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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 253 records · Page 14
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Exploring the fine structure at the limb in coronal holes

The fine structure of the solar limb in coronal holes is explored at temperatures ranging from 10(exp 4) to 10(exp 6) K. An image enhancement algorithm orignally developed for solar eclipse observations is applied to a number of simultaneous multiwavelength observations made with the Harvard Extreme Ultraviolet Spectrometer experiment on Skylab. The enhanced images reveal the presence of filamentary structures above the limb with a characteristic separation of approximately 10 to 15 sec . Some of the structures extend from the solar limb into the corona to at least 4 min above the solar limb. The brightness of these structures changes as a function of height above the limb. The brightest emission is associated with spiculelike structures in the proximity of the limb. The emission characteristic of high-temperature plasma is not cospatial with the emission at lower temperatures, indicating the presence of different temperature plasmas in the field of view.

Karovska, Magarita↗
NASA NTRS2008

Measuring the Electron Temperature in the Corona

We report on an experiment to demonstrate the feasibility of a new method to obtain the electron temperature and flow speed in the solar corona by observing the visible Kcoronal spectrum during the total solar eclipse on 29 March 2006 in Libya. Results show that this new method is indeed feasible, giving electron temperatures and speeds of 1.10 $\pm$ 0.05 MK, 103.0 $\pm$ 92.0 $kmsA{-l}$; 0.98 $\pm$ 0.12 MK, 0.0 + 10.0 $kmsA{-1)s; 0.70 $\pm$ 0.08 MK, 0.0 + 10.0 $kmsA{-l)$ at l.l{\it R)$ {\odot}$ in the solar north, east and west, respectively, and 0.93 $\pm$ 0.12 MK, 0.0 + 10.0 $kmsA{-l}$ at 1.2{\it R}$ {\odot}$ in the solar east. This new technique could be easily used from a space-based platform in a coronagraph to produce two dimensional maps of the electron temperature and bulk flow speed at the base of the solar wind useful for the study of heliospheric structure and space weather.

Davila, Joseph↗
NASA NTRS1977

The Lyman alpha coronagraph

The rocket-borne Lyman alpha coronagraph (RLAC) is to be used in the absence of a natural solar eclipse to determine coronal temperatures from measurements of the line width of Lyman-alpha and to determine neutral hydrogen densities of coronal material from the absolute intensity. The coronagraph consists of a 75-cm Fastie-Ebert scanning spectrometer with an AMR 641 photoelectric detection system, an off-axis parabolic primary mirror, and an occulting system. A special optical arrangement achieves rejection of radiation from the solar disk.

Kohl, J. L.↗
NASA NTRS2011

A Model fot the Sources of the Slow Solar Wind

Models for the origin of the slow solar wind must account for two seemingly contradictory observations: the slow wind has the composition of the closed-field corona, implying that it originates from the continuous opening and closing of flux at the boundary between open and closed field. On the other hand, the slow wind also has large angular width, up to approx.60deg, suggesting that its source extends far from the open-closed boundary. We propose a model that can explain both observations. The key idea is that the source of the slow wind at the Sun is a network of narrow (possibly singular) open-field corridors that map to a web of separatrices and quasi-separatrix layers in the heliosphere. We compute analytically the topology of an open-field corridor and show that it produces a quasi-separatrix layer in the heliosphere that extends to angles far from the heliospheric current sheet. We then use an MHD code and MDI/SOHO observations of the photospheric magnetic field to calculate numerically, with high spatial resolution, the quasi-steady solar wind, and magnetic field for a time period preceding the 2008 August 1 total solar eclipse. Our numerical results imply that, at least for this time period, a web of separatrices (which we term an S-web) forms with sufficient density and extent in the heliosphere to account for the observed properties of the slow wind. We discuss the implications of our S-web model for the structure and dynamics of the corona and heliosphere and propose further tests of the model. Key words: solar wind - Sun: corona - Sun: magnetic topology

Antiochos, S. K.↗
NASA NTRS2021

Detection of Anomalies in the UV/Vis Reflectances from the Ozone Monitoring Instrument

Various instrumental or geophysical artifacts, such as saturation, stray light, or obstruction of light (either coming from the instrument or related to solar eclipses), negatively impact satellite measured ultraviolet and visible Earthshine radiance spectra and downstream retrievals of atmospheric and surface properties derived from these spectra. In addition, excessive noise such as from cosmic ray impacts, prevalent within the South Atlantic Anomaly, can also degrade satellite radiance measurements. Saturation specifically pertains to observations of very bright surfaces such as sun glint over open water or thick clouds. When saturation occurs, additional photoelectric charge generated at the saturated pixel may overflow to pixels adjacent to a saturated area and be reflected as a distorted image in the final sensor output.When these effects cannot be corrected to an acceptable level for science quality retrievals, flagging of the affected pixels is indicated. Here, we introduce a straightforward detection method that is based on the correlation, r, between the observed Earthshine radiance and solar irradiance spectraover a 10 nm-spectral range; our Decorrelation Index (DI for brevity) is simply defined as DI=1-r. DI increases with anomalous additive effects or excessive noise in either radiances, the most likely cause indata from theOzone Monitoring Instrument (OMI),or irradiances. DI is relatively straight-forward to use and interpret and can be 20computed for different wavelength intervals. We developed a set of DIs for two spectral channelsof the OMI, a hyperspectral pushbroom imaging spectrometer. For each OMI spatial measurement, we define 14 wavelength-dependent DIs within the OMI visible channel (350-498 nm) and 6 DIs in its ultraviolet 2 (UV2) channel (310-370 nm). As defined, DIs reflect a continuous range of deviations of observed spectra from the reference irradiance spectrum that are complementary to the binary Saturation Possibility Warning (SPW) flags currently provided for each individual spectral/spatial pixel in the OMI radiance data set. Smaller values of DI are also caused by a number of geophysical factors; this allows one to obtain interesting physical results on the global distribution of spectral variations.

Space sensor↗
NASA NTRS1967

Surveyor III A preliminary report

Near the eastern shore of Oceanus Procellarum, 390 miles from Surveyor I, stands Surveyor III, now motionless and silent after a full lunar day's work during which the spacecraft transmitted to Earth 6315 photographs of its surroundings. A surface sampler, operated by command from the Earth and in view of Surveyor's television camera, conducted many tests of the character and structure of the lunar surface material, as well as digging four trenches. While Surveyor I put man's eyes on the Moon, Surveyor III added an arm and a hand with which to work. In this mission, Surveyor displayed remarkable adaptability and stability. Because the engines did not cut off before touchdown, the spacecraft in effect made three separate landings, giving information on surface bearing strength in several places. The spacecraft came to rest at an angle of about 14° from the vertical, well below the rim of a crater, making possible a detailed study of the floor and walls of a small lunar crater. The tilted position of the spacecraft also made it possible to obtain, for the first time from the surface of the Moon, photographs of a solar eclipse, and of the Earth in color. This report presents the preliminary findings from Surveyor III of the team of scientists and engineers of the Surveyor Program.

Surface property↗
NASA NTRS1969

Analysis of Surveyor Data, 1 July 1968 - 30 June 1969

This report presents some of the results of the extended postflight analysis of Surveyor data for the thermal, physical, and mechanical properties of the lunar surface, the photometric and polarimetric properties of the earth, and the colorimetric measurements of the solar eclipse and earth. Also presented are the optical systems and alignment procedures used in the Surveyor VI1 Laser Pointing Test.

Source record↗
NASA NTRS1971

The shadow band phenomenon

Shadow band phenomenon observed during solar eclipses and visible only minutes preceeding and following totality

Daly, C. J.↗