STUDY OF ASTROMETRY AND GEODYNAMICS BY MEANS OF INTERNATIONAL VLBI OBSERVATIONS

1. VLBI观测获得的结果（1）地球自转快速变化的探测国际地球自转服务组织（IERS）和国际GPS地球动力学服务组织（IGS）联合组织了国际观测活动，研究GPS探测地球自转快速变化的可行性。这次名为“EPOCH 92”的活动于7月27日至8月10日进行，参与活动的有已经建立的空间技术，即VLBI和SLR。我们作为VLBI太平洋网络的网络中心参加了EPOCH 92，并在为期2周的活动中组织了5次24小时的会议观测。美国海军天文台的相关中心最近完成了相关处理，数据库已交付给世界各地的分析中心。这项由科学资助计划资助的研究计划的其中一个科学目的，是透过一个天文观测系统， ...更多信息 分析了EPOCH 92活动期间获得的VLBI数据。该研究小组刚刚开始分析VLBI数据库。分析结果将提交即将举行的国际会议。(2)射电参考框架的南延我们利用澳大利亚塔斯马尼亚站的网络进行了VLBI观测。由于南方站的参与，我们可以观测到低至-30度赤纬的射电源，从而有助于以高精度将无线电参考框架扩展到南半球。我们还研究了所有观测到的射电源的位置变化，发现其中几个射电源的位置变化可能是由于结构的变化。由于大气载荷效应引起的台站位移考虑到目前VLBI三维定位的精度已接近亚厘米级，因此必须模拟产生这一位移量的所有可能的地球物理因素。特别是，模拟垂直位移是必不可少的监测海平面变化的背景下，全球变化。大气负荷效应是引起几mm到几cm垂直位移的主要原因之一，本文根据日本气象厅计算的全球气压资料，结合海洋响应的特点，估算了各站的垂直位移。用场面压力资料参数化的结果已被编入VLBI分析软件。少

1. Results obtained by VLBI observations(1) Detection of rapid variations of the earth's rotationThe International Earth Rotation Service (IERS) and the International GPS Geodynamics Service (IGS) jointly organized the international observational campaign to investigate feasibility of GPS in detecting rapid variations in the earth's rotation. The campaign entitled EPOCH92 was conducted from July 27 through August 10 with the participation of the already established space techniques, namely, VLBI and SLR. We participated in EPOCH92 as the network center of the VLBI Pacific network and organized five 24-hour session observations during the 2-week campaign. Correlation processing made at the correlation center at the US Naval Observatory was recently completed and the database has been delivered to the worldwide analysis centers. One of the scientific objectives of the research project supported by the scientific grant-in-aid is to clarify the characteristics of rapid earth rotation by an … More alyzing the VLBI data obtained during the EPOCH92 campaign. The research group has just started analysis of the VLBI database. The results of analysis will be presented at the coming international meetings.(2) Southern extension of the radio reference frameWe conducted VLBI observations using the network involving an Australian station, Tasmania. Due to the participation of the southern station, we could observe radio sources of declinations down to -30ﾟ and thereby contribute to extending the radio reference frame to the southem hemisphere with high accuracy. We also investigated position changes of all the observed radio sources and found that several of them have shown position changes probably due to the structure changes.2. Station displacements due to atmospheric loading effectsIn consideration of the current accuracy in three-dimensional positioning by VLBI is approaching to sub-centimeter level, it is indispensable to model all possible geophysical factors yielding this amount of displacements. In particular, modeling vertical displacement is essential in monitoring the sea level change in the context of global change. Atmospheric loading effect is one of them causing a few mm to a few cm vertical displacements.Based on the global pressure data calculated by the Japan Meteorological Agency, we estimated the vertical Displacements of all the stations taking account of the characteristics of ocean responses. The results parameterized by the sitesurface pressure data have been incorporated in the VLBI analysis software. Less