排序方式： 共有41条查询结果，搜索用时 15 毫秒
31.
Tobias Nilsson Robert Heinkelmann Maria Karbon Virginia Raposo-Pulido Benedikt Soja Harald Schuh 《Journal of Geodesy》2014,88(5):491-502
In this paper we investigate the accuracy of the earth orientation parameters (EOP) estimated from the continuous VLBI campaign CONT11. We first estimated EOP with daily resolution and compared these to EOP estimated from GNSS data. We find that the WRMS differences are about 31 $\upmu $ as for polar motion and 7 $\upmu $ s for length of day. This is about the precision we could expect, based on Monte Carlo simulations and the results of the previous CONT campaigns. We also estimated EOP with hourly resolution to study the sub-diurnal variations. The results confirm the results of previous studies, showing that the current IERS model for high-frequency EOP variations does not explain all the sub-diurnal variations seen in the estimated time series. We then compared our results to various empirical high-frequency EOP models. However, we did not find that any of these gave any unambiguous improvement. Several simulations testing the impact of various aspects of, e.g. the observing network were also made. For example, we made simulations assuming that all CONT11 stations were equipped with fast VLBI2010 antennas. We found that the WRMS error decreased by about a factor five compared to the current VLBI system. Furthermore, the simulations showed that it is very important to have a homogenous global distribution of the stations for achieving the highest precision for the EOP. 相似文献
32.
董刚 《地震工程与工程振动(英文版)》2002,1(1):20-26
Objectives of this task are to conduct research on seismic hazards, and to provide relevant input on the expected levels of
these hazards to other tasks. Other tasks requiring this input include those dealing with inventory, fragility curves, rehabilitation
strategies and demonstration projects. The corresponding input is provided in various formats depending on the intended use:
as peak ground motion parameters and/or response spectral values for a given magnitude, epicentral distance and site conditions;
or as time histories for scenario earthquakes that are selected based on the disaggregated seismic hazard mapped by the U.S.
Geological Survey and are incorporated in building codes. The user community for this research is both academic researchers
and practicing engineers who may use the seismic input generated by the synthesis techniques that are developed under this
task for a variety of applications. These include ground motions for scenario earthquakes, for developing fragility curves
and in specifying ground motion input for critical facilities (such as hospitals) located in the eastern U.S.
Supported in part by the Earthquake Engineering Research Centers Program of the National Science Foundation under Award Number EEC-9701471
to the Multidisciplinary Center for Earthquake Engineering Research. 相似文献
33.
34.
35.
36.
Tobias Nilsson Benedikt Soja Kyriakos Balidakis Maria Karbon Robert Heinkelmann Zhiguo Deng Harald Schuh 《Journal of Geodesy》2017,91(7):857-866
The very long baseline interferometry (VLBI) Intensive sessions are typically 1-h and single-baseline VLBI sessions, specifically designed to yield low-latency estimates of UT1-UTC. In this work, we investigate what accuracy is obtained from these sessions and how it can be improved. In particular, we study the modeling of the troposphere in the data analysis. The impact of including external information on the zenith wet delays (ZWD) and tropospheric gradients from GPS or numerical weather prediction models is studied. Additionally, we test estimating tropospheric gradients in the data analysis, which is normally not done. To evaluate the results, we compared the UT1-UTC values from the Intensives to those from simultaneous 24-h VLBI session. Furthermore, we calculated length of day (LOD) estimates using the UT1-UTC values from consecutive Intensives and compared these to the LOD estimated by GPS. We find that there is not much benefit in using external ZWD; however, including external information on the gradients improves the agreement with the reference data. If gradients are estimated in the data analysis, and appropriate constraints are applied, the WRMS difference w.r.t. UT1-UTC from 24-h sessions is reduced by 5% and the WRMS difference w.r.t. the LOD from GPS by up to 12%. The best agreement between Intensives and the reference time series is obtained when using both external gradients from GPS and additionally estimating gradients in the data analysis. 相似文献
37.
38.
Estimation and evaluation of real-time precipitable water vapor from GLONASS and GPS 总被引：1，自引：0，他引：1
Cuixian Lu Xingxing Li Maorong Ge Robert Heinkelmann Tobias Nilsson Benedikt Soja Galina Dick Harald Schuh 《GPS Solutions》2016,20(4):703-713
The revitalized Russian GLONASS system provides new potential for real-time retrieval of zenith tropospheric delays (ZTD) and precipitable water vapor (PWV) in order to support time-critical meteorological applications such as nowcasting or severe weather event monitoring. In this study, we develop a method of real-time ZTD/PWV retrieval based on GLONASS and/or GPS observations. The performance of ZTD and PWV derived from GLONASS data using real-time precise point positioning (PPP) technique is carefully investigated and evaluated. The potential of combining GLONASS and GPS data for ZTD/PWV retrieving is assessed as well. The GLONASS and GPS observations of about half a year for 80 globally distributed stations from the IGS (International GNSS Service) network are processed. The results show that the real-time GLONASS ZTD series agree quite well with the GPS ZTD series in general: the RMS of ZTD differences is about 8 mm (about 1.2 mm in PWV). Furthermore, for an inter-technique validation, the real-time ZTD estimated from GLONASS-only, GPS-only, and the GPS/GLONASS combined solutions are compared with those derived from very long baseline interferometry (VLBI) at colocated GNSS/VLBI stations. The comparison shows that GLONASS can contribute to real-time meteorological applications, with almost the same accuracy as GPS. More accurate and reliable water vapor values, about 1.5–2.3 mm in PWV, can be achieved when GLONASS observations are combined with the GPS ones in the real-time PPP data processing. The comparison with radiosonde data further confirms the performance of GLONASS-derived real-time PWV and the benefit of adding GLONASS to stand-alone GPS processing. 相似文献
39.
Gleich D. Gergic B. Cucej Z. Planinsic P. 《Geoscience and Remote Sensing Letters, IEEE》2004,1(2):90-93
In this letter, we propose a new image coding technique, which is a combination of space frequency quantization and a context-based modeling using fuzzy logic. The compression results showed that the proposed coder outperforms the state-of-the-art coders in the rate-distortion sense for compression of processed synthetic aperture radar amplitude data. 相似文献
40.
In this paper, we argue that the politics of aid in Sri Lanka 'after' the 2004 Indian Ocean tsunami accentuated what we call the 'politics of purification'– the fragmented ethnic politics of territoriality – in Sri Lanka's east. The politics of purification entail geographical imaginations of a nation as 'the same people living in the same place'. We illustrate this with a case study on Muslim geographies in Kalmunai Divisional Secretariat division, on the coast of Ampara District, southeast Sri Lanka, where the politics of relocating Muslim families from the buffer zone created the conditions for the geographical imaginations of the politics of purification to play out. At the same time, our study indicates the antinomies of purification and the political fragmentation of Muslim geographies. 相似文献