Tie vectors (TVs) between co-located space geodetic instruments are essential for combining terrestrial reference frames (TRFs) realised using different techniques. They provide relative positioning between instrumental reference points (RPs) which are part of a global geodetic network such as the international terrestrial reference frame (ITRF). This paper gathers the set of very long baseline interferometry (VLBI)–global positioning system (GPS) local ties performed at the observatory of Medicina (Northern Italy) during the years 2001–2006 and discusses some important aspects related to the usage of co-location ties in the combinations of TRFs. Two measurement approaches of local survey are considered here: a GPS-based approach and a classical approach based on terrestrial observations (i.e. angles, distances and height differences). The behaviour of terrestrial local ties, which routinely join combinations of space geodetic solutions, is compared to that of GPS-based local ties. In particular, we have performed and analysed different combinations of satellite laser ranging (SLR), VLBI and GPS long term solutions in order to (i) evaluate the local effects of the insertion of the series of TVs computed at Medicina, (ii) investigate the consistency of GPS-based TVs with respect to space geodetic solutions, (iii) discuss the effects of an imprecise alignment of TVs from a local to a global reference frame. Results of ITRF-like combinations show that terrestrial TVs originate the smallest residuals in all the three components. In most cases, GPS-based TVs fit space geodetic solutions very well, especially in the horizontal components (N, E). On the contrary, the estimation of the VLBI RP Up component through GPS technique appears to be awkward, since the corresponding post fit residuals are considerably larger. Besides, combination tests including multi-temporal TVs display local effects of residual redistribution, when compared to those solutions where Medicina TVs are added one at a time. Finally, the combination of TRFs turns out to be sensitive to the orientation of the local tie into the global frame.
[1]
Zuheir Altamimi,et al.
ITRF2000: A new release of the International Terrestrial Reference Frame for earth science applications
,
2002
.
[2]
L. Mervart,et al.
Bernese GPS Software Version 5.0
,
2007
.
[3]
P. Steigenberger,et al.
Absolute phase center corrections of satellite and receiver antennas
,
2005
.
[4]
Detlef Angermann,et al.
Frontiers in the combination of space geodetic techniques
,
2005
.
[5]
Zuheir Altamimi.
ITRF and co-location sites
,
2005
.
[6]
P. Sarti,et al.
Laser Scanner and Terrestrial Surveying Applied to Gravitational Deformation Monitoring of Large VLBI Telescopes’ Primary Reflector
,
2009
.
[8]
Detlef Angermann,et al.
Terrestrial data analysis and SINEX generation
,
2005
.
[9]
Z. Altamimi,et al.
ITRF2005 : A new release of the International Terrestrial Reference Frame based on time series of station positions and Earth Orientation Parameters
,
2007
.
[10]
M. Raymo,et al.
Geomagnetic excursions and paleointensities in the Matuyama Chron at Ocean Drilling Program Sites 983 and 984 (Iceland Basin)
,
2002
.
[11]
John W. Dawson,et al.
Indirect approach to invariant point determination for SLR and VLBI systems: an assessment
,
2007
.
[12]
Jim R. Ray,et al.
Evaluation of co-location ties relating the VLBI and GPS reference frames
,
2005
.
[13]
Luca Vittuari,et al.
Surveying co-located space-geodetic instruments for ITRF computation
,
2004
.