The IGS (International GPS Service) is an example of a network of GPS continuous operation stations and integrated service systems, based on approximately 200 global ground based GPS continuous operation stations. It provides various GPS information to global users free of charge, such as GPS precise ephemeris, fast ephemeris, predicted ephemeris, IGS station coordinates and their motion rates, phase and pseudorange data of GPS signals received by IGS stations, and Earth rotation rate. This information supports numerous scientific projects in geodesy and geodynamics, including ionosphere, meteorology, reference frames, precise time transfer, high-resolution estimation of Earth's rotation rate and its changes, and crustal movement.

　　(1) IGS currently provides three types of orbits: first, the final (precision) orbit, which needs to be obtained after 10-12 days and is commonly used for precision positioning; The second is to report the orbit quickly, which should be obtained after 1 day. It is commonly used for calculating atmospheric water vapor content, ionosphere, etc; Another type is the predicted orbit.

　　Currently, only two IGS analysis centers provide estimates of GPS clock bias. IGS currently uses nearly 70 external frequency standards among its nearly 200 permanently continuous global tracking stations, of which approximately 30 use hydrogen clocks, approximately 20 use cesium atomic clocks, approximately 20 use rubidium atomic clocks, and the rest use crystal oscillators inside GPS.

　　(2) IGS also provides information on pole shift and world time. The final daily polar coordinates (x, y) published by IGS have an accuracy of ± 0.1mas, while the corresponding accuracy of the quick report is ± 0.2mas. As a space geodetic technology, GPS itself does not have the function of measuring Universal Time (UT). However, due to the correlation between GPS satellite orbit parameters and UT, as well as the determination of Earth's rotation rate, which is the time derivative of UT, IGS can still provide daily length of day (LOD) values. IGS can now further determine the nutation term and high-resolution pole shift (up to once every 2 hours, instead of once a day). The latter is mainly due to the improvement of observation quality at IGS observation stations, rapid and timely data transmission, and improvements in data processing methods, without any fundamental changes. However, the former is a technological leap forward.

　　(3) One extremely useful and important information provided by IGS is the coordinates, corresponding frameworks, epochs, and station movement speeds of those continuous operating stations (tracking stations) of IGS. The former has better accuracy than 1cm, while the latter has better accuracy than 1mm/y. The coordinate reference framework used for IGS station coordinates is coordinated with IERS. Starting from the end of 1993, ITRF91 was used. From 1994, ITRF92 was used. From 1995 to mid 1996, ITRF93 was used. From mid 1996 to April 1998, ITRF94 was used. On March 1, 1998, ITRF96 was adopted and IGS began to adopt ITRF97.

　　(4) The new contribution of IGS in measuring short-term nutation. As is well known, the movement of the Earth's rotational axis on the Earth's surface is called polar motion, while its motion in inertial space is called precession and nutation.

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