New GPS Monument Design for Permanent GPS Installations in the Western Canada
Deformation Array

M. Schmidt, H. Dragert, W. Hill, N. Courtier
Geological Survey of Canada, NRCan

Up until 1998, the monumentation for GPS antenna installations in the Western
Canada Deformation Array (WCDA) consisted of steel re-enforced concrete piers
anchored in bedrock. While these piers provide level, stable monumentation that
permits the antenna to be oriented to north, there is little if any security
against theft of the choke-ring antenna. Furthermore, these conventional
concrete piers may be more vulnerable to near-field EM effects due to the "EM
cavity" formed by the space between the top of the pillar and the bottom of the
antenna groundplane. A new pier design incorporating a stainless steel pedestal
anchored in bedrock provides a level surface for the antenna with an antenna
groundplane location several wavelengths above the ground, the ability to orient
the antenna as required and a more secure method for attaching the antenna thus
minimizing the chance of theft. The use of external PVC shielding combined with
sand in the interior of the stainless steel pipe, minimizes the effect of
diurnal temperature variations. The new antenna domes developed by SCIGN have
also been adopted as part of the standard WCDA installations in order to provide
snow protection and minimize delay variations from one site to the next. The
installation of this new pier design is considerably easier compared to the
traditional concrete pier especially at remote sites. The first of these new
monuments was installed at the station CHWK in the fall of 1998. Recently,
similar stainless steel pedestals have been installed at new sites on the remote
west coast of Vancouver Island. The specification and installation of the new
monument are discussed and compared to concrete piers.