GPS campaigns at CHON and BANH. Antenna type names are according the IGS naming convention. Four types of receivers were used: (1) Trimble 4000SSi (with the TRM14523.00,
TRM334280.00+GP and TRM22020.00+GP antennae), (2) Trimble 4800 (with the TRM4800 antenna), (3) Trimble R7/5700 (with the TRM41249.00 and TRM39105.00 antenna)
and (4) Leica SR520/5320 (with the LEIAT502 antenna). The GPS points were continuously observed (in 24 h sessions) in campaign-mode for typically 5 to 7 days (shorter
observation periods were due to equipment problems). The GPS point at CHON was established in 1994 and is located on bedrock with a specially designed GEODYSSEA (screw-on
type) marker yielding a re-centering accuracy of 0.2 mm (Simons et al., 1999). Therefore the antenna setup always has the same vertical height above the marker. Since 2004 this
point was almost always re-observed with the same antenna type. BANH was built in 1994 and is part of the zero-order Thai GPS network and is equipped with a geodetic (metal
disk) survey marker on top of a (0.4×0.4×1.0 m) concrete monument that lies about 0.15 m above the ground. Qualified surveyors of RTSD have observed this point with a tripod.
Hereby the antenna is centered optically and verified with a plumb. Both antenna (height) setups are carefully registered on log sheets and accompanied with photos (since 2004 in
digital format) to verify the antenna height measurements.