Evaluation of Geoscience Australia’s Proposed GNSS CORS Antenna Mount Adaptors

Geoscience Australia (GA) designed two types of Global Navigation Satellite Systems (GNSS) antenna mount adaptors which allow antenna north reference marks to be easily and reliably aligned to the true north without changing the height of the antenna with respect to the reference mark. The antenna adaptors evaluated are proposed to be installed on GNSS Continuously Operating Reference Station (CORS) across Australia as new sites are built and commissioned or existing sites upgraded. The purpose of the report is to document the antenna adaptor testing experiments undertaken between 15/09/2021 and 18/10/2021, and determine if the mount adaptors have a significant impact on positioning quality when installed with GNSS antennas on typical GA CORS pillars. Specifically, the mount adaptors were evaluated for their effect on site multipath, position difference, and antenna calibration phase centre variations (PCV) models. Two types of mount adaptors were evaluated, a small adaptor with a diameter of 60 mm and a thickness of 26 mm and a large adaptor with a diameter of 100 mm and a thickness of 26 mm. Both adaptors were fabricated using solid stainless steel. After analysis of observations collected on typical GA tall (~1.5 m) and short (< ~0.2 m) pillars, with and without the adaptors installed, the following conclusions and recommendations can be made: a) The impact of the two types of antenna mount adaptors is small, causing less than 0.02 m change in average multipath based on one week data for L1 and L2 frequencies. b) There is around 1.1 mm for the tall pillar and 2.5 mm for the short pillar change in average position difference induced by the two types of adaptors for both horizontal and vertical components based on one week data. c) There is no significant impact (less than 1 mm for both L1 and L2 frequencies) on the PCV models induced by small antenna adaptor. d) The small antenna mount adaptor is recommended for tall pillar installations and the large mount adaptor is recommended for short pillar applications.