Mars surface properties observed by earth-based radar at 70-, 12.5-, and 3.8-cm wavelengths     

Richard A. Simpson  G.Leonard Tyler  Belinda J. Lipa 《Icarus》1977,32(2):147-167

A review of Mars radar data obtained through the 1973 opposition confirms that the surface of the planet has many diverse characteristics. Analysis of the quasi-specular echo component shows changes in apparent reflectivity of at least 5 to 1. If attributed entirely to variations in surface material, these correspond to dielectric constants between 1.6 and 4.0. Values of rms surface slope on 1- to 100-m scales range from as low as 0.5° in tablelands near Vlles Marineris to more than 3.0° (the upper limit for which these analysis techniques are appropriate) in certain other areas such as inside Coprates Chasma itself. There is weak correlation between the small-scale surface characteristics inferred from radar and those inferred from Mariner 9 images, geologic maps derived from those images, and other remote sensing data sets. Topography, a large-scale surface characteristic for which good correlation exists between radar and other data sets, was not considered in this study. A search for guidelines which would allow extrapolation of radar properties to new areas on the basis of those studied has been singularly unsuccessful. Data obtained during the 1973 opposition at Arecibo, Goldstone, and Haystack Observatories indicate that the scattering behavior of Mars varies little over the 70- to 3.8-cm wavelength range. Comparison of 1971 and 1973 Goldstone results shows no detectable variation with time.  相似文献   

Solar irradiance modulation by active regions during 1980     

Sabatino Sofia  Ludwig Oster  Kenneth Schatten 《Solar physics》1982,80(1):87-98

The solar irradiance modulation due to active regions during 1980 has been investigated in detail. Specifically, we estimate the uncertainties caused by ground-based data used as input in the modeling effort, and by our currently incomplete knowledge of the proper parameters that describe the angular variation of sunspot and facular contrasts. We conclude that the most significant uncertainties are due to errors in area measurements and, possibly, varying spot and facular brightness. A standard model for later use is derived by a best-fit technique of the currently available ACRIM irradiance data and the predictions of our models with appropriately varied parameters. Finally, we compute the expected irradiance for the entire year of 1980.NRC Senior Research Associate on leave from the Joint Institute for Laboratory Astrophysics and the Astro-Geophysics Department, University of Colorado at Boulder, Colo., U.S.A.  相似文献   

Mountain hazards     

Kenneth Hewitt Dr. 《GeoJournal》1992,27(1):47-60

The review examines mountain land risks, especially those that involve sudden, more or less localized bouts of damage and disasters. Geographers' studies to date have mainly dealt with natural hazards, emphasizing those like avalanches, large landslides or natural dams that are uniquely associated with mountain environments. Such work is briefly reviewed. Earthquake risks are then singled out to help define and discuss problems faced by this work. They are shown to depend strongly upon aspects of mountain environments other than seismicity. Human vulnerability appears to be mainly dependent upon socioeconomic and habitat conditions which, although they determine seismic impacts, may and usually do develop independent of it. Moreover, these ingredients of risk are most closely associated with, or definitive of, the mountain people and areas. They are most strongly influenced by human agency, both in deciding who and what are exposed to risk, and in actually increasing or decreasing unfavorable responses to earthquakes. Recent earthquake disasters in the mountains also record how rapid changes in these social and habitat conditions, rather than seismicity, are increasing the scale and altering the forms of damage. These changes in turn, however, are largely dependent upon developments, initiatives and penetration from outside the mountains, and responses of mountain people more or less enforced by them. The importance of so-called highland-lowland interactions, is even more obvious in the most destructive of human hazards discussed, those of war and other armed violence. Mountain lands and peoples are shown to have been subject to recurrent warring, and a disproportionate share of the deployment of state violence in this century. Most of the casualties are resident civilians. They have been usually threatened by other uses of armed violence, including insurgency and counter-insurgency warfare and genocidal actions by state forces. Refugees and expellees from war zones have included great numbers of mountain folk. Another fast growing hazard of the late twentieth century, not unrelated to war and militarism, the international trafficking in and addiction plagues of hard drugs, has a unique relation to mountains. The South American growers of the coca leaf, and Southwest and Southeast Asian growers of the opium poppy are mountain farmers. Their participation is bringing a range of severe risks to their high valleys, as well as benefits. Finally the paper addresses the conceptual problems brought about by the compounding of determinist assumptions in both mountain land and hazards research. These include not only environmental determinist notions, or related Neo-Malthusian and Social Darwinist ideas, but the various historicist ones of assumed technological, economic and political stages of development. It is argued that such social constructions of the problem of hazards and disaster are dubious, and have become a major impediment to understanding and risk mitigation. Alternative frameworks require more attention to the regional, state, and global patterns of influence shaping risk in mountain lands, but also to the human ecology of mountain societies taking account of matters to which the expediences of technocratic expertise have made us blind.  相似文献   

Climates of the soviet union | P.E. Lydolph, 1977. World survey of climatology, 7. Elsevier,Amsterdam, 443 pp., U.S. $ 81.75, Dfl. 200.00     

F. Kenneth Hare 《Earth》1978,14(2):174-175

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A time evolution study of limb spicule spectra     

Kenneth R. Krall  R. J. Bessey  Jacques M. Beckers 《Solar physics》1976,46(1):93-114

Time sequences of simultaneous spectra of limb spicules, obtained using the Sacramento Peak Observatory's tower telescope and echelle spectrograph are analyzed. Intensity determinations of H and K, H, 8498 and 8542 of calcium are tabulated for three observing heights. Electron densities averaged over the entire visible lifetimes of spicules are -6 × 10¹⁰ cm^–3 at observing heights of 6000km, while maximum and minimum values were -1.1 × 10¹¹ cm^–3 at 6000km and - 2 × 10¹⁰ cm^–3 at 10000km. Electron temperatures range between 12 000 K and 16 000 K. Profile halfwidths indicate turbulent velocities of 12 to 22 km s^–1, and spectral tilts are interpreted as caused by differential velocity fields of -3 km s^–1 per 1000 km. No large scale spicule expansions or contractions are observed, although possible expulsions or accretions of material are observed. Spicules may be wider in the calcium K and H lines than in H.Now at School of Science and Engineering, The University of Alabama in Huntsville, Huntsville, Alabama.  相似文献   

The Vivian Thompson Stereo-planigraph     

Kenneth  Mason 《The Photogrammetric Record》1975,8(45):371-371

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BRITISH FARMING IN THE GREAT DEPRESSION 1870–1914: AN HISTORICAL GEOGRAPHY. By Peter J. Perry     

Kenneth  Jackson 《New Zealand geographer》1975,31(1):93-94

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Cosmogenic nuclide methods for measuring long-term rates of physical erosion and chemical weathering     

James W. Kirchner  Clifford S. Riebe  Kenneth L. Ferrier  Robert C. Finkel 《Journal of Geochemical Exploration》2006,88(1-3):296

Understanding the evolution of geochemical and geomorphic systems requires measurements of long-term rates of physical erosion and chemical weathering. Erosion and weathering rates have traditionally been estimated from measurements of sediment and solute fluxes in streams. However, modern sediment and solute fluxes are often decoupled from long-term rates of erosion and weathering, due to storage or re-mobilization of sediment and solutes upstream from the sampling point. Recently, cosmogenic nuclides such as ¹⁰Be and ²⁶Al have become important new tools for measuring long-term rates of physical erosion and chemical weathering. Cosmogenic nuclides can be used to infer the total denudation flux (the sum of the rates of physical erosion and chemical weathering) in actively eroding terrain. Here we review recent work showing how this total denudation flux can be partitioned into its physical and chemical components, using the enrichment of insoluble tracers (such as Zr) in regolith relative to parent rock. By combining cosmogenic nuclide measurements with the bulk elemental composition of rock and soil, geochemists can measure rates of physical erosion and chemical weathering over 1000- to 10,000-year time scales.  相似文献   

Responses of resident marsh fishes to stages ofPhragmites australis invasion in three mid Atlantic estuaries     

Karen L. Hunter  Dewayne A. Fox  Lori M. Brown  Kenneth W. Able 《Estuaries and Coasts》2006,29(3):487-498

Modification of brackish marshes by nonindigenousPhragmites australis has occurred across a broad geographical area in eastern North America. Among its effects on marsh processes,Phragmites may be increasingly unfavorable to marsh surface fishes as its invasion progresses within an estuary. We assessed the effect of thePhragmites invasion on resident marsh surface fishes by examining the population response ofFundulus heteroclitus (mummichog, 5–48 mm TL) andF. luciae (spotfin killifish, 5–41 mm TL) to four distinct invasion stages in three estuaries of the U.S. mid Atlantic region (New Jersey, Delaware, and Maryland). We documented precipitous declines in mean catch per unit effort ofF. heteroclitus in pit traps from natural marsh (51.6), through initial (33.8), early (12.3), and late invasion stages (2.4) across all sites. A similar pattern was documented forF. luciae, with mean catch per unit effort in pit traps declining from natural marsh (48.9), through initial (39.1), early (9.3), and late invasion stages (2.7). Population structure of both species also changed somewhat across invasion stages such that we collected a narrower size range of individuals of both species from late invasion stages. Patterns suggest that as thePhragmites invasion progresses, there is a decline in habitat function for larval and juvenileF. heteroclitus and an increased risk of extirpation ofF. luciae from brackish marshes along the east coast of the U.S.  相似文献   

Variability in drift macroalgal abundance in relation to biotic and abiotic factors in two seagrass dominated estuaries in the Western Gulf of Mexico     

Andrea L. Kopecky  Kenneth H. Dunton 《Estuaries and Coasts》2006,29(4):617-629

We examined the spatial and temporal variability in drift macroalgal abundance in two seagrass dominated estuarine systems on the Texas coast: Redfish Bay (in the Copano-Aransas Estuary) and Lower Laguna Madre. Measurements of benthic macroalgal variability were made in conjunction with a suite of biotic (seagrass biomass, percent cover, blade width and length, shoot density, epiphyte biomass, seagrass blade C:N ratios, and drift macroalgal abundance and composition) and abiotic (inorganic nitrogen and phosphorus concentrations, chlorophylla, total suspended solids, light attenuation, salinity, temperature, total organic carbon and porewater NH₄ ⁺) indicators. All parameters were measured at 30 sites within each estuary semiannually from July 2002 to February 2004. Principal components analysis (PCA) was used to examine relationships between drift macroalgal abundance and biotic and abiotic parameters. In both Redfish Bay and Lower Laguna Madre, drift macroalgal distribution was widespread, and during three of four sampling periods, abundance was equal to abovegro und biomass ofThalassia testudinum, the dominant seagrass. Drift macro algal abundance was highly variable within sites, between sites, and between seasons in both estuaries. No significant differences in drift macroalgal abundance were found between Redfish Bay and Lower Laguna Madre. In Redfish Bay, drift macroalgae (90.1±10.2 gm⁻²) tended to accumulate in bare patches within seagrass beds. In Lower Laguna Madre, drift macroalgae (72.7±10.7 gm⁻²) tended to accumulate in areas of dense seagrass cover rather than in bare areas. We found no relationship between drift macroalgal abundance and low (<2μM) water column nutrient concentrations, and although several of our measured parameters were related to drift macroalgal abundance, none alone sufficiently explained the variability in abundance noted between the two estuarine systems. The contrasting patterns of macroalgal accumulation between Redrish Bay and Lower Laguna Madre likely reflect differences in water circulation characteristics between the two regions as dictated by local physiography, in cluding the shape and orientation of the lagoons, with seasonal variations in macroalgal abundance related to changes in freshwater inflow and nutrient loading.  相似文献