https://njuastrometry.github.io/en/author/f.-shu/F. ShuHugo Blox Builder (https://hugoblox.com)en-USFri, 27 Feb 2026 00:00:00 +0000https://njuastrometry.github.io/media/icon_hu1909758375025618910.pnghttps://njuastrometry.github.io/en/author/f.-shu/https://njuastrometry.github.io/en/publication/2026-raa-26-055005/Fri, 27 Feb 2026 00:00:00 +0000https://njuastrometry.github.io/en/publication/2026-raa-26-055005/<p><strong>Background and approach</strong></p> <p>The Asia-Pacific Space Geodynamics (APSG) program uses space-geodetic observations to investigate plate motion and crustal deformation in the Asia-Pacific region. Its VLBI campaigns provide direct measurements of station positions and inter-station baselines, complementing the global geodetic VLBI network.</p> <p>We analyse 54 APSG sessions conducted between October 1997 and September 2024, involving 22 stations. The study compares session-wise station coordinates and baseline lengths with those derived from other VLBI observations, evaluates the effect of including APSG sessions in global station-velocity solutions, and compares the estimated velocities with ITRF2020 and the MORVEL geological plate-motion model.</p> <p><strong>Main results</strong></p> <ul> <li>APSG station coordinate time series and baseline-length variations are consistent with those from other VLBI sessions. Station-coordinate formal uncertainties are generally about <strong>15% smaller</strong>.</li> <li>APSG improves network geometry by providing <strong>East Asia–Australia baselines</strong> and increasing the participation of several regional stations.</li> <li>Including APSG sessions in global station-velocity estimation reduces formal uncertainties at several stations by <strong>up to 25%</strong>.</li> <li>APSG-derived velocities agree with <strong>ITRF2020</strong>, particularly in the horizontal components. Differences from <strong>MORVEL</strong> at some stations point to regional deformation that is not fully represented by a geological plate-motion model.</li> <li>The limited number and cadence of APSG sessions constrain the detection of seasonal signals. Vertical velocity differences between solutions are also larger than horizontal differences.</li> </ul> <p>The results demonstrate the value of sustained regional VLBI observations for monitoring station motion and supporting terrestrial reference frames. The quoted uncertainty reductions concern formal uncertainties rather than an independently established improvement in absolute accuracy.</p>