Global ocean circulation patterns based on seasat altimeter data and the GEML2 gravity field     

Theo Engelis  Richard H. Rapp 《Marine Geophysical Researches》1984,7(1-2):55-67

The Seasat altimeter data has been completely adjusted by a crossing arc technique to reduce the crossover discrepancies to approximately ±30 cm in five regional adjustments. This data was then used to create sea surface heights at 1° intersections in the ocean areas with respect to the GRS80 ellipsoid. These heights excluded the direct tidal effects but included the induced permanent deformation. A geoid corresponding to these sea surface heights was computed, based on the potential coefficients of the GEML2 gravity field up to degree 6, augmented by Rapp's coefficients up to degree 180. The differences between sea surface heights and the geoid were computed to give approximate estimates of sea surface topography. These estimates are dominated by errors in both sea surface heights and geoid undulations. To optimally determine sea surface topography a spherical harmonic analysis of raw estimates was carried out and the series was further truncated at degree 6, giving estimates with minimum wavelengths on the order of 6000 km. The direction of current flow can be computed on a global basis using the spherical harmonic expansion of the sea surface topography. Ths has been done, not only for Seasat/GEML2 estimates, but also using the recent dynamic topography estimates of Levitus. The results of the two solutions are very similar and agree well with the major circulation features of the oceans.  相似文献   

Sustainable conjunctive use of groundwater for additional irrigation          下载免费PDF全文

N. Alam  Theo N. Olsthoorn 《水文研究》2014,28(20):5288-5296

The key to ‘sustainable conjunctive use of groundwater for additional irrigation’ is the salt balance of groundwater below an irrigated field. This paper aims to develop a mathematical tool to study the accumulation of salt in the groundwater below an irrigated field as caused by irrigation recirculation. This study derives a salt balance of groundwater to ensure that the additional irrigation from groundwater remains possible in the future. The water and salt budgets by themselves do neither provide information concerning farmers' options nor on the limits of the individual terms in the budget equations. It is presumed that farmers will intuitively aim for (1) an optimal value of the actual evapotranspiration, and (2) a return flow as a feasible low fraction of the available water. We, therefore, derive the irrigation from groundwater Q as a consequence of the predefined farmers' aims to achieve a high actual evapotranspiration in combination with a given optimally used irrigation system. Our model concludes that the required amount of drainage is only dependent on the ratio of the salinity in the surface irrigation water and the acceptable salinity of the groundwater. The final salinity in the saturated zone only depends on salt‐carrying inflows and outflows. From the aforesaid model, it is further concluded that sustainable conjunctive use of groundwater for additional irrigation requires long‐term salt management, which should be founded on the essential controlling factors as derived in this paper. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Autonomous and rapid deployment of a compact taut-wire mooring     

Theo Hillebrand 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(12):1158-1162

The deployment time of a taut-wire mooring is reduced to the time any transportation/hoisting device needs to put a payload at the sea surface. This is a matter of minutes rather than hours needed for deployment of long deep-ocean moorings in the regular way. It is achieved by extending the basic function of mooring parts to temporarily form a Launcher for Oceanographic Equipment and Instruments (LOEI). Full preparation of the mooring is done onshore where the instruments are prepared and programmed, and spooled onto the top-buoy together with the line. At sea, no other gear is required than a device that is able to lift a load of, say, 2000 kg, even for long deep-ocean moorings. The compact mooring method realizes considerable budget savings through deployments from non-research vessels and airborne transportation-deployment. Limitations lay in size and weight of the oceanographic instruments. We present a test-design shaped as a barbell and loaded with 940 m line and 3 current meters. Unfurling speed was maximally 2.3 m s⁻¹ and the descent speed amounted 1.2 m s⁻¹ until landing on the seabed. These speeds are comparable to those acquired during a conventional free-falling mooring deployment.  相似文献   

Multi-day activity scheduling reactions to planned activities and future events in a dynamic model of activity-travel behavior     

Linda Nijland  Theo Arentze  Harry Timmermans 《Journal of Geographical Systems》2014,16(1):71-87

Modeling multi-day planning has received scarce attention in activity-based transport demand modeling so far. However, new dynamic activity-based approaches are being developed at the current moment. The frequency and inflexibility of planned activities and events in activity schedules of individuals indicate the importance of incorporating those pre-planned activities in the new generation of dynamic travel demand models. Elaborating and combining previous work on event-driven activity generation, the aim of this paper is to develop and illustrate an extension of a need-based model of activity generation that takes into account possible influences of pre-planned activities and events. This paper describes the theory and shows the results of simulations of the extension. The simulation was conducted for six different activities, and the parameter values used were consistent with an earlier estimation study. The results show that the model works well and that the influences of the parameters are consistent, logical, and have clear interpretations. These findings offer further evidence of face and construct validity to the suggested modeling approach.  相似文献   

An agent-based micro-simulation framework for modelling of dynamic activity–travel rescheduling decisions     

Theo Arentze  Claudia Pelizaro 《International journal of geographical information science》2013,27(8):1149-1170

The simultaneous implementation of daily activity–travel schedules of individuals in a given spatial environment generally gives rise to time- and location-varying congestion levels, which affect the conditions for subsequent activity and travel choices. Although such dynamics are commonly recognized, current activity-based models typically ignore the adaptive behaviour of individuals. In this article, we propose an agent-based simulation system that allows one to simulate, in addition to activity-scheduling behaviour, also the execution of schedules in space and time. Congestion levels at specific times and places emerge in the system and may lead to discrepancies between scheduled and actual activity and travel times. Agents respond to such unforeseen events by reconsidering an existing schedule (within-day re-planning) and by adapting their expectations about traffic conditions for subsequent days (learning). The system is illustrated using the activity–travel diary data collected in the Eindhoven region, the Netherlands, to better understand the choice of urban parks in the study area. We discuss the merits of the system for transport and spatial planning and identify avenues for future research.  相似文献   

Buddha from space—An ancient object of art made of a Chinga iron meteorite fragment*     

Elmar BUCHNER  Martin SCHMIEDER  Gero KURAT  Franz BRANDSTÄTTER  Utz KRAMAR  Theo NTAFLOS  Jörg KRÖCHERT 《Meteoritics & planetary science》2012,47(9):1491-1501

Abstract– The fall of meteorites has been interpreted as divine messages by multitudinous cultures since prehistoric times, and meteorites are still adored as heavenly bodies. Stony meteorites were used to carve birds and other works of art; jewelry and knifes were produced of meteoritic iron for instance by the Inuit society. We here present an approximately 10.6 kg Buddhist sculpture (the “iron man”) made of an iron meteorite, which represents a particularity in religious art and meteorite science. The specific contents of the crucial main (Fe, Ni, Co) and trace (Cr, Ga, Ge) elements indicate an ataxitic iron meteorite with high Ni contents (approximately 16 wt%) and Co (approximately 0.6 wt%) that was used to produce the artifact. In addition, the platinum group elements (PGEs), as well as the internal PGE ratios, exhibit a meteoritic signature. The geochemical data of the meteorite generally match the element values known from fragments of the Chinga ataxite (ungrouped iron) meteorite strewn field discovered in 1913. The provenance of the meteorite as well as of the piece of art strongly points to the border region of eastern Siberia and Mongolia, accordingly. The sculpture possibly portrays the Buddhist god Vai?ravana and might originate in the Bon culture of the eleventh century. However, the ethnological and art historical details of the “iron man” sculpture, as well as the timing of the sculpturing, currently remain speculative.  相似文献   

Small‐Scale ASR Between Flow Barriers in a Saline Aquifer          下载免费PDF全文

Marloes van Ginkel  Bas des Tombe  Theo Olsthoorn  Mark Bakker 《Ground water》2016,54(6):840-850

Regular aquifer storage recovery, ASR, is often not feasible for small‐scale storage in brackish or saline aquifers because fresh water floats to the top of the aquifer where it is unrecoverable. Flow barriers that partially penetrate a brackish or saline aquifer prevent a stored volume of fresh water from expanding sideways, thus increasing the recovery efficiency. In this paper, the groundwater flow and mixing is studied during injection, storage, and recovery of fresh water in a brackish or saline aquifer in a flow‐tank experiment and by numerical modeling to investigate the effect of density difference, hydraulic conductivity, pumping rate, cyclic operation, and flow barrier settings. Two injection and recovery methods are investigated: constant flux and constant head. Fresh water recovery rates on the order of 65% in the first cycle climbing to as much as 90% in the following cycles were achievable for the studied configurations with constant flux whereas the recovery efficiency was somewhat lower for constant head. The spatial variation in flow velocity over the width of the storage zone influences the recovery efficiency, because it induces leakage of fresh water underneath the barriers during injection and upconing of salt water during recovery.  相似文献   

The future of containerization: perspectives from maritime and inland freight distribution     

Theo Notteboom  Jean-Paul Rodrigue 《GeoJournal》2009,74(1):7-22

As containerization enters its peak growth years, its potential future developments over maritime and inland freight transport systems are being questioned. A series of issues can either further accelerate the adoption of containerization worldwide or, alternatively, could impose an upper limit to the extraordinary contribution that containers have implied for logistics systems and global commodity chains. These mainly include macro-economic, technical/operational and governance factors. Future containerization will be largely determined by interactions within and between four domains ranging from a functional to a spatial perspective. The logistical domain involves the functional organization of transport chains and their integration in supply chains. The transport domain involves the operation of transport services and intermodal operations. The infrastructural domain involves the provision and management of basic infrastructure for both links and nodes in the transport system. The locational domain relates to the geographical location of nodes and sites in the economic space and forms a basic element for their intrinsic accessibility in terms of centrality or intermediacy. It is underlined that the future of containerization will dominantly be shaped by inland transport systems.  相似文献   

Measuring the goodness-of-fit of decision-tree models of discrete and continuous activity-travel choice: methods and empirical illustration     

Theo?ArentzeEmail author  Harry?Timmermans 《Journal of Geographical Systems》2003,5(2):185-206

The use of decision tree models for predicting activity-travel choice is receiving increasing attention, but raises two related problems that are considered in this study. First, commonly used deterministic action-assignment rules should be replaced by probabilistic action-assignment rules. We develop such probabilistic rules for both discrete and continuous choice problems. Second, common goodness-of-fit measures such as the hit-ratio need to be replaced by likelihood measures. In this paper, we develop and empirically illustrate the interrelated methods and measures. The findings suggest that the new measures add information to existing statistics for discrete as well as the continuous choice.  相似文献   

    

Li Weiping  Theo Chidiezie Chineke  Liu Xin  Wu Guoxiong 《大气科学进展》2001,18(2):257-269

Utilizing data from NCEP/ NCAR reanalysis, the summertime atmospheric diabatic heating due to different physical processes is investigated over the Sahara desert, the Tibetan Plateau, and the Bay of Bengal. Atmospheric circulation systems in summer over these three areas are also studied. Thermal adaptation theory is employed to explain the relationship between the circulation and the atmospheric diabatic heating. Over the Sahara desert, heating resulting from the surface sensible heat flux dominates the near-surface layer, while radiative cooling is dominant upward from the boundary layer. There is positive vorticity in the shallow boundary layer and negative vorticity in the middle and upper troposphere. Downward motion prevails over the Sahara desert, except in the shallow near—surface layer where weak ascent exists in summer. Over the Tibetan Plateau, strong vertical diffusion resulting from intense surface sensible heat flux to the overlying atmosphere contributes most to the boundary layer heating, condensation associated with large—scale ascent is another contributor to the lower layer heating. Latent heat release accompanying deep convection is critical in offsetting longwave radiative cooling in the middle and upper troposphere. The overall diabatic heating is positive in the whole troposphere in summer, with the most intense heating located in the boundary layer. Convergence and positive vorticity occur in the shallow near—surface layer and divergence and negative vorticity exist deeply in the middle and upper troposphere. Accordingly, upward motion prevails over the Plateau in summer, with the most intense rising occurring near the ground surface. Over the Bay of Bengal, summertime latent heat release associated with deep convection exceeds longwave radiative cooling, resulting in intense heating in almost the whole troposphere. The strongest heating over the Bay of Bengal is located around 400 hPa, resulting in the most intense rising occurring between 300 hPa and 400 hPa, and producing positive vorticity in the lower troposphere and negative vorticity in the upper troposphere. It is also shown that the divergent circulation is from a heat source region to a sink region in the upper troposphere and vice versa in lower layers. This work was jointly supported by “ National Key Program for Developing Basic Sciences” G1998040904 by NSFC projects 49805003, 49635170, 49823002, and 49825504.  相似文献