Demonstrating Vertical Stability Between Geodetic Techniques at SGF Herstmonceux, UK
Abstract:The most valuable geodetic sites contributing data for global reference frame determination are stations equipped with multiple co-located techniques regularly providing high quality data, located on stable ground, and which have well defined inter-technique local ties with demonstrably negligible relative motion.
The Space Geodesy Facility (SGF) in Herstmonceux, UK, operates a productive and precise GGOS ‘next generation’ satellite laser ranging station (HERL), two IGS GNSS sites (HERS, HERT) and a permanently situated absolute gravimeter. Over recent years an assessment of the stability of the site has been instigated, with a particular focus on measuring inter-technique height variation.
A campaign of fortnightly levelling surveys began in 2010 to monitor the relative heights of a series of monuments using a Lecia DNA03 bar-code levelling instrument, with instrumental accuracy of 0.3mm. The monuments include an absolute gravimeter pier, the SLR pillar and points on the GNSS monuments. In total 22 relative heights are measured during an approximately two hour survey run, which involves two members of the SGF team.
The results from four years of data show that the height differences between most of the monuments are highly stable at the sub-mm level and lack systematic variation. However, a well-defined annual height variation of magnitude ±0.5mm has been discovered between certain monuments, in particular the HERS tower.
These on-going levelling surveys lead us to conclude that the inter-technique ties at the Space Geodesy Facility are stable at the millimetre level and that consequently the Herstmonceux site will continue to make a major contribution to the ITRF in the context of the GGOS sub-mm goal.