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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1976

Surface roughness estimation at three points on the lunar surface using 23-CM monostatic radar

Differences in quasi-specular scattering by the lunar surface have been observed at 23-cm wavelength by using earth-based radar. By taking advantage of libration, three subradar points were isolated, and distinct scattering laws were identified for terrain near Hipparchus, Sinus Medii, and the crater Schroeter F. Interpretations of lunar radar data should henceforth incorporate a recognition that these variations take place. Unidirectional rms surface slope estimates of 6-8 deg in the Central Highlands and 4-5 deg in old mare are appropriate to horizontal scales of 100 m.

Simpson, R. A.↗
NASA NTRS1976

A program of data synthesis from the ALSEP/CPLEE ALSEP/SIDE, and Explorer 35 magnetometer to investigate lunar terminator and nightside particle fluxes and surface interactions

Lunar nightside electron fluxes were studied with the aid of the ALSEP/CPLEE and other instruments. The flux events were shown to be due to (a) electrons propagating upstream from the earth's bow shock, (b) electrons thermalized and scattered to the lunar surface by disturbances along the boundary of the lunar solarwind cavity, and (c) solar wind electrons scattered to the lunar surface by lunar limb shocks and/or compressional disturbances. These electrons were identified as a cause of the high night surface negative potentials observed in tha ALSEP/SIDE ion data. A study was also made of the shadowing of magnetotail plasma sheet electrons by interactions between the lunar body and the ambient magnetic field and by interactions between charged particles and lunar remnant magnetic fields. These shadowing effects were shown to modify lunar surface and near-lunar potential distributions.

Reasoner, D. L.↗
NASA NTRS1974

Evidence for a high altitude distribution of lunar dust

The crew of Apollo 17 saw streamers accompanying spacecraft sunrise. The time variations of the brightness of these streamers indicate that they were produced by light scattering in the lunar vicinity rather than brightness variations of material streamers emanating from the sun. The angular extent of the streamers indicate that the light scattering particulates extended from the lunar surface to above the orbital altitude of the spacecraft. Although observed as typical sunrise phenomena by Apollos 10 and 17, and possibly by 8 and 15 as well, streamers were not observed during the flight of Apollo 16. The scattering particles seem to be present sporadically, most likely lunar dust of tenth micron scale, and not a result of spacecraft contamination.

Mccoy, J. E.↗
NASA NTRS1961

Scatter Theories and Their Application to Lunar Radar Return

The research work being done under this NASA grant is divided into the following three categories: (1) An estimate of the radar return for the NASA Aerobee rocket shot at White Sands Missile Range. (WSMR) (2) Development of new scatter theories, modification and correlation of existing scatter theories, and application of the theories to moon-echo data for estimation of the surface features of the moon. (3) Acoustic modeling of the lunar surface and correlation of the theoretical with both full scale and acoustical experimental results.

Hayre, H. S.↗
NASA NTRS1989

Transport dynamics calculated under the full Mie scattering theory for micron and submicron lunar ejecta in selenocentric, cislunar, and geocentric space

In 1967, Lunar Explorer 35 was launched from the earth and placed into a stable orbit around the moon. The data from the dust particle experiment on this spacecraft were essentially continuous over a 5-yr period from the time of insertion in lunar orbit. Analysis of this data has been interpreted to show that micron-sized lunar ejecta leave the moon and traverse through selenocentric and cislunar space and obtain either interplanetary/heliocentric orbits or intercept the earth's magnetosphere and move into geocentric orbits. Extensive studies of the orbital trajectories of lunar particles in this size range have now been conducted that include a calculation of the solar radiation force using the full Mie scattering theory. A significant flux of particles with radii less than 0.1 micron are found to intercept the earth's magnetopause surface. This flux is shown to be strongly dependent upon both the particle's density and its index of refraction.

Hyde, T. W.↗
NASA NTRS2002

The Lunar Phase Curve in the Near Ultraviolet

We present results from an ongoing program to perform UV measurements (215.0 and 237.0 nm) of the Moon at varying solar phase angles to understand the lunar phase curve at ultraviolet wavelengths. We use new observations from the Ultraviolet Spectrometer (UVS) aboard the Student Nitric Oxide Explorer (SNOE) combined with existing observations from the Galileo UVS. The lunar UV phase curve can be used to further understand the scattering properties of the lunar surface. The Moon's scattering properties at visible wavelengths are well understood; studying scattering properties at shorter wavelengths may provide insight into the roles of volume scattering vs. surface scattering and how weathering processes may affect scattering properties. The UV lunar phase curve can also be helpful for UV observers, as the Moon is often used as a UV calibration source, but the UV brightness variation with phase angle has not been well understood.

Hendrix, A. R.↗
NASA NTRS1992

A Ground-based Search for Lunar Resources Using High-resolution Imaging in the Infrared

When humans return to the Moon, lunar resources will play an important role in the successful deployment and maintenance of the lunar base. Previous studies have illustrated the abundance of resource materials available on the surface of the Moon, as well as their ready accessibility. Particularly worth considering are the lunar regional (2,000-30,000 sq km) pyroclastic deposits scattered about the lunar nearside. These 30-50-m-thick deposits are composed of fine-grained unconsolidated titanium- and iron-rich mafic glasses and may be used as bulk feedstock for the beneficiation of oxygen, iron, titanium, sulfur, and other solar wind gases, or simply used as is for construction and shielding purposes. A groundbased observing survey of the resource-rich regions on the lunar nearside using a new imaging technique designed to obtain much higher resolution images, and more precise compositional analyses than previously obtainable is proposed.

Coombs, C. R.↗
NASA NTRS1979

Lunar radar backscatter studies

The lunar surface material in the Plato area is characterized using Earth based visual, infrared, and radar signatures. Radar scattering in the lunar regolith with an existing optical scattering computer program is modeled. Mapping with 1 to 2 km resolution of the Moon using a 70 cm Arecibo radar is presented.

Thompson, T. W.↗
NASA NTRS2012

Radar Scattering and Block Size Properties of Lunar Crater Ejecta From Mini-RF and LROC NAC Data

A major objective of the Mini-RF experiment is to distinguish lunar surfaces that may contain water/ice deposits [1,2]. Better understanding of the backscattering properties of craters of varying age and size is crucial for interpreting data received from the Mini-RF. The Mini-RF transmits a circularly polarized RF electromagnetic energy and coherently receives orthogonal linear polarization echoes [1]. The Mini- RF maps in two separate bands ( =12.6 and 4.5 cm) at a high resolution mode of 30 m/pixel [1]. Given the variables mentioned, the four stokes parameters are reconstructed. The Circular Polarization Ratio (CPR) is calculated for the purposes of understanding subsurface and surface roughness. The CPR is determined from reflections acquired from the ratio of power of the transmitted radio wave in same sense to the reflected radio wave in the opposite sense [1]. Ice in the permanently shadowed regions (PSRs) would be transparent to radar, but the inclusions of materials and imperfections would cause the radio wave to reflect multiple times [3], enhancing the number of same sense reflections and increasing the CPR. In addition, ice also displays the coherent backscatter opposition effect (CBOE), an interferrometric addition of same sense backscatter that further increases the CPR of ice targets [7]. High CPR values also correlate to multiple reflections and are typically associated with very rough surfaces [3]. The average dry lunar surface has a CPR in the range of 0.2-0.4 at 48deg incidence [3]. The purpose of this study is to begin to quantify degrees of surface wavelength-scale roughness with CPR and to understand how such surface roughness is created and gradually destroyed by erosion on the lunar surface. Another goal is to identify and isolate the possible causes of high CPR within the shadowed areas of anomalous polar craters [3]. All the studied craters are non-polar, so that we can see into their interiors in NAC images. The idea is to understand what controls blockiness in these craters so that we can rule out rocks (and rule in ice) for the anomalous polar dark ones [3].

Spudis, P. D.↗
NASA NTRS1978

Radar scattering laws and wavelength dependence of the lunar surface

Data from Apollo lunar bistatic radar experiments have been processed to give probability density functions for surface slopes. These show best agreement with a Hagfors scattering law, though data having both gaussian and exponential characteristics also exist. Surface roughness estimates range from 4 deg in maria to at least 8 deg in highlands, values which are appropriate to 25 m horizontal scales and which are areal averages over tens of square kilometers. Roughness varies with wavelength, most strongly in maria.

Simpson, R. A.↗
NASA NTRS1981

Seismic codas on the earth and the moon - A comparison

The seismic codas, representing that part of the seismogram following the arrival of the surface waves or the direct S waves, characteristic of the earth and moon are compared with regard to the implications of coda characteristics for scattering and attenuation. Scattering models based on single S-S scatter theory, in which seismic energy in the coda is assumed to be S waves that have undergone only one scattering without conversion, and on diffusion theory, which assumed that energy in the coda has been scattered many times, are examined, and situations where the single-scattering and multiple-scattering theories are applicable are distinguished by the ratio of attenuation distance to the scattering mean free path. Values of the attenuation distance and the mean free path derived from coda studies for the earth and moon are compared, and it is found that for the frequency range 0.5-10 Hz, diffusion scattering is important in lunar codas, while at frequencies from 1 to 25 Hz single scattering is important in terrestrial codas. It is pointed out that attenuation acts to eliminate scattering paths much longer than the attenuation length. The observed differences between terrestrial and lunar codas are thus attributed to lesser attenuation and greater scattering on the moon.

Dainty, A. M.↗
NASA NTRS1975

Continued support in the study of lunar and planetary surfaces

Radar observations of various planetary surfaces are discussed. A radar investigation of Mars was conducted in conjunction with the Viking landing site selection process. Quasi-specular scattering from the lunar surface was interpreted in terms of horizonal scale dependence upon observing wavelengths. Furthermore, the effect of the extremely high temperatures encountered on the surface of Venus upon the dielectric constant of geophysical materials, and hence on the interpretation of radar results, was considered. The use of radio and radar techniques for the study of Saturns rings was also investigated.

Howard, H. T.↗