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Robert A. West Martin G. Tomasko Bradford A. Smith Mahendra P. Wijesinghe Lyn R. Doose Harold J. Reitsema Stephen M. Larson 《Icarus》1982,51(1):51-64
We present spatially resolved measurements of Saturn's absolute reflectivity in methane bands at 6190, 7250, and 8900 Å and in nearby continuum regions. Images were obtained through narrow-band interference filters with a 500 × 500-pixel charge-coupled device. Band/continuum ratios were measured to high accuracy by referencing to the ring brightness in each image. Several data processing techniques enhanced the quality of the observations. These are the use of the ring symmetry to find center position and orientation, accurate subtraction of ring light, and constrained image deconvolution. Uncertainty in the continuum absolute reflectivity is ±10%. Uncertainties in band/continuum ratios are from one to several percent. The Equatorial Zone was much brighter than any other latitude in the strong 8900 band image. Northern mid-latitudes were brighter than southern mid-latitudes. The latter observation indicates fewer high-altitude aerosols in the south, a possible result of atmospheric dynamics or seasonal sublimation of NH3 crystals. The data are tabulated and presented in a form suitable for quantitative scattering model analyses. 相似文献
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We present an analytic method for producing the lightcurve of a system of spherical bodies in circular orbit about their common center of mass and then use it to model a lightcurve of 171 Ophelia. We find that a model in which the components have a diameter ratio of 1:2.96, have equal albedos, and circle one another in a synchronous orbit (period = 13.146 hr) inclined by 15° to our line of sight provides a reasonable fit to the observed lightcurve. An expression is given for the density in terms of the model parameters. If this lightcurve of Ophelia is produced by mutual eclipses of spherical components the mean density of the system can not exceed 1.7 g cm?3. In view of these results we conclude that it is possible for Ophelia to be a binary. 相似文献
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A study investigated the effect of truck‐traffic intensity and road water‐content on the quality of runoff water from unsealed forest roads. Three sections of a gravel‐surfaced forest road were instrumented and exposed to low and high levels of truck traffic during wet winter conditions and dry summer conditions between July 2001 and December 2002. Rainfall, runoff, road moisture, and traffic were measured continuously, and suspended and bedload sediments were integrated measurements over 2‐week site‐service intervals. The median suspended sediment concentration from the three road segments under low truck‐traffic conditions (less than nine return truck passes prior to a storm) was 269 mg l?1, increasing 2·7‐fold to a median of 725 mg l?1 under high truck‐traffic conditions (greater than or equal to nine return truck passes prior to a storm). These concentrations, and increases due to traffic, are substantially less than most previously reported values. When these data are expressed as modified universal soil loss equation (MUSLE) erodibility values K, accounting for differences in rainfall energy, site characteristics and runoff, high traffic resulted in a road surface that was four times more erodible than the same road under low traffic conditions. Using multiple regression, traffic explained 36% of the variation in MUSLE erodibility, whereas road water content was not significant in the model. There was little difference in the erodibility of the road when trafficked in low water‐content compared with high water‐content conditions (MUSLE K values of 0·0084 versus 0·0080 respectively). This study shows that, for a good quality well‐maintained gravel forest road, the level of truck traffic affects the sediment concentration of water discharging from the road, whereas the water content of the road at the time of that traffic does not (note that traffic is not allowed during runoff events in Victoria). These conclusions are conditional upon the road being adequately maintained so that trafficking does not compromise the lateral drainage of the road profile. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
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Nikos Kourampas Ian A. Simpson Nimal Perera Siran U. Deraniyagala W.H. Wijeyapala 《Geoarchaeology》2009,24(6):677-714
Kitulgala Beli‐lena, a rockshelter in gneiss in humid tropical southwestern Sri Lanka, was inhabited by Late Pleistocene–Early Holocene (>31,000–7880 B.P.) hunter‐gatherers who made geometric microliths and exploited rainforest resources. Micromorphological analysis of a ca. 3‐m‐thick succession of diamictic loams, clays, and breccia with cultural content suggests that relative contribution of episodic colluviation and roof fall, water seepage through joints and diverse human activity varied through time. Facies changes across the profile reflect monsoon weakening ca. 20,000–16,000 cal B.P. and abrupt intensification ca. 15,700 cal B.P., on the wane of the global Last Glacial Maximum (LGM). Post‐depositional modification included clay, sesquioxide, and minor phosphate translocation; termite and other arthropod bioturbation; and clast weathering on the rockshelter floor. Human input (tools and tool‐making refuse, reworked charcoal and associated combustion by‐products) is markedly higher in sediments younger than ca. 15,700 cal B.P., suggesting intensification of site use immediately after the LGM. © 2009 Wiley Periodicals, Inc. 相似文献
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