Report on the Asia Pacific Reference Frame (APREF) Project

This report overviews the status and development of the Asia Pacific Reference Frame (APREF) project, which is a major activity of the Geodetic Reference Framework for Sustainable Development Working Group of the United Nations Global Geospatial Information Management for Asia and the Pacific (UN-GGIM-AP), and the Reference Frame Sub-Commission 1.3e (SC1.3e) of the International Association of Geodesy (IAG). In this work, the APREF Continuously Operating Reference Station (CORS) network is reviewed. This is followed by an overview of the analysis methodology and strategy adopted for processing of data from the network. Coordinate time series, velocities as well as other parameters are generated for 450 CORS sites across the Asia-Pacific region and 200 International GNSS Service (IGS) core stations located around the world. An accuracy assessment of the output and products, including the estimated position and velocity field is presented. The position solutions have an internal accuracy of 1-4 mm and 4-8 mm in horizontal and vertical components, respectively, determined from position repeatability of the weekly solutions. When compared with the published IGS14 velocities for the 173 common sites, the velocity solutions have an external accuracy of 0.02 ± 0.29 mm/yr, 0.01 ± 0.32 mm/yr, and 0.08 ± 0.54 mm/yr for north, east and vertical components, respectively. Products of the APREF Project include the daily and weekly solutions, combined weekly solutions, position time series of long-term solutions, coordinates and velocity field of the CORS network in ITRF2014.