Anisotropic Mean Traveltime Curves: A Method to Estimate Anisotropic Parameters from 2D Transmission Tomographic Data

We present the mathematical deduction and properties of the mean traveltime curves for homogeneous elliptical anisotropic media. These curves generalize their isotropic counterparts which have been introduced in the past as a simple data quality analysis technique at the pre-inversion stage for 2D transmission experiments, allowing the inference of prior velocity models to gain stability at the tomographic inversion. Also, the anisotropy parameters (maximum velocity, anisotropic direction and ratio) are shown to affect the shape of these curves. The degree of asymmetry of the anisotropic mean traveltime curves (displacement of the mean time and standard deviation minima from the middle of the gathering line) is related to the direction of anisotropy which can then be visually estimated. Least squares’ fitting of the anisotropic theoretical models to their experimental counterparts is an effective method to estimate at the pre-inversion stage a macroscopic elliptical anisotropic velocity model, valid at the scale of the experiment, and able to match the experimental mean traveltime distribution. Sensitivity analysis has shown that the mean curve is less prone to errors than the standard deviation curve. Parameter identification from the standard deviation curve becomes unstable for noise levels higher than 5%; data errors produce smearing of the value of the estimated anisotropy ratio and wrong directions of anisotropy biased towards zero degrees. Also, identification from the mean traveltime curve becomes stable when the maximum velocity is well constrained. Finally, this methodology is illustrated with the application to the Grimsel data set. Performing MTC analysis is always recommended since it does not need high numerical requirements, and as shown in the sensibility analysis section, errors in data can be misinterpreted as geological anisotropies. J.L. Fernández Martínez is a visiting professor at UC Berkeley, Department of Civil and Environmental Eng., CA 94720-1710.     

省级基础测绘1：10000 DLG成果的质量检查

1∶10 000DLG是省级基础测绘的核心成果。本文论述了DLG成果质量检查现状以及检验方法和流程,就如何进一步提高1∶10 000DLG成果检验效率与质量做了一些分析与探讨。     

SAR影像在立体测图中的应用

通过对机栽2．5m分辨率SAR影像的布点、平差及单片计算,进一步构建了邻航线间SAR影像的立体模型配对,并通过FeatureStation工作平台的矢量化采集,完成了1：50000比例尺的DLG测图工作。     

Al3+掺杂锂皂石的合成及其性能研究

采用水热法合成锂皂石,以LiCl-MgCl2-Na2SiO3-H2O为主要反应体系,加入NaOH调节反应体系的pH值,通过加入Al2(SO4)3.18H2O而引入Al3+进行掺杂改性,合成了系列锂皂石。对所得产物进行XRD检测,探测了产物的结晶化度和结构组成。通过分光光度计和流变仪测定了产物的透光性及粘度性能,结果发现反应体系pH值的变化可引起锂皂石产品水分散体系的透明度;控制一定的Al3+加入量,可得到具有较高粘度的锂皂石产品。     

On-the-fly GPS-based attitude determination using single- and double-differenced carrier phase measurements

Carrier phase measurements are primary observations for GPS attitude determination. Although the satellite-related errors can be virtually eliminated by forming single differences, the baseline-related errors such as line biases are still present in the single-differenced carrier phase measurements. It is, therefore, difficult to resolve the single-differenced integer ambiguities due to the line biases. By forming double differences, the line biases of the single-differenced carrier phase measurements can be effectively removed. However, the main disadvantages of this method lie in the fact that the double-differenced measurements are mathematically correlated and consequently the attitude obtained from the double differences is noisy. This paper presents a new algorithm through which both single and double differences are used simultaneously to resolve these problems in real-time. The solution of the integer ambiguities can be obtained by searching for the most likely grid point in the attitude domain that is independent of the correlation with the double differences. Next, the line biases and corresponding single difference integer ambiguities can be resolved on the fly by using the noisy attitude solution obtained from the previous double difference procedure. In addition, the relationship between the physical signal path difference and the line bias is formed. A new method is also applied to derive the attitude angles through finding the optimal solution of the attitude matrix element. The proposed new procedure is validated using ground and flight tests. Results have demonstrated that the new algorithm is effective and can satisfy the requirement of real-time applications.     

Numerical modelling of spectral sky radiance during a total solar eclipse

Ground-based observations of the spectral sky radiance within the totality region during a total solar eclipse are of significant interest because the contribution from direct and single scattered light from the solar disk is eliminated. In the present paper, we develop a numerical model of the spectral sky radiance during totality, evaluate the contribution of double scattered sunlight to the sky radiance at totality and compare it to solar corona emissions. The results show that the single scattered coronal light is the major contaminant in ground-based observations of the corona, opposite to what was believed before. For observation directions outside the corona the double scattered sun radiation dominates over the single scattered coronal light.     

GEOWAY在土地利用调查中的应用

通过对宜兴土地详查作业过程阐述GEOWAY在土地利用调查中的作业流程和作业方法     

试论砂金矿勘探中小于可采宽度的矿体处理方法

本文以青海省某大型河谷型砂金矿特征为例,并结合其他已勘查过的河谷型砂金矿矿床特征分析,主张在砂金勘探中对小于可采宽度的矿体,除在施工中及时加密工程验证外,在储量计算时可用“边界米克值”衡量代替以“工业米克值”进行勘探线的矿与非矿判定,同时再配以“镶边”法处理较为合理。     

影响准东西向切变线运动的一些因子分析

本文认为江淮切变线是由于纬向风的不连续切变形成涡层的表现形式,且呈准东西向。对此涡层的分析得到一些关系到切变线移动的因素。     

网络技术在时间服务工作中的应用

主要介绍网络技术在授时中心守时实验室的守时及授时服务系统中的应用情况。守时系统是一种需要连续、可靠运转的复杂系统，包括守时钟组、比对测量系统、原子时归算等多个环节。原子时专用局域网是守时系统的一个重要的组成部分，它有效地提高了守时、原子时及相关数据资料的传递和交换速率。时间服务的网络化、自动化不仅有效提高了工作效率，减少了人工过多干预造成的误差，更重要的是可以提高守时系统的可靠性和合理性。章详细介绍原子时局域网络（ATLAN）系统和计算机网络授时系统的设计情况。