GPS快速精密定位的随机模型研究

综合与归纳了GPS精密定位的三种比较实用的随机模型,提出了将这三种随机模型用于GPS快速精密定位中,通过两个实例分析了三种随机模型对GPS快速精密定位的精度影响,得出几点有益的结论。     

A Procedure for Estimating the Variance Function of Linear Models and for Checking the Appropriateness of Estimated Variances: A Case Study of GPS Carrier-phase Observations

In many applications of linear model theory, homogeneous variances are assumed. In practice, however, the variances are frequently heterogeneous. Therefore, to improve the results, the unknown variances have to be estimated. The appropriateness of the estimated variances has then to be checked by a suitable statistical test procedure. Such a procedure is also useful to study models of global positioning system (GPS) carrier-phase observations. While the functional model of GPS carrier-phase observations is widely accepted, the stochastic model is still under development. As well as the neglected correlations of GPS observations, a homogenous variance function is frequently assumed. In Bischoff et al. (J Geod 78:397–404, 2005), we showed by statistical testing that the assumption of constant variances is not appropriate. In this paper, we give a procedure to estimate an individual variance function for a pair of satellites and a procedure to check the appropriateness of the estimated variances. As an example, the approach is applied to double-differenced carrier-phase GPS observations.     

选权迭代定位粗差时权函数参数之功能

本文研究了幂函数型权函数的参数与定位粗差能力的关系。提出了权函数基本变量的幂取值范围为-2.5～-4.0;计算权的基本变量对于第1,2次迭代用“放大余差”,以后则用余差;对余差进行统计判断的统计量采用“标准化余差”。     

High velocity anomaly beneath the Deccan volcanic province: Evidence from seismic tomography

Analysis of teleseismicP-wave residuals observed at 15 seismograph stations operated in the Deccan volcanic province (DVP) in west central India points to the existence of a large, deep anomalous region in the upper mantle where the velocity is a few per cent higher than in the surrounding region. The seismic stations were operated in three deployments together with a reference station on precambrian granite at Hyderabad and another common station at Poona. The first group of stations lay along a west-northwesterly profile from Hyderabad through Poona to Bhatsa. The second group roughly formed an L-shaped profile from Poona to Hyderabad through Dharwar and Hospet. The third group of stations lay along a northwesterly profile from Hyderabad to Dhule through Aurangabad and Latur. Relative residuals computed with respect to Hyderabad at all the stations showed two basic features: a large almost linear variation from approximately +1s for teleseisms from the north to—1s for those from the southeast at the western stations, and persistance of the pattern with diminishing magnitudes towards the east. Preliminary ray-plotting and three-dimensional inversion of theP-wave residual data delineate the presence of a 600 km long approximately N−S trending anomalous region of high velocity (1–4% contrast) from a depth of about 100 km in the upper mantle encompassing almost the whole width of the DVP. Inversion ofP-wave relative residuals reveal the existence of two prominent features beneath the DVP. The first is a thick high velocity zone (1–4% faster) extending from a depth of about 100 km directly beneath most of the DVP. The second feature is a prominent low velocity region which coincides with the westernmost part of the DVP. A possible explanation for the observed coherent high velocity anomaly is that it forms the root of the lithosphere which coherently translates with the continents during plate motions, an architecture characteristic of precambrian shields. The low velocity zone appears to be related to the rift systems (anomaly 28, 65 Ma) which provided the channel for the outpouring of Deccan basalts at the close of the Cretaceous period.     

GALILEO试验星GIOVE—A信号质量分析

介绍了GIOVE-A卫星信号,分析了GIOVE-A卫星信号质量;与GPS CA码信号质量进行了比较。     

ESTIMATION OF SOIL PARAMETERS FOR ASSESSING POTENTIAL WETNESS: COMPARISON OF MODEL RESPONSES THROUGH GIS

A geographic information system (GIS) is utilized to model wetness potential for a portion of Uwharrie National Forest, North Carolina. The wetness index is derived from TOPMODEL, a hillslope-scale runoff simulation model. The wetness index is a distributed-parameter model, with the input parameters obtained from a digital elevation model (DEM) and Soil Conservation Service (SCS) soils data. The primary objectives of the research are to: (1) compare methods of estimating soil parameters for input into the wetness potential model; and (2) determine how the model outputs vary spatially as a consequence of different methods of estimating soil parameters. Three methods of estimating soil parameters are used: (a) assuming uniform soil properties; (b) using SCS data presented as ranges; and (c) using alternative literature-based estimates of soil parameters. Results indicate that the wetness model responds similarly regardless of how the soil parameters are estimated, but differences in the spatial variability of the wetness potentials occur as a result of estimating soil parameters through alternative approaches. Correlation, pair-wise regression and analysis of regression residuals are used to compare model responses within a GIS environment.     

Galileo导航系统观测值的质量分析

从信噪比、伪距多路径效应、单差残差和非差观测值精度等方面对进入初始服务初期Galileo导航系统观测值的质量进行了对比分析,最后简要评估了Galileo导航系统的单点定位精度。结果表明:在信噪比方面,Galileo E5最高,E1、E5a和E5b次之且基本相当;在伪距多路径方面,Galileo E1最大,其次分别为E5b和E5a,而E5最小;在单差残差方面,Galileo导航系统单差相位残差基本在±4 mm内,单差伪距残差基本在±0.3 m内;在非差观测值精度方面,Galileo导航系统相位观测值精度E1最高,E5a、E5b和E5次之且基本相当,而伪距观测值精度E5最高,E5b最差;整体上而言,Galileo导航系统观测值的数据质量略优于GPS和BDS;Galileo导航系统单频伪距单点定位的水平精度约为2.2 m,与GPS和BDS的水平定位精度基本相当,而高程精度约为5.2 m,稍差于GPS和BDS,这与可观测卫星数和PDOP有很大的关系。     

巢湖悬浮物中有机氯农药的分布、来源与风险

利用GC-MS测定了2010年5月至2011年4月巢湖4个采样点悬浮物中有机氯农药(OCPs)含量,分析了悬浮物中OCPs残留水平的时空变化及其组成特征,探讨了悬浮物中主要OCPs的可能来源与生态风险.结果表明:(1)巢湖悬浮物中共检出17种OCPs,分别为六六六类(HCHs)农药的4种异构体(α-、β-、γ-、δ-HCH)、滴滴涕类(DDTs)农药的两种母体(o,p'-、p,p'-DDT)和3种代谢产物(o,p'-、p,p'-DDE,p,p'-DDD)、六氯苯、七氯、艾氏剂、异艾氏剂、氯丹的两种异构体(α-、γ-chlordane)、硫丹-I和灭蚁灵.(2)巢湖悬浮物中∑OCPs含量为172.7±434.9 ng/g,其中∑HCHs含量为15.1±10.3 ng/g,∑DDTs含量为138.8±407.3 ng/g;DDTs在夏季污染水平达到最高;空间上,污染程度为:东部湖区西部湖区中部湖区.(3)DDTs在总OCPs中占有绝对优势,DDTs比例夏季最高而秋季最低;HCHs仅在秋季为主要污染物.(4)HCHs主要来源于近期林丹的非法使用;而DDT主要来源于工业DDT的使用,在春季可能存在DDT的非法使用;悬浮物中DDT的降解环境主要为有氧环境.(5)巢湖悬浮物中p,p'-DDT和o,p'-DDT会对水生生物产生潜在的不利影响.     

POISSON'S RATIO VARIATIONS OF CRUSTAL MEDIA BEFORE AND AFTER XINYUAN-HEJING MS6.6 EARTHQUAKE IN 2012

We analyzed the variation characteristics of Poisson's ratio in crustal media from January 2009 to December 2012 at 11 fixed seismic stations(for station SCH, it is from January 2006 to December 2012)within an epicenter distance of 200km of the Xinyuan-Hejing M_S6.6 earthquake in Xinjiang on June 30, 2012 using the methods of P wave receiver functions, H-κ stacking of receiver functions, and time sliding window, and obtained the following conclusions: (1)The crustal media's Poisson ratio of five stations in an epicenter distance less than 130km showed a significant and long-lasting decline about 2~3 years before Xinyuan-Hejing M_S6.6 earthquake. Taking the crustal Poisson ratio mean value as reference, the decrease ranges between 0.003 and 0.014, the decrease in 4 stations are more than twice the mean error. The variations of the Poisson's ratio in crust are characterized by "V" shape or "double V" shape. Earthquakes occur at the end of the formation of "V" shape. After the occurrence of earthquakes, the Poisson's ratio continues to rise. The earliest initial fall appeared in July 2009 at WUS station which has the minimum epicentral distance(77km). The Poisson ratio of the crustal media of 6 stations with epicentral distance more than 150km fluctuated up and down around the mean value, and there is no significant decline or persistent low value. (2)We analyzed the arrival-time variations of the quasi-repetitive receiver functions Ps converted wave(t_Ps)of the 3 stations WUS, SCH and XNY and found that the travel times of Ps converted waves became smaller in the crust before the earthquake and increased after the earthquake. (3)Through the comprehensive analysis on the descending process, decline ranges, variations process, duration of Poisson' ratio, the Ps converted waves arrival time variations, the original time of earthquake, and the number of stations, it is inferred that the cause for Poisson's ratio anomalous variations is the change of physical properties of crustal media in the process of earthquake preparation and occurrence. Since the variation characteristics of crustal media may be related to the earthquake magnitude, the size of seismogenic area, the medium properties under stations, and the focal distance, whether the medium variation characteristics exist before and after Xinyuan-Hejing M_S6.6 earthquake will need more earthquake cases analyses. (4)The H-κ stacking of receiver functions is used to calculate the velocity ratio. Because P-wave velocity is given, this method can only be applied when the Ps converted wave velocity of Moho surface of receiver functions changes before an earthquake. With the application of receiver functions to the analysis of more earthquake cases, we can gain more insights into the variation of crustal medium parameters during the seismogenic process. This observation indicates that the receiver function method may become a new approach to detect the Poisson's ratio change of the crustal media before strong earthquake under the condition of high seismic network density.