Location: GNSS Activities in Korea: Retrospect and Prospects

Introduction
Korea Astronomy and Space Science Institute (KASI) is the only research institute in the field of Astronomy and Space Science funded by Korean government from 1974. KASI has wide variety of research areas such as optical, radio, theoretical, and applied astronomy and is expanding its research area to space science with various infrastructures including the 1.8m optical telescope, the 14m radio telescope, the solar telescope, the several robotic telescopes, real-time GPS network in Korea and other countries. Doing both pure scientific researches on the Universe and the developments of space-related techniques, KASI is leading the space science era of 21st century in Korea. The headquarter of KASI is located in DaeDoek Science Complex, Daejeon, the central part of South Korea.

PAST
At the end of 1989, three precise geodetic GPS receivers from Trimble were introduced to KASI (former name was Korea Astronomy Observatory). This was the starting point to involve in GNSS R&D activities of KASI. An epoch-making turning point in GPS research was when KASI GPS station played an active role of International GNSS Service (IGS) on 1st, January 1994. From that time, KASI had been involved in many GNSS-related projects with domestic and international collaboration.

The Continuously Operating Reference Station (CORS) systems of KASI, which consists of nine permanent GPS stations including an IGS site (DAEJ), have been operating from the beginning of the year 2000. The observation and DGPS/RTK correction data of reference stations are provided through the internet (HTML and TCP/IP) for the post-time and real-time user groups. Actually, several GPS networks for various purposes had been constructed in Korea during 1999-2001. As a result of the mutual collaboration between different research institutions and governmental agencies, Korean GPS Network (KGN) could be organized with more than 70 sites at 2000. The Continuously Operating Reference Stations of KGN are well distributed over the South Korea and the average distance between stations is about 40km (Fig. 1).

Figure 1. Korean GPS Network (KGN)

One of the outstanding outputs was the determination of coordinate transformation parameters between the WGS84 and the Korean datum. KASI had finished the 3-year project for this purpose in 1996, and the accuracy of coordinate transformation could be achieved within 20 cm for all components when using the results from the above projects and the geoid model developed by Pusan National University, Korea.

Figure 2. Horizontal velocity together with their error ellipse with confidence factor 95%