连续基准网GPS数据质量检测与分析

利用TEQC软件对中国地壳运动观测网络基准站1999年至2007年的原始观测数据进行质量检测,给出了各站Mp1、Mp2和CSR的月变化趋势图及年平均值;参照IGS的GPS观测数据质量标准对其进行统计分析,得出结论：网络工程基准站大部分站点观测数据质量优于IGS标准;数据质量较差的站为：shao、wuhn和yong。     

IGS站的数量与几何结构对GNSS星座近实时精密轨道影响研究

采用2016年年积日为99～101天不同数量和分布结构的IGS站的观测数据,利用滑动数据窗口内(48h)法方程叠加方法解算GNSS导航星座近实时精密轨道,结果表明,采用全球结构优化的40个IGS站的观测数据解算GNSS导航星座近实时精密轨道,其精度能达到0.087m,但IGS站数据达到一定数值以后继续增加IGS站观测数据,GNSS导航星座近实时精密轨道精度不会显著提高,反而会使近实时轨道解算的时间增长影响轨道解算的实时性;IGS站数量固定,其分布结构是影响GNSS导航星座近实时轨道精度的关键因素。     

导航星座快速精密轨道解算方法研究

基于2012年年积日为88~95 d的60个IGS站的观测数据,利用滑动数据窗口内短弧法方程综合的方法解算导航星座快速精密轨道,然后与IGS精密轨道做比较。结果表明,利用全球分布的60个IGS站的观测数据解算导航星座快速精密轨道,其径向、切向、法向的轨道精度RMS的均值为4.3、6.3、2.4 cm,平均为4.3 cm。     

GNSS导航星座近实时精密轨道解算方法研究

文章利用滑动数据窗口内短弧法方程叠加方法,基于2018年年积日为89天～91天60个IGS站的观测数据,进行解算GNSS导航星座近实时精密轨道,与CODE提供的精密轨道做比较,结果表明,采用全球均匀分布的60个IGS站的观测数据,解算GNSS导航星座近实时精密轨道,其轨道精度在径向、切向、法向RMS的均值分别为0.078m、0.120m和0.064m,平均为0.088m。     

天山地壳低频应变波特征研究

 依据新疆天山地区24 a的分量式钻孔应变观测资料,分析144个M≥4.0级地震的应变波记录数据。研究发现,在39个地震前出现明显应变波,其特征如下：(1) 周期为3～16 d,以3～7 d为主;(2) 应变波振幅为10－7～10－5,以10－6居多;(3) 随震级由小到大应变波有下列特征：① 应变波图像从简单到复杂;② 仪器记录应变波的比例逐步增强,从17%逐渐提高到100%;③ 仪器记录应变波的距离由近而远,并呈指数分布特点;④ 应变波持续时间逐步延长,从小震的几天到巨震的几年;⑤ 应变波出现、结束、最大幅度出现到地震发生时间间隔由短到长。应变波最重要的特征是出现在震前,与地震时才出现的地震波截然不同,这对灾害性地震预测有实际意义。     

双频GPS精密定位的实验与分析

GPS精密单点定位技术是近些年来人们研究的热点.利用IGS跟踪站的精密星历进行单点定位,可以直接得到厘米甚至毫米级的高精度的ITRF框架下的空间直角坐标.但观测多长时间可满足用户的精度要求人们并不清楚.文章利用CORS站的观测数据和IGS站联测的数据,使用Leica Geo Office软件,对CORS站的观测数据从10 min开始,依次增加10 min,直至10 h进行分段处理,得到不同时长的精密单点定位的在ITRF框架下坐标结果和精度,以研究定位结果的收敛性.结果表明,观测时长50 min,点位精度高于5 cm;观测时长220 min,点位精度高于1 cm.     

联合Sentinel-1A和GPS数据分析高雄地震形变

合成孔径雷达干涉测量(InSAR)技术具有高空间分辨率、覆盖范围广等特点,但只能获取雷达视线向的地表形变信息,无法得到真实的三维地表形变量。GPS数据可以得到高精度的E、N、U方向位移,但只能在离散的站点测量,空间分辨率低。本文提出一种联合InSAR和GPS数据计算地表三维形变的方法,采用覆盖研究区域的Sentinel-1A影像,结合重复轨道差分干涉测量技术(D-InSAR)和GPS同震位移测量结果获取了2016年台湾高雄Mw6.7地震的高密度三维同震形变信息。结果表明,此次地震的最大形变中心约位于120.40°E、22.90°N,雷达视线向最大形变量约为15cm,同震形变以垂直和东西方向形变为主。联合InSAR和GPS数据能够很好地反演地震的同震形变场,对于其产生机理的研究和分析具有重要意义。     

利用单站GPS测速信息进行地震监测

近年来,GPS测速已经成为研究GPS地震学的一种重要方法。本文介绍了GPS测速的原理,并尝试将GPS测速应用于地震监测中。利用单站高频GPS数据,对2011年日本大地震和2012年新疆地震期间的GPS测速结果和同震位移进行了分析。结果表明,单站GPS测速无需其他参考站信息和精密轨道钟差,其测速精度达到几个mm/s,同时能反演地震期间观测站的速度变化信息和震中与监测站的位置关系,可为地震监测提供一种有效可行的方式。     

利用高频GNSS资料进行强震的震相识别和震中反演

利用2011年日本东北Mw9.0地震和2008年汶川Mw7.9地震的高频GNSS观测资料,解算出震时的位移波形。对位移波形一阶差分得到速度时间序列,并采用S变换谱的方法对该速度时序进行地震波到时的拾取。其拾取结果用于震中位置和发震时刻反演,并将反演结果与USGS比较得出:日本地震震中位置相差约16km,发震时刻相差约0.7s;汶川地震震中相差约4km,发震时刻相差约0.4s,为强震预警和应急提供了支持和依据。     

基于CNES实时星历的精密单点定位精度分析

首先给出了实时GPS精密单点定位的数学模型以及改正了三类误差影响,详细阐述了扩展Kalman滤波过程。利用IGS的实时星历产品(CNES),对IGS三个站一天观测数据和实测的无人机动态GPS观测数据分别进行静态和动态实时GPS精密单点定位实验,结果表明:静态实时精密单点定位精度在XY方向优于0.102 m,Z方向优于0.211 m,处于分米级;动态实时精密单点定位精度优于0.244 m。实时精密单点定位精度低于事后,但能够应用于应急测绘、快速制图等时效性要求较强的测绘工作。     

不同基准下GPS网解算精度对比研究

为了得到可靠、可信的处理结果,有必要深入研究各种基准类型对网平差结果的影响。GPS观测网解算主要基准类型包括自由网解算、最小约束、约束参考测站和固定参考测站。利用一周的观测数据进行分析,涉及测站点包括五个中国大陆IGS测站和一个台湾IGS测站,即:BJFS,CHAN,KUNM,SHAO,WUHN和TWTF。采用四种基准对GPS观测网进行平差,客观地分析了各种基准对GPS观测网平差结果精度的影响。最后为选择一个合理的GPS观测网平差基准得出有益的结论。     

A method to model the effect of pre-existing cracks on P-wave velocity in rocks

Crack closure is one of the reasons inducing changes of P-wave velocity of rocks under compression.In this context,a method is proposed to investigate the relationships among P-wave velocity,pre-existing cracks,and confining pressure based on the discrete element method(DEM).Pre-existing open cracks inside the rocks are generated by the initial gap of the flat-joint model.The validity of the method is evaluated by comparing the P-wave velocity tested on a sandstone specimen with numerical result.As the crack size is determined by the diameter of particles,the effects of three factors,i.e.number,aspect ratio,and orientation of cracks on the P-wave velocity are discussed.The results show that P-wave velocity is controlled by the(i.e.number) of open micro-cracks,while the closure pressure is determined by the aspect ratio of crack.The reason accounting for the anisotropy of P-wave velocity is the difference in crack number in measurement paths.Both of the number and aspect ratio of cracks can affect the responses of P-wave velocity to the applied confining pressure.Under confining pressure,the number of open cracks inside rocks will dominate the lowest P-wave velocity,and the P-wave velocity of the rock containing narrower cracks is more sensitive to the confining pressure.In this sense,crack density is difficult to be back-calculated merely by P-wave velocity.The proposed method offers a means to analyze the effect of pre-existing cracks on P-wave velocity.     

Inconsistency of changes in uniaxial compressive strength and P-wave velocity of sandstone after temperature treatments

It is generally accepted that the uniaxial compressive strength(UCS)and P-wave velocity of rocks tend to decrease simultaneously with increasing temperature.However,based on a great number of statistical data and systematic analysis of the microstructure variation of rocks with temperature rising and corresponding propagation mechanism of elastic wave,the results show that(1)There are three different trends for the changes of UCS and P-wave velocity of sandstone when heated from room temperature(20
C or 25
C)to 800
C:(i)Both the UCS and P-wave velocity decrease simultaneously;(ii)The UCS increases initially and then decreases,while the P-wave velocity decreases continuously;and(iii)The UCS increases initially and then fluctuates,while the P-wave velocity continuously decreases.(2)The UCS changes at room temperaturee400
C,400
Ce600
C,and 600
Ce800
C are mainly attributed to the discrepancy of microstructure characteristics and quartz content,the transformation plasticity of clay minerals,and the balance between the thermal cementation and thermal damage,respectively.(3)The inconsistency in the trends of UCS and P-wave velocity changes is caused by the change of quartz content,phase transition of water and certain minerals.     

岩芯卸荷扰动的声学反应与卸荷敏感岩体

声波测试是工程岩体质量评价的最主要手段之一。将岩体与岩块的纵波波速比的平方定义为岩体的完整性系数。不仅为国内外学者广泛认同。而且是现行规范的定义。这是源于如下认识：原位岩体的纵波波速小于其中岩块的波速；岩体越破碎。小得越多。然而。通过润扬大桥声波测试发现。用通常手段得到的大部分岩体的测井波速反而大于岩样波速。对该桥基岩40余个钻孔数百个岩样进行了多种手段的对比研究和综合分析。探讨了测试结果的可靠性及产生原因。进而提出了岩芯卸荷扰动和卸荷敏感岩体的概念和相应的工程对策。     

花岗岩岩块饱水状态对纵波波速测试结果的影响

在岩土工程勘察中,采用纵波波速测试评价岩石的物理力学性质时,常会遇到岩块纵波波速试验值小于岩体纵波波速的异常情况。通过对青岛地铁勘察资料和勘察过程的调查分析,以花岗岩为例,采用对比试验模拟勘察试验过程进行验证,发现岩块饱水状态的变化和岩块纵波波速测试规程不严谨是导致岩块纵波波速测试结果不准确的重要原因之一。结合发现,文中对提高花岗岩岩块纵波波速测试结果准确性提出了建议。     

P波方位AVO在煤层裂缝探测中的应用

探测煤层中的裂缝对于煤田的安全生产具有重要的意义。由于地层上覆载荷的压实作用,水平和低角度裂缝近乎消失,保留下来的是高角度和近于垂直的裂缝,而正是这类裂缝引起了地震P波方位各向异性的传播特征。所以地震P波的方位各向异性反映了地下介质裂缝的发育情况,尤其是P波方位AVO属性,对裂缝的发育程度具有较好的敏感性。通过对P波方位AVO属性的分析,能得到地下介质裂缝的发育情况。基于利用P波方位AVO属性探测裂缝的理论和实用方法,对淮南煤田某矿区的纵波地震资料进行对比和分析,得到了本矿区某煤层的裂缝发育分布情况,其预测结果符合实际井孔实测资料,表明此方法有效。     

城市非正式绿地：概念、类型、价值及更新设计模式研究

为了解决存量背景下高密度建成区“无缝插绿”的困境,对目前关注较少的非正式绿地的概念、类型、价值和更新设计模式进行系统研究。对web of science及中国知网数据库的63篇中英文文献进行分析。非正式绿地具有无人管理及覆盖自发生长植被的特征,可分为面状、线性及点状绿地,具有增强绿色基础设施韧性、提升绿地公平性、增加城市生物多样性、营造居民安全健康社区环境等重要价值,居民对非正式绿地喜好存在偏差,研究表明该偏差与受访者年龄、受教育程度等个体特征密切相关。非正式绿地是城市绿地（广义）的一种重要类型,具有用地转变、低扰提质、界面融合三种更新设计模式。     

Effects of Air Bubbles on B-Value and P-Wave Velocity of a Partly Saturated Sand

The effects of the size and solubility of an air bubble on the B-value and P-wave velocity of a partly saturated sand are discussed. The relations between B-value and P-wave velocity are determined for large triaxial specimens with D_r = 64% and 84%. Theoretical formulas have been derived for determining the P-wave velocity of a partly saturated sand containing air bubbles. It is shown that: (1) the solubility of air bubbles in the pore-water significantly affects the relations between B-value and P-wave velocity; (2) the practical coefficient of solubility of air bubble pressured in the pore-water is about 0.002; (3) the B-value and P-wave velocity increase with a decrease in the air bubble size. This tendency is significant, when the diameter of the air bubble is less than about 0.005 mm.     

Application of machine learning in predicting the rate-dependent compressive strength of rocks

Accurate prediction of compressive strength of rocks relies on the rate-dependent behaviors of rocks, and correlation among the geometrical, physical, and mechanical properties of rocks. However, these properties may not be easy to control in laboratory experiments, particularly in dynamic compression experiments. By training three machine learning models based on the support vector machine (SVM), back-propagation neural network (BPNN), and random forest (RF) algorithms, we isolated different input parameters, such as static compressive strength, P-wave velocity, specimen dimension, grain size, bulk density, and strain rate, to identify their importance in the strength prediction. Our results demonstrated that the RF algorithm shows a better performance than the other two algorithms. The strain rate is a key input parameter influencing the performance of these models, while the others (e.g. static compressive strength and P-wave velocity) are less important as their roles can be compensated by alternative parameters. The results also revealed that the effect of specimen dimension on the rock strength can be overshadowed at high strain rates, while the effect on the dynamic increase factor (i.e. the ratio of dynamic to static compressive strength) becomes significant. The dynamic increase factors for different specimen dimensions bifurcate when the strain rate reaches a relatively high value, a clue to improve our understanding of the transitional behaviors of rocks from low to high strain rates.