兰州地磁台GPS差分方位角的测量

为了适应高采样率、高分辨率、高精度的新型地磁仪器对磁偏角和磁倾角观测的需要,应用GPS测定了改造后的兰州地磁台的7个观测墩（一个临时观测墩）至2个方位标志的方位角,共取得了13个方位角参数,使兰州地磁台在地磁偏角测量或仪器验收比测中可供6套仪器同时观测,并可做到全天候观测。     

差分GPS在中国地磁监测网地理方位角测量中的应用

中国地磁监测网由地磁台站和流动地磁测点构成,实现对观测网内地磁场的相对记录和绝对观测。它的绝对观测采用世界上最先进的F、D、I测量仪器组合,其中地磁偏角D是地理北和地磁北的夹角。对地磁偏角D的绝对测量要求在地磁台站投入正常观测前必须完成观测墩和观测标志的地理方位角测量,流动地磁测点在每次地磁偏角D观测前后至少进行地理方位角测量各一次。据地磁监测网《观测规范》要求,地磁偏角D的观测精度必须≤6″,所以中国地磁监测网采用天文和差分GPS地理方位角两种测量方法,且两种方法观测精度相当,均≤6″。与天文测量相比,差分GPS观测不受天气等自然因素的限制,操作简单,观测快捷,数据处理计算机程序化。随着GPS技术的普及,中国地磁监测网差分GPS地理方位角测量方法已基本取代了天文方法。本文主要介绍差分GPS在中国地磁监测网地理方位角测量中的应用。     

乌鲁木齐地震台地磁测量标志投入使用

为了进一步改善和提高乌鲁木齐地震台地磁资料观测精度,于1989年9月在乌鲁木齐地震台新修建了两个地磁测量标志。为保证新标志的观测精度和长期稳定性,在选点、设计和施工中,国家地震局地球物理研究所九室的周锦屏,赵学敏等同志进行了指导。标志建成后经过一年时间的保养维护,标志已处于稳定状态。标志方位角是测量磁偏角不可少的一个参照量,它的准确性以及长其稳定性直接关系到磁偏角的观测精度。建台时修建的两个测量标志由于在设计处理中没有直接和基岩相接触,所以经过十几年时间的变化影响,标志向一方倾斜,方位角发生了近1°7′的变化,给该台磁偏角观测带来了不应有的测量误差。另外,作为国家地磁一     

北京地磁台天文方位角测量及误差分析

论述了北京地磁台天文方位标志的选点定位、造标埋设、方位角的测量方法。对８个观测墩位一个测点进行了方位角测量。通过计算方位角绝对精度ΔＡ＝２．４９″，平均观测均方差Ｍ＝±１．１４″，相当于三等天文观测精度，能满足地磁偏角６″的精度要求。     

FHD 磁力仪分量线圈装置误差对磁偏角观测的影响分析

根据FHD 磁力仪观测磁偏角的原理, 计算了分量线圈不水平导致的磁偏角观测值误差,发现分量线圈仅在EW 方向的倾斜对磁偏角观测产生误差。文中将理论分析结果与实际观测结果进行了对比分析, 发现由于分量线圈底座水平的长期漂移, 仪器的垂直分量及磁偏角观测误差也会发生长期漂移, 长期漂移变化的周期约2 ~ 4 个月, 对垂直分量其幅度约3.5~ 11.0nT, 而磁偏角的幅度约0.1′~ 1.0′, 因此认为在将该仪器观测值用作绝对观测值进行地震异常分析时, 应注意回避这种长期漂移变化。     

分量核旋仪偏置电流对磁偏角测量的影响分析

从理论上定量地分析了FHD-1型分量核旋仪的偏置电流对磁偏角观测值的影响,结果表明偏置电流的漂移对磁偏角观测值的影响随偏置电流的漂移量的增大而增大、也随磁偏角观测值的增大而增大,该结果对指导台站提高该仪器磁偏角观测值的精度有一定意义。     

长春地磁台天文方位角测量及精度估计

本文论述了长春地磁台天文方位角的测量方法、原理及测量结果,同时做了测量精度估计,通过计算方位角理论最大误差为3.7″,实际观测最大误差为2.5″,能满足地磁偏角6″的精度要求。     

用普通便携式磁力仪独立测定磁偏角的尝试

本文主要介绍了用普通便携式磁力仪独立测定天文方位角,方法简便,为今后地磁台站核查标志方位问题作了先例。这种方法在目前观测磁偏角和流动磁测工作中可以广泛采用.     

机场地磁场测量及数据处理

地磁偏角(D)被广泛应用于飞行器的导航,磁罗经是最经典、最可靠的导航工具之一。结合中国机场地磁测量的需求和地磁观测的现状,详细描述罗经标定盘(Compass rose或Compass calibration pad)在机场选址、建设及应用过程中,利用质子旋进磁力仪(GSM-19T或G856)、磁通门无磁经纬仪(CTM-DI或Mingeo)和差分GPS(PROMARK 2或PROMARK 100)进行地磁总强度(F)梯度、地理方位角、地磁方位角和地磁偏角(D)的测量方法。同时描述观测数据仪器差的改正、日变通化和长期变计算方法,以供机场地磁测量应用。     

CJ6型磁力仪测定磁偏角的几个问题

本文讨论了使用CJ_6型磁力仪测定磁偏角中的几个问题。认为仪器材料磁性影响、仪器置平程度好坏、望远镜聚焦位置改变,正、倒镜读数差大小、悬丝扭力大小以及磁系翻转复位率都可以对观测结果产生影响。作者提出了在观测中提高磁系翻转复位率的几项措施,并对CJ_6型磁力仪的观测和仪器改进提出了有关建议。     

A Monte Carlo study of rainfall forecasting with a stochastic model

A procedure for short-term rainfall forecasting in real-time is developed and a study of the role of sampling on forecast ability is conducted. Ground level rainfall fields are forecasted using a stochastic space-time rainfall model in state-space form. Updating of the rainfall field in real-time is accomplished using a distributed parameter Kalman filter to optimally combine measurement information and forecast model estimates. The influence of sampling density on forecast accuracy is evaluated using a series of a simulated rainfall events generated with the same stochastic rainfall model. Sampling was conducted at five different network spatial densities. The results quantify the influence of sampling network density on real-time rainfall field forecasting. Statistical analyses of the rainfall field residuals illustrate improvement in one hour lead time forecasts at higher measurement densities.     

Information for authors

正SCIENCE CHINA Earth Sciences,an academic journal cosponsored by the Chinese Academy of Sciences and the National Natural Science Foundation of China,and published by Science China Press and Springer,is committed to publishing high-quality,original results in both basic and applied research.     

INTERNATIONAL RESEARCH AND TRAINING CENTER ON EROSION AND SEDIMENTATION(IRTCES)

正Director:Shangfu Kuang,China Vice-directors:Chunhong Hu,China Duihu Ning,China Guangquan Liu,China The International Research and Training Center on Erosion and Sedimentation(IRTCES)was jointly set up by the Government of China and UNESCO on July 21,1984.It aims at the promotion of international exchange of knowledge and cooperation in the studies of erosion and     

Calendar of events

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Dynamic process-response model of river channel development

Feedback mechanisms, which operate upstream through drawdown and backwater effects and downstream through sediment discharge are responsible for channel evolution. By combining these mechanisms with channel processes it euables a dynamic process-response model to be developed to simulate the initial evolution of straight gravel-bed channels. When erosion commences on a land surface, sediment entrained in the headwater reach by hydraulic action is selectively transported, deposited and reworked. This produces a damped oscillation between degradation and aggradation as the channel and valley respond to spatial and temporal variations in sediment calibre and hydraulic conditions. The initial cut and fill phases are responsible for valley incision and floodplain development while secondary and subsequent activity can produce river terraces. Eventually sediment entrainment in the headwaters declines as slopes are reduced. Subsequent channel evolution is relatively insignificant because it is dependent on local weathering activity producing material that can be transported on declining slopes. Therefore landforms produced during the initial phase of development, when local weathering was non-limiting, dominate the landscape.