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

甚长基线干涉测量技术（VLBI）于20世纪80年代初正式投入使用，在地球动力学领域取得了许多令人瞩目的科学成就。它们是：第一次探测到当代板块运动和沿板块边界的运动；通过章动、极运动和地球的变自转来洞察地核；精确理解固体地球、大气和海洋的角动量交换；建立基于精确定位星系外射电源的天文参考系；然而，由于GPS（全球定位系统）的出现，地面参考系的作用已逐渐被GPS所取代。因此，现在是VLBI明确其未来十年科学目标的时候了。通过建立高精度的全球VLBI网络来实现地球自转的连续监测。另一方面，从各国VLBI系统发展的历史来看，现有的记录系统是互不兼容的。例如，日本VLBI社区开发了K-4录音系统，其录音格式不同于美国开发的和之前的Mark-III系统。此外，加拿大VLBI社区开发了S2系统，与日本和美国的系统相比，该系统具有不同的记录格式。这种情况使得对地球动力学研究进行协调一致的全球VLBI观测变得困难。由于日本国立天文台（NAOJ）地球VLBI组只有K-4系统，一直无法参与全球VLBI观测。为了解决这个问题，我们正在努力在海外天线基地部署K-4记录系统。”1995学年末，在中国乌鲁木齐天文台和乌克兰克里米亚天体物理天文台部署了该系统，启动了K-4全球观测。然而，NAOJ的VLBI活动仍然局限于这个K-4网络，不能参与Mark-III VLBI网络。因此，我们计划通过这个为期两年的研究项目，开发一个接口系统，使我们能够同时处理K-4和Mark-III格式。在本研究项目中，我们引进了一套高密度数字磁带录音机（DR-101B，由INTERFEROMETRICS公司生产），开发并安装了一个可以读写K-4和Mark-III格式的接口电路。这已经成功地完成了，目前我们可以操作一个由两个不同的记录系统组成的网络。在我们的研究项目期间，NASA宣布了建立Mark-IV VLBI全球24小时连续观测网络的计划，该网络由七个网络组成。Mark-IV是Mark-III的升级版，比特率为0.5Gb/s。为了加入NASA Mark-IV网络，我们仍然需要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站进行大地测量VLBI观测。在这个项目中，我们计划与澳大利亚VLBI社区进行联合观测。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，我们计划将研究项目扩展到K-4， Mark-IV和S2系统之间的兼容性。这套系统称为“多格式系统”，将于一九九七至一九九八学年完成。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