data from two occasions with considerably different meteorological conditions are presented. Both sets have statistical and spectral parameters in good agreement with turbulence theory. Some of the data taken after a thunderstorm front passage show a slow gain reduction of the large antenna of up to 2 dB and an increase in variance to a level above that of the small antenna. The power spectral density of these data reveals that the excess fluctuation power is in the region of the spectrum which turbulence theory predicts to be flat. It shows an approximate 1/f dependence. It is attributed to refractive bending of up to 0.025 deg. Gain reductions due to turbulence or turbulence induced angle-of-arrival variations were estimated to be negligible.
Chemical abundances and physical conditions in the interstellar gas toward Omicron Per are analyzed using Copernicus UV spectrophotometric data on 69 lines due to ions and atoms as well as 19 lines of H2 and HD. The UV extinction toward the star is determined along with the column densities of atomic and molecular hydrogen, the atomic column densities and temperature in the H I region, and the nature of the ionized regions along the line of sight. It is concluded that: (1) Omicron Per is apparently embedded in the near edge of an extended dense molecular cloud, the outer parts of which give rise to the observed absorption lines; (2) the H I region may consist of more than one cloud; (3) the far-UV extinction rise is unusually steep, indicating a high proportion of small grains; (4) the element depletions are somewhat greater than in Zeta Oph, particularly for sulfur and argon; and (5) the molecular abundances are generally consistent with gas-phase formation models rather than with molecular formation on grain surfaces, unless a substantial amount of small grains is present to increase the available surface area.
The upcoming Vera Rubin Observatory Legacy Survey of Space and Time (LSST) will dramatically increase the number of strong gravitational lensing systems, requiring precise modeling of line-of-sight (LOS) effects to mitigate biases in lensing observations and cosmological inferences. We develop a method to construct joint distributions of external convergence (κ ext ) and shear (γ ext ) for strong lensing LOS by aggregating large-scale structure simulations with high-resolution halo renderings and non-linear correction. Our approach captures both smooth background matter and perturbations from halos, enabling accurate modeling of LOS effects. Here, we apply non-linear LOS corrections to κ ext and γ ext that address the non-additive lensing effects caused by objects along the LOS in strong lensing. We find that, with a minimum image separation of 1.0'', non-linear LOS correction due to the presence of a dominant deflector slightly increases the ratio of quadruple to double lenses; this non-linear LOS correction also introduces systematic biases of ∼ 0.1% for galaxy-AGN lens in the inferred Hubble constant (H 0 ) if not accounted for. We also observe a 0.66% bias for galaxy-galaxy lenses on H 0 , and even larger biases 1.02% for galaxy-AGN systems if LOS effects are not accounted for. These results highlight the importance of LOS for precision cosmology. The publicly available code and datasets provide tools for incorporating LOS effects in future analyses.
High resolution IUE spectra of SN 1993J in M81 show the existence of several clouds on the line of sight. These include local galactic gas at 0 km/s, gas in M81 at -130 km/s, a cloud in the halo in of the Milky Way near -45 km/s, and an intergalactic cloud near +140 km/s. Arguments for each of these locations are given. There is little gas in M81 in front of SN 1993J and no detectable CIV at or near -130 km/s. The gas of the halo of the Milky Way shows a large amount of CIV and SiIV. The intergalactic cloud shows a large velocity width extending from +100 km/s to +200 km/s and is very prominent in the absorption lines of AlIII, SiIV, and CIV. It may be related to energetic events in the M81 group galaxies.
The earliest IUE high-resolution spectra of SN 1987A have been studied and reveal the presence of several clouds in the line of sight to the LMC. In particular, there are two clouds with radial velocities of about 130 km/s and about 180 km/s. These clouds' velocities are between those of Galactic clouds at 0-80 km/s and those of LMC gas at about 270 km/s. Chemical-abundance determinations may help to determine the origin and location of these clouds. Curve-of-growth analysis and 21-cm observations show that they may be underabundant in heavy elements by about a factor of 2 as compared to solar abundances. No depletion indicative of grain formation can be seen.
Optimal estimation of atmospheric temperature and composition from limb sounding observations is extended to the direct retrieval of line-of-sight atmospheric structure that can be obtained in certain limb viewing geometries.
UAS Traffic Management (UTM) is a rapidly evolving space with increasing demand for regulation surrounding more complex operations. Beyond visual line of sight (BVLOS) operations are among these complex operations. The NASA UTM BVLOS sub-project is focusing on enabling more routine BVLOS operations through data collection for support of standards formulation. The Multi Operator Technology Assessment (MOTA) simulation is one of these activities that collects data on BVLOS operations within the same geographical area while sharing operational intents through a USS. Data collected includes workload, situation awareness, and usability on nominal and off-nominal operations. Results of this study are intended to provide recommendations for standards as well as provide insight on improvements to the systems under test. NASA intends to incorporate those improvements into their operations to support and updated BVLOS waiver from the FAA’s Near-Term Approval Process (NTAP).
UAS Traffic Management (UTM) is a rapidly evolving space with increasing demand for regulation surrounding more complex operations. Beyond visual line of sight (BVLOS) operations are among these complex operations. The NASA UTM BVLOS sub-project is focusing on enabling more routine BVLOS operations through data collection for support of standards formulation. The Multi Operator Technology Assessment (MOTA) simulation is one of these activities that collects data on BVLOS operations within the same geographical area while sharing operational intents through a USS. Data collected includes workload, situation awareness, and usability on nominal and off-nominal operations. Results of this study are intended to provide recommendations for standards as well as provide insight on improvements to the systems under test. NASA intends to incorporate those improvements into their operations to support and updated BVLOS waiver from the FAA’s Near-Term Approval Process (NTAP).
Mission analysis of Mars soft landing with line- of-sight communication between flyby bus and entry capsule - atmospheric entry
Observations of a few moderately reddened (0.3 is less than E(B-V) is less than 0.6) lines of sight through the outer edges of truly dense molecular clouds, not only show the overall depletions in these clouds to be as much as 0.5 (dex) greater than in comparably reddened diffuse clouds, but reveal a possible tendency for certain species to deplete preferentially. Possible methods of depletions are discussed.
This study evaluates a traffic management concept designed to enable simultaneous operations of multiple small unmanned aircraft systems (UAS) in the national airspace system (NAS). A five-day flight-test activity is described that examined the feasibility of operating multiple UAS beyond visual line of sight (BVLOS) of their respective operators in the same airspace. Over the five-day campaign, three groups of five flight crews operated a total of eleven different aircraft. Each group participated in four flight scenarios involving five simultaneous missions. Each vehicle was operated BVLOS up to 1.5 miles from the pilot in command. Findings and recommendations are presented to support the feasibility and safety of routine BVLOS operations for small UAS.
A topside ionospheric model (Bent Ionospheric Model) was developed for an accurate prediction of integrated total electron content (TEC), from a global data acquired for the years 1962 to 1969. In this paper the effects of line-of-sight electron density gradients on ground to satellite measurements are discussed. The results of analyses show that in the presence of increasing density gradients, deduced values of vertical electron content or slab thicknesses will be too large, while for decreasing gradients these values will be smaller than they should be.
This study evaluates a traffic management concept designed to enable simultaneous operations of multiple small unmanned aircraft systems (UAS) in the national airspace system (NAS). A five-day flight-test activity is described that examined the feasibility of operating multiple UAS beyond visual line of sight (BVLOS) of their respective operators in the same airspace. Over the five-day campaign, three groups of five flight crews operated a total of eleven different aircraft. Each group participated in four flight scenarios involving five simultaneous missions. Each vehicle was operated BVLOS up to 1.5 miles from the pilot in command. Findings and recommendations are presented to support the feasibility and safety of routine BVLOS operations for small UAS.
Several physical and observational effects contribute to the significant imbalances of magnetic flux that are often observed in active regions. We consider an effect not previously treated: the influence of electric currents in the photosphere. Electric currents can cause a line-of-sight flux imbalance because of the directionality of the magnetic field they produce. Currents associated with magnetic flux tubes produce larger imbalances than do smoothly-varying distributions of flux and current. We estimate the magnitude of this effect for current densities, total currents, and magnetic geometry consistent with observations. The expected imbalances lie approximately in the range 0-15%, depending on the character of the current-carying fields and the angle from which they are viewed. Observationally, current-induced flux imbalances could be indicated by a statistical dependence of the imbalance on angular distance from disk center. A general study of magnetic flux balance in active regions is needed to determine the relative importance of other- probably larger- effects such as dilute flux (too weak to measure or rendered invisible by radiative transfer effects), merging with weak background fields, and long-range connections between active regions.
The nature of dust-gas interactions, which are capable of modifying the size distribution of interstellar grains and thus causing changes in the selective extinction curve, are investigated through depletion studies. The gaseous abundances of 15 elements have been determined for several lines of sight toward moderately reddened stars, each having an anomalous extinction curve and a large abundance of cyanogen (CN). The basic result of this study is that certain elements appear to deplete preferentially in interstellar clouds having a large abundance of CN. Since CN is a sensitive indicator of the interstellar spatial density, the data might suggest that the unique pattern of enhanced depletion observed here represents the best observational evidence of accretion.
During the summer of 1984 the Marshall Space Flight Center's Airborne Doppler Lidar System (ADLS) made a series of wind measurements in the California Central Valley. This study quantifies the lidar beam angle errors and velocity errors through analysis of ground return signals. Line-of-sight elevation (LOSE) angle errors are under 1 deg. Apparent Doppler ground velocities, as large as 2m/s, are considerably less than in a previous flight experiment in 1981. No evidence was found of a Schuler resonance phenomenon common to inertial navigation systems (INS), however the aperiodic nature of the apparent velocities implies an error in the INS-derived ground speeds. Certain features and subtleties in the ground returns are explained in terms of atmospheric structure and characteristics of the ADLS hardware and software. Finally, least squares and low-pass filtering techniques are suggested for eliminating errors during post-processing.
The Goddard High Resolution Spectrograph aboard the Hubble Space Telescope was used with the G160M grating to obtain high-resolution (6.2 A) spectra of three very bright active galactic nuclei located behind voids in the nearby distribution of bright galaxies (i.e., CfA and Arecibo redshift survey regions). A total of eight definite (greater than or equal to 4 sigma) Ly(alpha) absorption lines were discovered ranging in equivalent width from 26 to 240 mA at Galactocentric velocities 1740-7740 km/s. Of these eight systems, we locate seven in supercluster structures and one, in the sight line of Mrk 501 at 7740 km/s, in a void. In addition, one of two tentative (3-4 sigma) Ly(alpha) absorption lines are found in voids. Thus, the voids are not entirely devoid of matter, and not all Ly(alpha) clouds are associated with galaxies. Also, since the path lengths through voids and superclusters probed by our observations thus far are nearly equal, there is some statistical evidence that the Ly(alpha) clouds avoid the voids. The nearest galaxy neighbors to these absorbing clouds are 0.45-5.9 Mpc away, too far to be physically associated by most models. The lower equivalent width absorption lines (W(sub lambda) less than or equal to 100 mA) are consistent with random locations with respect to galaxies and may be truly intergalactic, similar to the bulk of the Ly(alpha) forest seen at high z. These results on local Ly(alpha) clouds are in full agreement with those found by Morris et al. (1993) for the 3C 273 sight line but are different from the results for higher equivalent width systems where closer cloud-galaxy associations were found by Lanzetta et al. (1994). Pencil-beam optical and 21 cm radio line observations of the area of sky surrounding Mrk 501 fail to find faint galaxies near the velocities of the Ly(alpha) clouds in that sight line. Specifically, for the 'void absorption' system at 7740 km/s, we find no galaxy at comparable redshift to the absorber within 100 h(sub 75)(sup -1) kpc (H(sub 0) = 75 h(sub 75) km/s Mpc(sup -1)) with an absolute magnitude of B less than or equal to - 16 and no object with H I mass greater than or equal to 7 x 10(exp 8) h(sub 75)(sup -2) M(solar) within 500 h(sub 75)(sup -1) kpc. Thus, neither a faint optical galaxy nor a gas-rich, optically dim or low surface brightness galaxy is present close to this absorber.