DEVELOPMENT OF AN INTERFACE SYSTEM TO ENSURE COMPATIBLITY OF THE EXITING VARIOUS VLBI RECORDING SYSTEMS FOR GLOBAL GEODETIC OBSERVATIONS

甚长基线干涉测量(VLBI)自上世纪80年代初投入使用以来，在地球动力学领域取得了许多显著的科学成就。它们是：第一次探测当代板块运动和沿板块边界的运动，通过章动、极移和地球的可变自转来洞察地核，精确了解固体地球、大气和海洋的角动量交换，建立基于星系外射电源精确定位的天文参照系，基于精确确定站的坐标和运动建立地球参照系等。然而，由于全球定位系统的出现，地球参考系的作用已逐渐被全球定位系统取代。因此，现在是VLBI明确其未来十年的科学目标的时候了。这肯定会通过建立…来实现更高精度的全球VLBI网络用于连续监测地球自转。另一方面，根据各国VLBI系统的发展历史，现有的记录系统相互不兼容。例如，日本VLBI团体开发了K-4记录系统，其记录格式与美国开发的及其之前的Mark-III系统不同。加拿大VLBI社区也开发了S2系统，与日本和美国的系统相比，S2系统的记录格式不同。由于日本国家天文台(NAOJ)的地质学VLBI组只有K-4系统，我们一直无法参与全球VLBI观测。为了解决这一问题，我们已经努力在海外天线站点部署K-4记录系统。到1995学年末，我们在乌鲁木齐中国天文台和乌克兰克里米亚天体物理观测站部署了我们的系统，并启动了K-4全球观测，但NAOJ的VLBI活动仍然局限于这个K-4网，不能参与Mark-III VLBI网。因此，我们计划通过这项为期两年的研究项目，开发一种能够同时处理K-4和Mark-III格式的接口系统。在这个研究项目中，我们介绍了一套高密度数字磁带录音机(DR-101B，由INTERFEROMETRICS公司制造)，并开发并安装了一种可以读写K-4和Mark-III格式的接口电路。这一点已经成功完成，目前我们可以运行一个由两个不同记录系统组成的网络。未来计划在我们的研究项目期间，NASA宣布了建立Mark-IV VLBI全球连续24小时观测网络的计划，该网络由7个网络组成。MARK-IV记录仪是MARK-III的升级版，码率为0.5 GB/S。为了加入NASA的MARK-IV网络，我们还必须升级我们新开发的接口系统。此外，NAOJ正在与国家极地研究所合作，从明年开始在南极Syowa站进行大地VLBI观测。在这个项目中，我们计划与澳大利亚VLBI社区进行联合观察。澳大利亚目前使用的VLBI系统是加拿大的S2系统。因此，我们需要开发另一个接口来与S2系统兼容。因此，我们计划扩大我们的研究项目，使K-4、Mark-IV和S2系统兼容。这个名为“多格式系统”的系统将在1997至1998学年期间完成。较少

BackgroundVery Long Baseline Interferometry (VLBI), which was brought into regular operation in early 1980's, has made a number of remarkable scientific accomplishment in the field of geodynamics. They are, first detection of the contemporary plate motions and motions along the plate boundaries, insight of the earth's core by means of nutation, polar motion and earth's variable rotation, precise understanding of angular momentum exchange of solid earth, atmosphere and oceans, establishment of the astronomical reference frame based on precise positioning of extra-galactic radio sources, establishment of terrestrial reference frame based on precise determination of the station coordinates and motions, etc.However, due to the advent of GPS (Global Positioning System), the role of terrestrial reference system has been gradually taken over by GPS.Hence it is the time for VLBI to clearly define its future scientific targets for the next decade. This will be certainly realized by establishing … More a high-accuracy global VLBI networks for continuous monitoring of the earth's rotation.On the other hand, according to the history of VLBI system development made in various countries, the exiting recording systems are mutually incompatible. For example, Japanese VLBI community has developed K-4 recording system whose recording format is different from that of US developed and preceding Mark-III system. Also Canadian VLBI community has developed S2 system which has different recording format compared to the Japanese and US systems. This situation has made it difficult to make a concerting global VLBI observation for geodynamic research.AccomplishmentsAs the geotic VLBI group of the National Astronomical Observatory, Japan (NAOJ) has only K-4 system, we have been unable of participating global VLBI observations. In order to resolve the problem, we have made effort to deploy K-4 recording system to overseas antenna sites. By the end of the 1995 academic year, we deployed our system to the Urumqi Astronomical Observatory of China and the Crimean Astrophysical Observatory of Ukraine and initiated K-4 global observations.However, VLBI activities of NAOJ is still restricted to this K-4 network and cannot participate in the Mark-III VLBI networks. Hence we planned to develop an interface system which enables us to handle both K-4 and Mark-III format through this two-year research project.In this research project, we introduced a set of high density digital tape recorder (DR-101B,made by INTERFEROMETRICS), and developed and installed an interface circuit which is possible to read and write both K-4 and Mark-III formats. This has successfully been accomplished and at present we can operate a network composed of two different recording systems.Future PlanDuring the term of our research project, NASA announced the plan of forming Mark-IV VLBI global networks for continuous 24-hour observations, which is composed of seven networks. Mark-IV recorder is an up-graded version of Mark-III and has a bit rate of 0.5Gb/s. In order to join the NASA Mark-IV network, we still have to grade up our newly developed interface system. Also NAOJ is collaborating with the National Institute for Polar Research to conduct geodetic VLBI observations at the Antarctic Syowa station from the next year. In this project, we are planning to make joint observations with Australian VLBI community. The presently used VLBI system of Australia is Canadian S2 system. Hence we need to develop another interface to make compatibility with S2 system. Thus we are planning to extend our research project to make compatibility among K-4, Mark-IV and S2 systems. This system called 'Multi-Format System' will be completed during1997 to 1998 academic year. Less