Height dependence of the amplitudes of solar oscillations viewed with a potassium resonance scattering spectrometer     

Christopher J. Underhill  Clive C. Speake 《Solar physics》1996,163(2):231-240

Over the course of the year, the variation in the solar line-of-sight velocity causes a change in the heights in the photosphere which are analysed by the red and blue passbands of a resonance scattering spectrometer. This in turn would be expected to produce a variation in the ratio of acoustic amplitudes measured in each passband. Using data from the Tenerife spectrometer of the Birmingham Solar Oscillations Network (BiSON), we demonstrate such a seasonal change. We then use the Eddington-Barbier approximation and an atmospheric model to convert the magnitude of this trend in velocity ratio with line-of-sight velocity into an approximate value of 580 km for the velocity-amplitude scale height. However, a simple argument suggests that Doppler imaging causes this to be an overestimate of the true value.  相似文献   

Mechanisms of shrubland expansion: land use,climate or CO2?   总被引：11，自引：0，他引：11  

Steve Archer  David S. Schimel  Elisabeth A. Holland 《Climatic change》1995,29(1):91-99

Encroachment of trees and shrubs into grasslands and the thicketization of savannas has occurred worldwide over the past century. These changes in vegetation structure are potentially relevant to climatic change as they may be indicative of historical shifts in climate and as they may influence biophysical aspects of land surface-atmosphere interactions and alter carbon and nitrogen cycles. Traditional explanations offered to account for the historic displacement of grasses by woody plants in many arid and semi-arid ecosystems have centered around changes in climatic, livestock grazing and fire regimes. More recently, it has been suggested that the increase in atmospheric CO₂ since the industrial revolution has been the driving force. In this paper we evaluate the CO₂ enrichment hypotheses and argue that historic, positive correlations between woody plant expansion and atmospheric CO₂ are not cause and effect.Please direct all correspondence to the senior author.  相似文献   

Quality Assessment Of Digital Surface Models Generated From IKONOS Imagery     

Joanne  Poon  Clive S.  Fraser  Zhang  Chunsun  Zhang  Li  Armin  Gruen 《The Photogrammetric Record》2005,20(110):162-171

The growing applications of digital surface models (DSMs) for object detection, segmentation and representation of terrestrial landscapes have provided impetus for further automation of 3D spatial information extraction processes. While new technologies such as lidar are available for almost instant DSM generation, the use of stereoscopic high-resolution satellite imagery (HRSI), coupled with image matching, affords cost-effective measurement of surface topography over large coverage areas. This investigation explores the potential of IKONOS Geo stereo imagery for producing DSMs using an alternative sensor orientation model, namely bias-corrected rational polynomial coefficients (RPCs), and a hybrid image-matching algorithm. To serve both as a reference surface and a basis for comparison, a lidar DSM was employed in the Hobart testfield, a region of differing terrain types and slope. In order to take topographic variation within the modelled surface into account, the lidar strip was divided into separate sub-areas representing differing land cover types. It is shown that over topographically diverse areas, heighting accuracy to better than 3 pixels can be readily achieved. Results improve markedly in feature-rich open and relatively flat terrain, with sub-pixel accuracy being achieved at check points surveyed using the global positioning system (GPS). This assessment demonstrates that the outlook for DSM generation from HRSI is very promising.  相似文献   

Hyper Redundancy for Accuracy Enhancement in Automated Close Range Photogrammetry   总被引：1，自引：0，他引：1  

Clive S.  Fraser  Alex  Woods  Danny  Brizzi 《The Photogrammetric Record》2005,20(111):205-217

A generic network design in close range photogrammetry is one where optimal multi-ray intersection geometry is obtained with as few camera stations as practicable. Hyper redundancy is a concept whereby, once the generic network is in place, many additional images are recorded, with the beneficial impact upon object point precision being equivalent to the presence of multiple exposures at each camera position within the generic network. The effective number of images per station within a hyper redundant network might well be in the range of 10 to 20 or more. As is apparent when it is considered that a hyper redundant network may comprise hundreds of images, the concept is only applicable in practice to fully automatic vision metrology systems, where it proves to be a very effective means of enhancing measurement accuracy at the cost of minimal additional work in the image recording phase. This paper briefly reviews the network design and accuracy aspects of hyper redundancy and illustrates the technique by way of the photogrammetric measurement of surface deformation of a radio telescope of 26 m diameter. This project required an object point measurement accuracy of σ  = 0·065 mm, or 1/400 000 of the diameter of the reflector.  相似文献   

Method of Data Reduction and Uncertainty Estimation for Platinum-Group Element Data Using Inductively Coupled Plasma-Mass Spectrometry   总被引：1，自引：0，他引：1  

James C. Ely  Clive R. Neal 《Geostandards and Geoanalytical Research》2002,26(1):31-39

A data reduction method is described for determining platinum-group element (PGE) abundances by inductively coupled plasma-mass spectrometry (ICP-MS) using external calibration or the method of standard addition. Gravimetric measurement of volumes, the analysis of reference materials and the use of procedural blanks were all used to minimise systematic errors. Internal standards were used to correct for instrument drift. A linear least squares regression model was used to calculate concentrations from drift-corrected counts per second (cps). Furthermore, mathematical manipulations also contribute to the uncertainty estimates of a procedure. Typical uncertainty estimate calculations for ICP-MS data manipulations involve: (1) Carrying standard deviations from the raw cps through the data reduction or (2) calculating a standard deviation from multiple final concentration calculations. It is demonstrated that method 2 may underestimate the uncertainty estimate of the calculated data. Methods 1 and 2 do not typically include an uncertainty estimate component from a regression model. As such models contribute to the uncertainty estimates affecting the calculated data, an uncertainty estimate component from the regression must be included in any final error calculations. Confidence intervals are used to account for uncertainty estimates from the regression model. These confidence intervals are simpler to calculate than uncertainty estimates from method 1, for example. The data reduction and uncertainty estimation method described here addresses problems of reporting PGE data from an article in the literature and addresses both precision and accuracy. The method can be applied to any analytical technique where drift corrections or regression models are used.  相似文献   

A Reappraisal of Rb, Y, Zr, Pb and Th Values in Geochemical Reference Material BHVO-1     

William J. Chazey III  Clive R. Neal  Jinesh C. Jain  William S. Kinman 《Geostandards and Geoanalytical Research》2003,27(2):181-192

The geochemical reference material BHVO-1 was analysed by a variety of techniques over a six year period. These techniques included inductively coupled plasma-mass spectrometry and atomic emission spectroscopy (ICP-MS and ICP-AES, respectively), laser ablation ICP-MS and spark source mass spectroscopy. Inconsistencies between the published consensus values reported by Gladney and Roelandts (1988, Geostandards Newsletter) and the results of our study are noted for Rb, Y, Zr, Pb and Th. The values reported here for Rb, Y, Zr and Pb are generally lower, while Th is higher than the consensus value. This is not an analytical artefact unique to the University of Notre Dame ICP-MS facility, as most of the BHVO-1 analyses reported over the last ten to twenty years are in agreement with our results. We propose new consensus values for each of these elements as follows: Rb = 9.3 ± 0.2 μg g-1 (compared to 11 ± 2 μg g-1), Y = 24.4 ± 1.3 μg g-1 (compared to 27.6 ± 1.7 μg g-1), Zr = 172 ± 10 μg g-1 (compared to 179 ± 21 μg g-1), Pb = 2.2 ± 0.2 μg g-1 (compared to 2.6 ± 0.9 μg g-1) and Th = 1.22 ± 0.02 μg g-1 (compared to 1.08 ± 0.15 μg g-1).  相似文献   

Characterisation of Memory Effects and Development of an Effective Wash Protocol for the Measurement of Petrogenetically Critical Trace Elements in Geological Samples by ICP-MS     

Cathleen E. McGinnis  Jinesh C. Jain  Clive R. Neal 《Geostandards and Geoanalytical Research》1997,21(2):289-305

High sensitivity and low detection limits would seem to make inductively coupled plasma-mass spectrometry (ICP-MS) an ideal analytical tool for determining low (sub-μg g^-1) concentrations of the rare earth elements (REE), Y, Zr, Nb, Hf, Ta, Sn, W, Mo, Th, and U in most mafic materials (e.g. Hall and Plant 1992). However, the generally "sticky" nature exhibited by most of the high field strength elements (HFSEs: Zr, Nb, Hf, Ta, Th and U) as well as Sn, W and Mo can result in spurious results due to memory effects transmitted between unknowns and calibration samples. This, in turn, can seriously compromise the sensitivity, accuracy, and precision of ICP-MS analyses for these elements in geological materials. Data resulting from analyses with poor accuracy and precision can lead to erroneous interpretation and misleading petrogenetic modelling. To resolve this problem, we propose an effective wash protocol for these critical trace elements.  相似文献   

Evidence for focused hot fluid flow within the Britannia Field, offshore Scotland, UK   总被引：1，自引：0，他引：1  

S. G. Archer  H. L. Wycherley  G. R. Watt  M. L. Baron  J. Parnell  H. Chen 《Basin Research》2004,16(3):377-395

Fluid inclusion and scanning electron microscope‐cathodoluminescence evidence indicates focused hot, saline, diagenetic fluid flow within the Eastern Flank of the Britannia Field, offshore Scotland, UK. The fluid was sourced from the Andrew Salt Dome, 10 km to the east. The fluids, which promoted quartz cementation of the upper zones within the field, were up to ～30°C hotter and had salinities up to ～10 wt% NaCl equivalent higher than fluids from lower in the reservoir section. During diagenesis hot saline fluids migrated westwards as part of a radiating ‘diagenetic front’ from the Andrew Salt Dome. Structural dip associated with the Eastern Flank of the Fladen Ground Spur impeded the westward movement of the diagenetic fluid. The quartz cements from the upper and lower reservoir zones can be distinguished by morphology. In the upper zones the quartz cements have well‐developed macro‐crystalline zoning and heterogeneous luminescence across the grain. In the lower zones, the cements are much less developed, unzoned and very weakly luminescent. The diagenetic fluids were primarily focused into Zone 45 within the upper reservoir. Furthermore, within the Main Platform Area the most prolific producing zone is Zone 45, indicating the importance of this interval as a permeable flow unit during both diagenetic and production timescales. Within the Eastern Flank, the quartz overgrowths have a major impact on reservoir permeability and thus well productivity. The overgrowths are most extensive in the originally clean sandstones with low clay content. Clay in optimum volumes (5–10%) can inhibit nucleation of the damaging quartz overgrowths without having a detrimental effect on pore connectivity. These observations provide a predictive concept for use in the search for relative reservoir sweetspots within the degraded Eastern Flank.  相似文献   

Emplacement of the Cabezo María lamproite volcano (Miocene,SE Spain)     

Thomas M. Gernon  Samuel Spence  Clive N. Trueman  Rex N. Taylor  Eelco Rohling  Stuart J. Hatter  Ian C. Harding 《Bulletin of Volcanology》2015,77(6):1-13

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Near miss: the importance of the natural atmospheric CO2 concentration to human historical evolution     

David Archer 《Climatic change》2016,134(1-2):1-14

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