Earth-based 12.6-cm wavelength radar mapping of the Moon: New views of impact melt distribution and mare physical properties     

Bruce A. Campbell  Lynn M. Carter  Michael Nolan  Rebecca R. Ghent  Ross F. Anderson 《Icarus》2010,208(2):565-181

We present results of a campaign to map much of the Moon’s near side using the 12.6-cm radar transmitter at Arecibo Observatory and receivers at the Green Bank Telescope. These data have a single-look spatial resolution of about 40 m, with final maps averaged to an 80-m, four-look product to reduce image speckle. Focused processing is used to obtain this high spatial resolution over the entire region illuminated by the Arecibo beam. The transmitted signal is circularly polarized, and we receive reflections in both senses of circular polarization; measurements of receiver thermal noise during periods with no lunar echoes allow well-calibrated estimates of the circular polarization ratio (CPR) and the four-element Stokes vector. Radiometric calibration to values of the backscatter coefficient is ongoing. Radar backscatter data for the Moon provide information on regolith dielectric and physical properties, with particular sensitivity to ilmenite content and surface or buried rocks with diameter of about one-tenth the radar wavelength and larger.Average 12.6-cm circular polarization ratio (CPR) values for low- to moderate-TiO₂ mare basalt deposits are similar to those of rough terrestrial lava flows. We attribute these high values to abundant few-centimeter diameter rocks from small impacts and a significant component of subsurface volume scattering. An outflow deposit, inferred to be impact melt, from Glushko crater has CPR values near unity at 12.6-cm and 70-cm wavelengths and thus a very rugged near-surface structure at the decimeter to meter scale. This deposit does not show radar-brightness variations consistent with levees or channels, and appears to nearly overtop a massif, suggesting very rapid emplacement. Deposits of similar morphology and/or radar brightness are noted for craters such as Pythagoras, Rutherfurd, Theophilus, and Aristillus. Images of the north pole show that, despite recording the deposition of Orientale material, Byrd and Peary craters do not have dense patterns of radar-bright ejecta from small craters on their floors. Such patterns in Amundsen crater, near the south pole, were interpreted as diagnostic of abundant impact melt, so the fraction of Orientale-derived melt in the north polar smooth plains, 1000 km farther from the basin center, is inferred to be much lower.  相似文献   

How to survive a Lunar night     

Stephan Ulamec  Jens Biele  Ed Trollope 《Planetary and Space Science》2010,58(14-15):1985-1995

In the frame of the recent worldwide activities of Lunar research, including various studies for surface stations, the aspect of longevity of such stations has been identified as a particular technical challenge. The reason for this lies in the long (about 14 days) and cold Lunar night during which it is non-trivial to keep spacecraft systems alive and sensitive equipment within an acceptable temperature range.The following paper analyzes and compares various concepts to survive Lunar night, both with and without radioisotope heater technology.The latter normally implies the use of highly toxic material (typically plutonium), which is politically problematic and a driver for cost and safety procedures.Concepts without radioisotope heating need to foresee special measures, like extremely efficient thermal insulation or sub-surface positioning of all temperature sensitive components.Special emphasis has been taken on the thermal analysis of a penetrator-type surface station. The relevant issues are discussed and results for day–night cycles are presented, assuming a typical set of engineering parameters. This concept appears to be the easiest to implement from a thermal point of view, if the use of radioisotope heaters has to be avoided.  相似文献   

Geometry and pressure-temperature significance of the kyanite-sillimanite isograd in the Mica Creek area,British Columbia     

Edward D. Ghent  Philip S. Simony  Clifford C. Knitter 《Contributions to Mineralogy and Petrology》1980,74(1):67-73

Late Precambrian and Lower Paleozoic metapelitic rocks near Mica Creek, British Columbia, range in metamorphic grade from biotite zone to sillimanite zone. The kyanite-sillimanite isograd was established after phase 2 folding but was deformed by phase 3 folding. Topographic relief of about 2 km, combined with phase 3 folding, permits reasonably precise determination of the geometry of the isogradic surfaces. The effects of phase 3 folding have been accounted for and the isobaric surfaces at the time of metamorphism are inferred to have been dipping gently. Using the kyanite-sillimanite experimental phase diagram, intersection of the isobars and the isograd permits estimates of differences in temperature and pressure along a cross section. These estimates are about 400 bars and 20° C. Mineral geothermometry (garnet-biotite) and geobarometry (garnetplagioclase-Al ₂SiO₅-quartz) does not provide a fine enough resolution to detect these predicted differences.  相似文献   

Editorial: The Future of Mathematical Geology     

Michael Ed. Hohn 《Mathematical Geology》1998,30(1):1-3

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RXTE spectroscopy of GRS 1915+105     

Jochen Greiner  Ed H. Morgan  Ron A. Remillard 《New Astronomy Reviews》1998,42(9-10)

The galactic superluminal motion source GRS 1915+105 has been extensively observed with the RXTE satellite over the last two years. More than 250 RXTE pointings have been performed until mid-May 1998 with more than 1.5 Msec exposure time on roughly a weekly basis. Here we report on first results of our spectral analysis of a major part of these pointed RXTE observations. We establish the existence of at least 5 spectral components and present the changes of these components over the last two years.  相似文献   

Book reviews     

Michael Ed. Hohn  Melanie A. Wetzel  James R. Carr  W. E. Sharp  C. John Mann 《Mathematical Geosciences》1995,27(2):301-313

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Wet deposition of ammonium in Europe   总被引：2，自引：0，他引：2  

Ed Buijsman  Jan-Willem Erisman 《Journal of Atmospheric Chemistry》1988,6(3):265-280

Ammonium concentration data in precipitation have been compiled to derive a concentration and deposition field for ammonium in Europe. Measurements referring to a total number of 218 measuring sites have been considered. Because of changes in the ammonium concentrations due to the use of improper sampling procedures, a correction procedure is proposed. This makes allowance for the type of sampler used, the length of the sampling period, and whether or not light-protected sample bottles are used. Dependent on the specific sampling procedure used correction factors range from 0.75 to 1.20. According to our calculations, the total wet deposition flux of ammonium in Europe in the early 1980s amounts to 2.4 Mt NH₄ ⁺y^-1. However, for some parts of Europe the flux cannot be estimated very reliably because of the low number or even the absence of measuring sites. Compared to earlier estimates for around 1960, the ammonium wet deposition flux has increased by approximately 25% during the period 1960–1980.  相似文献   

Conditions and timing of high-pressure Variscan metamorphism in the South Carpathians, Romania   总被引：2，自引：0，他引：2  

Gordon Medaris Jr.  Mihai Ducea  Ed Ghent  Viorica Iancu 《Lithos》2003,70(3-4):141-161

High-pressure (HP) metamorphic rocks, including garnet peridotite, eclogite, HP granulite, and HP amphibolite, are important constituents of several tectonostratigraphic units in the pre-Alpine nappe stack of the Getic–Supragetic (GS) basement in the South Carpathians. A Variscan age for HP metamorphism is firmly established by Sm–Nd mineral–whole-rock isochrons for garnet amphibolite, 358±10 Ma, two samples of eclogite, 341±8 and 344±7 Ma, and garnet peridotite, 316±4 Ma.

A prograde history for many HP metamorphic rocks is documented by the presence of lower pressure mineral inclusions and compositional zoning in garnet. Application of commonly accepted thermobarometers to eclogite (grt+cpx±ky±phn±pg±zo) yields a range in “peak” pressures and temperatures of 10.8–22.3 kbar and 545–745 °C, depending on tectonostratigraphic unit and locality. Zoisite equilibria indicate that activity of H₂O in some samples was substantially reduced, ca. 0.1–0.4. HP granulite (grt+cpx+hb+pl) and HP amphibolite (grt+hbl+pl) may have formed by retrogression of eclogites during high-temperature decompression. Two types of garnet peridotite have been recognized, one forming from spinel peridotite at ca. 1150–1300 °C, 25.8–29.0 kbar, and another from plagioclase peridotite at 560 °C, 16.1 kbar.

The Variscan evolution of the pre-Mesozoic basement in the South Carpathians is similar to that in other segments of the European Variscides, including widespread HP metamorphism, in which P–T–t characteristics are specific to individual tectonostratigraphic units, the presence of diverse types of garnet peridotite, diachronous subduction and accretion, nappe assembly in pre-Westphalian time due to collision of Laurussia, Gondwana, and amalgamated terranes, and finally, rapid exhumation, cooling, and deposition of eroded debris in Westphalian to Permian sedimentary basins.  相似文献   

Rough seas and time-lapse seismic     

Robert Laws  Ed Kragh 《Geophysical Prospecting》2002,50(2):195-208

Time‐lapse seismic surveying has become an accepted tool for reservoir monitoring applications, thus placing a high premium on data repeatability. One factor affecting data repeatability is the influence of the rough sea‐surface on the ghost reflection and the resulting seismic wavelets of the sources and receivers. During data analysis, the sea‐surface is normally assumed to be stationary and, indeed, to be flat. The non‐flatness of the sea‐surface introduces amplitude and phase perturbations to the source and receiver responses and these can affect the time‐lapse image. We simulated the influence of rough sea‐surfaces on seismic data acquisition. For a typical seismic line with a 48‐fold stack, a 2‐m significant‐wave‐height sea introduces RMS errors of about 5–10% into the stacked data. This level of error is probably not important for structural imaging but could be significant for time‐lapse surveying when the expected difference anomaly is small. The errors are distributed differently for sources and receivers because of the different ways they are towed. Furthermore, the source wavelet is determined by the sea shape at the moment the shot is fired, whereas the receiver wavelet is time‐varying because the sea moves significantly during the seismic record.  相似文献   

Editorial     

G. Hasinger  K.-H.-Rdler  Ed v. d.Heuvel 《Astronomische Nachrichten》1996,317(1):1-1

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