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171.
172.
A precise and efficient algorithm is developed for determining the locations of radio beacons (e.g. of the ARGOS or COSPAS/SARSAT type) based on Doppler shift measurements in overflying satellites. The method distinguishes itself through: (1) the use of a very compact analytic orbital theory valid for all eccentricities, (2) autonomous orbit improvement based on Doppler data for one or more local reference beacons accessible at a single LUT, (3) simultaneous orbit improvement and calculation of beacon coordinates for an arbitrary number of satellites, satellite passes, and beacons, and (4) very efficient semi-analytic matrix inversion by partitioning into global, semi-global, and local parameters.The algorithm has been implemented in a FORTRAN program which can be run on a PC. Error statistics are presented from applications of the program to a large number of actual Doppler curves obtained with the ARGOS and COSPAS/SARSAT systems. 相似文献
173.
Challenges in global ballast water management 总被引:3,自引:0,他引:3
Endresen Ø Lee Behrens H Brynestad S Bjørn Andersen A Skjong R 《Marine pollution bulletin》2004,48(7-8):615-623
Ballast water management is a complex issue raising the challenge of merging international regulations, ship's specific configurations along with ecological conservation. This complexity is illustrated in this paper by considering ballast water volume, discharge frequency, ship safety and operational issues aligned with regional characteristics to address ecological risk for selected routes. A re-estimation of ballast water volumes gives a global annual level of 3500 Mton. Global ballast water volume discharged into open sea originating from ballast water exchange operations is estimated to approximately 2800 Mton. Risk based decision support systems coupled to databases for different ports and invasive species characteristics and distributions can allow for differentiated treatment levels while maintaining low risk levels. On certain routes, the risk is estimated to be unacceptable and some kind of ballast water treatment or management should be applied. 相似文献
174.
Mechanisms for interpreting anomalous decreases in radon in ground water prior to earthquakes are examined with the help of a case study to show that radon potentially is a sensitive tracer of strain changes in the crust preceding an earthquake. The 2003 Chengkung earthquake of magnitude (M) 6.8 on December 10, 2003, was the strongest earthquake near the Chengkung area in eastern Taiwan since 1951. The Antung radon-monitoring station was located 20 km from the epicenter. Approximately 65 d prior to the 2003 Chengkung earthquake, precursory changes in radon concentration in ground water were observed. Specifically, radon decreased from a background level of 780 pCi/L to a minimum of 330 pCi/L. The Antung hot spring is situated in a fractured block of tuffaceous sandstone surrounded by ductile mudstone. Given these geological conditions, we hypothesized that the dilation of brittle rock mass occurred at a rate faster than the recharge of pore water and gas saturation developed in newly created cracks preceding the earthquake. Radon partitioning into the gas phase may explain the anomalous decrease of radon precursory to the 2003 Chengkung earthquake. To support the hypothesis, vapor-liquid, two-phase radon-partitioning experiments were conducted at formation temperature (60 degrees C) using formation brine from the Antung hot spring. Experimental data indicated that the decrease in radon required a gas saturation of 10% developed in rock cracks. The observed decline in radon can be correlated with the increase in gas saturation and then with the volumetric strain change for a given fracture porosity. 相似文献
175.
Ole B. Andersen Gary D. Egbert Svetlana Y. Erofeeva Richard D. Ray 《Ocean Dynamics》2006,56(5-6):416-429
Overtides and compound tides are generated by nonlinear mechanisms operative primarily in shallow waters. Their presence complicates
tidal analysis owing to the multitude of new constituents and their possible frequency overlap with astronomical tides. The
science of nonlinear tides was greatly advanced by the pioneering researches of Christian Le Provost who employed analytical
theory, physical modeling, and numerical modeling in many extensive studies, especially of the tides of the English Channel.
Le Provost’s complementary work with satellite altimetry motivates our attempts to merge these two interests. After a brief
review, we describe initial steps toward the assimilation of altimetry into models of nonlinear tides via generalized inverse
methods. A series of barotropic inverse solutions is computed for the M tide over the northwest European Shelf. Future applications of altimetry to regions with fewer in situ measurements will
require improved understanding of error covariance models because these control the tradeoffs between fitting hydrodynamics
and data, a delicate issue in coastal regions. While M can now be robustly determined along the Topex/Poseidon satellite ground tracks, many other compound tides face serious aliasing
problems.
In memory of Christian Le Provost 相似文献
176.
Patterns and processes involved in litter breakdown on desert river floodplains are not well understood. We used leafpacks containing Fremont cottonwood (Populus deltoides subsp. wislizenii) leaf litter to investigate the roles of weather and microclimate, flooding (immersion), and macroinvertebrates on litter organic matter (OM) and nitrogen (N) loss on a floodplain in a cool-temperate semi-arid environment (Yampa River, northwestern Colorado, USA). Total mass of N in fresh autumn litter fell by 20% over winter and spring, but in most cases there was no further N loss prior to termination of the study after 653 days exposure, including up to 20 days immersion during the spring flood pulse. Final OM mass was 10–40% of initial values. The pattern of OM and N losses suggested most N would be released outside the flood season, when retention within the floodplain would be likely. The exclusion of macroinvertebrates modestly reduced the rate of OM loss (by about 10%) but had no effect on N dynamics over nine months. Immersion in floodwater accelerated OM loss, but modest variation in litter quality did not affect the breakdown rate. These results are consistent with the concept that decomposition on desert floodplains progresses much as does litter processing in desert uplands, but with periodic bouts of processing typical of aquatic environments when litter is inundated by floodwaters. The strong dependence of litter breakdown rate on weather and floods means that climate change or river flow management can easily disrupt floodplain nutrient dynamics. 相似文献
177.
A proposal for a new scenario framework to support research and assessment in different climate research communities 总被引:1,自引:0,他引:1
Detlef P. van Vuuren Keywan Riahi Richard Moss Jae Edmonds Allison Thomson Nebojsa Nakicenovic Tom Kram Frans Berkhout Rob Swart Anthony Janetos Steven K. Rose Nigel Arnell 《Global Environmental Change》2012,22(1):21-35
In this paper, we propose a scenario framework that could provide a scenario “thread” through the different climate research communities (climate change – vulnerability, impact, and adaptation - and mitigation) in order to support assessment of mitigation and adaptation strategies and climate impacts. The scenario framework is organized around a matrix with two main axes: radiative forcing levels and socio-economic conditions. The radiative forcing levels (and the associated climate signal) are described by the new Representative Concentration Pathways. The second axis, socio-economic developments comprises elements that affect the capacity for mitigation and adaptation, as well as the exposure to climate impacts. The proposed scenarios derived from this framework are limited in number, allow for comparison across various mitigation and adaptation levels, address a range of vulnerability characteristics, provide information across climate forcing and vulnerability states and span a full century time scale. Assessments based on the proposed scenario framework would strengthen cooperation between integrated-assessment modelers, climate modelers and vulnerability, impact and adaptation researchers, and most importantly, facilitate the development of more consistent and comparable research within and across these research communities. 相似文献
178.
179.