Geodetic Datum and Geodetic Control Networks - Geodesy: Introduction to Geodetic Datum and Geodetic Systems - page 96

Fig. 3.19 Distribution of IGS stations. Source: IGS
The IGS network is the world's largest satellite geodetic control network, and its
stations are distributed throughout the world as shown in Fig. 3.19 . Apart from IGS,
the IVS, ILRS, and IDS together have realized the International Terrestrial Refer-
ence Frame (ITRF) so as to realize the global three-dimensional geodetic datum.
Global ILRS Network
Presently there are more than 50 SLR stations all over the world and their distri-
bution is shown in Fig. 3.20 . To organize international connection and enhance
cooperation, the International Laser Ranging System (ILRS) was established in
November 1998 based on the original SLR Specialized Committee through recon-
sideration and reelection. Its central bureau was in GSFC (Goddard Space Flight
Center) of NASA (National Aeronautics and Space Administration). The ILRS
network is divided into four (several) subnets, which are introduced below.
NASA Network
In the late 1970s there appeared five stations such as MOBLAS (Mobile Laser
Ranging System) stations, McDonald Observatory, Hawaii Haleakala station, etc.
In the 1980s, four small mobile stations, TLRS 1-4, were added. Now, there are
nine sets of equipment distributed in the continental USA, South Pacific (Tahiti),
South America (Arequipa in Peru, TLRS 3), and Australia (Yarragadee). These
stations, all equipped with the third-generation system, employ the active/passive
mode-locked Nd:YAG (neodymium-doped yttrium aluminum garnet) laser pro-
duced by Quantel International (now known as Continuum). The pulse energy is
100-140 mJ (532 nm), the pulse width is 200 ps, and the repetition frequency
is 4-5 Hz. As for the aperture of the telescope, MOBLAS is 76 cm and TLRS is