Measuring Earth orientation with the global positioning system     

Adam P. Freedman 《Journal of Geodesy》1991,65(1):53-65

Summary A globally distributed network of high-precision receivers which obtain data from the full Global Positioning System (GPS) configuration of 18 or more satellites may soon become an efficient and economical method for the rapid determination of short-term variations in Earth orientation. A covariance analysis has been performed to evaluate the errors associated with GPS monitoring of Earth orientation. Earth orientation parameters were modeled either as constants over observing windows of various lengths, or as stochastic process-noise variables. The sensitivity of Earth orientation estimates to systematic errors in selected model parameters was also examined. GPS measurements appear to be highly competitive with those from other techniques, and have the potential to generate nearly continuous centimeter-level Earth orientation information to aid both spacecraft navigation and the study of high-frequency Earth orientation-related processes.  相似文献   

Origin of xenoliths in the trachyte at Puu Waawaa,Hualalai Volcano,Hawaii     

David A. Clague  Wendy A. Bohrson 《Contributions to Mineralogy and Petrology》1991,108(4):439-452

Rare dunite and 2-pyroxene gabbro xenoliths occur in banded trachyte at Puu Waawaa on Hualalai Volcano, Hawaii. Mineral compositions suggest that these xenoliths formed as cumulates of tholeiitic basalt at shallow depth in a subcaldera magma reservoir. Subsequently, the minerals in the xenoliths underwent subsolidus reequilibration that particularly affected chromite compositions by decreasing their Mg numbers. In addition, olivine lost CaO and plagioclase lost MgO and Fe₂O₃ during subsolidus reequilibration. The xenoliths also reacted with the host trachyte to form secondary mica, amphibole, and orthopyroxene, and to further modify the compositions of some olivine, clinopyroxene, and spinel grains. The reaction products indicate that the host trachyte melt was hydrous. Clinopyroxene in one dunite sample and olivine in most dunite samples have undergone partial melting, apparently in response to addition of water to the xenolith. These xenoliths do not contain CO₂ fluid inclusions, so common in xenoliths from other localities on Hualalai, which suggests that CO₂ was introduced from alkalic basalt magma between the time CO₂-inclusion-free xenoliths erupted at 106±6 ka and the time CO₂-inclusion-rich xenoliths erupted within the last 15 ka.  相似文献   

Geometry,bed topography and drainage system structure of the haut glacier d'Arolla,Switzerland     

Martin Sharp  Keith Richards  Ian Willis  Neil Arnold  Peter Nienow  Wendy Lawson  Jean-Louis Tison 《地球表面变化过程与地形》1993,18(6):557-571

As part of an integrated study of the hydrology, meltwater quality and dynamics of the Haut Glacier d'Arolla, Switzerland, the glacier's drainage network structure was determined from patterns of dye recovery in 342 injection experiments conducted from 47 moulins distributed widely across the glacier. This structure was compared with theoretical predictions based upon reconstructed patterns of water flow governed by (a) the subglacial hydraulic potential surface, and (b) the subglacial bedrock surface. These reconstructions were based on measurements of ice surface and bedrock topography obtained by a combination of ground survey and radio-echo sounding techniques. The two reconstructions simulate the drainage system structures expected for (a) closed channels, in which water is pressurized by the overlying ice, and (b) gravity-driven, open-channel flow. The closed-channel model provides the best fit to the observed structure, even though theoretical calculations suggest that, under summer discharge conditions, open-channel flow may be widespread beneath the glacier. Possible reasons for this apparent discrepancy are discussed.  相似文献   

Future changes of temperature and heat waves in Ontario,Canada     

Li  Zhong  Huang  Guohe  Huang  Wendy  Lin  Qianguo  Liao  Renfei  Fan  Yurui 《Theoretical and Applied Climatology》2018,132(3-4):1029-1038

Theoretical and Applied Climatology - Apparent changes in the temperature patterns in recent years brought many challenges to the province of Ontario, Canada. As the need for adapting to climate...  相似文献   

Variability of groundwater nitrate concentrations over time in arid basin aquifers: sources, mechanisms of transport, and implications for conceptual models     

Wendy Marie Robertson  John M. Sharp Jr. 《Environmental Earth Sciences》2013,69(7):2415-2426

In groundwater of the Trans-Pecos region of West Texas, unexpectedly high levels of nitrate (NO₃ ^?) are documented in four basins: Red Light Draw, Eagle Flats, Wild Horse and Michigan Flats, and Lobo and Ryan Flats. NO₃ ^? concentrations are changing over time in the majority (82.8 %) of wells and are increasing in most (69.8 %). The temporal change raises questions about the potential sources of NO₃ ^? and about flow dynamics in these basins. Presence of NO₃ ^? and temporal variability in concentration has implications beyond contamination risk because it indicates relatively rapid recharge (<60 years) to the basin groundwaters which was not expected based on previous estimates from chloride mass balance models and groundwater age-dating techniques. This research combines existing data ranging back to the 1940s with data collected in 2011 to document a multi-decadal trend of overall increasing NO₃ ^? concentration in deep basin groundwaters. Chlorofluorocarbon analyses of groundwater collected during 2011 indicate the presence of young (<70 years) water in the basins. The authors infer from these data that there are mechanism(s) by which relatively rapid and widespread recharge occurs on the basin floors; that recharge is spatially and temporally variable and that it results from both anthropogenic (irrigated agriculture) and natural (precipitation) sources. In light of these observations, fundamental conceptual models of flow in these basins should be re-evaluated.  相似文献   

Technical Note The b-function and variable stream buffer mapping: a note on ‘A GIS method for riparian water quality buffer generation’     

Wei-Ning Xiang  Wendy Lee Stratton 《International journal of geographical information science》2013,27(4):499-510

Abstract

Mapping variable stream buffers in a vector environment in which buffer width values are delineated often yields inaccurate results. Possible vector solutions are either ineffective or inefficient, An alternate raster approach is presented here in which a buffer effectiveness-achievement function (b-function) is introduced to map desirable buffer zones at an individual cell level based upon areal differentiations in physical and ecological conditions. The implementation of b-function is made feasible by a GIS procedure devised in this article. This tested method can be extended to a variety of variable buffer studies, such as visual buffers, noise buffers, greenways, and urban natural buffers.

‘A robe can never be made of the fur from one fox's axillae’ (A Chinese idiom).  相似文献   

Retrieval of water in Jupiter's deep atmosphere using microwave spectra of its brightness temperature     

Imke de Pater  David DeBoer  Richard Freedman 《Icarus》2005,173(2):425-438

Despite several spacecraft encounters and numerous groundbased investigations, we still do not know much about Jupiter's deep atmosphere; in fact, the Galileo probe results were so different than anyone had anticipated, that we understand even less about this planet's atmosphere now than before the Galileo mission. We formulate four basic questions in Section 1.3, which, if solved, would help to better understand the chemistry and dynamics in Jupiter's atmosphere. We believe that three out of the four questions (explanation of NH₃ altitude profile, characterization of hot spots, altitude below which the atmosphere is uniformly mixed) may be solved from passive sounding of Jupiter's deep (∼ tens of bars) atmosphere via a radio telescope orbiting the planet. Question nr. 4 (the water abundance in Jupiter's deep atmosphere) has been singled out by the Solar System Exploration Decadal Survey as a key question, since the water abundance in Jupiter's deep atmosphere is tied in with planet formation models. In this paper we investigate the sensitivity of microwave retrievals to the composition of Jupiter's deep atmosphere, in particular the water abundance. Based upon present uncertainties in the ammonia abundance and other known and unknown absorbers, including uncertainties in clouds (density and index of refraction), and uncertainties in the thermal structure and lineshape profiles, we conclude that the retrieval of water at depth from microwave spectra (disk-averaged and locally) will be highly uncertain. We show that, if the H₂O lineshape profile would be accurately known (laboratory data are needed!), an atmosphere with a near-solar H₂O abundance can likely be distinguished from one with an abundance of 10-20×solar O based upon the difference in their microwave spectra at wavelengths ?50 cm. This would be sufficient to distinguish between some proposed scenarios by which Jupiter acquired its inventory of volatile elements heavier than helium. If, in addition, limb-darkening measurements are obtained (again, the H₂O lineshape profile should be known), tighter constraints on the H₂O abundance can be obtained (see also Janssen et al., 2004, this issue).  相似文献   

Modeling spatiotemporal pattern of agriculture‐feasible land in China          下载免费PDF全文

Weihe Wendy Guan  Kang Wu  Fei Carnes 《Transactions in GIS》2016,20(3):426-447

This study applies a spatial fuzzy multi‐criteria evaluation model to determine agricultural feasibility in China based on physical variables (accumulated temperature, sunshine, precipitation, hydrology, elevation and soil properties). The resulting agricultural feasibility index layer is combined with nightlight images (1992‐2013) to determine the spatiotemporal variation of urban encroachment on feasible agriculture land. It reveals the severity of agricultural land losses to urbanization.  相似文献   

Towards modelling of evacuation behavior and planning for emergency logistics due to the Philippine Taal Volcanic eruption in 2020     

Lim  Hector R.  Lim  Ma. Bernadeth B.  Rojas  Ann Wendy M. 《Natural Hazards》2022,114(1):553-581

Natural Hazards - Emergency evacuation is the immediate escape of people away from a place of an imminent threat to a place of safety. The ability of the households to evacuate is a crucial...  相似文献   

Lessons learnt from Typhoons Fitow and In-Fa: implications for improving urban flood resilience in Asian Coastal Cities     

Chan  Faith Ka Shun  Gu  Xinbing  Qi  Yunfei  Thadani  Dimple  Chen  Yongqin David  Lu  Xiaohui  Li  Lei  Griffiths  James  Zhu  Fangfang  Li  Jianfeng  Chen  Wendy Y. 《Natural Hazards》2022,110(3):2397-2404

Natural Hazards - Frequent typhoons significantly affect many coastal cities via intensive rainstorms, tidal surges and strong wind. Natural factors induced by human disturbance such as climate...  相似文献