臺灣大地基準雙框架策略：構想與初步成果

The dual-frame strategy for Taiwan Geodetic Datum: conceptualization and preliminary results

臺灣法定坐標系統TWD97（Taiwan Geodetic Datum 1997），又稱為1997臺灣大地基準或一九九七坐標系統，是我國使用衛星定位測量技術並根據國際地球參考框架（International Terrestrial Reference Frame，ITRF）所建立的大地基準。TWD97屬於靜態基準，也就是控制點坐標是固定不變的。然而臺灣位於歐亞板塊與菲律賓海板塊的交界，地殼變動型態複雜且劇烈，導致TWD97控制點的持續位移。為因應此問題，TWD97陸續發展出三種不同成果版本。然而過於頻繁的更新TWD97控制點坐標成果將會導致實用上的困難，特別是對於土地行政、地籍測量等需要長期穩定性的業務而言。國際間最新趨勢為各國開始發展控制點坐標隨時間改變（time-dependent）的國家時變參考框架，例如美國、澳洲、日本等國。本研究的主旨為探討如何運用雙框架策略有效因應臺灣地區控制點持續位移的問題。亦即在TWD97靜態基準之外，藉由區域性加密國際地球參考框架建立一個臺灣時變參考框架（Taiwan Terrestrial Reference Frame，TTRF），並藉由發展臺灣地區地殼變位模型（crustal deformation model），實現TTRF與TWD97[2020]之間的坐標轉換。根據2020至2024年臺灣地區的CORS觀測網數據，以及2024年國土測繪中心LiDAR技術更新數值地形模型案之加密控制測量觀測資料，初步成果顯示雙框架策略確實可有效因應地殼變動之影響，維護大範圍控制測量的成果品質。

Taiwan Geodetic Datum 1997 (TWD97) -- also called 1997 coordinate system, is Taiwan’s national datum based on the International Terrestrial Reference Frame (ITRF) and established by using the GNSS positioning technique. However, Taiwan is located at the tectonic boundary of the Eurasia plate and Philippine Sea plate, with severe and complex crustal motion patterns. As a result, the TWD97 control points have shown severe and continuing displacements. To reflect the problem, TWD97 has developed three different versions. However, the update of TWD97 control point coordinates with excessive frequency is expected to cause difficulties for practical applications such as land administration and cadastral surveys, which require long-term stability. The latest trend for countries such as the United States, Australia, and Japan is to develop national time-dependent reference frames in which the coordinates of control points change over time. The objective of this study is to investigate how a dual-frame strategy can be effectively employed to address the issue of continuous displacement of control points in Taiwan. Specifically, in addition to the static TWD97 datum, Taiwan Terrestrial Reference Frame (TTRF) is established by regionally densifying the International Terrestrial Reference Frame. Furthermore, by developing a GNSS-based crustal deformation model, coordinate transformations between TTRF and TWD97[2020] can be achieved. Based on 2020-2024 CORS data collected in the Taiwan region, as well as densification control survey data from the 2024 National Surveying and Mapping Center LiDAR project, the preliminary results of this study indicate that the dual-frame strategy is effective in mitigating the effects of crustal movement and maintaining the quality of control surveys over large areas.