The GGOS as the backbone for global observing and local monitoring: A user driven perspective   总被引：1，自引：0，他引：1  

H.-P. Plag   《Journal of Geodynamics》2005,40(4-5):479

A key geodetic contribution to both the three Global Observing Systems and initiatives like the European Global Monitoring for Environment and Security is an accurate, long-term stable, and easily accessible reference frame as the backbone. Many emerging scientific as well as non-scientific high-accuracy applications require access to an unique, technique-independent reference frame decontaminated for short-term fluctuations due to global Earth system processes. Such a reference frame can only be maintained and made available through an observing system such as the Global Geodetic Observing System (GGOS), which is currently implemented and expected to provide sufficient information on changes in the Earth figure, its rotation and its gravity field. Based on a number of examples from monitoring of infrastructure, point positioning, maintenance of national references frames to global changes studies, likely future accuracy requirements for a global terrestrial reference frame are set up as function of time scales. Expected accuracy requirements for a large range of high-accuracy applications are less than 5 mm for diurnal and sub-diurnal time scales, 2–3 mm on monthly to seasonal time scales, better than 1 mm/year on decadal to 50 years time scales. Based on these requirements, specifications for a geodetic observing system meeting the accuracy requirements can be derived.  相似文献   

The International Laser Ranging Service and its support for IGGOS     

Michael Pearlman  Carey Noll  Peter Dunn  Julie Horvath  Van Husson  Paul Stevens  Mark Torrence  Hoai Vo  Scott Wetzel 《Journal of Geodynamics》2005,40(4-5):470

The International Laser Ranging Service (ILRS) was established in September 1998 as a service within the IAG to support programs in geodetic, geophysical, and lunar research activities and to provide data products to the International Earth Rotation Service (IERS) in support of its prime objectives. Now in operation for 5 years, the ILRS develops: (1) the standards and specifications necessary for product consistency and (2) the priorities and tracking strategies required to maximize network efficiency. The service collects, merges, analyzes, archives and distributes satellite and lunar laser ranging data to satisfy a variety of scientific, engineering, and operational needs and encourages the application of new technologies to enhance the quality, quantity, and cost effectiveness of its data products. The ILRS works with: (1) the global network to improve station performance; (2) new satellite missions in the design and building of retroreflector targets to maximize data quality and quantity and (3) science programs to optimize scientific data yield. The ILRS Central Bureau maintains a comprehensive web site as the primary vehicle for the distribution of information within the ILRS community. The site, which can be accessed at: http://ilrs.gsfc.nasa.gov is also available at mirrored sites at the Communications Research Laboratory (CRL) in Tokyo and the European Data Center (EDC) in Munich.During the last 2 years, the ILRS has addressed very important challenges: (1) data from the field stations are now submitted hourly and made available immediately through the data centers for access by the user community; (2) tracking on low satellites has been significantly improved through the sub-daily issue of predictions, drag functions, and the real-time exchange of time biases; (3) analysis products are now submitted in SINEX format for compatibility with the other space geodesy techniques; (4) the Analysis Working Group is heavily engaged in Pilot Projects as it works toward an ILRS “standard” global solution and (5) SLR has significantly increased its participation in the International Terrestrial Reference Frame (ITRF) activity, which is important to the success of IGGOS.  相似文献   

Formation of Paleoproterozoic eclogitic mantle, Slave Province (Canada): Insights from in-situ Hf and U–Pb isotopic analyses of mantle zircons     

Stefanie S. Schmidberger  Larry M. Heaman  Antonio Simonetti  Robert A. Creaser  Harrison O. Cookenboo 《Earth and Planetary Science Letters》2005,240(3-4):621-633

In-situ Hf isotope analyses and U–Pb dates were obtained by laser ablation-MC-ICP-MS for a zircon-bearing mantle eclogite xenolith from the diamondiferous Jericho kimberlite located within the Archean Slave Province (Nunavut), Canada. The U–Pb zircon results yield a wide range of ages (2.0 to 0.8 Ga) indicating a complex geological history. Of importance, one zircon yields a U–Pb upper intercept date of 1989 ± 67 Ma, providing a new minimum age constraint for zircon crystallization and eclogite formation. In contrast, Hf isotope systematics for the same zircons display an intriguing uniformity, and corresponding Hf depleted mantle model ages range between 2.1 ± 0.1 and 2.3 ± 0.1 Ga; the youngest Hf model age is within error to the oldest U–Pb date.

The Jericho eclogites have previously been interpreted as representing remnants of metamorphosed oceanic crust, and their formation related to Paleoproterozoic subduction regimes along the western margin of the Archean Slave craton during the Wopmay orogeny. Hf isotope compositions and U–Pb results for the Jericho zircons reported here are in good agreement with a Paleoproterozoic subduction model, suggesting that generation of oceanic crust and eclogite formation occurred between 2.0 and 2.1 Ga. The slightly older Hf depleted mantle model ages (2.1 to 2.3 Ga) may be reconciled with this model by invoking mixing between ‘crustal’-derived Hf from sediments and more radiogenic Hf associated with the oceanic crust during the 2 Ga subduction event. This results in intermediate Hf isotope compositions for the Jericho zircons that yield ‘fictitiously’ older Hf model ages.  相似文献   

地理学研究进展与前沿领域   总被引：72，自引：6，他引：72  

郑度  陈述彭 《地球科学进展》2001,16(5):599-606

现代地理学涵盖自然地理学、人文地理学和地理信息科学，其发展趋势是：相邻学科的交叉、渗透与融合，加强地理学内部的综合研究，地理过程的微观研究进一步深化，结合实践拓宽应用研究领域，实验与研究手段的现代化，理论思维模式的转变。地理学应在陆地表层过程与格局、全球环境变化及其区域响应、自然资源保障与生态环境建设、区域可持续发展及人地系统的机理与调控、地理信息科学和数字地球战略等前沿领域开拓创新，为促进地球系统科学的发展、协调人地关系等做出积极的贡献。  相似文献   

陆相二叠系-三叠系界线研究进展   总被引：8，自引：0，他引：8  

彭元桥  殷鸿福  杨逢清 《地球科学进展》2001,16(6):769-776

着重介绍了几个目前陆相二叠系—三叠系界线（TPTB）研究的重点剖面及其生物地层学研究进展；分析了陆相二叠系—三叠系界线综合地层学研究现状，包括生物地层学、事件地层学、同位素年代学、磁性地层学和层序地层学等；剖析了陆相二叠系-三叠系界线地层学研究中存在的问题及进一步的研究方向。生物地层方面，陆相二叠系-三叠系界线附近存在晚二叠世与早三叠世生物混生的层位，其中不同类别生物的时间界线常不一致，又由于陆相界线地层中含脊椎动物化石的层位一般较少，以脊椎动物化石（Lystrosaurus）为标准的精确界线常不确定，因而需重新寻找并确定陆相三叠系底界的标准化石。事件地层标志可能会成为连结海、陆相二叠系-三叠系界线地层高精度对比的纽带。  相似文献   

Formation of terrestrial planets in a dissipating gas disk with Jupiter and Saturn     

Junko Kominami  Shigeru Ida 《Icarus》2004,167(2):231-243

We have performed N-body simulations on final accretion stage of terrestrial planets, including the eccentricity and inclination damping effect due to tidal interaction with a gas disk. We investigated the dependence on a depletion time scale of the disk, and the effect of secular perturbations by Jupiter and Saturn. In the final stage, terrestrial planets are formed through coagulation of protoplanets of about the size of Mars. They would collide and grow in a decaying gas disk. Kominami and Ida [Icarus 157 (2002) 43-56] showed that it is plausible that Earth-sized, low-eccentricity planets are formed in a mostly depleted gas disk. In this paper, we investigate the formation of planets in a decaying gas disk with various depletion time scales, assuming disk surface density of gas component decays exponentially with time scale of τ_gas. Fifteen protoplanets with are initially distributed in the terrestrial planet regions. We found that Earth-sized planets with low eccentricities are formed, independent of initial gas surface density, when the condition (τ_cross+τ_growth)/2?τ_gas?τ_cross is satisfied, where τ_cross is the time scale for initial protoplanets to start orbit crossing in a gas-free case and τ_growth is the time scale for Earth-sized planets to accrete during the orbit crossing stage. In the cases satisfying the above condition, the final masses and eccentricities of the largest planets are consistent with those of Earth and Venus. However, four or five protoplanets with the initial mass remain. In the final stage of terrestrial planetary formation, it is likely that Jupiter and Saturn have already been formed. When Jupiter and Saturn are included, their secular perturbations pump up eccentricities of protoplanets and tend to reduce the number of final planets in the terrestrial planet regions. However, we found that the reduction is not significant. The perturbations also shorten τ_cross. If the eccentricities of Jupiter and Saturn are comparable to or larger than present values (∼0.05), τ_cross become too short to satisfy the above condition. As a result, eccentricities of the planets cannot be damped to the observed value of Earth and Venus. Hence, for the formation of terrestrial planets, it is preferable that the secular perturbations from Jupiter and Saturn do not have significant effect upon the evolution. Such situation may be reproduced by Jupiter and Saturn not being fully grown, or their eccentricities being smaller than the present values during the terrestrial planets' formation. However, in such cases, we need some other mechanism to eliminate the problem that numerous Mars-sized planets remain uncollided.  相似文献   

Surveying co-located space-geodetic instruments for ITRF computation   总被引：2，自引：2，他引：0  

P.?SartiEmail author  P.?Sillard  L.?Vittuari 《Journal of Geodesy》2004,78(3):210-222

A new and comprehensive method is presented that can be used for estimating eccentricity vectors between global positioning system (GPS) antennas, doppler orbitography and radiopositioning integrated by satellites (DORIS) antennas, azimuth-elevation (AZ-EL) very long baseline interferometry (VLBI) telescopes, and satellite laser ranging (SLR) and lunar laser ranging (LLR) telescopes. The problem of reference point (RP) definition for these space-geodetic instruments is addressed and computed using terrestrial triangulation and electronic distance measurement (EDM) trilateration. The practical ground operations, the surveying approach and the terrestrial data processing are briefly illustrated, and the post-processing procedure is discussed. It is a geometrically based analytical approach that allows computation of RPs along with a rigorous statistical treatment of measurements. The tight connection between the geometrical model and the surveying procedure is emphasized. The computation of the eccentricity vector and the associated variance–covariance matrix between an AZ-EL VLBI telescope (with or without intersecting axes) and a GPS choke ring antenna is concentrated upon, since these are fundamental for computing the International Terrestrial Reference Frame (ITRF). An extension to RP computation and eccentricity vectors involving DORIS, SLR and LLR techniques is also presented. Numerical examples of the quality that can be reached using the authors approach are given. Working data sets were acquired in the years 2001 and 2002 at the radioastronomical observatory of Medicina (Italy), and have been used to estimate two VLBI-GPS eccentricity vectors and the corresponding SINEX files.  相似文献   

GPS卫星的激光测距和应用研究   总被引：2，自引：0，他引：2  

许华冠 《天文学进展》1998,16(4):251-259

简述了SLR和GPS跟踪技术的发展概况。详细介绍了近几年来对GPS－35、36卫星的激光测距进展和应用研究的情况。给出了残差分析的初步结果,并指出了目前GPS卫星的稀少的激光测距资料对卫星精密定轨和站坐标的解算是有价值的。同时,也简单地评述了GPS卫星的微波和激光跟踪技术各自的优势和弱点．建议联合利用GPS-35、36卫星的SLR和GPS观测资料来开展有关的应用研究。最后,对今后的应用研究工作提出了建议．  相似文献   

利用地下流体氦同位素比值估算大陆壳幔热流比例   总被引：12，自引：2，他引：10  

汪洋 《地球物理学报》2000,43(6):762-770

地下流体中的氦同位素 3He来自地幔的排气作用 ,4He则是铀、钍衰变的产物 .由于铀、钍元素在大陆地壳中富集 ,4He通量与地壳热流呈正相关关系 ;同时 3He通量与地幔热流之间呈正相关 .所以地下流体的氦同位素比值 （3He / 4 He）与大陆壳幔热流比值 （qc/qm）呈反相关关系 .根据欧亚大陆和加拿大地盾的地下流体氦同位素比值数据和相应的壳幔热流比值数据 ,统计出 qc/ qm 与 3He / 4 He之间的回归关系 :qc/ qm =0 81 5- 0 30 0ln（3He / 4 He） ;此处 3He/ 4 He的单位是RA（大气的 3He/ 4 He比值 ） .有了地表热流值和壳幔热流比值即可得到地壳热流和地幔热流 .利用该公式以及热流值估算了中国主要盆地的壳幔热流值 ;根据这些数值得出的热岩石圈厚度和地壳平均生热率结果与地震学研究成果一致 .氦同位素比值是区分大陆热流中地壳热流值和地幔热流值的有用参数 .  相似文献   

Terrigenous dissolved organic matter along an estuarine gradient and its flux to the coastal ocean     

Antonio Mannino  H. Rodger Harvey   《Organic Geochemistry》2000,31(12)

The contribution of terrigenous organic matter (TOM) to high molecular weight dissolved and particulate organic matter (POM) was examined along the salinity gradient of the Delaware Estuary. Dissolved organic matter (DOM) was fractionated by ultrafiltration into 1–30 kDa (HDOM) and 30 kDa–0.2 μm (VHDOM) nominal molecular weight fractions. Thermochemolysis with tetramethylammonium hydroxide (TMAH) was used to release and quantify lipids and lignin phenols. Stable carbon isotopes, fatty acids and lignin content indicated shifts in sources with terrigenous material in the river and turbid region and a predominantly algal/planktonic signal in the lower estuary and coastal ocean. Thermochemolysis with TMAH released significant amounts of short chain fatty acids (C₉–C₁₃), not seen by traditional alkaline hydrolysis, which appear to be associated with the macromolecular matrix. Lignin phenol distributions in HDOM, VHDOM and particles followed predicted sources with higher concentrations in the river and turbid region of the estuary and lower concentrations in the coastal ocean. TOM comprised 12% of HDOM within the coastal ocean and up to 73% of HDOM within the turbid region of the estuary. In the coastal ocean, TOM from high molecular weight DOM comprised 4% of total DOC. The annual flux of TOM from the Delaware Estuary to the coastal ocean was estimated at 2.0×10¹⁰ g OC year⁻¹ and suggests that temperate estuaries such as Delaware Bay can be significant sources of TOM on a regional scale.  相似文献