Simultaneous spline approximation and topographic analysis for lidar elevation data in open-source GIS   总被引：4，自引：0，他引：4  

Mitasova  H. Mitas  L. Harmon  R.S. 《Geoscience and Remote Sensing Letters, IEEE》2005,2(4):375-379

Application of a spline approximation method to computation and analysis of lidar-based digital elevation models is investigated to determine its accuracy and capability to create surfaces at different levels of detail. Quadtree segmentation that adapts to the spatial heterogeneity of data points makes the method feasible for large datasets. The results demonstrate the importance of smoothing for the surface accuracy and noise reduction. A tension parameter is effective for tuning the level of detail in the elevation surface. Simultaneous computation of topographic parameters is applied to extraction of sand dunes' features for assessment of dune migration and beach erosion.  相似文献   

A note regarding CIF3 as an alternative to BrF5 for oxygen isotope analysis   总被引：1，自引：0，他引：1  

James Borthwick  Russell S Harmon 《Geochimica et cosmochimica acta》1982,46(9):1665-1668

Chlorine trifluoride (ClF₃) is recommended as a comparable alternative to bromine pentafluoride (BrF₅) for the quantitative extraction of oxygen from silicate minerals.  相似文献   

Carbon Stores, Sinks, and Sources in Forests of Northwestern Russia: Can We Reconcile Forest Inventories with Remote Sensing Results?     

Olga N. Krankina  Mark E. Harmon  Warren B. Cohen  Doug R. Oetter  Zyrina Olga  Maureen V. Duane 《Climatic change》2004,67(2):257-272

Forest inventories and remote sensing are the two principal data sources used to estimate carbon (C) stocks and fluxes for large forest regions. National governments have historically relied on forest inventories for assessments but developments in remote sensing technology provide additional opportunities for operational C monitoring. The estimate of total C stock in live forest biomass modeled from Landsat imagery for the St. Petersburg region was consistent with estimates derived from forest inventory data for the early 1990s (272 and 269 TgC, respectively). The estimates of mean C sink in live forest biomass also agreed well (0.36 and 0.34 Mg C ha^–1 yr^–1). Virtually all forest lands were accumulating C in live biomass, however when the net change in total ecosystem C stock was considered, 19% of the forest area were a net source of C. The average net C sink in total ecosystem biomass is quite weak (0.08 MgC ha^–1 yr^–1 and could be reversed by minor increases in harvest rates or a small decline in biomass growth rates.  相似文献   

Petrography of Lower Cretaceous sandstones on Spitsbergen     

Harmon D. Maher  Jr.    Troy Hays  Robert Shuster  Jeremy Mutrux 《Polar research》2004,23(2):147-165

The sandstone petrography of sample suites from four sites spanning the Rurikfjellet (Hauterivian) to Carolinefjellet (Aptian-Albian) formations in central Spitsbergen was investigated. The sandstones show a distinct stepwise shift in composition from quartz arenites to sublitharenites and lithic arenites, typically within the upper part of the Helvetiafjellet Formation. This shift is related to the introduction of 10 - 25% (grain%) plagioclase grains and volcanic lithics, and a notable increase in basement and sedimentary lithics. Quartz grain character also changes, and grain shapes become more varied. The shift is also associated with the transgressive arrival of marine sediments in the area, and the introduction of sands from the east-northeast by shore-parallel transport. Regional regression and subsequent transgression, and the change in sandstone composition is attributed to the development of the High Arctic Large Igneous Province in the region. The relative constancy of sand composition and volume of volcanic detritus within the Carolinefjellet Formation suggests long term (∼20 M) stability of the sediment system and a large volcanic source area, consistent with LIP (Large Igneous Province) derivation, along with significant exposure of basement rocks. Sample spacing and sediment recycling and mixing do not allow detection of events that would have changed sandstone composition that were less than ∼1 M duration. Preservation of significant amounts of plagioclase in a sediment-starved shelf can be explained by relatively cold climatic conditions.  相似文献   

Bimodal Density Distribution of Cryptodome Dacite from the 1980 Eruption of Mount St. Helens,Washington     

Richard P. Hoblitt  Russell S. Harmon 《Bulletin of Volcanology》1993,55(6):421-437

The explosion of a cryptodome at Mount St. Helens in 1980 produced two juvenile rock types that are derived from the same source magma. Their differences-color, texture and density-are due only to vesicularity differences. The vesicular gray dacite comprises bout 72% of the juvenile material; the black dacite comprises the other 28%. The density of juvenile dacite is bimodally distributed, with peaks at 1.6 g cm^-3 (gray dacite) and 2.3 g cm^-3 (black dacite). Water contents, deuterium abundances, and the relationship of petrographic structures to vapor-phase crystals indicate both rock types underwent pre-explosion subsurface vesiculation and degassing. The gray dacite underwent a second vesiculation event, probably during the 18 May explosion. In the subsurface, gases probably escaped through interconnected vesicles into the permeable volcanic edifice. We suggest that nonuniform degassing of an initially homogeneous magma produced volatile gradients in the cryptodome and that these gradients were responsible for the density bimodality. That is, water contents less than about 0.2–0.4 wt% produced vesicle growth rates that were slow in comparison to the pyroclast cooling rates; greater water contents produced vesicle growth rates that were fast in comparison to cooling rates. In this scheme, the dacite densities are bimodally distributed simply because, following decompression on 18 May 1980, one clast population vesiculated while the other did not. For clasts that did vesiculate, vesicle growth continued until it was arrested by fragmentation.  相似文献   

Tectonic history of the ophiolitic rocks of the highland border fracture zone, Scotland: Stable isotope evidence from rock-fluid interactions during obduction     

Nicholas P. Ikin  Russell S. Harmon 《Tectonophysics》1984,106(1-2)

The mafic and ultramafic rocks of the Highland Border Fracture Zone are ophiolitic remnants of a pre-Grampian marginal basin that opened either within, or to the north of, the Dalradian sedimentary pile. Closure of the basin was achieved through a combination of northerly-directed subduction, and obduction of ophiolitic thrust-slices onto the basin's southern margin. During the early stages of obduction, young hot peridotite slabs were thrust over the cold upper surfaces of lower thrust sheets, producing a dynamothermal metamorphic sole. Serpentinisation of these peridotites, whilst they were still cooling, occurred in a near-surface position through the interaction of meteoric waters. Subsequently, the ophiolitic thrust-sheets, which comprise lizardite serpentinites, spilitic pillow lavas, and aureole rocks, were thrust over the uppermost Dalradian nappes which were themselves being expelled southwards, thereby accommodating basement shortening. Grampian regional metamorphism of the nappe pile and overlying Highland Border Suite ophiolitic thrust sheets, produced greenschist metaspilites from the spilitic pillow lavas, induced minor retrogression in the aureole rocks, and caused the lizardite in the serpentinites to be recrystallised and replaced by antigorite. The Highland Border Suite greenschist facies metamorphic fluids were D-enriched compared with low-grade Dalradian metamorphic waters, and may have been mixtures of the latter and D-rich dehydration fluids released from the mafic rocks during dynamothermal metamorphism. Brittle fracturing and shearing in the serpentinites were responses to late deformation at different crustal levels during the final stages of emplacement, which involved gravity-sliding as well as downbending of the Dalradian nappes and ophiolitic thrust-sheets against the elevated Midland Valley block.  相似文献   

Detection of large grains in the coma of Comet C/2001 A2 (LINEAR) from Arecibo radar observations     

Michael C. Nolan  John K. Harmon  Donald B. Campbell 《Icarus》2006,181(2):432-441

Arecibo S-band () radar observations of Comet C/2001 A2 (LINEAR) on 2001 July 7-9 showed a strong echo from large coma grains. This echo was significantly depolarized. This is the first firm detection of depolarization in a grain-coma radar echo and indicates that the largest grains are at least λ/2π or 2 cm in radius. The grains are moving at tens of m s⁻¹ with respect to the nucleus. The nondetection of the nucleus places an upper limit of 3 km on its diameter. The broad, asymmetric echo power spectrum suggests a fan of grains that have a steep (differential number ∼a⁻⁴) size distribution at cm-scales, though the observed fragmentation of this comet complicates that picture.  相似文献   

Radar observations of 8P/Tuttle: A contact-binary comet     

John K. Harmon  Michael C. Nolan  Ellen S. Howell 《Icarus》2010,207(1):499-502

Arecibo radar imagery of Comet 8P/Tuttle reveals a 10-km-long nucleus with a highly bifurcated shape consistent with a contact binary. A separate echo component was also detected from large (>cm-size), slow-moving grains of the type expected to contribute to the Ursid meteor stream.  相似文献   

Correlation between melting, deformation and fluid interaction in the continental crust of the High Himalayas, Langtang Valley, Nepal     

J.A. Massey  S.M. Reddy  N.B.W. Harris  R.S. Harmon 《地学学报》1994,6(3):229-237

Combined metamorphic, stable-isotope and structural studies from the High Himalayan Crystalline sequence in the Langtang Valley of north-central Nepal reveal a strong positive correlation between distance above the base of the section (the Main Central Thrust), the amount of melt material and evidence of prolonged fluid and deformation histories, thus suggesting that these processes are strongly interdependent. Kyanite-grade rocks at the base of the section are unmelted and have undergone little syn- or post-metamorphic internal deformation and little prograde or retrograde fluid-rock interaction. By contrast sillimanite-grade rocks higher in the section contain progressively larger volumes of melt, have suffered increasingly complex syn- and post-metamorphic deformation and show increasing evidence for the presence of fluids. Although the factors that initiated these processes remain problematic, it is suggested that fluid distributions within the Langtang section have been passively controlled by the movement of melts. These melts may have provided a primary control on deformation during both the magmatic stage and, subsequently, through the exsolution of exsolved aqueous fluids.  相似文献   

Chemical determination of particulate nitrogen in San Francisco Bay. A comparison of two estimates     

S.W. Hager  D.D. Harmon 《Estuarine, Coastal and Shelf Science》1984,19(2):181-191

Particulate nitrogen was measured by both the ultra-violet light-catalyzed peroxide method and the high temperature combustion method. The difference between values obtained with the two methods (combustion minus UV) was found to be linearly correlated with the concentration of total suspended particulate matter (SPM) in the sample. The slope of this correlation was taken to be the concentration of refractory nitrogen associated with the suspended matter, which may be ammonium ions fixed in lattices of clay minerals or organic nitrogen compounds did not vary significantly with SPM, location, water depth or salinity. Refractory nitrogen concentration were possibly related to concentrations of chlorophyll a and to cruise date, but in neither case was the evidence conclusive. Based on the indirect evidence presented, the UV method appears to provide a good measure of biologically reactive nitrogen in this system.  相似文献