The ionospheric eclipse factor method (IEFM) and its application to determining the ionospheric delay for GPS

A new method for modeling the ionospheric delay using global positioning system (GPS) data is proposed, called the ionospheric eclipse factor method (IEFM). It is based on establishing a concept referred to as the ionospheric eclipse factor (IEF) λ of the ionospheric pierce point (IPP) and the IEF’s influence factor (IFF) . The IEF can be used to make a relatively precise distinction between ionospheric daytime and nighttime, whereas the IFF is advantageous for describing the IEF’s variations with day, month, season and year, associated with seasonal variations of total electron content (TEC) of the ionosphere. By combining λ and with the local time t of IPP, the IEFM has the ability to precisely distinguish between ionospheric daytime and nighttime, as well as efficiently combine them during different seasons or months over a year at the IPP. The IEFM-based ionospheric delay estimates are validated by combining an absolute positioning mode with several ionospheric delay correction models or algorithms, using GPS data at an international Global Navigation Satellite System (GNSS) service (IGS) station (WTZR). Our results indicate that the IEFM may further improve ionospheric delay modeling using GPS data.     

Two-step method for the determination of the differential code biases of COMPASS satellites

The differential code bias (DCB) in satellites of the Global Navigation Satellite Systems (GNSS) should be precisely corrected when designing certain applications, such as ionospheric remote sensing, precise point positioning, and time transfer. In the case of COMPASS system, the data used for estimating DCB are currently only available from a very limited number of global monitoring stations. However, the current GPS/GLONASS satellite DCB estimation methods generally require a large amount of geographically well-distributed data for modeling the global ionospheric vertical total electron content (TEC) and are not particularly suitable for current COMPASS use. Moreover, some satellites with unstable DCB (i.e., relatively large scatter) may affect other satellite DCB estimates through the zero-mean reference that is currently imposed on all satellites. In order to overcome the inadequacy of data sources and to reduce the impact of unstable DCB, a new approach, designated IGGDCB, is developed for COMPASS satellite DCB determination. IGG stands for the Institute of Geodesy and Geophysics, which is located in Wuhan, China. In IGGDCB, the ionospheric vertical TEC of each individual station is independently modeled by a generalized triangular series function, and the satellite DCB reference is selected using an iterative DCB elimination process. By comparing GPS satellite DCB estimates calculated by the IGGDCB approach based on only a handful (e.g., seven) of tracking stations against that calculated by the currently existing methods based on hundreds of tracking stations, we are able to demonstrate that the accuracies of the IGGDCB-based DCB estimates perform at the level of about 0.13 and 0.10?ns during periods of high (2001) and low (2009) solar activity, respectively. The iterative method for DCB reference selection is verified by statistical tests that take into account the day-to-day scatter and the duration that the satellites have spent in orbit. The results show that the impact of satellites with unstable DCB can be considerably reduced using the IGGDCB method. It is also confirmed that IGGDCB is not only specifically valid for COMPASS but also for all other GNSS.     

A new approach to GPS ambiguity decorrelation

Ambiguity decorrelation is a useful technique for rapid integer ambiguity fixing. It plays an important role in the least-squares ambiguity decorrelation adjustment (Lambda) method. An approach to multi-dimension ambiguity decorrelation is proposed by the introduction of a new concept: united ambiguity decorrelation. It is found that united ambiguity decorrelation can provide a rapid and effective route to ambiguity decorrelation. An approach to united ambiguity decorrelation, the HL process, is described in detail. The HL process performs very well in high-dimension ambiguity decorrelation tests. Received: 9 March 1998 / Accepted: 1 June 1999     

大地测量学家 周江文教授

周江文教授是我国著名的大地测量学家和误差理论专家,八十有三的周老精神瞿铄,思维敏捷,充满着对我国大地测量事业和年轻同志成长的关心.他对我国大地测量的贡献更为学术界所赞赏.正如大地测量和固体地球物理学家许厚泽院士所评价:"周江文教授是我国大地测量和测量误差理论研究领域中最有造诣的一位优秀科学家.60多年来,他为大地测量学的发展作出了巨大贡献.他自1958年到中科院测地所工作,为我所科技事业发展和人才培养呕心沥血,作了很多贡献".他以严肃的态度治学育人,60年如一日,为我国大地测量学术界树立了一座丰碑.     

基于规则格网数据断面极值法的一种改进方法

在研究基于规则格网数据地形特征提取过程中,主要有断面极值法和流水模拟法.在断面极值法中,针对传统断面极值法生成的特征线存在零碎、并行交叉等缺点,我们改进了传统的局部断面极值法,在特征线连接过程中增加了“将特征点邻域内其它候选特征点设置为已被引用、根据特征线长度与范围阈值筛选特征线“等条件,以克服生成的特征线存在的零碎和并行交叉问题.     

Evolution of the variability of surface temperature and vegetation density in the great plains

This study focuses on how the variability of land surface temperature and vegetation density at the SGP ARM-CART site changes over episodic (day to day) and seasonal time scales using AVHRR satellite data. Four drying periods throughout the year are analyzed. Land surface temperature had an erratic relationship with time exhibiting no deterministic pattern from day-to-day or season-to-season. Furthermore, it did not exhibit spatial pattern persistence. On the other hand, vegetation density had a consistent spatial pattern and temporal decay during average length drying periods (less than 7 days) as well as within a season. However, there were distinct differences in the seasonal pattern of variation between winter and growing seasons. In addition, the paper highlights a methodology to quantify the relationships that exist at the land surface between the primary parameter of interest and the controlling variables.     

Equivalent force control method for generalized real‐time substructure testing with implicit integration

This paper presents a new method, called the equivalent force control method, for solving the nonlinear equations of motion in a real‐time substructure test using an implicit time integration algorithm. The method replaces the numerical iteration in implicit integration with a force‐feedback control loop, while displacement control is retained to control the motion of an actuator. The method is formulated in such a way that it represents a unified approach that also encompasses the effective force test method. The accuracy and effectiveness of the method have been demonstrated with numerical simulations of real‐time substructure tests with physical substructures represented by spring and damper elements, respectively. The method has also been validated with actual tests in which a Magnetorheological damper was used as the physical substructure. Copyright © 2007 John Wiley & Sons, Ltd.     

Pushover analysis procedure for systems considering SSI effects based on capacity spectrum method

This paper presents a new procedure to transform an SSI system into an equivalent SDOF system using twice equivalence. A pushover analysis procedure based on the capacity spectrum method for buildings with SSI effects （PASSI） is then established based on the equivalent SDOF system, and the modified response spectrum and equivalent capacity spectrum are obtained. Furthermore, the approximate formulas to obtain the dynamic stiffness of foundations are suggested. Three steel buildings with different story heights （3, 9 and 20） including SSI effects are analyzed under two far-field and two near-field historical records and an artificial seismic time history using the two PASSI procedures and the nonlinear response history analysis （NLhRHA） method. The results are compared and discussed. Finally, combined with seismic design response spectrum, the nonlinear seismic response of a 9-story building with SSI effects is analyzed using the PASSI procedures, and its seismic performance is evaluated according to the Chinese ＇Code for Seismic Design of Buildings. The feasibility of the proposed procedure is verified.     

Fuzzy random vibration of multi-degree-of-freedom hysteretic systems subjected to earthquakes

Earthquake excitation not only has evident randomness but also has strong fuzziness owing to the uncertainties in the definition of earthquake intensity and site soil classification. In this paper, the seismic ground motion is simulated as a stationary filtered white noise with fuzzy parameters, an analytical procedure is proposed to analyse the fuzzy random vibration of multi-degree-of-freedom (MDOF) hysteretic systems, and the covariance matrix of the fuzzy random responses is derived by the equivalent linearization technique. Finally, some numerical results for a two-storey shear hysteretic frame are presented to demonstrate the validity and effectiveness of the procedure proposed.     

鲜水河断裂带古构造残余应力场对大地震的控制

以岩体正交异性弹性理论为基础,用X射线法,在鲜水河断裂带测区沿7条测线,测量了岩体三维残余应力,绘成区域残余应力等值线图、主应力线图及其应变能密度等值线图,探讨了其对带内大地震的控制作用